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

  • Author(s): Armstrong, A
  • Chakraborty, A
  • Speck, J S
  • DenBaars, S P
  • Mishra, U K
  • Ringel, S A
  • et al.
Abstract

Deep levels were observed using capacitance deep level optical spectroscopy (DLOS) in an AlGaN/GaN heterostructure equivalent to that of a heterojunction field effect transistor. Band gap states were assigned to either the AlGaN or GaN regions by comparing the DLOS spectra in accumulation and pinch-off modes, where the former reflects both AlGaN- 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 AlGaN region, and deep levels at E-c-2.64 eV and E-c-3.30 eV were associated with the GaN layers. Both the AlGaN 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. (c) 2006 American Institute of Physics.

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