1. Heterostructures & Optoelectronic Devices
Light generation in semiconductor
Light emission diode (LED)
Semiconductor laser
Heterojunction transistors
Photo-detector

2. Compound Semiconductor Device Market

3. Light Emission in Semiconductors
electron
conduction
band - h
Band
gap
Electron-hole
recombination +
valence
band
hole
Si: Eg = 1.1 eV
GaAs: Eg = 1.4 eV,  = 880 nm
AlAs: Eg = 2.2 eV,  = 565 nm
Si: indirect bandgap, ineffective
GaAs: direct bandgap, effective

4. Electron-Hole Recombination and photon Energy
If the electron-hole
recombination occurs
not at the minimum gap
point, the emitted photon
can have a higher energy.
When the recombination
involves an impurity state
in the gap, lower-energy
photon is generated.
h > Eg

5. Light Emission Diode More efficient Simple PN Junction LED
heterojunction LED
Simple PN Junction LED

6. Lattice Matching in Heteroepitaxy

7. Semiconductor Laser
Lateral confinement by proper
electrode design

8. Heterojunction and HEMT
Band Offset
High electron-mobility transistor (HEMT) with electron gas from the heavily-doped AlGaAs layer moving in the undoped GaAs channel

9. Quantum Well and Superlattice
Bound states in quantum well to mini-band in superlattice
Strained superlattice
Adjustable bandgap

10. III-V Nitride Optoelectronic Devices
(see: S.C. Jain et al., J. Appl. Phys. 87 (2000) 965)

11. III-V Nitride Optoelectronic Devices
GaN on sapphire with an
AlN buffer layer
GaN-InGaN DH LED

12. Large-scale application of LED

13. Photo-detector E h Reverse biased! Simple detector: conductivity
electron
conduction
band - h
Band
gap
Reverse biased!
Electron-hole
generation +
valence
band
hole
Si: Eg = 1.1 eV, c= 1130 nm
Simple detector: conductivity
increase of semiconductor
when illuminated.
P-I-N photo-detector: low dark
current, quick response.