Magnetotransport, excitonic transition and electronic subband studies in modulation-doped In xGa 1− xAs/In yAl 1− yAs step quantum wells

Abstract

Shubnikov–de Haas (S–dH), Van der Pauw Hall-effect and photoluminescence (PL) measurements were carried out to investigate the magnetotransport and excitonic transition properties of modulation-doped In x Ga 1− x As/In y Al 1− y As asymmetric step quantum well. High-resolution transmission electron microscopy measurements showed a shallow In 0.53Ga 0.47As well and a deep In 0.65Ga 0.35As well bounded by two In 0.52Al 0.48As barriers. The results of S–dH measurements and the observation of the quantum Hall plateaus at 1.5 K demonstrated clearly the existence of a quasi-two-dimensional electron gas (2DEG) in the In x Ga 1− x As step quantum wells. The fast Fourier transformation results for the S–dH data indicated clearly that the 2DEG occupied two subbands in the In x Ga 1− x As quantum wells. Temperature-dependent PL measurements were performed to characterize the excitonic transition and the Fermi-edge singularity in the In x Ga 1− x As strained step quantum well. The electronic subband levels, the corresponding wavefunctions, and the dispersion relations in the In x Ga 1− x As/In y Al 1− y As step quantum well were calculated by a self-consistent method which took into account the exchange-correlation effect together with the nonparabolicity and strain effects. These results can help improve understanding for the applications of step quantum wells in high-speed electronic and optoelectronic devices.