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)

CONCLUSIONS

• GaAsSb is a promising material for 1.5 micron photonic device that is compatible with high quality AlGaSb/AlSb Bragg Mirrors

• We have clearly shown that adding As to GaSb increases photoluminescence strength, a positive sign for photonic devices