Deep levels and DX centers in AlxGa1−xAs/GaAs. II. Field effect deep level transient spectroscopy study

Abstract

The field effect has been investigated on the deep levels and DX centers in molecular-beam epitaxilly-grown AlxGa1−xAs on n+ GaAs for several compositions. We have measured the isothermal and isofield capacitance transients for the major energy levels with the applied potential in the range from −0.1 to −3 V. In samples with x=0.5, two electron trap levels (E1 and E2) were detected. While E1 was strongly field dependent (changed from 0.499 to 0.287 eV) E2 was practically unchanged (0.305 eV) with respect to energy, cross section, and peak broadening. Contrary to this in pure GaAs (samples x=0), we observed three energy levels, one hole trap (E1=0.239 eV), one electron trap (E2=0.512 eV), and the usual EL2 trap (E3=0.72 eV). At this composition, however, levels E1 and E2 were absent at low reverse fields (at −1 V) and EL2 remained unchanged at 0.72 eV. We have considered the recent theories of Pool–Frenkel effect and tunneling for electron–phonon interaction to interpret the results. In particular, for AlxGa1−xAs with x=0.5, the electron–phonon coupling factor (S) was found to be about 4 and the deep centers were identified as neutral to repulsive.