Hot-Electron Trapping and Hole-Induced Detrapping in GaN-Based GITs and HD-GITs

Abstract

This paper investigates the trapping mechanisms in gate-injection transistors (GITs) without and with a pdrain electrode, referred to as GITs and Hybrid-Drain-embedded GITs (HD-GITs), respectively, used to inject holes and reduce charge trapping effects. We compare the two sets of devices under both the OFF-state and semi- ON state, to investigate the role of hot electrons in favoring the charge trapping. The analysis is based on combined pulsed characterization, transient measurements, and electroluminescence (EL) characterization. We demonstrate the following relevant results: 1) GITs and HD-GITs have comparable and negligible dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ when trapping is induced in the OFF-state; under semi- ON state conditions, GITs suffer from significant dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ , while HD-GITs show no additional trapping with respect to OFF-state; 2) EL characterization carried out until ${V}_{\mathsf {DS}}= 500$ V in semi- ON conditions shows comparable features, suggesting that the electric field and hot-carrier density are similar in GITs and HD-GITs. This result indicates that the hot-electron trapping rate is identical for the two sets of samples, so the difference observed in dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ must be ascribed to a different detrapping rate; 3) transient ${R}_{ \mathrm{\scriptscriptstyle ON}}$ measurements indicate that the traps filled in the OFF-state conditions are the same as those filled by hot electrons in semi- ON, with ${E}_{a}= 0.8$ eV (possibly ${C}_{N}$ ); and 4) EL analysis under constant bias indicates that in GITs there is a time-dependent increase in the luminescence signal at the drain terminal, when the devices are biased with ${V}_{\mathsf {DS}}= 300$ V. Such effect, indicative of hot-electron trapping, is not observed in HD-GITs. Based on the experimental evidence collected within this paper, we conclude that—in the semi- ON state—the main difference between GITs and HD-GITs consists in a faster detrapping rate of hot electrons, achieved through hole injection from the pdrain terminal.