Influence of the substrate misorientation on the properties of N-polar GaN films grown by metal organic chemical vapor deposition

The authors have developed a comprehensive model for the growth of N-polar and Ga-polar In x Ga 1−x N by N 2 plasma-assisted molecular beam epitaxy. GaN films of both polarities were coloaded and In x Ga 1−x N was grown in the composition range of 0.14Ͻ x Ͻ 0.59 at different growth temperatures keeping all other conditions identical. The compositions were estimated by triple-axis-2 x-ray diffraction scans as well as by room temperature photoluminescence measurements. The dependence of the In composition x in In x Ga 1−x N on growth temperature and the flux of incoming atomic species is explained using a comprehensive growth model which incorporates desorption of atomic fluxes as well as decomposition of InN component of In x Ga 1−x N. The model was found to be in good agreement with the experimental data for In x Ga 1−x N of both polarities. A N-polar In 0.31 Ga 0.69 N / In 0.05 Ga 0.95 N multi-quantum-well structure grown with conditions predicted by our growth model was found to match the compositions of the active layers well besides achieving a smooth surface morphology at the quantum-well/barrier interface. The understanding of growth kinetics presented here will guide the growth of In x Ga 1−x N for various device applications in a wide range of growth conditions.

We report the demonstration of a N-polar InGaN based green light emitting diode (LED) grown by N 2 plasma-assisted molecular beam epitaxy (PAMBE). High quality multiple quantum well LEDs with In 0:29 Ga 0:71 N quantum wells were grown at a temperature of 600 C by applying a new growth model. LED structures exhibited green emission, and electroluminescence measurements on the test structure showed peak emission wavelengths varying from 564.5 to 540 nm. The full width at half-maximum reduced from 74 to 63 nm as the drive current was increased to 180 A/cm 2. This work is the first demonstration of an N-polar LED with emission in the green wavelength range.

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Above-band-edge absorption spectra of reactively sputtered Zn- and O-rich samples exhibit free exciton and neutral acceptor bound exciton (A0X) features. It is shown that the residual acceptors which bind excitons with an energy of 75meV reside about 312meV above the valence band, according to effective mass theory. An intra-band-gap absorption feature peaking at 2.5eV shows correlation with the characteristically narrow A-free exciton peak intensity, suggesting a compensation mechanism of the centers involving oxygen vacancy (VO) related donors. In order to enhance free exciton concentration relative to competing neutral bound exciton density, relevant annealing processes are performed without disturbing the residual shallow acceptor profile which is necessary for at least background p-type conductivity.

Current–voltage (I–V) measurements of Ag/n-ZnO have been carried out at temperatures of 200–500 K in order to understand the temperature dependence of the diode characteristics. Forward-bias I–V analysis results in a Schottky barrier height of 0.82 eV and an ideality factor of 1.55 at room temperature. The barrier height of 0.74 eV and Richardson constant of 0.248 A K−2 cm−2 were also calculated from the Richardson plot, which shows nearly linear characteristics in the temperature range 240–440 K. From the nkbT/q versus kbT/q graph, where n is ideality factor, kb the Boltzmann constant, T the temperature and q the electronic charge we deduce that thermionic field emission (TFE) is dominant in the charge transport mechanism. At higher sample temperatures (>440 K), a trap-assisted tunnelling mechanism is proposed due to the existence of a deep donor situated at Ec—0.62 eV with 3.3 × 10−15 cm2 capture cross section observed by both deep-level transient spectroscopy (DLTS) and lnI0 versus 1/kbT plots. The ideality factor almost remains constant in the temperature range 240–400 K, which shows the stability of the Schottky contact in this temperature range.

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