3.46 PHOTONIC MATERIALS AND DEVICES Lecture 12: Crystal Growth

Lecture Notes

Compound Semiconductor Crystal Growth

Intensive Variables

P, T, μ

Gibbs Phase Rule

V = C – P + 2

One Component System

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 1 of 8

Lecture Notes

Two Component System

Solidification Crystalline State

1) First order phase transition G TΔ =Δ U +PV − Δ S

2) Composition Cs is richer in B than the liquid CL.

3) ΔHf latent heat of fusion is evolved. 4) Composition of solid varies continuously

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 2 of 8

Lecture Notes

Immiscible Systems

Csk = CL

Compound formation

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 3 of 8

Lecture Notes

Crystal Growth from the Melt Requirements: 1) melts congruently 2) does not decompose before melting 3) no phase transition between TMP and RT.

Methods: Czochrakski growth • seed • melt with crucible • heat flow (ΔHf )

Gradient freeze • boat with melt • traveling ∇T

Solution Growth

Cs

1) Diffusion of solute to S/L interface 2) Attachment of solute atom to crystal 3) Evolution of ΔHf

Vapor Phase Growth Molecule Beam Epitaxy MBE Chemical Vapor Deposition CVD Metal Organic Chemical Vapor Deposition

MOCVD

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 4 of 8

Lecture Notes

Vapor Phase Growth:

Gas Phase Equilibrium for AB compounds

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 5 of 8

Lecture Notes

MBE Growth

10−9 −10−12 • UHV torr • molecular flow MFP >> chamber size

πO O )−1

MFP = λ =( 2 Nd2

molecule diameter molecule

2cm

0.05 torr mm ⋅ �λ300 K

10 P

−3T ⇒λ = 50 mm

760 T =1 atm ⇒λ = 70 nm

E kT

⎤[ ]∝ exp ⎡⎢⎣−P ⎥⎦

1

φ ∝P MT )− 2(

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 6 of 8

Lecture Notes

CVD Growth

• mass transport + source reaction • gas phase diffusion • homogenous gas phase reactions • heterogeneous reaction at substrate

Source + transport

halide 1H2Ga +HCl ⎯⎯→GaCl + H2 + 2

hydride

H24AsCl3 + 6H2 ⎯⎯→ As4 +12HCl halide

H24AsH3 ⎯⎯→ As4 + 6H hydride2

Deposition

As4 + 4GaCl + 2H → 4GaAs + 4HCl 2

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 7 of 8

Lecture Notes

MOCVD Growth

• no source or transport reactions • chemistry controlled by pyrolysis of

(CH3 ) Ga adsorbed on substrate 3

H2(CH3 ) Ga + AsH3 ⎯⎯→GaAs + 3CH43

LPE Growth

• In-rich side of phase diagram • Lower T ⇒ super saturation • Quartz reactor, H2 (reduces slag) • Solid composition determined by melt

composition + T

3.46 Photonic Materials and Devices Lecture 12: Crystal Growth Prof. Lionel C. Kimerling Page 8 of 8