Modification of Electrical Transport in a Grating-Electrode GaN/AlGaN Quantum-Well Device by Ti3C2Tx MXene Under 254 nm Illumination

Ultraviolet (UV) photodetectors are essential for flame monitoring, environmental sensing, UV photography, optical communication, and biochemical analysis, and III-nitride quantum-well structures are promising platforms for such devices. Two-dimensional Ti3C2Tx MXene, which combines metallic conductivity with a termination-dependent work function, offers an attractive route to modifying the surface and interface transport of GaN-based photodetectors. The purpose of this work is to determine whether integrating a Ti3C2Tx MXene surface region onto a grating-electrode GaN/AlGaN asymmetric coupled-quantum-well UV photodetector selectively enhances the photoresponse or predominantly modifies the overall device conductance. The device was fabricated and assessed under 254 nm illumination. Optical and scanning electron microscopy verified the patterned device and the continuous grating region, and the fabrication sequence explained the integration procedure. Static current–voltage (I–V) characteristics of the same device were measured both before and after Ti3C2Tx MXene coverage. Nonlinear transport and a discernible light–dark current gap were present in both states. Before MXene coverage, the device produced a dark current of 1.98 μA, a net photocurrent of 1.90 μA, and a light-to-dark current ratio of 1.96 at +3 V; after coverage, the corresponding values were 0.837 mA, 0.835 mA, and 2.00. The increase in the dark current was reproduced on three grating-electrode devices, for which MXene coverage raised the dark current by a factor of between about 4 × 102 and 1.3 × 103 depending on the device and the sweep direction, whereas a control structure without the grating electrode remained nearly three orders of magnitude below the MXene-covered devices. Switching the 254 nm source at a fixed bias of +1 V produced reproducible switching between two current levels with a light-to-dark ratio of 2.10–2.15; the transitions were completed within the 0.1 s sampling interval. Ti3C2Tx MXene coverage raised the total current level in both electrical states while maintaining a detectable relative light–dark contrast from +1 to +5 V, indicating that the dominant measured change was an increase in device conductance rather than a selective enhancement of the relative photoresponse. Within the scope of this transport study centered on static I–V measurements and supplemented by a single-device time-resolved measurement, the results demonstrate static separation between the dark and 254 nm-illuminated states and modification of the overall electrical transport by MXene coverage on the same device; they do not claim an improvement in photodetector figures of merit, and absolute figures of merit are not reported because the optical power incident on the device was not calibrated.