ELECTRON-CAPTURE BY MULTIPHONON EMISSION AT THE B-CENTER IN GALLIUM-ARSENIDE

Ridley's theory (1978) of the multiphonon capture rate at defect centres in semiconductors is compared with the low-temperature experimental results of Henry and Lang (1977) for the B centre in GaAs more critically than hitherto. It is found that the Huang-Rhys factor S=3.0 gives a good fit to both the magnitude and the temperature dependence of the capture cross-section at low temperatures. This is in contrast to Ridley's result of S=1 that only accounts for the temperature variation, albeit for a wider temperature range; the magnitude of the cross-section with S=1 is underestimated by some eight orders of magnitude. In this paper S is determined from an experimental capture cross-section at the lowest possible temperature. This gives a reliable value of S because the capture cross-section varies approximately as Sp, where p is the depth of the level in units of the zone-centre optical phonon energy and is equal to 20 for the B centre in GaAs. It is pointed out that a value of S so derived could be used not only as a means of identifying a deep level but also could be used to help analyse other experiments on the same centre involving electron-phonon coupling, e.g. measurement of photoionisation spectra.