M4 Generation-Recombination

Topic

A deep level within this semiconductor material's bandgap—the same deep level already established by another model in this set—mediates Shockley-Read-Hall (SRH) recombination between an electron and a hole; this deep level first captures one of the two charge carriers (depending on the order of arrival) and then the other, allowing them to recombine via the deep level rather than directly across the full bandgap. Consequently, a higher density of these deep levels in the semiconductor material leads to more frequent SRH recombination.

This SRH recombination combines—according to Matthiessen's rule—with radiative recombination (where an electron and hole recombine directly between bands, emitting a photon) and Auger recombination (where the energy released during electron-hole recombination is transferred to a third charge carrier instead of being emitted as a photon) to determine the material's total minority carrier lifetime. Matthiessen's rule sums the recombination rates contributed by each of these three mechanisms, meaning that the fastest mechanism—rather than an average of the three—dominates the total minority carrier lifetime. Since SRH recombination (mediated by the deep level) is faster than both radiative and Auger recombination, the total minority carrier lifetime is consequently determined primarily by SRH recombination. Consequently, this model—characterized by these three recombination mechanisms and the initial total minority-carrier lifetime—establishes that this total lifetime is the critical parameter governing two distinct models within the set: one describing a photovoltaic device and the other describing an LED or semiconductor laser. The shorter this total minority-carrier lifetime, the less time each minority charge carrier survives before recombining; consequently, the photovoltaic device, LED, or semiconductor laser becomes less efficient at utilizing that carrier before losing it. Furthermore, an increase in the density of these deep-level states—the same defect density that degrades the minority-carrier lifetime (per the Messenger-Spratt relationship) when displacement damage introduces such states—causes SRH recombination to dominate even more strongly over radiative and Auger recombination within the total minority-carrier lifetime.

ID:4504