Molecular Beam Epitaxial Growth and Characterization of Superlattice Avalanche Photodiodes.

Abstract

The investigations reported here relate to growth and characterization of high quality single-layer III-V semiconductors, GaAs/AlGaAs and InGaAs/InAlAs heterostructures, single quantum wells and superlattices with varying well and barrier widths. The performance characteristics of avalanche photodiodes made with these multilayered materials have been investigated in detail. Low temperature photoluminescence (PL) measurements indicate that the transition associated with electron-heavy hole free excitons in 120A GaAs/AlGaAs single quantum wells (SQW) have a linewidth of 0.3 meV at 2K, which is one of the lowest values ever reported. In the case of In$\\sb{0.53}$Ga$\\sb{0.47}$As/In$\\sb{0.52}$Al$\\sb{0.48}$As quantum wells lattice-matched to InP, the role of growth interruption at the hetero-interfaces was investigated. We have measured a steady decrease in the PL linewidth of SQWs with increasing period of growth interruption. This behavior is due to an improvement in the interface quality due to interruption. Analysis of the measured 10meV linewidth in a 120A SQW, which is among the smallest ever reported, indicates that the InGaAs/InAlAs interface can be described by two-dimensional isl and s which have a height of 2 monolayers and a lateral extent of about 100A. Avalanche photodiodes were fabricated with GaAs/AlGaAs and ${\\rm In\\sb{0.53}Ga\\sb{0.47}As/In\\sb{0.52}Al\\sb{0.48}As}$ superlattice active layers. A systematic measurement of the impact ionization coefficients in these multilayered materials was made at $300\\sp\\circ{\\rm K}$ and lower temperatures. A large enhancement of the $\\alpha/\\beta$ ratio $\\sim 10$ is observed in GaAs/AlGaAs MQW with L$\\sb{Z}$ and L$\\sb{B}\\sim 500$A. Photodiodes made with superlattice absorption regions exhibit responsivities $\\sim 0.4$ A/W in GaAs/AlGaAs and $\\sim 0.9$ A/W in InGaAs/InAlAs devices at a reverse biase of 0.5 ${\\rm V}\\sb{BR}.$ Avalanche gains $>10\\sp3$ are measured in the GaAs/AlGaAs devices. The best frequency response in devices with diode area equal to $5.4\imes 10\\sp{-5}$ ${\\rm cm\\sp2}$ is characterized by a 3dB roll-off at 12 GHz, which make these devices extremely attractive for high bit rate optical communication. (Abstract shortened with permission of author.)