Hysteresis, which is induced by both extrinsic and intrinsic causes, is often observed in molybdenum disulphide (MoS2) field-effect transistors (FETs), and several extrinsic hysteresis effects have been reported in unpassivated bottom-gate MoS2 device structures. In this study, interface-trap-induced hysteresis and other electrical properties are examined. We experimentally investigate thermally activated trap charges near a silicon-dioxide (SiO2)-MoS2 interface that gives rise to hysteresis in a multilayer MoS2 FET in a temperature region of 10–300 K. The threshold voltage (VTH) and field-effect mobility (μFE) decrease with the increase in temperature, regardless of the gate-bias sweep direction. The hysteresis that coincides with the trend of subthreshold swing increases sharply above T = 150 K as the released charges from interface traps become dominant over the fixed charges. Based on a temperature-dependent hysteresis analysis, we discussed the activation energy of interface traps and maximum interface trap density of the fabricated multilayer MoS2 FET.

Deep-ultraviolet (DUV) photodetectors based on wide-band-gap semiconductors have attracted significant interest across a wide range of applications in the industrial, biological, environmental, and military fields due to their solar-blind nature. As one of the most promising wide-band-gap materials, β-Ga2O3 provides great application potential over detection wavelengths ranging from 230 to 280 nm owing to its superior optoelectronic performance, stability, and compatibility with conventional fabrication techniques. Although various innovative approaches and device configurations have been applied to achieve highly performing β-Ga2O3 DUV photodetectors, the highest demonstrated responsivity of the β-Ga2O3 photodetectors has only been around 105 A/W. Here, we demonstrate a β-Ga2O3 phototransistor with an ultrahigh responsivity of 2.4 × 107 A/W and a specific detectivity of 1.7 × 1015 Jones, achieved by engineering a photogating effect. A β-Ga2O3/MgO heterostructure with an Al2O3 encapsulation layer is employed not only to reduce photogenerated electron/hole recombination but also to suppress the photoconducting effects at the back-channel surface of the β-Ga2O3 phototransistor via a defect-assisted charge transfer mechanism. The measured photoresponsivity is almost 2 orders of magnitude higher than the highest previously reported value in a β-Ga2O3-based photodetector, to the best of our knowledge. We believe that the demonstrated β-Ga2O3/MgO heterostructure configuration, combined with its facile fabrication method, will pave the way for the development of ultrasensitive DUV photodetectors utilizing oxide-based wide-band-gap materials.

Van der Waals (vdW) 2D/3D heterostructures are extensively studied for high-performance photodetector applications. Until now, the type of 2D materials has been the primary area of interest rather than the design of 3D semiconductors. In this study, high-speed broadband photodiodes (PDs) based on vdW p-WSe 2 /n-Ge heterojunctions are reported, and the performance compared with different n-Ge regions formed via the ion-implantation process. The fabricated PD with a typical long n-Ge region and low doping concentration responds to a broad spectral range from visible to infrared near 1550 nm with a response time of ≈3 µs and responsivity of 1.3 A W −1 . The inferior responsivity of PDs with short n-Ge regions can be improved as demonstrated by experimental results and process simulation. Density functional theory calculations are performed to estimate the variation of the energy band structures with the doping concentration of n-Ge. Fast photoresponse and efficient carrier separation across the heterojunction can be expected regardless of the n-Ge doping concentration. Based on the experimental results together with theoretical band structure and process simulation, it is shown that the heterojunction with an optimized n-Ge design is a promising high-speed broadband photodetector that can be implemented with complementary metal-oxidesemiconductor design and fabrication processes.

Ge/MoS 2 van der Waals heterostructure enables bias-dependent selective detection of visible and near infrared.

GaN nanowires and InGaN disk heterostructures are grown on an amorphous SiO₂ layer by a plasma-assisted molecular beam epitaxy. Structural studies using scanning electron microscopy and high-resolution transmission electron microscopy reveal that the nanowires grow vertically without any extended defect similarly to nanowires grown on Si. The as-grown nanowires have an intermediate region consisting of Ga, O, and Si rather than SiNx at the interface between the nanowires and SiO₂. The measured photoluminescence shows a variation of peak wavelengths ranging from 580 nm to 635 nm because of non-uniform indium incorporation. The nanowires grown on SiO₂ are successfully transferred to a flexible polyimide sheet by Au-welding and epitaxial lift-off processes. The light-emitting diodes fabricated with the transferred nanowires are characterized by a turn-on voltage of approximately 4 V. The smaller turn-on voltage in contrast to those of conventional nanowire light-emitting diodes is due to the absence of an intermediate layer, which is removed during an epitaxial lift-off process. The measured electroluminescence shows peak wavelengths of 610-616 nm with linewidths of 116-123 nm.