Abstract
In the context of a comparative study of MBE and MOCVD PM-HEMT structures on 3″ GaAs substrates, utilization of photoreflectance indicated that the technique can provide substantial information both non-destructively as well as at room temperature. Concentrating on the structure of the photoreflectance trace below 1.4 eV, the technique can provide information on the combined effect of thickness and In composition in the InGaAs quantum well. In particular, photoreflectance was found to be especially useful for mapping the uniformity over a single wafer as well as for mapping the reproducibility from wafer to wafer. Representative, characteristic patterns were consistently observed for MBE-grown layers, distinct from equally characteristic patterns of MOCVD-grown layers. More importantly, these patterns, obtained by room temperature photoreflectance, were found to coincide with those obtained by low temperature photoluminescence. Although the two techniques identify different electronic transitions, room temperature photoreflectance proves to be equally well adapted as an acceptance test for layer uniformity as low temperature photoluminescence. In probing the reason of non-uniformities, however, low temperature photoluminescence does provide more information. Experimental results are presented for both MBE and MOCVD PM-HEMT structures as well as information extracted from their treatment by modeling in the quantum wells.