Current relaxation analysis in AlGaN/GaN high electron mobility transistors

Current relaxations in AlGaN/GaN high electron mobility transistors (HEMTs) often show a broad spread of relaxation times. These are commonly linked to the ionization energies of the traps in different regions of the devices and the relaxations are assumed to be exponential. To explain the observed spread of parameters, the presence of multiple centers is assumed. However, in actual spectra, only a few main peaks in the lifetimes distributions are observed, with considerable broadening of the peaks. In this paper, the authors examine the possible origin of the relaxation time broadening, including the presence of disorder giving rise to extended exponential decays and to physical broadening of discrete levels into bands. The latter is modeled by Gaussian broadening of the logarithm of relaxation time. The authors demonstrate the analysis of the peak positions and widths of the first derivative of the current transient by the logarithm in time, which is quite useful in deriving the relevant broadening parameters. They illustrate the approach for current relaxations in HEMTs for different pulsing modes. (C) 2017 American Vacuum Society.