Effect of Growth Conditions on Optical Response of GaAs Grown at Low Substrate Temperature by MBE
- PDF / 420,377 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 84 Downloads / 231 Views
EFFECT OF GROWTH CONDITIONS ON OPTICAL RESPONSE OF GaAs GROWN AT LOW SUBSTRATE TEMPERATURE BY MBE W.J. Schaff, S.D. Offsey, X.J. Song, L.F. Eastman, Department of Electrical Engineering, Cornell University, Ithaca, New York 14853 T.B. Norris, W.J. Sha, G.A. Mourou, Ultrafast Science Lab, University of Michigan, Ann Arbor, Michigan 48109 ABSTRACT The effect of growth conditions on the properties of GaAs grown by molecular beam epitaxy at low substrate temperatures has been studied. It has been found that the response time to 100 fsec 830nm light pulses is a function of substrate temperature and arsenic flux. The reason for variation of optical response with growth conditions is related to the nature of the incorporation of excess arsenic. A recent model proposed by Warren and others is invoked to explain the change in optical response with growth conditions. Further substantiation of this model comes from experiments on the annealing of low substrate temperature GaAs which has been doped with silicon. INTRODUCTION The applications of Low substrate Temperature GaAs (LT GaAs)1 grown by molecular beam epitaxy (MBE) exploit its properties of high resistivity 2 , high breakdown voltages 3 and fast optical response4 . Applications for materials with fast optical response include the generation of THz frequency signals from subpicosecond optical pulses. The maximum frequencies which can be obtained are limited by recombination time of carriers following optical excitation. The study reported here has two purposes. First, the effect of growth conditions on optical response has been examined to determine the conditions leading to the fastest optical response. Second, this data has been analyzed to learn more about the nature of the recombination process and the role that excess arsenic plays in this process. The nature of excess arsenic incorporation following annealing is studied through electrical characterization. EXPERIMENTAL 5 Excess arsenic incorporation in GaAs grown at low substrate temperatures (-200°C) is an unusual phenomena when compared to the properties of GaAs grown at high temperatures (above -300'C) where As is in near perfect concentration ratio with Ga. Optically generated carriers recombine at 0 in GaAs rates orders of magnitude faster 100A "C 58 GaAs 10 min growth 6 grown at low temperatures than for 580°C interruption fo:s nnteation f . higher temperature grown material. A relationship might be expected to exist l r.e.a. .r. .. L.. excess arsenic concentration :between w emperLoure 5min growth and optical response times. The experiments reported here are aimed at interruption for GaAs 580°C i00A understanding this relationship. temperature change Two techniques exist for adding excess AlGaAs/GaAs Superlattice 2.1p1tm arsenic to GaAs. As noted above, substrate temperature strongly affects GaAs arsenic incorporation. The Substrate magnitude of arsenic flux would also be expected to play a role in controlling SFemtosec These two arsenic concentration. parameters were studied using the optical excitation sh
