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Physical understanding and technological control of carrier lifetimes in semiconductor materials and devices: A critique of conceptual development, state of the art and applications
Abstract This paper surveys the current understanding of the diverse types of carrier lifetime in semiconductor physics, a fundamental physical parameter determining different terminal properties of semiconductor devices and a vital performance index of the degree of cleanliness of a semiconductor material or fabrication line. According as a recombination or generation mechanism is involved, two primary categories of carrier lifetime have been distinguished, namely, recombination and generation lifetimes. Depending on the recombination process, the recombination lifetime has been sub classified as phonon-assisted Shockley-Read-Hall recombination lifetime, photon-assisted radiative recombination lifetime and Auger recombination lifetime. Further from the viewpoint of injection level, lifetime has been divided into low-level and high-level types. Also, a demarcation has been made between lifetime in bulk semiconductor and lifetime in a region of semiconductor device. Both recombination and generation lifetimes or any of their classes, has been associated with a surface recombination/generation velocity and hence a surface lifetime; the measured lifetime value is the combined effect of the bulk and surface components. Quantum-mechanical theories of lifetime have been reviewed. After introduction of the Shockley-Read-Hall (SRH) theory of recombination-generation statistics, the Dhariwal-Kothari-Jain modification, Dhariwal-Landsberg generalization and Landsberg's extension of SRH theory have been dealt with. Landsberg-Kousik model of dependence of carrier lifetime on doping concentration has been outlined. Beattie-Landsberg Auger recombination lifetime theory has been briefly treated followed by Auger recombination theory for non-interacting free-particle approximation and then Coulomb-enhanced Auger recombination theory based on the Hangleiter and Hacker quantum-mechanical approach. The correlation of lifetime with device properties such as the current gain of bipolar transistors as well as forward voltage drop, reverse leakage current and switching times of devices like thyristors and insulated gate bipolar transistors has been elucidated. Various lifetime measurement techniques have been discussed. The technological steps for preserving or killing lifetime during semiconductor device fabrication have been presented. Experimental investigations of lifetime for material, unit process/manufacturing line and device characterization have been described, the process-induced influence on carrier lifetime has been explained and the main considerations in the analysis of lifetime results have been pointed out.
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