Study of Self-Heating and High-Power Microwave Effects for Enhancement-Mode p-Gate GaN HEMT

The self-heating and high-power microwave (HPM) effects that can cause device heating are serious reliability issues for gallium nitride (GaN) high-electron-mobility transistors (HEMT), but the specific mechanisms are disparate. The different impacts of the two effects on enhancement-mode p-gate AlGaN/GaN HEMT are first investigated in this paper by simulation and experimental verification. The simulation models are calibrated with previously reported work in electrical characteristics. By simulation, the distributions of lattice temperature, energy band, current density, electric field strength, and carrier mobility within the device are plotted to facilitate understanding of the two distinguishing mechanisms. The results show that the upward trend in temperature, the distribution of hot spots, and the thermal mechanism are the main distinctions. The effect of HPM leads to breakdown and unrecoverable thermal damage in the source and drain areas below the gate, while self-heating can only cause heat accumulation in the drain area. This is an important reference for future research on HEMT damage location prediction technology and reliability enhancement.

Enhancement-mode normally-off β-Ga2O3:Si metal-semiconductor field-effect deep-ultraviolet phototransistor

In this work, a solar-blind ultraviolet (UV) photodetector based on a three-terminal enhancement-mode (E-mode) Si-doped β-Ga2O3 (β-Ga2O3:Si) metal-semiconductor field-effect transistor (MESFET) structure is demonstrated, whose threshold voltage (Vth) and subthreshold swing (SS) are 4.04 V and 1.4 V/dec, respectively. A 400-nm-thick β-Ga2O3:Si thin film is prepared on sapphire substrate by using metal-organic chemical vapor deposition (MOCVD) method. Controlling the channel currents by the Schottky gate voltage in the dark and under illuminations, the photodetector shows dark current (Idark) as low as 13.4 pA, photo-to-dark current ratio (PDCR) of 4.85×104 and linear dynamic range (LDR) of 29.6 dB, illuminated by 254 nm UV light of 245 μW cm-2. As the UV light is turned on and off, the output current rise and decay time (τr and τd) are 420 ms and 350 ms. Moreover, at drain voltage (Vds) of 5 V and gate voltage (Vgs) of 0 V, the responsivity (R), specific detectivity (D*) and external quantum efficiency (EQE) are achieved as 74 A W-1, 2.15×1014 cm Hz1/2 W-1 (Jones) and 3.6×104%, respectively.

Adoption of the Wet Surface Treatment Technique for the Improvement of Device Performance of Enhancement-Mode AlGaN/GaN MOSHEMTs for Millimeter-Wave Applications

In this work, a low-power plasma oxidation surface treatment followed by Al2O3 gate dielectric deposition technique is adopted to improve device performance of the enhancement-mode (E-mode) AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOSHEMTs) intended for applications at millimeter-wave frequencies. The fabricated device exhibited a threshold voltage (Vth) of 0.13 V and a maximum transconductance (gm) of 484 (mS/mm). At 38 GHz, an output power density of 3.22 W/mm with a power-added efficiency (PAE) of 34.83% were achieved. Such superior performance was mainly attributed to the high-quality Al2O3 layer with a smooth surface which also suppressed the current collapse phenomenon.