Surface Functionalization of p-(Al)GaN with MXenes – Contact Engineering for Efficient Deep-UV Emitters – MXENEGAN

Deep-ultraviolet (deep-UV) emitters based on high-aluminum-content AlGaN offer numerous advantages over conventional mercury lamps, which are still widely used. These advantages include low toxicity, compact size, long operating lifetimes, no warm-up time, and low operating voltages. However, a major limitation of these devices is their low emission efficiency, which results from several factors, including a high density of threading dislocations in AlGaN layers and low hole concentrations in p-AlGaN. Another significant challenge is identifying a suitable p-type contact material that combines high UV transparency with low electrical resistivity.

Currently, p-GaN and p-AlGaN are commonly used as contact layers in deep-UV light-emitting diodes (LEDs). Unfortunately, p-GaN exhibits strong UV absorption. Although using p-AlGaN improves light extraction efficiency, it also leads to degraded electrical contact properties and shorter device lifetimes. For p-AlGaN contact layers, electrode materials with a high work function are required to achieve ohmic contact behavior. Conventional metal electrodes, such as Ni/Au and Ni/Al, typically exhibit high forward voltages, resulting in increased heat generation and, consequently, shorter LED lifetimes. Furthermore, the substantial lattice mismatch between GaN and most metallic electrode materials can lead to discontinuities at the metal–semiconductor interface, accompanied by lattice distortions and interfacial defects. In recent years, a new class of two-dimensional (2D) materials known as MXenes has emerged, offering a range of unique properties, including metallic conductivity, mechanical flexibility, high optical transmittance, and chemical stability. These characteristics make MXenes promising candidates for electrode applications in optoelectronic and electronic devices. A review of the scientific literature indicates that previous research has primarily focused on integrating Ti₃C₂Tₓ MXene layers with n- and p-type GaN. To the best of our knowledge, no experimental studies on the integration of other MXenes with p-AlGaN have been reported. The proposed research will investigate the integration of p-AlGaN with high-work-function MXenes and its impact on the electrical properties of the resulting structures, including hole concentration, resistivity, and current–voltage (I–V) characteristics. The central hypothesis of this project is that surface functionalization of p-AlGaN using appropriately selected MXene materials will improve the electrical characteristics of ohmic contacts to Mg-doped, high-aluminum-content AlGaN (approximately 60% Al).

As part of the project, group III-nitride (III-N) samples will be grown using molecular beam epitaxy (MBE) and metalorganic vapor-phase epitaxy (MOVPE). MXene/p-(Al)GaN structures will subsequently be fabricated using a simple drop-casting technique. Since the surface functional groups of MXenes significantly influence their work function, the effects of thermal treatment on the 2D layers will also be investigated. The successful implementation of this innovative approach is expected to advance our understanding of the physical phenomena occurring at MXene/III-N interfaces and help overcome one of the key factors limiting the emission efficiency of semiconductor-based deep-UV emitters.