Ji Zi-Wu

Influences of excitation power and temperature on photoluminescence in phase-separated InGaN quantum wells

The photoluminescence (PL) properties of a green and blue light-emitting InGaN/GaN multiple quantum well structure with a strong phase separated into quasi-quantum dots (QDs) and an InGaN matrix in the InGaN epilayer are investigated. The excitation power dependences of QD-related green emissions (PD) and matrix-related blue emissions (PM) in the low excitation power range of the PL peak energy and line-width indicate that at 6 K both PM and PD are dominated by the combined action of Coulomb screening and localized state filling effect. However, at 300 K, PM is dominated by the non-radiative recombination of the carriers in the InGaN matrix, while PD is influenced by the carriers transferred from the shallower QDs to deeper QDs by tunnelling. This is consistent with the excitation power dependence of the PL efficiency for the emission.

Photoluminescence of Nanoporous GaN Films Prepared by Electrochemical Etching

Nanoporous (NP) GaN is prepared by electrochemical etching on a GaN epilayer grown on a sapphire substrate by metal-organic chemical vapor deposition. Scanning electron microscopy reveals that the average pore diameter and inter-pore spacing are approximately 25 and 45 nm, respectively. The photoluminescence (PL) spectra show that in contrast to the initial as-grown GaN epilayer, the NP GaN exhibits a high near-band-edge UV intensity, significant relaxation of compressive strain, and a lower yellow luminescence intensity. Both the line shape and line width of the PL spectra are almost the same for these two samples. The high quality of the NP GaN can be explained by the enhancement of the PL extraction efficiency and the decrease of impurity and defect density after etching.

Influence of the AlGaN barrier thickness on polarization Coulomb field scattering in an AlGaN/AlN/GaN heterostructure field-effect transistor

In this study rectangular AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with 22-nm and 12-nm AlGaN barrier layers are fabricated, respectively. Using the measured capacitance–voltage and current–voltage characteristics of the prepared devices with different Schottky areas, it is found that after processing the device, the polarization Coulomb field (PCF) scattering is induced and has an important influence on the two-dimensional electron gas electron mobility. Moreover, the influence of PCF scattering on the electron mobility is enhanced by reducing the AlGaN barrier thickness. This leads to the quite different variation of the electron mobility with gate bias when compared with the AlGaN barrier thickness. This mainly happens because the thinner AlGaN barrier layer suffers from a much stronger electrical field when applying a gate bias, which gives rise to a stronger converse piezoelectric effect.

Growth and photoluminescence properties of inclined ZnO and ZnCoO thin films on SrTiO3(110) substrates

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO3(STO)(110) substrates. Inclined ZnO and cobalt-doped ZnO (ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy, with the c-axis 42? inclined from the normal STO(110) surface. The growth geometries are ZnCoO[100]//STO[11?0] and ZnCoO[11?1]//STO[001]. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D0X emissions associated with A0X emissions, and the characteristic emissions for the 2E(2G)?4A2(4F) transition of Co2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co2+ ions at the lattice positions of the Zn2+ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.

Photoluminescence characteristics of ZnTe bulk crystal and ZnTe epilayer grown on GaAs substrate by MOVPE

Excitation power and temperature-dependent photoluminescence (PL) spectra of the ZnTe epilayer grown on (100) GaAs substrate and ZnTe bulk crystal are investigated. The measurement results show that both the structures are of good structural quality due to their sharp bound excitonic emissions and absence of the deep level structural defect-related emissions. Furthermore, in contrast to the ZnTe bulk crystal, although excitonic emissions for the ZnTe epilayer are somewhat weak, perhaps due to As atoms diffusing from the GaAs substrate into the ZnTe epilayer and/or because of the strain-induced degradation of the crystalline quality of the ZnTe epilayer, neither the donor–acceptor pair (DAP) nor conduction band-acceptor (e–A) emissions are observed in the ZnTe epilayer. This indicates that by further optimizing the growth process it is possible to obtain a high-crystalline quality ZnTe heteroepitaxial layer that is comparable to the ZnTe bulk crystal.

Investigation of the inhibiting outdiffusion of erbium atoms to a silicon-on-insulator surface after annealing at high temperature

The annealing behaviour of 400 keV Er ions at a fluence of 2×1015 cm−2 implanted into silicon-on-insulator (SOI) samples is investigated by Rutherford backscattering spectrometry of 2.1 MeV He2+ ions with a multiple scattering model. It is found that the damage close to the SOI surface is almost removed after being annealed in O2 and N2 atmospheres, successively, at 900°C, and that only a small number of the Er atoms segregated to the surface of the SOI sample, whereas a large number of Er atoms diffused to a deeper position because of the affinity of Er for oxygen. For the SOI sample co-implanted with Er and O ions, there is no evident outdiffusion of Er atoms to the SOI surface after being annealed in N2 atmosphere at 900°C.