UV-induced change in channel conductivity in AlGaN/GaN high electron mobility transistors to measure doping

Abstract

AlGaN/GaN High Electron Mobility Transistors (HEMTs) frequently show an UV-induced increase in channel conductivity (persistent photoconductivity—PPC). PPC is a generic effect that exists for a wide range of HEMT configurations irrespective of the substrate material or the nominal buffer doping type and magnitude. Simulations demonstrate that the magnitude of the PPC effect can be explained by the UV-induced change in electronic band bending in the buffer below the 2D electron gas (2DEG). It only has a significant magnitude for p-type buffers that result from the presence of intentional or unintentional carbon doping and allows the net deep-level doping density (i.e., |NA-ND|) below the 2DEG to be quantified, a parameter that is extremely difficult to evaluate by any other means. Transient measurements indicate a PPC recovery time extending to several days, with leakage along dislocations playing an important role in this recovery.