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

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_ON when trapping is induced in the OFF-state; under semi-ON state conditions, GITs suffer from significant dynamic RON, while HD-GITs show no additional trapping with respect to OFF-state; 2) EL characterization carried out until V_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_ON must be ascribed to a different detrapping rate; 3) transient R_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 VDS = 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.

I. Introduction

Over the last years, gallium nitride (GaN) has demonstrated to be an excellent material for the fabrication of power semiconductor devices. GaN shows better performance than the conventional semiconductors like gallium arsenide (GaAs) and silicon (Si); in fact, GaN exhibits wide bandgap (3.4 eV), high electron mobility (up to 2000 cm²/), and high critical breakdown electric field (3.3 MV/cm) [1]. Around 10 years ago, gate-injection transistors (GITs) have been presented as normally-OFF GaN-based devices for application in power electronics. In these devices, normally-OFF operation is reached through the use of a p-GaN gate layer deposited on top of the AlGaN/GaN heterostructure, to deplete the channel at zero gate bias [2].