Electronic states in modulation doped p-AlGaN/GaN superlattices

The properties of p-AlGaN/GaN modulation doped superlattices (SLS) prepared by molecular beam epitaxy were studied by means of conductivity versus tem perature, admittance spectroscopy, photoinduced current spectroscopy, micro cathodoluminescence (MCL) spectra measurements, and measurements of effecti ve diffusion lengths. It is shown that in SLs grown on GaN underlayers the sheet resistivity is about two orders of magnitude lower than for reference p-GaN films and the resistivity of SLs remains lower up to temperatures of about 350 degreesC. For SLS grown on AlGaN underlayers the gain in resisti vity is much more moderate and certain advantages in using such SLs are env isaged only for temperatures below room temperature. The reason for this lo wer gain is a considerable decrease in hole mobility compared to p-GaN. The effect is somewhat tentatively attributed to worse crystalline perfection of these SLs. It is also shown that such SLs are characterized by a strongl y broadened MCL peak and the presence of additional hole traps with activat ion energy of about 0.4 eV. Despite that, the photosensitivity and MCL inte nsity of these SLs are much better than for reference p-GaN samples. (C) 20 01 American Institute of Physics.