Qinghong Zheng

MgZnO-based metal-semiconductor-metal solar-blind photodetectors on ZnO substrates

Using lattice matched ZnO substrates, wurtzite single crystalline Mg0.49Zn0.51O films were obtained by reactive magnetron cosputtering method, and the heterostructures of MgZnO/ZnO were fabricated into metal-semiconductor-metal solar-blind photodetectors (SBPDs). Calculated and experimental results demonstrate that the response of the ZnO substrate can be suppressed by adopting a thick MgZnO epilayer. The SBPD with a 2 μm thick MgZnO epilayer shows a peak responsivity of 304 mA/W at 260 nm under 10 V bias, which is comparable to the highest value ever reported in MgZnO-based SBPDs. A rejection ratio (R260 nm/R365 nm) over 5×102 is also observed, indicating fully suppression of the signal from ZnO substrate.

High-responsivity solar-blind photodetector based on Mg 0.46Zn0.54O thin film

Adopting relatively high substrate temperature and low growth rate, single-phase wurtzite Mg0.46Zn0.54O film is grown on a quartz substrate by homemade magnetron sputtering. Solar-blind photodetector is fabricated based on the MgZnO film and shows a peak responsivity of 3.4 A/W at 265 nm with a cutoff wavelength of 280 nm under 10 V. As applied voltage increased to 70 V, the peak responsivity is up to 31.1 A/W corresponding to an internal gain of 148 times. The large internal gain was attributed to the trapping of photoionized holes at Ev + 282 meV deep level through deep-level transient spectral measurement.

Fabrication and Energy Band Alignment of n-ZnO/p-CuI Heterojunction

N-ZnO/P-CuI heterojunctions are fabricated by growing undoped n-type ZnO thin films on p-type γ-CuI (111) single-crystal substrates using radio-frequency magnetron sputtering. The ZnO films are identified to be columnar structured with c-axis-preferred orientation by using X-ray diffraction and scanning electron microscope. Measurements of the energy band alignment of ZnO/CuI interface by using X-ray photoelectron spectroscopy result in a valence band offset of 1.74 eV and a conduction band offset of -1.37 eV, meaning a type-II band alignment at the interface. A typical diodelike behavior of the current-voltage curve indicates its possible applications in optoelectronics with further development.

Dependence of structural and optoelectronic properties of sputtered Mg0.50Zn0.50O films on substrate

Mg0.50Zn0.50O thin films were grown on MgO, sapphire and quartz substrates by a home-made magnetron sputtering system under the same deposition conditions. The Mg compositions in all these MgxZn1−xO films are around 50%, independent of the growth substrates. X-ray diffraction measurements reveal that the lattice structures of these Mg0.50Zn0.50O films depend on the lattice structures of growth substrates and are cubic (C), wurtzite (W) and mixed phase, respectively. Transmission spectra show that the cutoff wavelength of C-Mg0.50Zn0.50O is located in the UV-C (200–280 nm) region, while that of W-Mg0.50Zn0.50O is located in the UV-B (280–320 nm) region. Though Mg compositions of the Mg0.50Zn0.50O films are the same, the energy-band gap of the C-Mg0.50Zn0.50O film (5.1 eV) is much larger than that of the W-Mg0.50Zn0.50O film (4.3 eV) due to the different electronic structure between the cubic and wurtzite structures. Metal–semiconductor–metal structure solar-blind and visible-blind UV photodetectors were fabricated based on the C-Mg0.50Zn0.50O and W-Mg0.50Zn0.50O films, respectively.