2. OSC’s Industrial Affiliates Workshop, Tucson, Arizona March, 2005 GaAsSb QUANTUM WELLS FOR OPTOELECTRONICS AND INTEGRATED OPTICS Alan R. Kost, Xiaolan Sun, and Nasser Peyghambarian Optical Sciences Center, University of Arizona Nayer Eradat Department of Physics and Astronomy, Middle Tennessee State University Espen Selvig Norwegian Defense Research Establishment Bjorn-Ove Fimland Norwegian University of Science and Technology David H. Chow HRL Laboratories

3. 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

4. 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

5. BRAGG MIRRORS Semiconductor Bragg Mirror n high, /4 n low, /4 n high, /4 n low, /4 n high, /4 n low, /4 Semiconduc- tor Substrate A semiconductor Bragg mirror is a quarter wavelength stack. Photonic devices that use both 1.5  m semiconductors and Bragg mirrors are: 1. Vertical Cavity Surface Emitting Lasers (VCSELs) 2. Nonlinear Mirrors

6. CONVENTIONAL InGaAsP SEMICONDUCTORS FOR 1.5 MICRON DEVICES GaAs InP LATTICE CONSTANT IN ANGSTROMS 0.5 1.0 1.5 2.0 5.65.75.85.96.06.16.2 BAND GAP WAVELENGTH (MICRONS) InAs 2.5 3.0 3.5 In 0.53 Ga 0.47 As In 0.16 Ga 0.84 As 0.39 P 0.61 InGaAs Substrate In 1-x Ga x As y P 1-y 1.Has band gap near 1.5  m for x  0.84 and y  0.39 2.Has the same lattice constant as InP for x = 0.1894y/(0.4184- 0.013y)

7. BRAGG MIRRORS FOR InGaAsP Bragg Mirror Problem n high - n low ~ 0.3 (relatively small)  30 periods required (for VCSELs)  High thermal and electrical resistance  Poor device performance InGaAsP n high InP n low InGaAsP n high InP n low InGaAsP n high InP n low InGaAsP InP Substrate Solutions Find another mirror pair for InGaAsP - eg. InGaSb/AlGaSb Find a better mirror pair and then look for a compatible 1.5  m semiconductor.

8. BRAGG MIRRORS ON GaSb Bragg Mirror Advantage n high - n low ~ 0.8 (relatively high) Challenge Find a compatible 1.5  m semiconductor AlGaSb n high AlSb n low AlGaSb n high AlSb n low AlGaSb n high AlSb n low GaSb Substrate

9. GaSb MATERIALS FOR 1.5 MICRON DEVICES GaAs LATTICE CONSTANT IN ANGSTROMS 0.5 1.0 1.5 2.0 5.65.75.85.96.06.16.2 BAND GAP WAVELENGTH (MICRONS) 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

10. 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

11. GaAsSb QUANTUM WELLS FOR PHOTONICS AlSb GaAs x Sb 1- x Confinement Energy ~1.5  m Well width is adjusted for each As fraction so that band gap is near 1.5  m 5 samples for X=0, 0.091, 0.151, 0.188, 0.31 respectively The samples were grown by HRL Laboratories 50 Å GaSb Cap AlSb GaAs x Sb 1-x AlSb Al 0.32 Ga 0.68 Sb AlSb 1000 Å GaSb Buffer GaSb Substrate 60X 5X

12. 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 Detector Sample Reference Sample

13. 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 PL Intensity (a.u.) Wavelength (  m)

14. 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