First demonstration of robust tri-gateß-Ga2O3nano-membrane field-effect transistors.

Nano-membrane tri-gateß-gallium oxide (ß-Ga2O3) field-effect transistors (FETs) on SiO2/Si substrate fabricated via exfoliation have been demonstrated for the first time. By employing electron beam lithography, the minimum-sized features can be defined with the footprint channel width of 50 nm. For high-quality interface betweenß-Ga2O3and gate dielectric, atomic layer-deposited 15 nm thick aluminum oxide (Al2O3) was utilized with tri-methyl-aluminum (TMA) self-cleaning surface treatment. The fabricated devices demonstrate extremely low subthreshold slope (SS) of 61 mV dec-1, high drain current (IDS) ON/OFF ratio of 1.5 × 109, and negligible transfer characteristic hysteresis. We also experimentally demonstrated robustness of these devices with current-voltage (I-V) characteristics measured at temperatures up to 400 °C.

Solar-Blind UV Photodetector Based on Atomic Layer-Deposited Cu2O and Nanomembrane ß-Ga2O3 pn Oxide Heterojunction.

Herein, we present a solar-blind ultraviolet photodetector realized using atomic layer-deposited p-type cuprous oxide (Cu2O) underneath a mechanically exfoliated n-type ß-gallium oxide (ß-Ga2O3) nanomembrane. The atomic layer deposition process of the Cu2O film applies bis(N,N'-di-secbutylacetamidinato)dicopper(I) [Cu(5Bu-Me-amd)]2 as a novel Cu precursor and water vapor as an oxidant. The exfoliated ß-Ga2O3 nanomembrane was transferred to the top of the Cu2O layer surface to realize a unique oxide pn heterojunction, which is not easy to realize by conventional oxide epitaxy techniques. The current-voltage (I-V) characteristics of the fabricated pn heterojunction diode show the typical rectifying behavior. The fabricated Cu2O/ß-Ga2O3 photodetector achieves sensitive detection of current at the picoampere scale in the reverse mode. This work provides a new approach to integrate all oxide heterojunctions using membrane transfer and bonding techniques, which goes beyond the limitation of conventional heteroepitaxy.

Thermodynamic Studies of ß-Ga2O3 Nanomembrane Field-Effect Transistors on a Sapphire Substrate.

The self-heating effect is a severe issue for high-power semiconductor devices, which degrades the electron mobility and saturation velocity, and also affects the device reliability. On applying an ultrafast and high-resolution thermoreflectance imaging technique, the direct self-heating effect and surface temperature increase phenomenon are observed on novel top-gate ß-Ga2O3 on insulator field-effect transistors. Here, we demonstrate that by utilizing a higher thermal conductivity sapphire substrate rather than a SiO2/Si substrate, the temperature rise above room temperature of ß-Ga2O3 on the insulator field-effect transistor can be reduced by a factor of 3 and thereby the self-heating effect is significantly reduced. Both thermoreflectance characterization and simulation verify that the thermal resistance on the sapphire substrate is less than 1/3 of that on the SiO2/Si substrate. Therefore, maximum drain current density of 535 mA/mm is achieved on the sapphire substrate, which is 70% higher than that on the SiO2/Si substrate due to reduced self-heating. Integration of ß-Ga2O3 channel on a higher thermal conductivity substrate opens a new route to address the low thermal conductivity issue of ß-Ga2O3 for power electronics applications.