Gate controllability is a key factor that determines the performance of GaN high electron mobility transistors (HEMTs). However, at the traditional metal‐GaN interface, direct chemical interaction between metal and GaN can result in fixed charges and traps, which can significantly deteriorate the gate controllability. In this study, Ti3C2Tx MXene films are integrated into GaN HEMTs as the gate contact, wherein van der Waals heterojunctions are formed between MXene films and GaN without direct chemical bonding. The GaN HEMTs with enhanced gate controllability exhibit an extremely low off‐state current (IOFF) of 10−7 mA mm−1, a record high ION/IOFF current ratio of ≈1013 (which is six orders of magnitude higher than conventional Ni/Au contact), a high off‐state drain breakdown voltage of 1085 V, and a near‐ideal subthreshold swing of 61 mV dec−1. This work shows the great potential of MXene films as gate electrodes in wide‐bandgap semiconductor devices.
Crucial commercial and space applications require the detection of broadband ultraviolet (UV) rays spanning from UV-A to UV-C. In this study, the authors demonstrate a broadband UV photodetector employing a p-type NiOx layer and an n-type β-Ga2O3 heterostructure in PIN configuration for the first time. Simulations are conducted to optimize the doping concentration and thickness of the NiOx layer, ensuring that (a) a reasonable depletion width is maintained within the NiOx layer for UV-A and UV-B light absorption; (b) anode ohmic contacts are formed on the nondepleted NiOx film, and (c) >70% of the UV-C light is absorbed by β-Ga2O3. The optimized NiOx/ β-Ga2O3 PIN photodiode exhibits good responsivity to incident light wavelengths in the UV-A, UV-B, and UV-C regions. While the NiOx layer is considered to be responsible for providing good photoresponsivity in the UV-A and UV-B regions, a highly resistive (near-intrinsic) β-Ga2O3 layer is required for the absorption of incident UV-C light. A record detectivity of >1011 cmHz0.5W−1 for the UV-B and UV-C regions and >1010 cmHz0.5W−1 for the UV-A region is observed in the NiOx/ β-Ga2O3 heterostructure PIN photodiode during the self-powered operation. The results presented in this study are promising and instigate device design strategies for (ultra)wide bandgap semiconductor-based broadband UV PIN photodetectors.
In this Letter, we report on a monolithically integrated β-Ga2O3 NMOS inverter integrated circuit (IC) based on heteroepitaxial enhancement mode (E-mode) β-Ga2O3 metal-oxide-semiconductor field-effect transistors on low-cost sapphire substrates. A gate recess technique was employed to deplete the channel for E-mode operation. The E-mode devices showed an on-off ratio of ∼105 with a threshold voltage of 3 V. In comparison, control devices without the gate recess exhibited a depletion mode (D-mode) with a threshold voltage of [Formula: see text]3.8 V. Furthermore, depletion-load NMOS inverter ICs were fabricated by monolithically integrating D- and E-mode transistors on the same substrate. These NMOS ICs demonstrated inverter logic operation with a voltage gain of 2.5 at VDD = 9 V, comparable with recent GaN and other wide-bandgap semiconductor-based inverters. This work lays the foundation for heteroepitaxial low-cost and scalable β-Ga2O3 ICs for monolithic integration with (ultra)wide bandgap Ga2O3 power devices.
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