화합물반도체 - GaN 1

화합물 반도체 ( II-1 )Heterostructure Growth

2007 / 가을 학기

화합물반도체 - GaN 2

화합물 반도체 박막 성장 - MBE Growth

MBE ( Molecular Beam Epitaxy )

* Molecular beam - vacuum 상태에서는 분자

의운동이 light와유사

- ultra-high-vacuum evaporation ( base pressure ~ 10-11 Torr )

* 가장얇은막을키울수있다.

V( gas flow ) < V( molecular beam )

- thin film 성장가능 ~ 5 Å ( mono-layer 성장 )

- 6” 에피성장이상용화

* EPI 사의 GEN 20000 MBE 장비

- 7 x 6 inch wafer 에피성장가능

- Uniformity 개선이큰 size에서는문제

* 4” GaAs 계열 epi-wafer ; 600~1000 $/wafer

* MOCVD 에피성장방법과경쟁.

화합물반도체 - GaN 3

Typical MBE System – VG V90S

화합물반도체 - GaN 4

in situ monitoring system of MBE

Ref.: X. Wang and A. Yoshikawa, Progress in Crystal Growth andCharacterization of Materials, pp. 42-103, 48/49 (2004)

화합물반도체 - GaN 5

Reflection High-Energy Electron Diffraction (RHEED)

Ref.: J. R. Arthur, Surface Science 500 (2002) 189–217

화합물반도체 - GaN 6

RHEED Oscillation in MBE Growth

화합물반도체 - GaN 7

Phase-Locked Epitaxy

화합물반도체 - GaN 8

Migration Enhanced Epitaxy

Absence of As4 during Ga deposition Enhanced Ga Surface Mobility

Better Surface (Increased RHEED Oscillation)

RHEED Oscillation

화합물반도체 - GaN 9

MBE Growth for GaN

< Plasma Induced MBE >- ECR or RF-plasma cracking of N2 gas

화합물반도체 - GaN 10

Various CVD Reactors

화합물반도체 - GaN 11

Growth Rate in CVD

Ref.: M. Masi, et al., Progress in Crystal Growth and Characterization of Materials 47 (2003), pp. 239-270

화합물반도체 - GaN 12

Equilibrium N2 pressures over the III-N (s) system

화합물반도체 - GaN 13

MOCVD Growth of Nitrides and Various Issues

suppression of pre-reactions (formation of (CH3)xM-NHx adducts)

at the higher total flow rate

Cracking of NH3

require high substrate temperature

Etching of InN with hydrogen from ammonia

Ref.: S. Keller, et al., Journal of CrystalGrowth 248 (2003) pp. 479–486

화합물반도체 - GaN 14

Two-Flow MOCVD for GaN Growth

Ref.: S. Nakamura et al., pp. 2021-2023, App. Phys. Lett. 58 (18),May 1991

use of subflow (N2+H2) to help NH3 cracking

화합물반도체 - GaN 15

Horizontal MOCVD Reactors

SNU’s preheated ammonia GaN reactor – save NH3 consumption

Aixtron’s GaN reactor (separate MO and hydride injectors)

Two-Flow Reactors

화합물반도체 - GaN 16

Three-Flow Horizontal MOCVD Reactors

(different gasflow recipe)N2

MO+H2NH3

Nippon Sanso’s GaN reactor

rotation speed

~ 10 rpm

화합물반도체 - GaN 17

Vertical MOCVD Reactors

Emcore’s vertical high-speed rotating disk D180GaN reactor

(high rotation speed ~ 1000rpm)

Thomas Swan close-coupled-showerheadGaN reactor

(high rotation speed ~ 500rpm)

MO NH3NH3 H2H2

화합물반도체 - GaN 18

Flow-Rate Modulation Epitaxy

Similar to Atomic Layer Epitaxy (ALE)

화합물반도체 - GaN 19

MBE versus MOCVD

* MBE

: 초진공상태(base pressure ~10-11torr)에서의 evaporation

GaAs MBE --- 6″ x 5장

* P : 발화성, 흡수성

chamber cleaning 필요

일반상태

P4 P2 : MBE 성장어려움

P4 P2 P

(cracked phosphor cell)

cracked phosphor cell의개발로인해 P-based compound의MBE 성장가능

* 진공에서 surface monitoring tool의사용

heating

heating 고온 heating

*MOCVD

:Metal Organic Chemical Vapor Deposition

Ga(CH3)3 + AsH3 GaAs↓ + CH4↑

In(CH3)3 + PH3 InP↓ + CH4↑

MOCVD system – (6″ x 3장)

* 두꺼운 P-compound 성장시MOCVD 사용

* Reflectometer의사용을통해 RHEED와같은 2-D growth & growth rate monitoring 기능수행

Very toxic!! AsH3대신 “Tertiary Butyl Arsenic (TBAs)를사용하면 safety 개선

화합물반도체 - GaN 20

Pseudomorphic and Relaxed Growth Mode for SiGe on Si

Lattice Mismatch

sub

sublayer

a

aaf

−= = 4.2 % for Si-Ge

화합물반도체 - GaN 21

Critical Layer Thickness ( hc )

* InGaAs single quantum well between GaAs layers

* Matthews and Blakeslee model of misfit-dislocation propagation

- In0.25GaAs의경우: hc ~ 120Å

- In0.3GaAs channel : rarely reported

(non-uniformity & reproducibility 문제)

화합물반도체 - GaN 22

SiGe Strained Epitaxy on Si Substrate

- SiGe strained epitaxy의 critical thickness

는 InGaAs 경우와는달리 metastable 상태

에서도 defect free한 epitaxy가가능함.

- 그러나, 이후에고온처리가있을경우,

defect가발생함.

Matthews and Blakeslee’smechanical equillibrium model

hc for SiGeepitaxy

화합물반도체 - GaN 23

Dependence of hc on the Growth Temperature

* SiGe Strained Layer Epitaxy * InGaAs Strained Layer Epitaxy

-성장온도가 550 ºC 이하에서는모든Ge % 에대해서 2D 성장가능

-저온성장의경우 critical thickness 증가- crystal 구조의성장을 저온에서제대로수행하기위하여서는 oxygen free의 moreclean한 environment 필요

화합물반도체 - GaN 24

Strain-Compensated Structure

In0.52Al0.48AsIn0.7Ga0.3As channel

thin InyGaAs

InP substrateIn0.52Al0.48As

tensile (y<0.53)

compressive- tensile layer의삽입으로

compressive layer의 hc증가

l.m. buffer : In0.52AlAs

strained buffer : In0.48AlAs

channel : In0.75GaAs

Ref.: JVST B, p. 1658, 2000