Trustees of Boston University v. Apple, Inc.

Filing 1

COMPLAINT against Apple, Inc. Filing fee: $ 400, receipt number 0101-4527400 (Fee Status: Filing Fee paid), filed by Trustees of Boston University. (Attachments: # 1 Exhibit A, # 2 Civil Cover Sheet, # 3 Civil Category Form)(Belt, Erik) (Attachment 3 replaced on 7/11/2013) (Maynard, Timothy).

11111

United States Patent

[19]

Moustakas
HIGBLY INSULATING MONOCRYSTALLINE
GALLIUM NITRIDE THIN FILMS

[75]

Inventor:

[73]

Assignee: Trustees of Boston University, Boston,
Mass.

[21]

Appl. No.: 372,113

[22]

Filed:

Theodore D. Moustakas, Dover, Mass.

Jan. 13, 1995
Related U.S. Application Data

[63]

Continuation of Ser. No. 113,964, Aug. 30, 1993, Pat No.
5,385,862, which is a continuation of Ser. No. 670,692, Mar.
18, 1991, abandoned.

[51]
[52]

Int. CI. 6

............................. BOlL 33100; HOIL 29120
U.S. CI............................... 257/103; 257/94; 257/79;
257/615
Field of Search ................................ 257/103, 94, 79,

257/615

[56]

US005686738A

[11]
[45]

[54]

[58]

111111111111111111111111111111111111111111

References Cited

8/1972 Pankove.
6/1974 Stevenson et aI ..
8/1974 Logan et aI..

(Ust continued on next page.)
FOREIGN PATENT DOCUMENTS
3802732
4006449
64-30110
208143
2081483
0143420
2-143420

8/1988
9/1990
8/1989

3/1990
3/1990
6/1990
6/1990

2257678 10/1990

Germany.
Germany.
Japan .
Japan .
Japan .
Japan .
Japan .
Japan .

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Maruska et al. Solid State Elec 1974 vol. 17 pp. 1171-1179
"Mechanism ... Diodes".
Boulon et al, Philips Tech Rev. 37, pp. 237-240 1977 No.
9/10 "Ught-emitting diodes based on GaN".

5,686,738
Nov. 11, 1997

T. Sasaki et aI., "Substrate-polarity dependence of metalorganic vapor phase epitaxy-grown GaN on SiC," J. Appl.
Phys., Nov., 1988, pp. 4531-4535.
R.E Davis et aI., "Critical Evaluation of the Status of the
Areas for Future Research Regarding the Wide Band Gap
Semiconductors Diamond, Gallium Nitride and Silicon Carbide," Materials Science and Engineering, 1988, pp.
77-104.
S. Yoshida et al., ''Epitaxial growth of GaNlAIN heterostructures," J. Vac. Sci. Technol., Apr.-Jun. 1983, pp.
250-253.
Z. Sitar et al., "Growth of AIN/GaN layered structures by
gas source molecular-beam epitaxy," J. Vac. Sci. Techno!.,
MarJApr. 1990, pp. 316-322.
H. Amano et ai., "Wand blue electroluminescence from
Al/GaN:MglGaN LED Treated with low-energy electron
beam irradiation (LEEBI)," Proceedings of the SPIE-The
International Society for Optical Engineering, vol. 1361,
Part 1, 1991, pp. 138-149.
S. Zembutsu et al., "Growth of GaN single crystal fibns
using electron cyclotron resonance plasma excited metalorganic vapor phase epitaxy," Appl. Phys. Lett., Mar. 1986, pp.
870-872.
(Ust continued on next page.)

U.S. PATENT DOCUMENfS
3,683,240
3,819,974
3,829,556

Patent Number:
Date of Patent:

Primary Examiner-Jerome Jackson
Attome)\ Agent, or Firm-Baker & Botts, L.L.P.
[57]

ABSTRACT

This invention relates to a method of preparing highly
insulating GaN single crystal films in a molecular beam
epitaxial growth chamber. A single crystal substrate is provided with the appropriate lattice match for the desired
crystal structure of GaN. A molecular beam source of Ga and
source of activated atomic and ionic nitrogen are provided
within the growth chamber. The desired film is deposited by
exposing the substrate to Ga and nitrogen sources in a two
step growth process using a low temperature nucleation step
and a high temperature growth step. The low temperature
process is carried out at 100-400° C. and the high temperature process is carried out at 600-900° C. The preferred
source of activated nitrogen is an electron cyclotron resonance microwave plasma.

21 Claims, 4 Drawing Sheets

5,686,738
Page 2

u.s. PATENI' DOCUMENTS
4,144,116
4,153,905
4,396,929
4,473,938
4,476,620
4,589,015
4,608,581
4,615,766
4,792,467
4,819,057
4,819,058
4,855,249
4,866,007
4,897,149
4,911,102
4,918,497
4,946,547
4,946,548
4,960,728
4,966,862
4,966,867
4,983,249
5,005,057
5,006,908
5,010,033
5,015,327
5,027,168
5,042,043
5,063,421
5,068,204
5,076,860
5,093,576
5,097,298
5,117,267
5,119,540
5,122,845
5,140,385
5,173,751
5,178,911
5,182,670
5,192,419
5,200,022
5,205,905
5,210,051
5,218,216
5,237,182
5,243,204
5,248,631
5,272,108
5,290,393
5,298,767
5,304,820
5,306,662
5,307,363
5,313,078
5,323,022
5,329,141
5,334,277
5,338,944
5,359,345
5,385,862

3/1979
5/1979
8/1983
10/1984
10/1984
5/1986
8/1986
10/1986
12/1988
4/1989
4/1989
8/1989
9/1989
1/1990
3/1990
4/1990
8/1990
8/1990
10/1990
1011990
1011990
1/1991
4/1991
4/1991
4/1991
5/1991
6/1991
8/1991
11/1991
11/1991
12/1991
3/1992
3/1992
5/1992
6/1992
6/1992
8/1992
12/1992
111993
1/1993
311993
4/1993
411993
5/1993
6/1993
8/1993
9/1993
9/1993
12/1993
311994
3/1994
4/1994
4/1994
411994
5/1994
6/1994
7/1994
8/1994
8/1994
10/1994
1/1995

Jacob et aI ..
Olamakadze et aI ..
Ohki et aI.••••.•......•••••••••••••••••• 257/103
Kobayashi et aI ..
Ohki et aI..
Nakata et aI ..
Bagratishvilli et aI ........•••••••.• 257/103
Jackson et aI..
Melas et aI ..
Naito et aI..
Nishizawa.
Akasaki et aI ..
Taguchi et aI..
Suzuki et aI..
Manabe et aI ..
Edmond.
PaImour et aI ..
Kotaki et aI ..
Sbaake et aI ..
Edmond.
Crotti et aI ..
Taguchi et aI. .
Izumiya et aI ..
Matsuoka et aI ..
Tokunaga et aI ..
Taguchi et aI..
Edmond.
Hatano et aI ..
Suzuki et aI..
Kukimoto et aI..
Ohba et aI ..
Edmond et aI ..

Ebara.
Kimoto et aI ..
Kong et aI..
Manabe et aI ..
Kukimoto et aI ..
Ota et aI ..
Gordon et aI..
Khan et aI..
Matsuura et aI ..
Kong et aI..
Kotaki et aI..
Carter, Jr..
Manabe et aI ..
Kitagawa et aI..
Suzuki et aI ..
Park et aI ..
Kozawa.
Nakamura.

Shor et aI. .
Tokunaga et aI ..
Nakamura et aI ..
Hosokawa et aI ..

Fujii et aI ..
Glass et aI ..
Suzuki et aI ..
Nakamura.
Edmond et aI..
Hunter.
Moustakas.

OTHER PUBLICATIONS
M.J. Paisley, "Growth of cubic phase gallium nitride by
modified molecular-beam epitaxy" J. Vac. Sci. Technol.,
May/Jun. 1989, pp. 701-705.
T.L. Chu, "Gallium Nitride Films," J. Electrochemical Society, Jui 1971, pp. 1200-1203.

"P-Type Conduction in MG-Doped GaN Treated with
Low-Energy Electron Beam Irradiation (LEEBl)", Hiroshi
Amano et al., Japanese Journal of Applied Physics, 28 No.
12, pp. L2112-L2214 (Dec., 1989).
"Growth of High-Resistivity Wurtzite and Zincblende
Structure Single Crystal Gan By Reactive-Ion Molecular
Beam Epitaxy", R.C. Powell et al., Materials Research
Society Symposium Proceedings, 162, pp. 525-530 (Nov.!
Dec., 1989)
"Growth of Cubic GaN Films on (100) Si by ECRAssisted
MBE", T. Lei et al,. Bulletin of the American Physical
Society, 36 N. 3 (Mar., 1991).
"Growth of GaN Films on the a-plane of Sapphire by ECR
Assisted MBE", G. Merion et al., Bulletin of the American
Physical Society, 36 No.3 (Mar., 1991).
"Growth of Single Crystalline GaN Films on the R-plane of
Sapphire by ECR Assited", C.R. Eddy et al., Bulletin of the
American Physical Society, 36 No.3 (Mar., 1991).
''Electron Beam Effects on Blue Luminescence of ZincDoped GaN", HiroshiAmano et al., 40 and 41, pp. 121-122
(Feb., 1988) Jour. of Luminescence.
"Commercialization of GaN Blue LED with The Highest
Reported Light Intensity in The World", unknown author,
Japanese R&D Trend Analysis, 33 (Jan. 1991).
Sitar, Z., Design and Performance of an Electron Cyclotron
Resonance Plasma Source for Standard Molecular Beam
Epitaxy Equipment, Rev. Sci. Instrum., 61(9), Sep. 1990, pp.
2407-2411.
Kiode, et al., Effect of an AIN Buffer Layer on AIGaNI
a-Alz0 3 Heteroepitaxial Growth by MOVPE (in Japanese),
vol. 13, No.4, 1986, pp. 218-225.
S. Yoshida, et aI., Improvements on the electrical and
luminescent properties of reactive molecular beam epitaxially grown GaN films by using ALN-coated sapphire substrates, Appl. Phys. Lett, 42(5), Mar. 1983, pp. 427-429.
H. Amano, et al., Effect Of The Buffer Layer in Metalorganic
Vapour Phase Epitaxy of GaN on Sapphire Substrate, TIrin
Solid Films, 163, 1988, pp. 415-420.
H. Amano, et aI., Metalorganic vapor phase epitaxial
growth of a high quality GaN film using an AlN buffer layer,
Appl. Phys. Lett. 48 (5), Feb. 1986, pp. 353-355.
M.R.H. Khan, et aI., Edge Emission of AlxGa1_..N, Solid
State Communications, vol. 60, No.6, 1986, pp. 509-512.
H. Amano, et aI., P-Type Conduction in Mg-Doped GaN
Tread with Low-Energy Electron Beam Irradiation
(LEEBl), Japanese Journal of Applied Physics, vol. 28, No.
12, Dec. 1989, pp. L2112-L2114.
T. Nagatomo, et al., Epitaxial Growth of GaN films by Low
Pressure Metalorganic Chemical Vapor Diposition, Abstract
#1156, 104b Extended Abstracts Fall Meeting, Honolulu,
Hawaii, Oct. 1987, pp. 1602-1603.
H. Kawakami, et al., Epitaxial Growth of A1N Film with an
Initial-Nitriding Layer on u-AlZ0 3 Substrate' Japanese Journal of Applied Physics, vol. 27, No.2, Feb. 1988, pp.
L16l-L163.
I. Akasaki, et aI., Effects of AIN Buffer Layer on Crystallographic Structure and On Electrical and Optical Properties
of GaN and Ga1_..AI..N (O<x~O.4) Films Grown on Sapphire Substrate by MOVPE, Journal of Crystal Growth 98,
1989, pp. 209-219.
B. Goldenberg, et al., Ultraviolet and Violet Light-Emitting
GaN Diodes Grown By Law-Pressure Metalorganic Chemical Vapor Deposition, Appl. Phys. Lett. 62 (4), Jan. 1993,
pp. 381-383.

5,686,738
Page 3

T. Mariizumi, et al., Epitaxial Vapor Growth of ZnTe on
InAs, Japan. J. Appl. Phys. 9 (1970), pp. 849-850.
L Akasaki, et al., Photoluminescence of Mg-doped p-type
GaN and electroluminescence of GaN p-n junction LED,
Journal of Luminescence 48 & 49, 1991, pp. 666-670.
A. Yoshikawa, et al., Effects of Ar ion laser irradiation on
MOVPE of ZnSe using DMZn and DMSe as reactants,
Journal of Crystal Growth 107, 1991, pp. 653-658.
Sitar, et al., Design and performance of an electron cyclotron resonance plasma source for standard molecular beam
epitaxy equipment, Rev. Sci Instrum., vol. 61, No.9, Sep.
1990, pp. 2407-2411.
Program of the 1991 March Meeting, Bulletin ofthe American Physical Society, vol. 36, Number 3, Mar. 1991, pp.
543-544.
T. Lei, et al., Epitaxial Growth of zinc-blende and wurtzitic
gallium nitride thin films on (001) silicon, Appl Phys. Lett.
59 (8), Aug. 1991, pp. 944-946.
T. Lei, et al., Epitaxial Growth and Characterization of
zinc-blende gallium nitride on (001) silicon, J. Appl. Phys.
71 (to), May 1992, pp. 4933-4943.
T.D. Moustakas, et al., A Comparative Stude of GaN Films
Grown on Different Faces of Sapphire by ECR-Assisted
MBE, Mat Res. Soc. Symp. Proc., vol. 242, 1992, pp.
427-432.
T. Lei, et al., A Comparative Study ofGaN Epitaxy on Si(OOl
and SI(111) Substrates, Mat Res. Soc. Symp. Proc., vol
242, 1992, pp. 433-439.
c.R. Eddy, Jr., et al., Growth of Gallium Nitride Thin Films
By Electron Cyclotron Resonance Microwave Plasma-AssistedMolecularBeamEpitaxy, J.ApplPhys. 73,Jan.1993,
pp. 448-455.
R.J. Molnar, et al., Electron Transport Mechonism in Gallium Nitride, Appl. Phys. Lett. 62 (1), Jan. 1993, pp. 72-74.
J.S. Foresi, et al., Metal Contacts to Gallium Nitride, Appl.
Phys. Lett. 62 (22), May 31,1993, pp. 2859-2861.
T. Lei, et al., Heteroepitaxy, Polymorphism, and Faulting In
GaN Thin Films on Silicon and Sapphire Substrates, J. Appl
Phys. 74 (7), Oct 1993, pp. 4430-4437.
M. Fanciulli et al., Conduction~lectron spin resonance in
zinc-blende GaN Thin Films, Physical Review B, vol. 48,
No. 20, Nov. 1993, pp. 15144-15147.
T.D. Moustakas, et al., Growth and Doping of GaN Films by
ECR-Assisted MBE, Mat Res. Soc. Symp. Proc., vol. 281,
1993, pp. 753-763.
R.J. Molnar, et al., High Mobility GaN Films Produced by
ECR-Assisted MBE, Mat. Res. Soc. Symp. Proc., Vol. 281,
1993, pp. 765-768.
T.D. Moustakas, et al., Growth of GaN by ECR-Assisted
MBE, Physics B 185 (1993) pp. 36-49.
M.S. Brandt, et aI., Hydrogenation of GaUium Nitride, MRS
Meeting, 1993, six pages.

R. Singh, et al., Intensity Dependence of Photoluminescence
in GaN Thin Films, Appl. Phys. Lett. 64 (3), Jan. 1994, pp.
336-338.
M.S. Brandt, et al., Hydrogenation ofJrtype gallium nitride,
Applied Physics Letters, vol. 64, No. 17, Apr. 1994, pp.
2264-2266.
M.S. Brandt, et al, Local Vibrational Modes In Mg-Doped
Gallium Nitride, Physical Review B. Condensed Matter, vol.
49, No. 20, May 1994, pp. 14,758-14,761.
H. Teisseyre, et al., Temperature dependence of the energy
gap in GaN bulk single crystals and epitaxial layer; J. Appl.
Phys. 76 (4), Aug. 1994, pp. 2429-2434.
S.N. Basu, et al., Microstructures of GaN Films Deposited
On (001) and (111) Si Substrates Using Electron Cyclotron
Resonance Assisted-Molecular Beam Epitaxy, J. Mater,
Res., vol. 9, No.9, Sep. 1994, pp. 2370-2378.
R.J. Molnar, et al., Growth of Gallium Nitride by ElectronCyclotron Resonance Plasma-Assisted Molecular-Beam
Epitaxy: The Role of Charged Species, J. Appl. Phys. 76(8),
Oct. 1994, pp. 4587-4595.
M. Leszcynski, et al., Thermal Expansion of Gallium
Nitride, J. Appl. Phys. 76 (8), Oct. 1994, pp. 4909-4911.
M. Manfra, et al., Reactive Ion Etching of GaN Thin Films,
Mat. Res. Soc. Symp. Proc., vol. 324, 1994, pp. 477-480.
R.J. Molnar,Blue-Violet Light Emitting Gallium Nitride p-n
Junctions Grown by Electron Cyclotron Resonance-assisted
Molecular Beam Epitaxy, Applied Physics Letters, Jan.
1995, three pages.
J.T. Glass, et aI., Diamond, Silicon Carbide and Related
Wule Bandgap Semiconductors, Materials Research Society
Symposium Proceedings, vol. 162, 1989, pp. 525-530.
H. Amano, et al., Electron Beam Effects on Blue Luminescence of Zinc-Doped GaN, Journal of Luminescence 40 &
41, 1988, pp. 121-122.
H. Amano, et al., Stimulated Emission Near Ultraviolet at
Room Temperature from a GaN Film Grown on Sapphire by
MOVPE Using an ALN Buffer Layer; Japanese Journal of
Applied Physics, vol. 29, No.2, Feb. 1990, pp. L205-L206.
KRI Fax News #53, Commercialization of GaN Blue LED
With the Highest Reported Light Intensity in The World,
Japanese R&D Trend Analysis, Jan. 1991.
G. Menon, Growth of Intrinsic Monocrystalline Gallium
Nitride Thin Films by Electron Cyclotron Resonance Microwave Plasma Assisted Molecular Beam Epitaxy, Boston
University College of Engineering Thesis. 1990.
T. Lei, Heteroepitaxial Growth of Gallium Nitride And
Native Defect Formation In III-V Nitrides, Boston University Graduate School Dissertation, 1993.
R. Molnar, The Growth and Doping of Gallium Nitride
(GaN) Thin Films By Electron Cyclotron Resonance Plasma
Assisted Molecular; Boston University, College of Engineering, Disseration. Jun. 1994.

u.s. Patent

Nov. 11, 1997

FIG. 1

Sheet 1 of 4

5,686,738

u.s. Patent

B~~~g~t

Nov. 11, 1997

Sheet 2 of 4

5,686,738

SAMPLE: GANI9 FILE: GANI9.RD

BP 3.50
3./5
2.BO

2.45
2./0

1.75
1.40
1.05
0.70
0.35 ~............~......,..-__""~

U

1
___........- -...........

/5.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0

FIG.2A

u.s. Patent

BPOBCF
~x~ 0 5 ,

Nov. 11, 1997

Sheet 3 of 4

5,686,738

SAMPLE: GAN26 FILE: GAN26.RD

3.00
2.70
2.40
2.10
1.80

1.50
1.20
0.90
0.60
0.30
20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0

FIG.2B

u.s. Patent

Nov. 11, 1997

Sheet 4 of 4

22

-II

FIG.3

5,686,738

5,686,738
1
mGHLY INSuLATING MONOCRYSTALLINE
GALLIDM NITRIDE THIN FILMS

2

possible to prepare intrinsic GaN. Additionally, it is desirable to control the doping process in GaN films, thereby
enabling the production of p-n junctions. The present invenThis application is a continuation of application Ser. No.
tion presents a method to prepare near-intrinsic monocrys08/113,964, filed Aug. 30, 1993, now U.S. Pat. No. 5,538, 5 talline GaN films and to selectively dope these films n- or
862, entitled "A MEfHOD FOR THE PREPARATION
p-type.
AND DOPING OF IDGHLY INSULATING MONOCRYSTALLINE GAILIUM NTIRIDE THIN FILMS", which is a
SUMMARY OF THE INVENTION
continuation of application Ser. No. 07/670,692, filed Mar.
The method accorrding to this invention for preparing
18, 1991, which is abandoned.
10 highly insulating near-intrinsic monocrystaI1ine GaN films
BACKGROUND OF THE INVENTION
uses ECR-assisted MBE. In a preferred embodiment, a
This invention relates to a method of preparing monocmolecular beam source of Ga and an activated nitrogen
rystalline gallium nitride thin films by electron cyclotron
source is provided within an MBE growth chamber. The
resonance microwave plasma assisted molecular beam epidesired substrate is exposed to Ga and activated nitrogen. A
taxy (ECR-assisted MBE). The invention further relates to a 15 film is epitaxially grown in a two step process comprising a
method for the preparation of n-type or p-type gallium
low temperature nucleation step and a high temperature
nitride (GaN) films.
growth step. The nucleation step preferably occurs by expoEfforts have been made to prepare monocrystalline GaN
sure of the substrate to gallium and a nitrogen plasma at a
because of its potentially useful electrical and optical proptemperature in the range of 100°-400° C. and the high
erties. GaN is a potential source of inexpensive and compact 20 temperature growth step is preferably carried out in the
solid-state blue lasers. The band gap for GaN is approxitemperature range of 600°-900° C. Preferred substrates
mately 3.4 eV, which means that it can emit light on the edge
include, but are not limited to, (100) and (111) silicon and
of the UV-visible region. For intrinsic GaN, the carrier
(0001), (11-20) and (1-102) sapphire, (111) and (100)
concentration, ni , is 5.2x103 cm-3 , the mobility is 330
gallium arsenide, magnesium oxide, zinc oxide and silicon
cm2V-1 s-1 and the resistivity is 3.6x1012 Q-cm.
25 carbide. The preferred source of activated nitrogen species is
a nitrogen plasma which can be generated by electron
Despite the desirability of a monocrystalline GaN film, its
cyclotron resonance microwave plasma or a hot tungsten
development has been hampered by the many problems
filament or other conventional methods.
encountered during the growth process. Previous attempts to
prepare monocrystaIIine GaN firms have resulted in n-type 30
In a preferred embodiment, the nitrogen plasma pressure
films with high carrier concentration. The n-type characterand Ga flux pressure are controlled, thus preventing the
istic is attributed to nitrogen vacancies in the crystal strucbearing of metallic gallium on the film surface and the
ture which are incorporated into the lattice during growth of
forming of nitrogen vacancies within the lattice. The Ga flux
the film. Hence, the film is unintentionally doped with
is preferably in the range of 2.0-5.0x10-7 torr. There is
nitrogen vacancies during growth. Nitrogen vacancies affect 35 preferably an overpressure of nitrogen in the growth
the electrical and optical properties of the film.
chamber, more preferably in the range of 10-3 _10-5 torr.
ECR-assisted metaIorganic vapor phase epitaxy gave
In yet another preferred embodiment, the low temperature
GaN films that were highly conductive and unintentionally
nucleation step includes exposure of the substrate to Ga and
doped n-type (S. Zembutsu and T. Sasaki l. Cryst. Growth
nitrogen for a period of time in the range of 3-15 minutes.
77, 25-26 (1986». Carrier concentrations and mobilities 40 A film with a thickness of 200-500 A is deposited, which is
were in the range of 1x1019 cm-3 and 50-100cm2V-1s-1,
amorphous at the low temperatures of the nucleation step.
respectively. Efforts to dope the film p-type were not sucThe amorphous film can be crystaIlized by heating at
cessful. The carrier concentration was reduced by
600°-900° C. in the presence of activated nitrogen. Subsecompensation, that is, the effect of a donor impurity is
quent treatment at higher temperatures, preferably
"neutralized" by the addition of an acceptor impurity.
45 600°-900° C., results in the epitaxial growth of monocrysHighly resistive films were prepared by sputtering using
talline near-intrinsic GaN film. Preferred thickness of the
an ultra-pure gallium target in a nitrogen atmosphere. The
growth layer is in the range of 0.5-10 ~.
films were characterized n-type and the high resistivity was
In another aspect of this invention, the monocrystaI1ine
attributed to the polycrystalline nature of the films (E.
GaN film is preferentially doped n- or p-type. To generate a
Lakshmi, et al. Thin Solid Films 74, 77 (1977».
50 p-type semiconductor, the MBE growth chamber is
In reactive ion molecular beam epitaxy, gallium was
equipped with Ga, activated nitrogen and acceptor sources.
supplied from a standard effusion cell and nitrogen was
Acceptor sources include Group n elements such as Be, Zn,
supplied by way of an ionized beam. MonocrystaI1ine films
Cd, and Ca. The substrate is bombarded with electrons either
6
were characterized n-type, but higher resistivities of 10
by applying a positive bias to the substrate surface or a metal
Q-cm and relatively low carrier concentrations and mobili- 55 grid placed directly in front of the substrate. Conditions for
ties (1014 cm-3 and 1-10 cm2y-1 s-1, respectively) were
low and high temperature deposition are as described above.
obtained (R. C. Powell, et al. in "Diamond, Silicon Carbide
Exposing the substrate to Ga, nitrogen and acceptor sources
and Related Wide Bandgap Semiconductors" Vol. 162,
results in a doped GaN film. whereby the acceptor takes on
edited by J. T. Glass, R. Messier and N. Fujimori (Material
an electron and is incorporated into the lattice as a negatively
Research Society, Pittsburgh, 1990) pp.525-530).
60 charged species. A charged acceptor species requires less
The only reported p-type GaN was a Mg-doped GaN
energy to incorporate into the GaN lattice than a neutral
treated after growth with low energy electron beam irradiaacceptor. To dope the material n-type the substrate is bomtion. P-type conduction was accomplished by compensation
barded with positive ions by biasing either the substrate or
of n-type GaN (H. Areario et al. lap. J Appl. Phys. 28(12),
the grid negatively. Thus, the donor impurities incorporate
L2112-L2114 (1989».
65 into the GaN in their charged state. This requires less energy
Current methods of preparing GaN do not permit control
than to incorporate a neutral donor species. Suitable donors
include Groups IV and VI elements.
of nitrogen vacancies within the lattice. Thus it has not been

5,686,738

3

4

Practice of this invention affords near-intrinsic GaN fihns
energy electrons. The lower electromagnet 17 then guides
with resistivities of up to 1010 ohms-cm and mobilities of
the ions through the effusion pert 12 towards a substrate 19
100 em2 V-1 s- 1 at 200° C. P-type and n-type semiconductors
which is positioned on a continuous azimuthal rotation
can be selectively prepared simply by choice of surface or
(C.A.R.) unit 20 in a growth chamber 21 of the MBE system
grid bias and impurity source. It is possible to efficiently 5 11. The C.A.R. 20 can be rotated between 0 and 120 rpm. On
manufacture p-n junctions using the methods of this
certain substrates, GaN films grow in the wurtzitic structure
invention,
and on others in the zincblende structure. Such substrates
include for example sapphire (GaN in wurtzitic structure)
BRIEF DESCRIPTION OF THE DRAWING
and Si(l00) (GaN in the zincblende structure). GaIliumflux
10 is generated in a Knudsen effusion cell 22.
FIG. 1 is a cross-sectional view of an ECR-assisted MBE
In a typical process, the substrate 19 was sputter-etched
growth chamber.
by the nitrogen plasma at 600° C. The substrate was cooled
FIG. 2a is a an X-ray diffraction pattern from a GaN film
down to 270° C. in the presence of the nitrogen plasma. A
on (11-20) sapphire grown from a one-step process.
Ga shutter 23 was then opened to deposit the initial buffer
FIG. 2b is a an X-ray diffraction pattern from a GaN film 15 layer of GaN. The use of an activated nitrogen source
on (11-20) sapphire grown from a two-step process.
permitted the deposition of GaN at this low temperature. The
FIG. 3 is a schematic illustration of the method for doping
buffer layer was allowed to nucleate over ten minutes and
GaN films.
then the Ga shutter 23 was closed to stop the nucleation of
the film. The substrate was then brought slowly to 600° C.
DESCRlPfION OF THE PREFERRED
20 at the rate of 4°C. every 15 seconds in the presence of the
EMBODIMENT
nitrogen plasma. The nitrogen overpressure also helped
reduced the formation of nitrogen vacancies.
The unintentional doping of GaN has been attributed to
Once at 600° C., the substrate 19 was kept at this
the formation of nitrogen vacancies in the GaN lattice. GaN
temperature for 30 minutes in the presence of nitrogen
decomposes (and loses nitrogen) at about 650° C., well
below the processing temperatures of the above processes 25 plasma to ensure that the GaN buffer layer had crystallized.
The Ga shutter 23 was opened once again to grow the GaN
(>10000° C.). Therefore, the growth process itself provides
monocrystaIline film, The thickness of the film was about 1
sufficient thermal energy for vacancy formation. Growth
pm, although in theory there is no limitation to film thickprocesses at lower temperatures should reduce the number
ness. Nitrogen pressure and gallium flux are kept constant
of nitrogen vacancies in the lattice, prevent the unintentional
n-type doping of the GaN lattice and result in intrinsic GaN. 30 during the entire process.
The two step growth process allows for the nucleation of
The practice of the present invention forms GaN at
a buffer layer. The buffer layer is grown at a temperature in
significantly lower processing temperatures using an actithe range of 100°-400° C. Because the temperature is low,
vated nitrogen source. An ECR microwave nitrogen plasma
is the preferred activated nitrogen source. A two step heating 35 the probability of nitrogen vacancy formation is reduced. As
the temperature increases to 600° c., the amorphous film
process pennits the formation of monocrystalline GaN at
crystallizes. Any further growth takes place on the crystallower processing temperatures.
lized GaN buffer layer. The films grown by this two step
The ECR-MBE system used in this invention is shown in
process are superior to those grown by a one step growth
FIG. 1. An ECR-system 10 was integrated with an MBE
system 11 by attaching the ECR system 10 to an effusion 40 process.
FIG. 2 shows the X-ray diffraction (XRD) pattern of a
pert 12. The ECR system includes a microwave generator
GaN film grown on the a-plane of sapphire (11-20) in a
13, a waveguide 14, a high vacuum plasma chamber 15, and
one-step process (FIG. 2a) and a two-step process (FIG.2b).
two electromagnets 16 and 17. The microwaves at 2.43 GHz
The two peaks at ca. 20=35° of FIG. 2a are attributed to a
are created in the microwave generator 13 and travel down
the rectangular waveguide 14. The microwave power 45 defective GaN crystal. FIG. 2b has a single peak indicating
a film of better quality. This is because the majority of the
(100-500 W) passes from the waveguide 14 into the plasma
film grows on the top of the GaN buffer and does not see the
chamber 15. Nitrogen flows into the plasma chamber 15
underlying substrate. The growth layer of GaN ''recognizes''
through a mass flow controller 18. The mass flow controller
the GaN buffer layer and on which it can grow without
18 maintains an adjustable constant flow rate. The plasma
chamber 15 is surrounded by the two electromagnets 16 and 50 defects. The buffer is the only part of the film which is highly
defective.
17. The upper magnet 16 is powered by a 2 kW power
supply (not shown) and the lower magnet 17 is powered by
Films grown by the method described above were highly
resistive at room temperature (1010 Q-em). The mobility of
a 5 kW power supply (not shown). Positioning of the
this material is 10 cm2 V-1 s-1 , a reasonable value compared
electromagnets in this way results in a more intense and
stable plasma.
55 to the theoretic mobility of intrinsic GaN 330 which is
Q_em-3 •
The upper electromagnet 16 sets the free electrons in the
chamber 15 into cyclotron orbits. The cyclotron frequency is
GaN films are doped n-type or p-type by incorporating the
dependent upon the strength of the magnetic field and the
proper impurities in their charged state. This is because the
electron charge-to-mass ratio. Since all the electrons assume
energy to incorporate a charged impurity into the lattice is
cyclotron orbits, the energy lost in random motion and 60 lower than the energy needed to incorporate a neutral
impurity. FIG. 3 is a schematic illustration of the doping of
collisions is reduced. Additionally, the plasma will be cona charged acceptor into the GaN lattice. The substrate 19 or
fined to the center of the chamber 15. The magnetic field is
adjusted such that the frequency of oscillation of the microa grid 19a directly in front of it is positively biased. FIG. 3
waves is exactly equal to the cyclotron frequency of the
shows both substrate 19 and grid 19a connected to a voltage
electrons. N 2 is then introduced into the chamber through the 65 source. In practice of this invention, either substrate 19 or
mass flow controller 18 and is decomposed to high energy
grid 19a would be positively biased. Electrons are therefore
atomic and ionic nitrogen species by impact with the high
attracted to the substrate surface, while positive ions such as

5,686,738
5
W are repelled. The growth process is carried out as

6

9. A semiconductor device comprising:
described above with addition of an acceptor source 24 so
a substrate, said substrate consisting of a material selected
that Ga, nitrogen and acceptor are deposited on the electronfrom the group consisting of (100) silicon, (111)
rich surface of the substrate. As the acceptor atom
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
approaches the surface, it takes on an electron and is 5
sapphire, (111) gallium aresenide, (100) gallium
incorporated into the lattice as a negative species, the energy
aresenide, magnesium oxide, zinc oxide and silicon
of incorporation being lower than that of the neutral acceptor
carbide;
species. The same procedure is used to dope the GaN lattice
a non-single crystalline buffer layer, comprising a fast
with donor impurities, except that a negative bias is used on
material grown on said substrate, the first material
the substrate or the grid. Alternately, a charged surface can 10
consisting essentially of gallium nitride;
be generated by bombarding the substrate with electrons or
a first growth layer grown on the buffer layer, the first
positive ions. Electron guns and ion guns, respectively, are
growth layer comprising gallium nitride and a first
conventional sources of these species.
dopant material;
Suitable acceptor species include, but are not limited to,
a second growth layer grown on the first growth layer, the
zinc, magnesium, beryllium, and calcium. Suitable donor
second growth layer comprising gallium nitride and a
species include, but are not limited to, silicon, germanium, 15
second dopant material; and
oxygen, selenium and sulfur.
wherein the first growth layer comprises a first conducWhat is claimed is:
tivity type and the second growth layer comprises the
1. A semiconductor device comprising:
opposite conductivity type.
a substrate, said substrate consisting of a material selected
10. The semiconductor device of claim 9 wherein the first
from the group consisting of(100) Silicon, (111) 20
conductivity type is n-type.
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
sapphire, (111) gallium aresenide, (100) gallium
11. A semiconductor device comprising:
aresenide, magnesium oxide, zinc oxide and silicon
a substrate, said substrate consisting of a material selected
carbide;
from the group consisting of(l00) silicon, (111) silicon,
a non-single crystalline buff~r layer having a thickness of 25
(0001) sapphire, (11-20) sapphire, (1-102) sapphire,
about 30 A to about 500 A, comprising a first material
(111) gallium aresenide, (100) gallium aresenide, maggrown on said substrate, the first material consisting
nesium oxide, zinc oxide and silicon carbide;
essentially of gallium nitride; and
a non-single crystalline buffer layer, comprising a first
a first growth layer grown on the buffer layer, the first
material grown on said substrate, the first material
growth layer comprising gallium nitride and a first 30
consisting essentially of gallium nitride;
dopant material.
a first growth layer grown on the buffer layer, the first
2. The semiconductor device of claim 1 further comprisgrowth layer comprising gallium nitride and a first
ing:
dopant material;
a second growth layer grown on the first growth layer, the
wherein the buffer layer is a recrystallized , partially
second growth layer comprising gallium nitride and a 35
amorphous layer.
second dopant material.
12. The semiconductor device of claim 3 wherein the
3. The semiconductor device of claim 1 wherein the buffer
buffer layer is a recrystallized, partially amorphous layer.
layer is grown at a first temperature and wherein the first
13. A semiconductor device comprising:
growth layer is grown at a second temperature higher than
a substrate, said substrate consisting of a material selected
the first temperature.
40
4. The semiconductor device of claim 3 wherein the first
from the group consisting of (100) silicon, (111)
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
temperature is in the range of about 100° C. to about 400°
sapphire, (111) gallium aresenide, (100) gallium
C.
5. The semiconductor device of claim 3 wherein the
aresenide, magnesium oxide, zinc oxide and silicon
carbide;
second temperature is in the range of about 600° C. to about 45
900° C.
a non-single crystalline buffer layer, comprising a first
6. The semiconductor device of claim 1 wherein the buffer
material grown on said substrate, the first material
layer is grown by exposing the substrate to gallium and
comprising gallium nitride; and
nitrogen at the first temperature for about 3 to about 15
a near intrinsic gallium nitride layer grown on the buffer
minutes.
50
layer and having a resistivity of greater than 108 n·cm.
7. The semiconductor device of claim 1 wherein the first
at room temperature.
dopant material is a donor.
14. The semiconductor device of claim 13, wherein the
8. A semiconductor device comprising:
near intrinsic gallium nitride layer has a resistivity in the
a substrate, said substrate consisting of a material selected
range of about 108 n·cm to about 1012 n·cm at room
from the group consisting of(l00) silicon, (111) silicon, 55 temperature.
(0001) sapphire, (11-20) sapphire, (1-102) sapphire,
15. A semiconductor device having an activated p-type
(111) gallium aresenide. (100) gallium aresenide, maglayer comprising:
nesium oxide, zinc oxide and silicon carbide;
a substrate, said substrate consisting of a material selected
a non-single crystalline buffer layer, comprising a first
from the group consisting of (100) silicon, (111)
material grown on said substrate, the first material 60
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
consisting essentially of gallium nitride;
sapphire, (111) gallium aresenide, (100) gallium
a first growth layer grown on the buffer layer, the first
aresenide, magnesium oxide, zinc oxide and silicon
growth layer comprising gallium nitride and an accepcarbide;
tor dopant material;
a non-single crystalline buffer layer having a thickness of
a second growth layer grown on the first growth layer, the 65
about 30 A to about 500 A comprising a first material
second growth layer comprising gallium nitride and a
grown on said substrate, the first material consisting
donor dopant material.
essentially of gallium nitride; and

5,686,738

7

8

silicon, (0001) sapphire, (11-20) sapphire, (1-102)
an activated p-type growth layer compnsmg gallium
sapphire, (111) gallium aresenide, (100) gallium
nitride and an acceptor dopant material formed without
aresenide, magnesium oxide, zinc oxide and silicon
the use of a post-growth activation step.
carbide;
16. A semiconductor device comprising:
a non-single crystalline buffer layer, comprising a first
a substrate, said substrate consisting of a material selected 5
material grown on said substrate, the first material
from the group consisting of (100) silicon, (0001)
consisting essentially of gallium nitride; and
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
sapphire, (111) gallium aresenide, (100) gallium
a growth layer grown on the buffer layer, the growth layer
aresenide, magnesium oxide, zinc oxide and silicon
comprising gallium nitride and a first dopant material.
carbide;
10
20. A semiconductor device having an activated p-type
layer comprising:
a non-single crystalline buffer layer having a thickness of
about 30 A to about 500 A grown on the substrate and
a substrate, said substrate consisting of a material selected
comprising a first material consisting essentially of a
from the group consisting of(l00) silicon, (111) silicon,
Group III nitride grown at a temperature of about 100°
(0001) sapphire, (11-20) sapphire, (1-102) sapphire,
0
C. to about 400 C. from a molecular Group III source 15
(111) gallium aresenide, (100) gallium aresenide, magand an activated nitrogen source in a molecular beam
nesium oxide, zinc oxide and silicon carbide;
epitaxial growth chamber; and
a non-single crystalline buffer layer, comprising a matea first growth layer grown on the buffer layer and comrial grown on said substrate, the material consisting
prising gallium nitride and a first dopant material, the 20
essentially of gallium nitride; and
first growth layer being grown at a temperature of at
an activated p-type growth layer comprising gallium
least about 6000 C. from a molecular gallium source
nitride and a dopant material formed without the use of
and an activated nitrogen source in a molecular beam
a post-growth activation step.
epitaxial growth chamber.
21. A semiconductor device comprising:
17. The semiconductor device of claim 16 wherein the 25
a substrate, said substrate consisting of a material selected
Group III nitride is gallium nitride.
from the group consisting of (100) silicon, (111)
18. A semiconductor device comprising:
silicon, (0001) sapphire, (11-20) sapphire, (1-102)
a substrate, said substrate consisting of a material selected
sapphire, (111) gallium aresenide, (100) gallium
from the group consisting of (100) silicon, (111)
aresenide, magnesium oxide, zinc oxide and silicon
silicon, (0001) sapphire, (11-20) sapphire, (1-102) 30
carbide;
sapphire, (111) gallium aresenide, (100) gallium
a non-single crystalline buffer layer grown on the subaresenide, magnesium oxide, zinc oxide and silicon
strate and comprising a material consisting essentially
carbide;
of a Group ill nitride grown at a temperature of about
a non-single crystalline buffer layer having a first
1000 C. to about 400 0 C. from a molecular Group ill
thickness, comprising a first material grown on said 35
source and an activated nitrogen source in a molecular
substrate, the first material consisting essentially of
beam epitaxial growth chamber; and
gallium nitride; and
a growth layer grown on the buffer layer and comprising
a growth layer grown on the buffer layer having a second
gallium nitride and a first dopant material, the growth
thickness which is at least ten times greater than the
layer being grown at a temperature of at least about
first thickness, the growth layer comprising gallium 40
6000 C. from a molecular gallium source and an
nitride and a first dopant material.
activated nitrogen source in a molecular beam epitaxial
19. A semiconductor device comprising:
growth chamber.
a substrate, said substrate consisting of a material selected
from the group consisting of (100) silicon, (111)
* * * * *