Study of minority carrier traps in p -GaN gate HEMT by optical deep level transient spectroscopy

Abstract

Properties of minority carrier (electron) traps in Schottky type p-GaN gate high electron mobility transistors were explicitly investigated by optical deep level transient spectroscopy (ODLTS). By temperature-scanning ODLTS, three electron traps, namely, E1, E2, and E3, were revealed, together with activation energy, capture cross section, and trap concentration. A thermally accelerated electron-releasing process of traps was quantitatively studied by Laplace ODLTS with individual emission time constant disclosed. At 300 K, the emission time constant was determined to be 0.21 and 1.40 s for E2 and E3, respectively, which adjacently existed in the bandgap and held activation energies of over 0.6 eV. As varying the optical injection pulse duration, a three-dimensional mapping of capacitance transient was obtained for each trap, attesting to the electron capture capability of each trap. By varying the reverse bias, the analysis of the ODLTS signal amplitude indicates that all three electron traps are located inside the p-GaN layer rather than the surface defect related.