[en] The strain evolution of a GaN layer grown on a high-temperature AlN interlayer with varying AlN thickness by metalorganic chemical vapour deposition is investigated. In the growth process, the growth strain changes from compression to tension in the top GaN layer, and the thickness at which the compressive-to-tensile strain transition takes place is strongly influenced by the thickness of the AlN interlayer. It is confirmed from the x-ray diffraction results that the AlN interlayer has a remarkable effect on introducing relative compressive strain to the top GaN layer. The strain transition process during the growth of the top GaN layer can be explained by the threading dislocation inclination in the top GaN layer. Adjusting the AlN interlayer thickness could change the density of the threading dislocations in the top GaN layer and then change the stress evolution during the top GaN layer's growth

[en] Performance of InGaN-based laser diodes (LDs) with different Mg concentrations of electron blocking layer (EBL) is investigated by simulation and experimental methods. It is found from the simulation results that the threshold current decreases and slope efficiency increases, when the Mg concentration of EBL increases from 2 × 10¹⁸ to 6 × 10¹⁹ cm⁻³; it is attributed to the suppression of the leakage of electrons and the enhancement of the injection of holes due to the variation of potential barrier for them as the increase of Mg concentration of EBL. These simulation results agree well with the experimental ones, when the Mg concentration of EBL is lower than 7.5 × 10¹⁸ cm⁻³. However, it deteriorates when the Mg concentration increases to 1.2 × 10¹⁹ cm⁻³. It may be due to the increase of the absorption loss of LDs.

[en] An interesting GaN photodetector structure, which can be used for characterizing the wavelength of incident ultraviolet light, is proposed. It is composed of two back-to-back integrated diodes, i.e. p–n and p–i–n GaN ultraviolet photodiodes with different spectral response. The wavelength of monochromatic ultraviolet light could be identified by measuring the photocurrent ratio value through a simple electronic circuit

[en] Perovskite-structured Ba_1−xLa_xSnO₃ (x = 0–0.10) films have been directly grown on (0001) sapphire substrates by a sol-gel method. Optical properties and bandgap energy of the films have been investigated by transmittance spectra from 10 K to 450 K. It indicates that these films exhibit a high transmission of more than 80% in the visible region. With increasing temperature, there is a significant bandgap shrinkage of about 0.5 eV for lightly La doping (x ≤ 0.04) films. For heavily La doping concentration (x ≥ 0.06), the bandgap remains nearly stable with the temperature and La composition. This is due to the fact that the lattice expansion caused by La doping is close to the saturation for the film doped with x = 0.06. Moreover, temperature dependent conductivity behavior shows a similar pattern, which suggests that the doping concentration of La-doped BaSnO₃ (BLSO) films has a saturated state. The La introduction can modify the Sn 5s-O 2p antibonding state and the nonbonding O 2p orbital, which remarkably affect the electronic bandgap of the BLSO films

[en] AlInN/GaN thin films were implanted with Mn ions and subsequently annealed isochronically at 750 and 850 deg. C. X-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques were employed to study the microstructural properties of the implanted/annealed samples. The effect of annealing on implantation-induced strain in thin films has been studied in detail. The strain was found to increase with dose until it reached a saturation value and after that it started decreasing with a further increase in the dose. RBS measurements indicated the atomic diffusion of In, Al, Ga and Mn in implanted samples. The in- and out-diffusion of atoms has been observed after annealing at 750 deg. C and 850 deg. C, respectively. Strong decomposition of the samples took place when annealed at 850 deg. C

[en] AlInGaN quaternary epilayers with varying In mole fraction were investigated using triple-axis x-ray diffraction and photoluminescence measurements. The indium compositional fluctuation is enhanced with increasing In mole fraction, whereas the mosaicity of the AlInGaN epilayers is determined through the GaN template quality. Based on the analysis of the temperature dependence of the PL peak position, it is found that the localization effect strengthens with increasing In mole fraction due to the larger fluctuations of the In distribution. Increasing the influence of the localized state results in increasing the emission intensity and FWHM with the In content

[en] The unexpected decrease in measured responsivity observed in a specific GaN Schottky barrier photodetector (PD) at high reverse bias voltage was investigated and explained. Device equivalent transforms and small signal analysis were performed to analyse the test circuit. On this basis, a model was built which explained the responsivity decrease quantitatively. After being revised by this model, responsivity curves varying with bias voltage turned out to be reasonable. It is proved that the decrease is related to the dynamic parallel resistance of the photodiode. The results indicate that with a GaN Schottky PD, the choice of load resistance is restricted according to the dynamic parallel resistance of the device to avoid responsivity decay at high bias voltage

[en] This work presents a study of the correlation between the electrical properties and the structural defects in nominally undoped InN films. It is found that the density of edge-type threading dislocations (TDs) considerably affects the electron concentration and mobility in InN films. The Hall-effect measured electron concentration increases, while the Hall mobility decreases with the increase in the edge-type TD density. With the combination of secondary ion mass spectrometry and positron annihilation analysis, we suggest that donor-type point defects at the edge-type TD lines may serve as dominant donors in InN films and affect the carrier mobility

[en] Visible-blind p-i-n avalanche photodiodes (APDs) were fabricated with high-quality GaN epilayers deposited on c-plane sapphire substrates by metal-organic chemical vapour deposition. Due to low dislocation density and a sophisticated device fabrication process, the dark current was as small as ∼0.05 nA under reverse bias up to 20 V for devices with a large diameter of 200 μm, which was among the largest device area for GaN-based p-i-n APDs yet reported. When the reverse bias exceeded 38 V the dark current increased sharply, exhibiting a bulk avalanche field-dominated stable breakdown without microplasma formation or sidewall breakdown. With ultraviolet illumination (360 nm) an avalanche multiplication gain of 57 was achieved.

[en] The effects of growth temperature and V/III ratio on the InN initial nucleation of islands on the GaN (0 0 0 1) surface were investigated. It is found that InN nuclei density increases with decreasing growth temperature between 375 and 525 °C. At lower growth temperatures, InN thin films take the form of small and closely packed islands with diameters of less than 100 nm, whereas at elevated temperatures the InN islands can grow larger and well separated, approaching an equilibrium hexagonal shape due to enhanced surface diffusion of adatoms. At a given growth temperature of 500 °C, a controllable density and size of separated InN islands can be achieved by adjusting the V/III ratio. The larger islands lead to fewer defects when they are coalesced. Comparatively, the electrical properties of the films grown under higher V/III ratio are improved