Carbon impurities in GaN form both acceptors and donors. Donor-to-acceptor ratios (DARs) determine the semi-insulating behavior of carbon-doped GaN (GaN:C) layers and are still debated. Two models are discussed; both can theoretically achieve semi-insulating behavior: the dominant acceptor model (DAM, DAR<1) and the auto-compensation model (ACM, DAR=1). We perform a capacitance–voltage analysis on metal/GaN:C/nGaN (n-doped GaN) structures, exhibiting Fermi-level pinning in GaN:C, 0.7 eV above the valence band maximum. This observation coupled with further interpretation clearly supports the DAM and contradicts the ACM. Furthermore, we reveal a finite depletion width of a transition region in GaN:C next to nGaN, where carbon acceptors drop below the Fermi level becoming fully ionized. Calculation of the potential drop in this region exhibits DAR values of 0.5–0.67 for GaN:C with total carbon concentrations of 1018 cm3 and 1019 cm3. Based on those results, we re-evaluate formerly published density functional theory (DFT)-calculated formation energies of point defects in GaN. Unexpectedly, growth in thermodynamic equilibrium with the bulk carbon phase contradicts our experimental analysis. Therefore, we propose the consideration of extreme carbon-rich growth conditions. As bulk carbon and carbon cluster formation are not reported to date, we consider a metastable GaN:C solid solution with the competing carbon bulk phase being kinetically hindered. DFT and experimental results agree, confirming the role of carbon at nitrogen sites as dominant acceptors. Under N-rich conditions, carbon at gallium sites is the dominant donor, whereas additional nitrogen vacancies are generated under Ga-rich conditions.

1.
K. J.
Chen
,
O.
Häberlen
,
A.
Lidow
,
C. L.
Tsai
,
T.
Ueda
,
Y.
Uemoto
, and
Y.
Wu
, “
GaN-on-Si power technology: Devices and applications
,”
IEEE Trans. Electron Devices
64
,
779
795
(
2017
).
2.
J. B.
Webb
,
H.
Tang
,
S.
Rolfe
, and
J. A.
Bardwell
, “
Semi-insulating C-doped GaN and high-mobility AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy
,”
Appl. Phys. Lett.
75
,
953
955
(
1999
).
3.
M.
Huber
,
I.
Daumiller
,
A.
Andreev
,
M.
Silvestri
,
L.
Knuuttila
,
A.
Lundskog
,
M.
Wahl
,
M.
Kopnarski
, and
A.
Bonanni
, “
Characterization of AlN/AlGaN/GaN:C heterostructures grown on Si(111) using atom probe tomography, secondary ion mass spectrometry, and vertical current-voltage measurements
,”
J. Appl. Phys.
119
,
125701
(
2016
).
4.
H.
Ahmad
,
T. J.
Anderson
,
J. C.
Gallagher
,
E. A.
Clinton
,
Z.
Engel
,
C. M.
Matthews
, and
W.
Alan Doolittle
, “
Beryllium doped semi-insulating GaN without surface accumulation for homoepitaxial high power devices
,”
J. Appl. Phys.
127
,
215703
(
2020
).
5.
S.
Heikman
,
S.
Keller
,
S. P.
DenBaars
, and
U. K.
Mishra
, “
Growth of Fe doped semi-insulating GaN by metalorganic chemical vapor deposition
,”
Appl. Phys. Lett.
81
,
439
441
(
2002
).
6.
M.
Kubota
,
T.
Onuma
,
Y.
Ishihara
,
A.
Usui
,
A.
Uedono
, and
S. F.
Chichibu
, “
Thermal stability of semi-insulating property of Fe-doped GaN bulk films studied by photoluminescence and monoenergetic positron annihilation techniques
,”
J. Appl. Phys.
105
,
083542
(
2009
).
7.
J. L.
Lyons
,
A.
Janotti
, and
C. G. V.
de Walle
, “
Carbon impurities and the yellow luminescence in GaN
,”
Appl. Phys. Lett.
97
,
152108
(
2010
).
8.
A. F.
Wright
, “
Substitutional and interstitial carbon in wurtzite GaN
,”
J. Appl. Phys.
92
,
2575
2585
(
2002
).
9.
C. H.
Seager
,
A. F.
Wright
,
J.
Yu
, and
W.
Götz
, “
Role of carbon in GaN
,”
J. Appl. Phys.
92
,
6553
6560
(
2002
).
10.
C.
Zhou
,
Q.
Jiang
,
S.
Huang
, and
K. J.
Chen
, “
Vertical leakage/breakdown mechanisms in AlGaN/GaN-on-Si devices
,”
IEEE Electron Device Lett.
33
,
1132
1134
(
2012
).
11.
A.
Chini
,
G.
Meneghesso
,
M.
Meneghini
,
F.
Fantini
,
G.
Verzellesi
,
A.
Patti
, and
F.
Iucolano
, “
Experimental and numerical analysis of hole emission process from carbon-related traps in GaN buffer layers
,”
IEEE Trans. Electron Devices
63
,
3473
3478
(
2016
).
12.
D.
Bisi
,
M.
Meneghini
,
C.
De Santi
,
A.
Chini
,
M.
Dammann
,
P.
Bruckner
,
M.
Mikulla
,
G.
Meneghesso
, and
E.
Zanoni
, “
Deep-level characterization in GaN HEMTs-part I: Advantages and limitations of drain current transient measurements
,”
IEEE Trans. Electron Devices
60
,
3166
3175
(
2013
).
13.
M.
Uren
,
S.
Karboyan
,
I.
Chatterjee
,
A.
Pooth
,
P.
Moens
,
A.
Banerjee
, and
M.
Kuball
, “‘Leaky dielectric’ model for the suppression of dynamic Ron in carbon-doped AlGaN/GaN HEMTs,” in IEEE Transactions on Electron Devices (IEEE, 2017), pp. 1–9.
14.
C.
Koller
,
G.
Pobegen
,
C.
Ostermaier
, and
D.
Pogany
, “Evidence of defect band in carbon-doped GaN controlling leakage current and trapping dynamics,” in 2017 IEEE International Electron Devices Meeting (IEDM) (IEEE, 2017), pp. 33.4.1—33.4.4.
15.
M.
Singh
,
M. J.
Uren
,
T.
Martin
,
S.
Karboyan
,
H.
Chandrasekar
, and
M.
Kuball
, “
‘Kink’ in AlGaN/GaN-HEMTs: Floating buffer model
,”
IEEE Trans. Electron Devices
65
,
3746
3753
(
2018
).
16.
A.
Armstrong
,
C.
Poblenz
,
D. S.
Green
,
U. K.
Mishra
,
J. S.
Speck
, and
S. A.
Ringel
, “
Impact of substrate temperature on the incorporation of carbon-related defects and mechanism for semi-insulating behavior in GaN grown by molecular beam epitaxy
,”
Appl. Phys. Lett.
88
,
082114
(
2006
).
17.
R. A.
Smith
,
Semiconductors
(
Cambridge University Press
,
1978
).
18.
C.
Poblenz
,
P.
Waltereit
,
S.
Rajan
,
S.
Heikman
,
U. K.
Mishra
, and
J. S.
Speck
, “
Effect of carbon doping on buffer leakage in AlGaN/GaN high electron mobility transistors
,”
J. Vac. Sci. Technol. B
22
,
1145
1149
(
2004
).
19.
G.
Meneghesso
,
M.
Meneghini
, and
E.
Zanoni
,
Gallium Nitride-Enabled High Frequency and High Efficiency Power Conversion
(
Springer
,
2018
).
20.
G.
Verzellesi
,
L.
Morassi
,
G.
Meneghesso
,
M.
Meneghini
,
E.
Zanoni
,
G.
Pozzovivo
,
S.
Lavanga
,
T.
Detzel
,
O.
Häberlen
, and
G.
Curatola
, “
Influence of buffer carbon doping on pulse and ac behavior of insulated-gate field-plated power AlGaN/GaN HEMTs
,”
IEEE Electron Device Lett.
35
,
443
445
(
2014
).
21.
G.
Curatola
and
G.
Verzellesi
, “Modelling of GaN HEMTs: From device-level simulation to virtual prototyping,” in Power GaN Devices: Materials, Applications and Reliability, edited by M. Meneghini, G. Meneghesso, and E. Zanoni (Springer International Publishing, Cham, 2017), pp. 165–196.
22.
B.
Rackauskas
,
M. J.
Uren
,
S.
Stoffels
,
M.
Zhao
,
S.
Decoutere
, and
M.
Kuball
, “
Determination of the self-compensation ratio of carbon in AlGaN for HEMTs
,”
IEEE Trans. Electron Devices
65
,
1838
1842
(
2018
).
23.
C.
Koller
,
G.
Pobegen
,
C.
Ostermaier
,
M.
Huber
, and
D.
Pogany
, “
The interplay of blocking properties with charge and potential redistribution in thin carbon-doped GaN on n-doped GaN layers
,”
Appl. Phys. Lett.
111
,
032106
(
2017
).
24.
C.
Koller
,
G.
Pobegen
,
C.
Ostermaier
, and
D.
Pogany
, “
Effect of carbon doping on charging/discharging dynamics and leakage behavior of carbon-doped GaN
,”
IEEE Trans. Electron Devices
65
,
5314
5321
(
2018
).
25.
M. J.
Uren
and
M.
Kuball
, “
Impact of carbon in the buffer on power switching GaN-on-Si and RF GaN-on-SiC HEMTs
,”
Jpn. J. Appl. Phys.
60
,
SB0802
(
2021
).
26.
C.
Koller
,
G.
Pobegen
,
C.
Ostermaier
,
G.
Hecke
,
R.
Neumann
,
M.
Holzbauer
,
G.
Strasser
, and
D.
Pogany
, “
Trap-related breakdown and filamentary conduction in carbon doped GaN
,”
Phys. Status Solidi B
256
,
1800527
(
2019
).
27.
B.
Rackauskas
,
S.
Dalcanale
,
M. J.
Uren
,
T.
Kachi
, and
M.
Kuball
, “
Leakage mechanisms in GaN-on-GaN vertical pn diodes
,”
Appl. Phys. Lett.
112
,
233501
(
2018
).
28.
J.
Wang
,
H.
You
,
H.
Guo
,
J.
Xue
,
G.
Yang
,
D.
Chen
,
B.
Liu
,
H.
Lu
,
R.
Zhang
, and
Y.
Zheng
, “
Do all screw dislocations cause leakage in GaN-based devices?
,”
Appl. Phys. Lett.
116
,
062104
(
2020
).
29.
J. L.
Lyons
,
A.
Janotti
, and
C. G.
Van de Walle
, “
Effects of carbon on the electrical and optical properties of InN, GaN, and AlN
,”
Phys. Rev. B
89
,
035204
(
2014
).
30.
J. L.
Lyons
and
C. G. V.
de Walle
,
Comput. Mater.
3
,
12
(
2017
).
31.
C. G.
Van de Walle
and
J.
Neugebauer
, “
Universal alignment of hydrogen levels in semiconductors, insulators and solutions
,”
Nature
423
,
626
628
(
2003
).
32.
A. I.
Duff
,
L.
Lymperakis
, and
J.
Neugebauer
, “
Ab initio-based bulk and surface thermodynamics of InGaN alloys: Investigating the effects of strain and surface polarity
,”
Phys. Status Solidi B
252
,
855
865
(
2015
).
33.
H.
Abu-Farsakh
and
J.
Neugebauer
, “
Enhancing nitrogen solubility in GaAs and InAs by surface kinetics: An ab initio study
,”
Phys. Rev. B
79
,
155311
(
2009
).
34.
L.
Lymperakis
,
T.
Schulz
,
C.
Freysoldt
,
M.
Anikeeva
,
Z.
Chen
,
X.
Zheng
,
B.
Shen
,
C.
Chèze
,
M.
Siekacz
,
X. Q.
Wang
,
M.
Albrecht
, and
J.
Neugebauer
, “
Elastically frustrated rehybridization: Origin of chemical order and compositional limits in InGaN quantum wells
,”
Phys. Rev. Mater.
2
,
011601
(
2018
).
35.
M.
Albrecht
,
L.
Lymperakis
,
J.
Neugebauer
,
J. E.
Northrup
,
L.
Kirste
,
M.
Leroux
,
I.
Grzegory
,
S.
Porowski
, and
H. P.
Strunk
, “
Chemically ordered AlxGa1xN alloys: Spontaneous formation of natural quantum wells
,”
Phys. Rev. B
71
,
035314
(
2005
).
36.
G.
Stringfellow
, “
A critical appraisal of growth mechanisms in MOVPE
,”
J. Cryst. Growth
68
,
111
122
(
1984
).
37.
G. B.
Stringfellow
, “
Fundamentals of vapor phase epitaxial growth processes
,”
AIP Conf. Proc.
916
,
48
68
(
2007
).
38.
M.
Pristovsek
,
A.
Kadir
, and
M.
Kneissl
, “
Surface transitions during InGaN growth on GaN(0001) in metal–organic vapor phase epitaxy
,”
Jpn. J. Appl. Phys.
52
,
08JB23
(
2013
).
39.
A.
Munkholm
,
G. B.
Stephenson
,
J. A.
Eastman
,
C.
Thompson
,
P.
Fini
,
J. S.
Speck
,
O.
Auciello
,
P. H.
Fuoss
, and
S. P.
DenBaars
, “
Surface structure of GaN(0001) in the chemical vapor deposition environment
,”
Phys. Rev. Lett.
83
,
741
744
(
1999
).
40.
C. G.
Van de Walle
and
J.
Neugebauer
, “
First-principles surface phase diagram for hydrogen on GaN surfaces
,”
Phys. Rev. Lett.
88
,
066103
(
2002
).
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