A Study of Band Alignment in GaAs/GaInP(Partially Ordered) Heterostructures with High Pressure
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381 Mat. Res. Soc. Symp. Proc. Vol. 499 ©1998 Materials Research Society
SAMPLE STRUCTURES, GROWTH CONDITIONS AND CHARACTERISTICS The GaInP samples reported in this paper were all grown by metal-organic vapor phase epitaxy (MOVPE) on a GaAs buffer layer which was in turn grown on a semiinsulating GaAs substrates. Depending on the growth conditions, substrate orientations and structure, the samples have been divided into three series. The first series of GaInP samples were grown by Mr. Noto of the ISOBE Semiconductor Laboratory, Shin-Etsu Handoutai Company, Japan, using GaAs substrates with different degrees of mis-orientation from the [001] direction towards the [OTT ]A equivalent directions. These samples have been labeled as SI to S4 and their degrees of mis-orientation increases from 00 to 150 in steps of 5*. The sample S1 which was grown on a [001] oriented substrate has the highest degree of ordering and therefore also the lowest energy emission peak at room temperature (1.86 eV) while the sample S4 is most disordered and has the highest energy emission peak energy (1.92 eV). All the Sseries samples were grown at 700 * C with V/III ratio and growth rate of 100 and 3 jim/hour, respectively. The thickness of the GaInP epilayers is I1P in all cases and the lattice mismatch between the GaInP layers and the GaAs substrate was determined by xray diffraction to be less than 0.1%. A comparison of the {0 11} electron diffraction pattern from the samples S1 and S4 are shown in Figure 1. Figure 1. (011) electron diffraction patterns
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S4
The extra diffraction spots found in the pattern from Sample 51 but not in sample S4 shown in Figure 1 are evidence of CuPt ordering present in sample S1. A second series of three samples were grown in Nippon Sanso Company, Japan, on 1mm thick GaAs substrate with [001] orientation but at different growth temperatures. These samples have been labeled as T650, T700, and, T750 according to their growth temperatures which varies from 650 °C to 750 *C. The thickness of these samples is also jli and they were
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grown with a V/IIl ratio of about 200 for the GaInP layer and a ratio of 50 for the GaAs buffer layer. All three samples show high degrees of ordering as indicated by the energies of their low temperature excitonic emission peaks: 1.895 eV (T650), 1.888 eV (T700) and 1.928 eV (T750). A series of four "quantum well" (QW) samples (labeled as the V samples) were grown by low pressure (50 torr) MOVPE in Nippon Sanso Company on [001] GaAs substrates at 550 'C. All four samples contain a 100 A thick GaAs QW layer sandwiched between 1000 A thick GaInP barrier layers. The V/Ill ratio for the growth of the GaInP and GaAs layers were 150 and 50, respectively. The main difference between these four samples lies in the presence or absence of thin GaP layers between the GaAs QW and the adjacent GaInP layers. In sample V1 there are no GaP layers between GaAs and GaInP layers. In sample V2 and V3 there is only one layer of GaP between the GaAs QW and the GaInP layers. In case of V2 the GaP
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