Photoluminescence Study of GaAs/AlGaAs Quantum Wells Grown On Si Substrates
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PHOTOLUMINESCENCE STUDY OF GaAs/A1GaAs QUANTUM WELLS GROWN ON Si
SUBSTRATES C. Jagannath, S. Zemon, P. Norris, B.S. Elman, S.K. Shastry, GTE Laboratories Incorporated, 40 Sylvan Road, Waltham, MA 02254 ABSTRACT Photoluminescence and photoluminescence excitation spectroscopies are utilized to study excitons in GaAs/AlGaAs quantum wells (QW's) fabricated using MBE on MOCVD grown GaAs/Si. The experimental results are understood in terms of the biaxial tension of approximately 3 kbar present in the plane of growth for both the QW's and the GaAs buffer. An important consequence of the biaxial tension is that for QW's with well widths larger than =-15 nm the light- and heavy- hole sub-bands cross each other in energy. This results in the light-hole exciton energy being lower than that of the heavy-hole exciton, opposite to the case of QW's grown on GaAs substrates. INTRODUCTION The growth of GaAs directly on Si (GaAs/Si) is of considerable current interest owing to the possibility of integrating the advantages of both Si and GaAs technologies[l]. In this connection, recent reports of fabrication of GaAs/AlGaAs Quantum Well (QW) devices on GaAs/Si are a promising first step[2-5]. It has been demonstrated that GaAs/Si is under biaxial tensile stress of =-2.5 kbar [6] at 4.2K. This has been attributed to differential thermal contraction between GaAs and Si from the growth temperature[6,71. Since stress is known to affect both the electronic and optical properties of semiconductors through the modification of their band-structure, an understanding of the effect of stress on the conduction and valence sub-bands in QW's is very important. Also, since the wavefunction of the exciton in QW's is confined to within
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100A, excitons can be utilized as probes of the spatial uniformity of stress
along the growth direction. We report a photoluminescence (PL) and photoluminescence excitation (PLE) study of GaAs/AlGaAs quantum wells, with varying well thicknesses, Lz, fabricated on GaAs/Si. As a result of the biaxial tension in the plane of the wells both the light-hole (LH) and heavy-hole (HH) excitons move to lower energies with the LH exciton energy decreasing faster than the corresponding HH exciton energy. For sufficiently large Lz the LH exciton is observed to shift to lower energy than the HH exciton, opposite to the case of unstressed QW's. Further, the biaxial stress in the single quantum wells (SQW's) is found to be the same as in the GaAs buffer. Finally, the good agreement between theory and experiment for the different wells strongly suggests that the MBE growth rate is similar for QW's on GaAs and GaAs/Si substrates.
Mat. Res. Soc. Symp. Proc. Vol. 91.
1987 Materials Research Society
250
RESULTS AND DISCUSSION The QW's were grown by MBE on a MOVPE GaAs/Si buffer layer following the MOVPE two step growth process described previously[81. Low pressure MOVPE was used to grow GaAs (approximately 2 gtm thick) layers , at 600 °C at a rate of 1.7 [tm/hr, directly on Si substrates oriented 40 from (100) towards (110). Subs
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