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Three dimensional diamond ultraviolet (UV) photodetector have been fabricated on diamond epitaxial layer through down-top approach, where diamond epitaxial layer was grown between metal electrodes. A thin diamond epitaxial layer was first grown on high-pressure high-temperature single crystal diamond substrate. Then, the diamond epitaxial layer was covered by interdigitated tungsten electrodes. Furthermore, another diamond epitaxial layer was grown on uncovered area. At last, UV-Ozone treatment was used to oxidize the surface. The optoelectronic performance of the photodetector was characterized, exhibiting a large responsivity and a repeatable transient response behavior. Moreover, down-top process is beneficial for the electrode conductivity stability. Also, an ohmic contact could be formed between tungsten and diamond during growth. The results indicate that down-top process is an efficient way for fabrication of three dimensional diamond photodetectors.

Ohmic property for AlGaN/GaN high electron mobility transistor was investigated by insetting a highly Al-doped ZnO between the metal and AlGaN/GaN structure. The Al-doped ZnO was deposited by dc magnetron sputtering method and Ti/Al/Ni/Au was deposited on the ZnO by evaporation. Prior to the ZnO deposition, the surface of the samples was treated by O2 plasma, HCl and NH4OH, respectively. Good ohmic performance was obtained with contact resistance of 2.7 Ω mm even without annealing. The lowest contact resistance was 2.0 Ω mm after being annealed at 300 °C for the sample with HCl treatment before ZnO deposition.

By introducing the AlInGaN/AlGaN quaternary system as an active region, we fabricated an UV light-emitting diode (LED) with an emission wavelength of 348 nm. The optical power is 1 mW at an injection current of 50 mA under a bare-chip geometry, which is the highest report among UV–LEDs with an emission wavelength of around 350 nm grown on sapphire substrate. It means that the optical power of such LEDs is high enough to be used in practical application. In contrast to it, a similar UV–LED based on GaN/AlGaN system as an active region has been also grown, whose optical power is less than that of the AlInGaN/AlGaN-based UV–LED by one order of magnitude. The temperature-dependent photoluminescence study indicates that there exists a strong exciton-localization effect in the AlInGaN/AlGaN material system, while there is no distinguished exciton-localization effect in the GaN/AlGaN material system. Therefore, the high performance of the AlInGaN/AlGaN-based UV–LED can be attributed to the enhanced exciton-localization effect.

Extremely uniform and high-density In0.15Ga0.85As/GaAs quantum wires (QWRs) were naturally formed on a (553)B-oriented GaAs substrate by molecular-beam epitaxy. The density of the QWRs is as high as 4.0×105 cm−1. The strong photoluminescence peak at λ=868 nm from the (553)B QWRs shows a large polarization anisotropy [p=(I∥−I⊥)/(I∥+I⊥)=0.22] and a very small full width at half maximum of 9.2 meV at 12 K. Based on the modulation-doped (553)B QWR structure, self-organized QWR field-effect transistors were fabricated (the channel along the QWRs’ direction). The devices demonstrate very good saturation characteristics and pinch-off behavior at room temperature. A maximum transconductance (gm) of 135 mS/mm is measured for 2 μm gate-length devices.