X-ray photoelectron spectroscopy (XPS) was used to measure the energy discontinuity in the MgO (111)/ZnO (0002) heterostructure. The valence band offset (VBO) was determined to be 1.22±0.23 eV and a type-I heterojunction with a conduction band offset (CBO) of 3.24±0.23 eV was obtained. The discrepancy of VBO values between MgO/ZnO and ZnO/MgO heterojunctions was mainly attributed to the internal electric field induced by spontaneous polarization effect in ZnO layer.Highlights► Valence band offset of MgO (111)/ZnO (0002) heterojunction was measured by X-ray photoelectron spectroscopy. ► A type-I band alignment with a valence band offset of ΔEV=1.22±0.23 eV was obtained. ► The discrepancy of VBO values between MgO/ZnO and ZnO/MgO heterojunctions was observed and discussed. ► Inner electric field induced by spontaneous polarization effect in ZnO layer makes VBO value diverse from ZnO/MgO system.

GaN thin films were grown with InGaN as an interlayer. The GaN films show different stress states with and without an InGaN interlayer. The influence of the In composition in InGaN on the properties of the high temperature (HT) GaN overlayer was discussed and potential stress-free points were extrapolated. The effect of H2 on the growth of HT GaN was found to be that it assisted the decomposition of InGaN. A nearly stress free GaN single-crystalline film with mirror-like morphology and single polarity was obtained by inserting an appropriate InGaN interlayer and the growth mechanism of GaN, with a regular network as the template, was discussed. Our research on the controllable growth of high-quality GaN thin film is very important for GaN-based optoelectronic and electronic devices.

Vertically well-aligned InN nanorods have been synthesized successfully by introducing diethylzinc (DEZn) into metal–organic chemical vapor deposition system. X-Ray diffraction and transmission electron microscopy measurements show that InN nanorods are single-crystalline and Zn-doped. In-depth studies indicate that DEZn inhibits the InN growth along m-plane and further leads to the self-formation indium droplets acting as catalyst. The whole growth process of InN nanorods is a combined result of the restriction effect from DEZn and catalytic effect from indium droplets. Also, the temperature effect on the growth has been studied intensively. Our research on the controlled growth of high-quality InN nanorods is very important for InN-based optoelectronic and electronic nano-devices.

We report the synthesis and characterization of Zn-doped InN nanorods by metal-organic chemical vapor deposition. Electron microscopy images show that the InN nanorods are single-crystalline structures and vertically well-aligned. Energy-dispersive X-ray spectroscopy analyses suggest that Zn ions are distributed nonhomogenously in InN nanorods. Simulations based on diffusion model show that the doping concentration along the radial direction of InN nanorod is bowl-like: from the exterior to the interior, the doping concentration decreases, and such dopant distribution result in a bimodal EDXS spectrum of Zn across the nanorod. The study of the mechanism of doping effect is useful for the design of InN-based nanometer devices. Also, high-quality Zn-doped InN nanorods will be very attractive as building blocks for nano-optoelectronic devices.

Both In2O3 and ZnO are potential oxide semiconductor materials for optoelectronics devices. Semi-polar (101) plane wurtzite (w-)ZnO films were grown on bcc-In2O3(111) by metal organic chemical vapor deposition and the epitaxial relation is w-ZnO(101) ∥bcc-In2O3(111). We have measured the valence band offset (VBO) of w-ZnO(101)/bcc-In2O3(111) heterojunction to settle the question of the band line-up of the ZnO/ In2O3 heterojunction. Our result shows that the valence band maximum (VBM) of ZnO (101) lies ∼0.49eV below the VBM of bcc- In2O3(111), and the conduction band maximum (CBM) of w-ZnO(101) is about 0.05 eV lower than the CBM of bcc-In2O3(111), which shows that their CBMs are nearly at the same level.

X-ray photoelectron spectroscopy (XPS) was used to measure the energy discontinuity in the MgO (111)/ZnO (0002) heterostructure. The valence band offset (VBO) was determined to be 1.22±0.23 eV and a type-I heterojunction with a conduction band offset (CBO) of 3.24±0.23 eV was obtained. The discrepancy of VBO values between MgO/ZnO and ZnO/MgO heterojunctions was mainly attributed to the internal electric field induced by spontaneous polarization effect in ZnO layer.Highlights► Valence band offset of MgO (111)/ZnO (0002) heterojunction was measured by X-ray photoelectron spectroscopy. ► A type-I band alignment with a valence band offset of ΔEV=1.22±0.23 eV was obtained. ► The discrepancy of VBO values between MgO/ZnO and ZnO/MgO heterojunctions was observed and discussed. ► Inner electric field induced by spontaneous polarization effect in ZnO layer makes VBO value diverse from ZnO/MgO system.

Polar and non-polar ZnMgO were synthesized on different crystallographic planes (C-, R- and M-planes) of sapphire (Al2O3) substrates by metal organic chemical vapor deposition, respectively. Under the same experimental condition, polar ZnMgO nanorods were obtained on C-Al2O3 substrate whereas non-polar ZnMgO thin films were obtained on R- and M-Al2O3 substrates. The surface morphology was significantly influenced by the competition of the preferable growth directions on different sapphire substrates. On C-Al2O3 substrate, ZnMgO nanorods were vertically well-aligned with typical lengths in the range 330–360 nm. On R- and M-Al2O3 substrates, however, ZnMgO thin films with flat surfaces were obtained, whose thickness were 150 and 20 nm, respectively. Under the same condition, the C-ZnMgO deposited on C-Al2O3 substrate has the maximum growth velocity (11 nm/nim), followed by A-ZnMgO deposited on R-Al2O3 substrate (5 nm/min), and the M-ZnMgO deposited on M-Al2O3 substrate has the minimum one (0.67 nm/min). The Near-Band-Edge (NBE) emission in Photoluminescence (PL) spectra shows a clear blueshift and a slight broadening compared with that of pure ZnO samples, which suggest that the Mg content has successfully incorporated into ZnO. The different energy blueshifts (67 meV and 98 meV) of the NBE emission demonstrate that A-ZnMgO deposited on R-Al2O3 substrate has higher Mg incorporation efficiency than C-ZnMgO on C-Al2O3 substrate.

Well-aligned Zn1−xMgxO nanorods and film with Mg-content x from 0 to 0.051 have been successfully synthesized by metal organic chemical vapor deposition (MOCVD) without any catalysts. The characterization results showed that the diameters and lengths of the nanorods were in the range of 20–80 nm and 330–360 nm, which possessed wurtzite structure with a c-axis growth direction. As the increase of Mg precursor flows into the growth chamber, the morphology of Zn1−xMgxO evolves from nanorods to a film with scale-like surface and the height of the nanorods and the film was almost identical, it is suggested that the growth rate along the c-axis was hardly changed while the growth of six equivalent facets of the type {1 0 1¯ 0} of the Zn1−xMgxO has been improved. Photoluminescence and Raman spectra show that the products have a good crystal quality with few oxygen vacancies. With the Mg incorporation, multiple-phonon scattering become weak and broad, and the intensities of all observed vibrational modes decrease. And the ultraviolet near-band-edge emission shows a clear blueshift (x=0.051, as much as 90 meV) and slightly broadening compared with that of pure ZnO nanorods.