Quantitative observation and discrimination of AlGaN- and GaN-related deep levels in AIGaN/GaN heterostructures using capacitance deep level optical spectroscopy

摘要

Deep levels were observed using capacitance deep level optical spectroscopy (DLOS) in an AIGaN/GaN heterostracture equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AIGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AIGaN- and GaN-related defects, and the latter emphasizes defects residing in the GaN. A band gap state at E_c-3.85 eV was unambiguously identified with the AIGaN region, and deep levels at E_c-2.64 eV and E_c-3.30 eV were associated with the GaN layers. Both the AIGaN and GaN layers exhibited additional deep levels with large lattice relaxation. The influence of deep levels on the two-dimensional electron gas sheet charge was estimated using a lighted capacitance-voltage method.