Microwave-Detected Photoconductivity-Transient Spectroscopy For Non-Destructive Evaluation Of Gaas Wafers

Abstract

A coincident CW microwave beam and pulsed optical beam have been used to observe recom-bination and trapping mechanisms in semiconductor wafers. A GaAs laser (904nm), AlGaAs laser (850nm) and xenon flash lamp (spectral peak at 550nm) have been used to generate mobile carriers throughout GaAs wafers by excitation from impurity levels, to generate electron-hole pairs within a micron of the surface by band-to-band generation and to generate electron-hole pairs within one-tenth micron of the surface respectively. By observing the peak amplitude of the photoresponse and the transient decay, information about deep levels in semi-insulating (S.I.) GaAs wafers and doped channel layers (as well as surface recombination levels) can be obtained. Results are presented on undoped liquid encapsulated Czochralski (LEC) wafers, with and without implanted channels from many vendors. Less extensive comparisons with chromium-doped LEC wafers with epitaxially-grown channels, chromium-doped LEC wafers and undoped horizontal gradient freeze (HGF) S.I. wafers are presented, along with initial wafer mapping and variable temperature results on S.I. wafers with GaAs laser excitation.