Fermi level pinning, capacitance hysteresis, tunnel effect, and deep level in AlGaN/GaN high-electron-mobility transistor

Abstract

This paper presents a detailed investigation of the degradation of two (Pt/Au)–Al 0.2 Ga 0.8 N/GaN/Al 2 O 3 high-electron-mobility transistor(HEMT) structures, denoted as HEMT1 and HEMT2, by capacitance–voltage ( C–V ), forward current–voltage ( I–V ), and capacitance deep-level transient spectroscopy (DLTS)measurements in the temperature range of 40–320K. The C–V measurements confirmed the Fermi level pinning in our structures. In addition, the C–V measurements showed abnormal behaviors such as residual capacitance variation, capacitance hysteresis , and pinch-off voltage shift. These parasitic effects are explained by the thermal activation of trap centers in the Al 0.2 Ga 0.8 N/GaN/Al 2 O 3 HEMTs. Moreover, the consideration of the various current transport mechanisms and numerical adjustments of forward I–V curves showthat the tunnel effect assisted by defects is preponderant in our structures. Using the DLTS technique, we verified the existence of two hole traps, H1 and H2, in HEMT1 and HEMT2,respectively.They extended from the GaN layer to the (Pt/Au)–AlGaN interface.A detailed analysis of these results is presented. • The C–V measurements confirmed the pinning of the Fermi level in HEMTs, and reveal an hysteresis effect and a variations in the pinch-off voltage. • From the fitting I(V) , it follows that the tunnelling current is the dominant component in the samples investigated. • Existence of a strong relationship between the extended defect and the hysteresis phenomenon.