Yuantao Zhang

Preparation of intrinsic and N-doped p-type ZnO thin films by metalorganic vapor phase epitaxy

The intrinsic p-type ZnO thin films were prepared by controlling the oxygen partial pressure during growth. The E2 (high) mode at 432.2cm−1 appeared in the Raman spectrum of the film. The photoluminescence spectra taken at 77 K showed the emission band C in the violet region, which originated from zinc vacancy and varied in intensity in accordance with the quantity of the carrier concentration in the films. The N-doped p-type ZnO films were realized by N2 plasma. The Raman spectrum showed the dominant A1 (LO) mode at 580cm−1, that was the result of the host-lattice defects generated by N dopant rather than the N-related local vibration modes.

Visual-infrared electroluminescence emission from ZnO∕GaAs heterojunctions grown by metal-organic chemical vapor deposition

The light-emitting diode of p-ZnO∕n-GaAs heterojunction was grown by metal-organic chemical vapor deposition. The p-ZnO films have been formed by the doping As atoms which diffuse into ZnO film from GaAs substrate. The p-type behavior of As-doped ZnO films based on As-doped p-ZnO∕n-GaAs, p-ZnO∕p-GaAs heterojunction was studied by carrying out I-V measurements and x-ray photoelectron spectroscopy. The I-V characteristic of p-ZnO∕n-GaAs heterojunction showed characteristic of rectifying diode and visual-infrared electroluminescence emission under forward current injection at room temperature. The I-V of the heterounction had a threshold voltage of ∼2.5V.

Study on the p-MgZnO/i-ZnO/n-MgZnO light-emitting diode fabricated by MOCVD

A p-MgZnO/i-ZnO/n-MgZnO light-emitting diode was fabricated on a GaAs substrate by metal–organic chemical vapour deposition. The I–V curve of the device exhibited typical rectifying behaviour of the p–i–n diode and the forward turn-on voltage was about 7 V. An obvious ultraviolet peak can be observed in the electroluminescence spectrum corresponding to the radiative recombination of carriers. The dependences of the characteristics on the thickness of the ZnO interlayer were also studied. The results showed that the intensity of the UV peak increased as the thickness of the ZnO layer decreased. A clear blue shift can also be observed at the same time. The thickness of the ZnO layer had an important effect on the optical qualities of the device.

Structural and optoelectrical properties of ZnO thin films deposited on GaAs substrate by metal-organic chemical vapour deposition (MOCVD)

ZnO thin films were deposited on semi-insulating (0 0 1) GaAs substrates at different growth conditions by metal-organic chemical vapour deposition. The effect of growth temperature and ambient oxygen partial pressure on the properties of the ZnO films was studied. It was found that these two important parameters affected the structure, crystallinity, surface morphology, and optical and electrical characteristics of the ZnO films. At the present growth conditions, the full width at half maximum of a ZnO (0 0 2) diffraction peak decreased to 0.185° at 610 °C under an oxygen partial pressure of 45 Pa. By increasing the oxygen partial pressure from 45 to 68 Pa, the surface of the ZnO films became smoother and the grain size smaller and more homogeneous. In addition, the near-band-edge emission and the deep-level emission in the photoluminescence spectra and the electrical properties of the ZnO thin films strongly depended on the ambient oxygen content.

Band alignment of InN/6H-SiC heterojunction determined by x-ray photoelectron spectroscopy

The valence band offset (VBO) of InN/6H-SiC heterojunction has been directly measured by x-ray photoelectron spectroscopy. The VBO is determined to be −0.10 ± 0.23 eV and the conduction band offset is deduced to be −2.47 ± 0.23 eV, indicating that the heterojunction has a type-II band alignment. The accurate determination of the valence and conduction band offsets is important for applications and analysis of InN/6H-SiC optoelectronic devices.

Studies on Crystal Orientation of ZnO Film on Sapphire Using High-throughout X-ray Diffraction

The orientation of the nano-columnar ZnO films grown on sapphire using the technique of metal-organic chemical vapor deposition (MOCVD) exhibits deviation because of the mismatch between the crystal lattices of the films and the sapphire substrate. A high-throughout X-ray diffraction method was employed to determine the crystal orientation of the ZnO films at a time scale of the order of minutes based on the general area detection diffraction system (GADDS). This rapid, effective, and ready method, adapted for characterizing the orientation of the nano-columnar crystals is used to directly explain the results of observation of the X-ray diffraction images, by the measurements of the orientations of the crystal columns of the ZnO films along c -axis and in parallel to ab plane.

Metal-organic chemical vapor deposition of GaSb/GaAs quantum dots: the dependence of the morphology on growth temperature and vapour V/III ratio

GaSb quantum dots have been widely applied in optoelectronic devices due to its unique electrical and optical properties. The effects of metal-organic chemical vapor deposition(MOCVD) parameters, such as growth temperature and vapour V/III ratio[V/III ratio means the molar ratio of trimethylgallium(TMGa) and triethylantimony( TESb)], were systematically investigated to achieve GaSb quantum dots with high quality and high density. The features of surface morphology of uncapped GaSb quantum dots were characterized by atomic force microscope( AFM) images. The results show that the surface morphologies of quantum dots are strongly dependent on growth temperature and vapour V/III ratio. GaSb quantum dots with an average height of 4.94 nm and a density of 2.45×1010 cm–2 were obtained by optimizing growth temperature and V/III ratio.

Effect of the magnesium composition on the properties of MgxZn1−xO-based homojunction light-emitting diodes

MgxZn1?xO p?n homojunction light-emitting diodes (LEDs) with different Mg compositions were fabricated on GaAs (1?0?0) substrates by metal?organic chemical vapor deposition. The effects of variation of the Mg composition on the properties of the LEDs were researched. The I?V curve exhibited typical rectifying behavior of a p?n diode. The near-band emission peaks in the photoluminescence and the deep-level emission peaks in the electroluminescence spectra were both blueshifted due to the wide band gap. The full-width at half-maximum value and the intensity of the DLE peak were also affected by the increasing defect density.

Optical and electronic properties of ZnO:P/n+-Si heterostructures fabricated by metalorganic chemical vapour deposition

ZnO:P/n+-Si heterostructures were fabricated on n+-Si substrates by metalorganic chemical vapour deposition. The substrates were heavily doped with phosphorus. The crystallinity and optical properties of ZnO films were characterized by photoluminescence spectra and x-ray diffraction, respectively. X-ray photoelectron spectroscopy (XPS) showed that phosphorus atoms existed in ZnO films. The current–voltage (I–V) curve showed current rectification characteristic behaviour.

Polarization-induced hole doping in N-polar III-nitride LED grown by metalorganic chemical vapor deposition

Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.Polarization-induced doping has been shown to be effective for wide-bandgap III-nitrides. In this work, we demonstrated a significantly enhanced hole concentration via linearly grading an N-polar AlxGa1-xN (x = 0–0.3) layer grown by metal-organic chemical vapor deposition. The hole concentration increased by ∼17 times compared to that of N-polar p-GaN at 300 K. The fitting results of temperature-dependent hole concentration indicated that the holes in the graded p-AlGaN layer comprised both polarization-induced and thermally activated ones. By optimizing the growth conditions, the hole concentration was further increased to 9.0 × 1017 cm−3 in the graded AlGaN layer. The N-polar blue-violet light-emitting device with the graded p-AlGaN shows stronger electroluminescence than the one with the conventional p-GaN. The study indicates the potential of the polarization doping technique in high-performance N-polar light-emitting devices.