Ultrahigh Photoresponsivity of W/Graphene/ß-Ga2O3 Schottky Barrier Deep Ultraviolet Photodiodes.

The integration of graphene with semiconductor materials has been studied for developing advanced electronic and optoelectronic devices. Here, we propose ultrahigh photoresponsivity of ß-Ga2O3 photodiodes with a graphene monolayer inserted in a W Schottky contact. After inserting the graphene monolayer, we found a reduction in the leakage current and ideality factor. The Schottky barrier height was also shown to be about 0.53 eV, which is close to an ideal value. This was attributed to a decrease in the interfacial state density and the strong suppression of metal Fermi-level pinning. Based on a W/graphene/ß-Ga2O3 structure, the responsivity and external quantum efficiency reached 14.49 A/W and 7044%, respectively. These values were over 100 times greater than those of the W contact alone. The rise and delay times of the W/graphene/ß-Ga2O3 Schottky barrier photodiodes significantly decreased to 139 and 200 ms, respectively, compared to those obtained without a graphene interlayer (2000 and 3000 ms). In addition, the W/graphene/ß-Ga2O3 Schottky barrier photodiode was highly stable, even at 150 °C.

Control of Ni/ß-Ga2O3 Vertical Schottky Diode Output Parameters at Forward Bias by Insertion of a Graphene Layer.

Controlling the Schottky barrier height (ϕB) and other parameters of Schottky barrier diodes (SBD) is critical for many applications. In this work, the effect of inserting a graphene interfacial monolayer between a Ni Schottky metal and a ß-Ga2O3 semiconductor was investigated using numerical simulation. We confirmed that the simulation-based on Ni workfunction, interfacial trap concentration, and surface electron affinity was well-matched with the actual device characterization. Insertion of the graphene layer achieved a remarkable decrease in the barrier height (ϕB), from 1.32 to 0.43 eV, and in the series resistance (RS), from 60.3 to 2.90 mΩ.cm2. However, the saturation current (JS) increased from 1.26×10−11 to 8.3×10−7(A/cm2). The effects of a graphene bandgap and workfunction were studied. With an increase in the graphene workfunction and bandgap, the Schottky barrier height and series resistance increased and the saturation current decreased. This behavior was related to the tunneling rate variations in the graphene layer. Therefore, control of Schottky barrier diode output parameters was achieved by monitoring the tunneling rate in the graphene layer (through the control of the bandgap) and by controlling the Schottky barrier height according to the Schottky−Mott role (through the control of the workfunction). Furthermore, a zero-bandgap and low-workfunction graphene layer behaves as an ohmic contact, which is in agreement with published results.

Physical Operations of a Self-Powered IZTO/ß-Ga2O3 Schottky Barrier Diode Photodetector.

In this work, a self-powered, solar-blind photodetector, based on InZnSnO (IZTO) as a Schottky contact, was deposited on the top of Si-doped ß-Ga2O3 by the sputtering of two-faced targets with InSnO (ITO) as an ohmic contact. A detailed numerical simulation was performed by using the measured J-V characteristics of IZTO/ß-Ga2O3 Schottky barrier diodes (SBDs) in the dark. Good agreement between the simulation and the measurement was achieved by studying the effect of the IZTO workfunction, ß-Ga2O3 interfacial layer (IL) electron affinity, and the concentrations of interfacial traps. The IZTO/ß-Ga2O3 (SBDs) was tested at a wavelength of 255 nm with the photo power density of 1 mW/cm2. A high photo-to-dark current ratio of 3.70×105 and a photoresponsivity of 0.64 mA/W were obtained at 0 V as self-powered operation. Finally, with increasing power density the photocurrent increased, and a 17.80 mA/W responsivity under 10 mW/cm2 was obtained.