In this work,metal–semiconductor–metal solar-blind ultraviolet photoconductors were fabricated based on theβ-Ga_(2)O_(3) thin films which were grown on the c-plane sapphire substrates by molecular beam epitaxy.Then,the effects ofβ-Ga_(2)O_(3) annealing on both its material character-istics and the device photoconductivity were studied.Theβ-Ga_(2)O_(3) thin films were annealed at 800,900,1000,and 1100°C,respectively.Moreover,the annealing time was fixed at 2 h,and the annealing ambients were oxygen,nitro-gen,and vacuum(4.9×10^(-4 )Pa),respectively.The crys-talline quality and texture of theβ-Ga_(2)O_(3) thin films before and after annealing were investigated by X-ray diffraction(XRD),showing that higher annealing temperature can result in a weaker intensity of(402)diffraction peak and a lower device photoresponsivity.Furthermore,the vacuum-annealed sam-ple exhibits the highest photoresponsivity compared with the oxygen-and nitrogen-annealed samples at the same annealing temperature.In addition,the persistent photoconductivity effect is effectively restrained in the oxygen-annealed sample even with the lowest photoresponsivity.
Tuo ShengXing-Zhao LiuLing-Xuan QianBo XuYi-Yu Zhang
High-resistivity β-Ga203 thin films were grown on Si-doped n-type conductive β-Ga203 single crystals by molecular beam epitaxy （MBE）. Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6 x 10^6 %. The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4 x 10^18 cm-3 and 7.6 V, respectively. The ultra-violet （UV） photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7 x 10%2% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β-Ga203 thin films and the n-type conductive β-Ga203 single-crystal substrate.
The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.
