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 Engineering University of Florida, Gainesville, FL USA (2) Department of Chemical Engineering University of Florida, Gainesville, FL USA (3) Department of Electrical Engineering National Central University, Chung-Li, Taiwan (4) Sandia National Laboratories Albuquerque, NM USA (5) Consultant, Stevenson Ranch, CA USA
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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
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
• 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
• 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).