OSC’s Industrial Affiliates Workshop, Tucson, Arizona
March, 2005
GaAsSb QUANTUM WELLS FOR OPTOELECTRONICS AND INTEGRATED OPTICS
Alan R. Kost, Xiaolan Sun, and Nasser PeyghambarianOptical Sciences Center, University of Arizona
Nayer EradatDepartment of Physics and Astronomy, Middle Tennessee State University
Espen SelvigNorwegian Defense Research Establishment
Bjorn-Ove FimlandNorwegian University of Science and Technology
David H. ChowHRL Laboratories
OUTLINE
1. Applications for materials with a band gap near 1.5 microns
2. Disadvantage of conventional materials on InP substrates for devices that use Bragg Mirrors
3. Novel antimony-based semiconductors
4. Photoluminescence studies of GaAsSb 5. Conclusions
APPLICATIONS FOR 1.5 MICRON SEMICONDUCTORS
OPTICAL COMMUNICATIONS
Motivation 1.5 microns is an absorption minimum for optical fibers
Important Devices:- Semiconductor Lasers (including VCSELs)- Photodiodes- Nonlinear Mirrors (Reflective Saturable Absorbers) for
Laser Modelocking
LASER RANGING AND LASER RADAR
Motivation 1.5 microns is an eye-safe wavelength
Important Device:- Nonlinear Mirrors for Laser Q-Switching
BRAGG MIRRORS
SemiconductorBragg Mirror nhigh, /4
nlow, /4
nhigh, /4
nlow, /4
nhigh, /4
nlow, /4
Semiconduc-tor Substrate
A semiconductor Bragg mirror is aquarter wavelength stack.
Photonic devices that use both 1.5 msemiconductors and Bragg mirrors are:
1. Vertical Cavity Surface Emitting Lasers (VCSELs)
2. Nonlinear Mirrors
CONVENTIONAL InGaAsP SEMICONDUCTORS FOR 1.5 MICRON DEVICES
GaAs InP
LATTICE CONSTANT IN ANGSTROMS
0.5
1.0
1.5
2.0
5.6 5.7 5.8 5.9 6.0 6.1 6.2
BA
ND
GA
P W
AV
EL
EN
GT
H(M
ICR
ON
S)
InAs
2.5
3.0
3.5
In0.53Ga0.47As
In0.16Ga0.84As0.39P0.61
InGaAs
Substrate
In1-x GaxAsyP1-y
1. Has band gap near 1.5 m for x 0.84
and y 0.39
2. Has the same latticeconstant as InPfor x = 0.1894y/(0.4184-0.013y)
BRAGG MIRRORS FOR InGaAsP
BraggMirror
Problem
nhigh - nlow ~ 0.3 (relatively small)
30 periods required (for VCSELs) High thermal and electrical resistance Poor device performance
InGaAsP nhigh
InP nlow
InGaAsP nhigh
InP nlow
InGaAsP nhigh
InP nlow
InGaAsP
InPSubstrate
Solutions
Find another mirror pair for InGaAsP - eg. InGaSb/AlGaSb
Find a better mirror pair and then lookfor a compatible 1.5 m semiconductor.
BRAGG MIRRORS ON GaSb
BraggMirror
Advantagenhigh - nlow ~ 0.8 (relatively high)
Challenge
Find a compatible 1.5 m semiconductor
AlGaSb nhigh
AlSb nlow
AlGaSb nhigh
AlSb nlow
AlGaSb nhigh
AlSb nlow
GaSbSubstrate
GaSb MATERIALS FOR 1.5 MICRON DEVICES
GaAs
LATTICE CONSTANT IN ANGSTROMS
0.5
1.0
1.5
2.0
5.6 5.7 5.8 5.9 6.0 6.1 6.2
BA
ND
GA
P W
AV
EL
EN
GT
H(M
ICR
ON
S)
2.5
3.0
3.5
Substrate
AlSb
GaSb
AlGaSb
GaAsSb
Candidates
AlGaSb(nearly indirect band gap)
GaSb Quantum Wells(indirect gap)
GaAsSb Quantum Wells
INDIRECT-GAP of GaSb/AlSb MULTIQUANTUM WELLS
G.Griffiths, K.Mohanned, S.Subbana, H.Kroemer and J.L.Merz 1983 Appl. Phys.
Lett. 43(11) 1059-1061
L
Г
X
L
Г
X
Adding Al +Quantum
Confinement
Indirect band gap
Adding As + Quantum
Confinement
GaAsSb QUANTUM WELLS FOR PHOTONICS
AlSb
GaAsxSb1-x
Confinement Energy
Confinement Energy
~1.5m
Well width is adjusted for each As fraction so that band gap is near 1.5m
5 samples for X=0, 0.091, 0.151, 0.188, 0.31
respectivelyThe samples were grown by
HRL Laboratories
50 Å GaSb Cap
AlSb
GaAsxSb1-x
AlSb
Al0.32Ga0.68Sb
AlSb
1000 Å GaSb Buffer
GaSb Substrate
60X
5X
BAND GAP DETERMINED BY PHOTOLUMINESCENCE
A reference sample is used for absolute measurements of PL strength
Computer
Argon Laser(488nm)
Spectrometer
Lock-in Amplifier
Voltage Frequency
Chopper
Mirror
Lens
LensLens
Detector
Sample
Reference Sample
GaAsSb QUANTUM WELLS
Photoluminescence increases dramatically with As content
1.2 1.3 1.4 1.5 1.6 1.7 1.8
0.00
0% As Sb1690
9.1% As
GaAsSb/AlSb
Quantum Wells
15.1% As
18.8% As
31% As Sb1704
Sb1707
Sb1720
Sb1682
P
L In
ten
sity
(a.
u.)
Wavelength ( m)