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We present a detailed investigation of the trapping and detrapping mechanisms that take place in the gate region of β-Ga2O3 vertical finFETs and describe the related processes. This analysis is based on combined pulsed characterization, transient measurements, and tests carried out under monochromatic light, with photon energies between 1.5 and 5 eV. The original results presented in this article demonstrate that: (i) when submitted to positive gate stress with VGS > 3 V, the devices show a significant threshold voltage variation; (ii) this effect is not recoverable in 10 000 s in rest condition (zero bias, dark condition). (iii) VTH can quickly recover its initial value when the device is illuminated with UV-C light at 280 nm. (iv) Stress-recovery experiments carried out at different photon energies allowed us to estimate the threshold energy for the release of carriers from the Al2O3/Ga2O3 interface, and for the injection of electrons from metal to the Al2O3 insulator (conduction band discontinuity at the metal/Al2O3 interface). [ABSTRACT FROM AUTHOR]

We demonstrate that the residual carbon concentration in the drift region can have a significant impact on the reverse leakage, breakdown voltage, and breakdown stability of GaN-on-GaN vertical diodes. Two generations (Gen1, Gen2) of polarization-doped p-n junctions with different C concentrations were compared, in terms of avalanche voltage, avalanche instability, and deep-level concentration. The original results collected within this paper show that: 1) both generations of devices can safely reach the avalanche regime; diodes with a lower residual CN have a higher reverse leakage and a lower avalanche voltage, due to an uneven distribution of the electric field; 2) the presence of residual carbon can lead to breakdown walkout, i.e. a recoverable increase in breakdown voltage under reverse-bias stress. Specifically, devices with higher C concentration show a fully-recoverable breakdown walkout, whereas the breakdown voltage is stable in devices with lower C concentration; and 3) steady-state photocapacitance measurements confirm the presence of CN in both generations, and are used to assess the relative difference in concentration between Gen1 and Gen2, even for levels below secondary ion mass spectroscopy (SIMS) sensitivity. The results described in this paper indicate the existence of a trade-off between breakdown voltage (increasing by improving compensation) and breakdown stability (improving by reducing CN concentration) and are of fundamental importance for the optimization of GaN power devices. [ABSTRACT FROM AUTHOR]

This paper shows that vertical GaN-on-GaN p–i–n diodes are able to withstand long-term operation in moderate avalanche conduction regime, thus proving the excellent stability of the gallium nitride material system. Under constant stress in stronger avalanche regime, the devices show a significant increase in the series resistance, a slight increase in forward voltage and a measurable increase in avalanche voltage. Degradation is ascribed to the generation of defects, a process which is likely occurring in the intrinsic region. The time-dependence of the performance loss is explained by considering the simultaneous presence of field-assisted trapping in the avalanche region and of charge de-trapping in the medium-field region of the devices. An interpretative model based on these assumptions is proposed to explain the full set of the experimental data. [ABSTRACT FROM AUTHOR]

We demonstrate the avalanche capability and the existence of breakdown walkout in GaN-on-GaN vertical devices with polarization doping. By means of combined electrical and optical characterization, we demonstrate the following original results: 1) vertical p-n junctions with polarization doping have avalanche capability; 2) stress in avalanche regime induces an increase in breakdown voltage, referred to as breakdown walkout; 3) this process is fully-recoverable, thus being related to a trapping mechanism; 4) temperature-dependent measurements of the breakdown walkout identify $\text{C}_{N}$ defects responsible for this process; and 5) capacitance deep level transient spectroscopy (C-DLTS) and deep level optical spectroscopy (DLOS) confirm the presence of residual carbon in the devices under test. A possible model to explain the avalanche walkout is then proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]