Laser Quality AlGaAs-GaAs Quantum Wells Grown on Low Temperature GaAs
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LASER QUALITY AIGaAs-GaAs QUANTUM WELLS GROWN ON LOW TEMPERATURE GaAs Y. Hwang, D. Zhang, T. Zhang, M. Mytych and R.M. Kolbas Department of Electrical and Computer Engineering North Carolina State University, Raleigh, NC 27695-7911 ABSTRACT In this work we demonstrate that photopumped quantum well heterostructure lasers with excellent optical quality can be grown on High top of a LT GaAs buffer layer by molecular beam epitaxy. temperature thermal annealing of these lasers blue-shifts the laser emission wavelengths but the presence/absence of a LT GaAs layer had little effect on the overall laser thresholds. Also, to first order it was not necessary to include an AlAs barrier layer to prevent adverse effects (as has been necessary in the gate stack of MESFETs to prevent carrier compensation).
INTRODUCTION Low temperature GaAs (LT GaAs) grown by molecular beam epitaxy (MBE) at a low substrate temperature of 200'C and subsequently in situ annealed at high temperatures (600'C, for example) has been shown to be highly resistive and optically inactive. These properties are attributed to a combination of excess Despite its arsenic and a large quantity of antisite defects [1,2]. seemingly undesirable electrical and optical properties, LT GaAs has been used in GaAs MESFETs [3,4], GaAs based HEMTs [5], photodetectors [6] and optical switches [7]. When LT GaAs is used as an insulator under the gate or as a buffer layer in MESFET structures, some adverse effects associated with the subsequent high A thin AlAs layer has been temperature in situ anneal occur [8]. shown to prevent these adverse effects by preventing the outdiffusion of excess arsenic related defects in the LT GaAs [8]. EXPERIMENTAL The separate confinement single quantum well heterostructures (SCSQWH) used in this study were grown by MBE (Varian 360) on
Mat. Res. Soc. Symp. Proc. Vol. 241. @1992 Materials Research Society
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undoped semi-insulating (100) oriented GaAs substrates. The SCSQWHs were grown by first depositing buffer layer(s) and then an A10. 4 GaO.6 As-AlO. 2Galo.sAs-GaAs separate confinement heterostructure as shown in Figure 1. Two sets of samples were prepared to: 1) compare a regular GaAs buffer to a LT GaAs buffer, and; 2) to compare regular GaAs to LT GaAs both with a 200A AlAs layer. The LT GaAs layer was grown at 200'C and in situ annealed at 590'C for 10 minutes under arsenic overpressure prior to deposition of the subsequent layers.
S0.2pro5900C GaAs 0.61trm AIo.4Gao.rAs 6860C 500A AIo.2GaoesAs 686oC
{
0.21gm LT GaAs 5900C
GaAs OW 500A AIo.2Gao.BAs
6860C
0 0.6jim AIO.4Gao.6As 686 C
Buffer Layer Substrate
6
200A AlAs 6400C 0.2grm GaAs 5900C
.200A AlAs 6400C
L 0.2jim LT GaAs 5900C
Figure 1: Schematic cross section of the SCSQWH laser samples with four different buffer layers grown by MBE. Post growth annealing was done in sealed quartz ampoules evacuated to 10-6 Torr with sufficient arsenic (5mg) to provide an arsenic overpressure of approximately 0.1 atmosphere in the range from 650-900'C. Laser samples were prepared by sel
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