properties and effects of hydrogen in ganpearton.mse.ufl.edu/presentations/peh_gan.pdf ·...
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Properties and Effects of Hydrogen in GaN
S.J. Pearton(1), H. Cho(1), F. Ren(2), J.-I. Chyi(3), J. Han(4) and R.G. Wilson(5)
(1) Department of Materials Science and EngineeringUniversity of Florida, Gainesville, FL USA
(2) Department of Chemical EngineeringUniversity of Florida, Gainesville, FL USA
(3) Department of Electrical EngineeringNational Central University, Chung-Li, Taiwan
(4)Sandia National LaboratoriesAlbuquerque, NM USA
(5)Consultant, Stevenson Ranch, CA USA
Acknowledgments
•UF Funding : NSF DMR (L.D. Hess), DMR 97-32865: DARPA/EPRI (D. Radack/J. Melcher)
MDA 972-98-1-0006: ONR (J.C. Zolper)
•NCU : NSC/ROC, NSC-88-2215-E-008-012
•Sandia : DOE, DEAC04-94-AL85000
•RGW : ARO (J.M. Zavada)
EARLY WORK -- NAKAMURA (1992-1993)
0 200 400 600 800 1000Temperature (ºC)
107
106
105
104
103
102
101
100
10-1
Res
isti
vity
(Ω
⋅Ω
⋅m)
NH3 Ambient
N2 Ambient
REPASSIVATION IN NH3 AMBIENTGaN(Mg) - ANNEALED IN N2
REF: NAKAMURA et.al. JJAP 31 (1992).
H in GaN - What is Known
• As-Grown GaN(Mg) By AP-MOCVD Is Highly Resistive- Thermal Annealing (≥≥700oC) in N2- E-Beam Irradiation (≥≥25oC)- Forward Biasing (≥≥100oC)All Produce p-Type Conductivity
• Thermal Annealing In NH3 Reverts GaN(Mg) To Highly Resistive State
• As-Grown GaN(Mg) By LP-MOCVD, RBME Can Be p-Type Without Annealing(Lower H2 Flux, Vacuum Anneal)
• [H] Tracks Active [Mg] In Most Growth Techniques
• Mg-H Complexes are Detected By LVM
• Si-H Not Yet Detected (Suspicious Profiles However!)
• H Enters GaN During Many Process Steps, Even At 100oC
H in GaN - What is Not Completely Established
• Charge-States for H+, H-, Ho; Energy Levels
• Molecules, Larger Clusters : H2, Hn
• Role of H in Facilitating p-Type Doping- Van Vechten (H Compensates Native Defects)- Neugebauer, Van de Walle, Neumark (Mg↑↑, Nv↓↓ in Presence of Hydrogen)
• Role of Line and Point Defects in enhancing H Diffusion (Heteroepitaxy vs. ELO GaN)
•Solubility
=−
=−
+
−
)1995,,(
,05.2
47.0
)1999(..,3.2
)0(
)0(
WalledeVanNeugebauerlyrespective
eVandeVarecubicforvalues
eVEE
aletWrightMyerseVEE
C
C
Passivation of Acceptor Dopants in GaN
Table I. p-dopants found to be passivated by atomic hydrogen in GaN
Dopant Comments ReferencesMg residual hydrogen in growth ambient Amano et.al., HHAP (1989)
leads to high resistivity in as-grown Nakamura et.al., JJAP (1991, 1992)GaN(Mg)
Zn electron injection increases Zn-related Amano et.al., J. Lumin (1988)emissions in GaN(Zn)
C H2 plasma exposure decreases hole Pearton et.al., Electron. Lett. (1994)density by a factor of 3 - thermallyreversible
Ca H2 plasma exposure decreases hole Lee et.al., Electron. Lett. (1996)density by a factor of 10 - thermallyreversible
Cd formation of Cd-H complexes seen by Burchard et.al., MRS Proc. (1997)PAC - dissociate at <350oC
POSSIBLE CONFIGURATIONS OF H-DOPANT COMPLEXES IN GaN
FORMATION ENERGY FOR ACCEPTORS, DEFECTS, HI ANDMg-H COMPLEX
REF: NEUGEBAUER & VAN DE WALLE, MRS PROC. Vol. 423 (1996).
Incorporation of Hydrogen During Growth
MOCVD : (CH3)3 Ga + NH3 → GaN + CH4 + H2 (Generally use H2 Carrier Gas)
: Tg = 1040oC (Solubility?)
: Long Cool-Down After Growth- 400-700oC (?)- Cooled Under NH3
- H2 Carrier Gas
: p-GaN(Mg) Resistive After AP-Growth- Cp2Mg- Annealing Not Necessary in LP-Growth with N2 Carrier Gas
(Toshiba Laser)
: (Mg-H)0 ↔ Mg¯ + H+ (Plus Subsequent H2 Formation?)
SOURCE OF HYDROGEN IN MOCVD GROWTH OF p-GaN
REF. SUGIURA et. al. APL 72 1748 (1998)
• H2 CARRIER GAS CONTRIBUTES ~ 50% OF THE RESIDUAL HYDROGEN• (CH3)3Ga, NH3 AND Cp2 Mg CONTRIBUTE THE OTHER 50%• FOR THIS REASON, POST-GROWTH ANNEALING IS STILL REQUIRED FOR
HIGHEST p-TYPE DOPING
Table. Resistivity (ρ), Mg concentration (NMg), acceptor concentration (NA-ND), carrier concentration (p) and Hall mobility (µ) of p-type Mg-doped GaN obtained by the conventional H2-rich growth with subsequentthermal annealing, N2-rich growth (2.4%-H2) and H2-free growth.
The symbol × indicates that the value is unable to be measured.
ρ (Ω⋅cm) NMg (cm-3
) NA - ND (cm-3
) P (cm-3
) µ (cm2/V⋅s)H2 - rich growth
(as - grown)High
resistivity× × × ×
H2 - rich growth(annealed)
1 - 2 6 ×10
196 - 10 ×
1018
3 - 5×10
1
7
5 - 10
N2 - rich growth(as - grown)
3 - 4 3 - 6×
1018
3 - 4 ×10
182 - 3
×10
17
5 - 14
H2 - free growth(as - grown)
0.8 - 1 6 ×10
196 - 8 ×
1018
0.8 - 2×
1018
5 - 10
HYDROGEN IN AS-GROWN GaN
Si-DOPED NOMINALLY UNDOPED
HYDROGEN IN AS-GROWN AND ANNEALED, MOCVDGaN(Mg)
0.0 0.5 1.0 1.5 2.0
Depth (µm)
Al
H after annealing
H before annealing
1.0E+21
1.0E+20
1.0E+19
1.0E+18
1.0E+17
1.0E+16
Mg after annealing
Mg before annealing
Ato
mic
con
cent
rati
on (
cm-3
)
RESISTIVE AS-GROWN; p=1018cm-3 AFTER 700oC, 60 MIN N2
REF: YUAN et.al. JECS (1995) - AP MOCVD.
USE OF LVMS TO MONITOR THE REACTIVATION OF PASSIVATED Mg
REF: HARIMA et.al., APL 75 1383 (1999).
657 cm-1 band: Mg acceptors
3123 cm-1 band: Mg-H complex(close to NH3 molecule value, suggests Mg-N-H, with H at (ABN)).
Typical Impurity Contents in GaNImpurity densities in III-nitrides (cm-3)
Nitride Growth H C O Si
GaN MOCVD(Source A)
5x174x184x182x192x197x19
1.5x181x182x18
1x177x163x172x172x172x198x177x174x18
1x182x184x185x186x185x191x181x18
2.5x19
5x162x172x161x163x16
-5x177x177x17
GaN MOCVD(Source B)
3x175x172x173x182x18
6x153x163x16
2.5x175x16
6x162x171x179x172x17
1.5x171.5x173x165x17
-
GaN MOCVD(Source C)
4x182x19
1.5x183x17
8x185x18
8x172x17
GaN MOCVD(Source D)
<1x172x19
1x153x17
1x165x16
5x1015
-
GaN MOCVD(Source E)
1x17 3x15 2x16 2x1015
GaN MOCVD(Source F)
2x175x17
3x161x17
1x171x17
3x161x17
GaN MBE 4x199x18
1.5x181.2x18
2x192x18
3x175x17
GaN LA 1x20 1x21 1x21 1x19AlN MOCVD 1-2x18 7x17 2x18 1.5x19AlN CVD 3x18
4x203x151x18
5x185x19
3x161x19
AlN CVD 1x19 5x18 8x18 -AlN CVD 4x18 1.5x18 8x18 8x17AlGaN MOCVD 2x19 2x18 5x18 3x18AlGaN MOCVD 7x18 8x18 2x19 7x17AlInN MOMBE 5x18 3x18 2x19 1x20InN MOMBE 8x20 7x19 1x21 2x19
REF: R.G. Wilson - SIMS Analysis of Widebandgap Semiconductors (1998).
Effect of Hydrogen on Device Performance - HBT
Al2O3
Ti/Al/Pt/Au
Ni/Au
Ti/Al/Pt/Au
LT-GaN
MOCVD GaN
5000 Å n+-GaN
4000 Å n--GaN
2000 Å p-GaN
n+-GaN
• Base doping is reduced
• RC is increased
- ohmic heating of contact
- reliability problems
- reduced switching speed
• time dependent gain as injection
reactivates the Mg dopant
Hydrogen in As-Grown Device Structure - npnp Thyristor
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
1E+22
0 1 2 3 4 5 6
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
SE
CO
ND
AR
Y IO
N IN
TE
NS
ITY
(ct
s/se
c)GaN (counts)->
C
O
H
Si
Mg
29 Sep 1999 CS FILE: B2067'03
Structure 2, Thyristor
Hydrogen in As-Grown Device Structure - pin Diode
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
1E+22
0 1 2 3 4 5
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
SE
CO
ND
AR
Y IO
N IN
TE
NS
ITY
(ct
s/se
c)
GaN (counts)->
-C
O
H
Si
29 Sep 1999 CS FILE: B2067c02
Structure 1, Pin
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 1 2 3 4 5
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
Mg
29 Sep 1999 O2 FILE: B2067c07
Structure 1, Pin
Hydrogen in Device Structures - GaN/AlGaN HBT
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
0 0.5 1 1.5 2
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
SE
CO
ND
AR
Y IO
N IN
TE
NS
ITY
(ct
s/se
c)
GaN->
Ga->
Mg
Al->
O->
O2 beam: Positive SIMS
18 Aug 98 O2 FILE: 74522G15
Sample I.D: U.of. Florida: ND0616B
1E+14
1E+15
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
1E+22
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
SE
CO
ND
AR
Y IO
N IN
TE
NS
ITY
(ct
s/se
c)
GaN->
H
Al->
Ga->
Cs Beam: Negative SIMS
18 Aug 98 Cs FILE: AROBO11a
Sample I.D: U.of.Florida (ND0616B)
Hydrogen in As-Grown Device Structure -Schottky Rectifier
1E+16
1E+17
1E+18
1E+19
1E+20
1E+21
1E+22
0 0.5 1 1.5 2 2.5 3
DEPTH (microns)
CO
NC
EN
TR
AT
ION
(at
oms/
cc)
1E+00
1E+01
1E+02
1E+03
1E+04
1E+05
1E+06
1E+07
SE
CO
ND
AR
Y IO
N IN
TE
NS
ITY
(ct
s/se
c)
GaN (counts)->-C
O
H
Si
29 Sep 1999 CS FILE: B2067c05
Sample NE 0308
REACTIVATION OF Mg IN GaN BY MINORITY CARRIER INJECTION
FORWARD BIAS (8V)THERMAL ANNEAL
REF: M. MIYACHI et.al. APL (1998).
AS-GROWNFORWARD BIAS (400oC)THERMAL ANNEALING (800oC)
DIFFUSION IN LED STRUCTURE EFFECT OF ANNEALING AMBIENTON Mg REACTIVATION
H IN HETEROSTRUCTURES
DIFFUSION IN LED STRUCTURE EFFECT OF ANNEALING AMBIENTON Mg REACTIVATION
H IN HETEROSTRUCTURES
MULTIPLE SITES FOR 2H IN GaN
THERMAL STABILITY OF PLASMA AND IMPLANTED H IN GaN
Incorporation During Processing
Table II. Processing steps in which hydrogen is found to be incorporated into GaN.
Process Temperature(o C)
Max. [H] (cm -3) IncorporationDepth (µµm)
H 2O Boil 100 1020 1.0PECVD SiNX 125 3x1019 0.6
Dry Etch 170 1019-1020 >0.2Implant Isolation 25 Dose Dependent 2.0
Wet Etch 85 2x1017 0.6
DIFFUSION OF IMPLANTED 2H
n-TYPE GaN p-TYPE GaN
WEINSTEIN/STAVOLA et.al. APL (1998).
• 1H IMPLANTED• 400oC ANNEAL• CLOSE TO VIBRATIONAL FREQUENCIES PREDICTED FOR VGa-Hn
COMPLEXES (Van de Walle, PRB 1997)
VIBRATIONAL SPECTROSCOPY OF 1H IMPLANTED GaN
HIGH CONCENTRATIONS OF H INCORPORATED BY IMPLANTATION
REF: MYERS et. al. MIJ-NSR 4S1 G5.8 (1999).WAMPLER et. al. MIJ-NSR 4S1 G3.73 (1999).MYERS et. al. PRB (1999).
• AT CONCENTRATION > 1 at%, FACETTED H2 BUBBLE FORM in GaN• AT CONCENTRATION ≤ 0.1 at%, NO BUBBLES, H LOCATED AT DEFECTS IN
[0001] CHANNEL
HR-TEM of bubbles in GaN (2×1016cm-2/50keV; 886oC 1hr)(a) plan view in [0001] (b) cross-section in [1120]
Conclusions
• H Tracks Electrically Active Mg in As-grown Device Structures and Decorates Regions of Strain
• Reactivation By Thermal Annealing at 7000C Does Not Remove H From GaN, But Does (Mostly) Reactivate The Mg Acceptors. Repassivation Is a Problem Under These Conditions.
• Benefits of H (Passivation of Defects/dislocations; Suppressing Self-compensation in GaN(Mg))Are Unclear
• Effect of High Defect Density in Conventional Heteroepitaxial GaN Is Likely an Enhancement of H Diffusivity (Comparisons With Bulk, ELO GaN Have Not Yet Been Made).