Thermal Stability Study of Oxygen Implanted Algaas/Gaas Single Quantum Well Structures Using PhotoreflectancE
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Abstract The effects of interdiffusion on the band structure of two Al.Ga1.As/GaAs single quantum well (SQW) structures were studied using room temperature photoreflectance. Rapid thermal annealing of the SQW structures at temperatures of 800°C, 900°C and 1000°C for times up to 180 seconds resulted in limited interdiffusion. Low dose (1014 cm 2) oxygen implantation reduced the thermal stability of these structures where the extent of the interdiffusion was found to be greater for the implanted samples for identical annealing conditions. Introduction The optical properties of quantum well (QW) structures have been the focus of much attention for many years for the development of novel optical devicestxl. Tailoring their properties has been achieved through the modification of the confinement profile of the QW structure using controlled interdiffusion across the well/barrier interfacel21. This interdiffusion of the QW results in a modification of the subband structure, and thus the bandgap and optical properties, of the as-grown QW (AGSQW). Thermal annealing of Al.Gal. 1As/GaAs AGSQW structures results in the interdiffusion of Ga atoms from the well layer and Al atoms from the barrier layers across the well/barrier interface to produce a graded compositional profile.
"permannent address is Department
of Electrical engineering, University of Hong Kong, Hong Kong
331 Mat. Res. Soc. Symp. Proc. Vol. 354 01995 Materials Research Society
However, it has been shown that the rate of interdiffusion may be enhanced significantly through the introduction of specific impurities, such as oxygen1 31 , or vacancies141 using ion implantation or surface Si0 2 layers respectively, followed by annealing to remove the implantation damage. Ion implantation is particularly useful for the introduction of the required impurities at selected locations due to the high degree of control in both spatial and depth dimensions, making it the desired process for the implementation of interdiffusion for the fabrication of devices. In addition, studies of GaAs and AlGaAs materials have shown that the presence of oxygen atoms result in the formation of highly resistive materials due to the reduction of free carrier levels in the sample1 51 which has been used for the electrical isolation of devices such as heterostructures lasers161. As transition energies of the QW depend upon the shape of the confinement profile, the AI-Ga interdiffusion can be measured optically by monitoring the systematic 'blue' shift of the QW transition energies as a function of the annealing temperature and time. Photoreflectance[71 (PR) is an optical technique which detects all the transitions in a QW structure is therefore well suited for the study of interdiffusion in QW structures. Experimental Method The two AGSQW structures investigated here were grown by metal-organic vapour phase epitaxy (MOVPE) on (100) semi-insulating GaAs substrate. Both structures have nominal AlxGal-.s barrier layer thicknesses of 1000A above and below the well and are terminated with a 50A
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