Download 3A Physics of Electronic Devices

Heterostructures & Optoelectronic Devices

Light generation in semiconductor

Light emission diode (LED)

Semiconductor laser

Heterojunction transistors

Photo-detector
Compound
Semiconductor
Device
Market
Light Emission in Semiconductors
E
conduction electron
band
-
h
Band
gap
valence
band
+
Electron-hole
recombination
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
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
Light Emission Diode
Simple PN Junction LED
More efficient
heterojunction LED
Lattice Matching in Heteroepitaxy
Semiconductor Laser
Lateral confinement by proper
electrode design
Heterojunction and HEMT
Band Offset
High electron-mobility
transistor (HEMT) with
electron gas from the heavilydoped AlGaAs layer moving in
the undoped GaAs channel
Quantum Well and Superlattice
Bound states in quantum well to
mini-band in superlattice
Adjustable bandgap
Strained superlattice
III-V Nitride Optoelectronic Devices
(see: S.C. Jain et al., J. Appl. Phys. 87 (2000) 965)
III-V Nitride Optoelectronic Devices
GaN on sapphire with an
AlN buffer layer
GaN-InGaN DH LED
Large-scale
application
of LED
Photo-detector
E
conduction electron
band
-
h
Band
gap
valence
band
+
Reverse biased!
Electron-hole
generation
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.