GaN MOCVD Growth

1
Park Jae Young
GaN MOCVD Growth
? ? ? ? ? ?
2005? 11? 3?
Photonic Electronic Thin Film Lab, Dept. of
Mat. Sci. Engg, Chonnam National University,
Korea
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History of LED
? 1923? SiC? ??? ???? ?? ? GaP? ?? III-V ???????
LED ???? ???? ??. ? 1968? GaAsP ?? LED? ????
???? (?? ?????? ??) ? ??? ??? Si ??? ???? ????
??, LED ????? ?? ???? ???? ?? ? ??? ??
????? ???? ??? LED ?? ??. ? 1980?? ??? ?? AlGaAs
LED ?? (?? ???? ???? ?? ?? ??). ? 1993? ???
Nichia?? ????? ??? InGaN ?? LED ??. ? 1995? ???
InGaN ?? LED? ??? (??? ?? ?????? ??). ? 1996? ??
LED? ????? ???? ?? LED? ??. ? 2000? ???
Agilent??? ??? InGaAlP? ??? ?? LED? ?????
??? ?? 100 lm/w? ?? (??? ?? ??? ??).
3
Crystal structure of GaN
Mg
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Chemical, Thermal, and Mechanical Stable
???? ??? ?? ?? ??????? ???? ??? ??? ??? ??? ??
Wide Band Gap Semiconductor? ???? ???? ?? ???
??? ??, ???, ??? ??? ?? ??
600oC ??? ?? ?????? ? ?? ??? ??? ???
??? (Al-N2.88 eV, Ga-N2.20 eV, In-N1.93 eV)
??? ?????? ?? ??? ???? ?? ? order ?? ??? 500oC
??? ???? ??? ??? ???? ??? ???? ?? ??? ???
H3PO4H2SO4 ??? ??
5
GaN Crystal Structure
Schematic Illustration of GaN Growth onto
Sapphire (0001) Surface
Wurtzite structure
(0001) GaN // (0001) sapphire with a 30
rotation lattice mismatch between GaN and
sapphire 13.8
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Why GaN ? (From Red To UV)
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Visible Semiconductors
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Optical Data Storage System I

• HD-DVD? CD(?? 650MB), DVD(?? 4.7GB)? ?? ?3??
  Optical Storage??
• Blue Laser? ???? ?? 20GB ??? ??? ? ?? Disc?.

7?
6?

• User Key Benefit
• - ??? HD ??? 2?? ?? ?? ??
• - ?? ???? ?? (SD?) 13?? ?? ????

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Optical Data Storage System II
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Why MOCVD ?

• Very high quality of grown layers (high
  growth rate and doping uniformity/reproducibility)
  
• High throughput and no ultra high vacuum needed
  (-compared to MBE) (Economically
  advantageous, high system up-time)
• Highest flexibility (Different materials can
  be grown in the same system)
• Growth of sharp interfaces possible very
  suitable for heterostructures, (e.g., multi
  quantum wells (MQW))

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Components of a MOCVD System
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Basic Reaction I (By MOCVD)
Ga(CH3)3 NH3 GaN 3CH4 (by-products)
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Basic Reaction II (By MOCVD)
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GaN thin films growth process
1) Growth process of the GaN layer on AlN
nucleation layer
(b) Lateral Growth
(a) Island Growth
GaN
LT-AlN
Sapphire
(d) Quasi 2-D Growth
(c) Coalescence
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Buffer-layer growth technique
GaN ??? ??????? ????? ?? ( relaxation) ??
1. ???? 2. ?? ?? 3. ????(?? )
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Nitride-based Semiconductor materials growth
Issues

• 1) GaN ??? ??
• a-Al2O3 (sapphire), 6H-SiC, MgO, ZnO ??
• ???? ???(16 for sapphire, 3.5 for SiC)
• ????? ??
• ?? dislocation ?? (1081010cm-2)
• (???) Buffer ?? (AlN or GaN), ELOG GaN
  , Pendeo GaN
• 2) P-? ??? p-? ?? ??
• Mg ??? ???? ? (160meV in p-GaN)
• H-passivation LEEBI, ???,UV ??
• Hole ??? ??
• ?? ????? ?? ???(work function )? ?? ?? ??
• ??? ?? ?? ??
• (???) Carrier gas N2 ??, Co-doping

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• 3) InGaN/GaN ???? ? QW ?? ??
• ?? In ??? ?? ???
• ??? InGaN ???
• ???? ??? ?? ?? ???
• (???) Co dopoing, ???? ??
• 4) AlGaN/GaN ??
• ?? ? ??
• Crack ?? AlGaN ?? ? Al ??? ??
• (???) Modulation doping, InGaN ?? ?
  strain compensation ??
• 5) Device ??
• Not chemical etching
• Dry etching
• Not cleaving
• Metal contact

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Quantum well structure (QW)
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Crystal Defect Formation ( Dislocation )
During HT Epi-layer Growth
. Crystal quality ?? (Dislocation) .
InGaN/GaN MQWs ??? ? p-GaN ?? ? ?? ?? ?
????(VF / 20 mA) ?? gt ???
??? ??
??? ?? ?? ?
Growth Issue
7 / 14
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Dislocations in LEDs

• (??)
• ??? ??? ??? ?? ??? (-16 for sapphire, 3.5 for
  SiC)
• ????? ???? ?? ?? (-34 for sapphire, 25 for
  SiC)
• (LED ? ??? ??)
• Traps (?)
• Non-radiative recombination centers (?)
• Negative-charged scattering centers (?)
• P-type doping efficiency (?)
• Leakage current pathway
• Electronic discharges
• Device life time

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Applications I
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Applications II
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Applications III
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Applications IV