High quality indium tin oxide (ITO) thin films were grown without oxygen by both dc and RF magnetron sputtering techniques on glass substrates. The effects of substrate temperature, film thickness and sputtering method on the structural, electrical and optical properties of the as-grown films were investigated. The results showed that the substrate temperature had substantial effects on the film properties, in particular on the crystallization and resistivity. When the substrate temperature was increased to 150 • C, crystallization in the (2 2 2) plane started appearing for both dc and RF sputtered films. We additionally found that with further increments of substrate temperature, the preferred crystallization orientation changed differently for dc and RF sputtered films. Optical transmission in the visible region for a film thickness of 70 nm was found to be above 85%. The bandgap was calculated to be about 3.64 eV for the substrate temperature of 150 • C for a 70 nm thick film. The value of the bandgap increased with respect to the increment in film thickness as well as substrate temperature. We also measured the temperature dependence of the resistivity and Hall coefficient of the films, and calculated the carrier concentration and Hall mobility. Very low room temperature resistivities for dc and RF magnetron sputtered grown films of about 1.28 × 10 −4 cm and 1.29 × 10 −4 cm, respectively, were obtained.

Ga-rich (0001)-oriented In x Ga 1Àx N alloys grown by molecular beam epitaxy or metal-organic vapour phase epitaxy on GaN/ sapphire templates were investigated by spectroscopic ellipsometry at room temperature. The analysis of the extracted dielectric function yielded the characteristic transition energies, i.e., for the band gaps and the high-energy critical points (van Hove singularities). Accounting for strain by using the k Á p formalism, a band-gap bowing parameter of 1.65 AE 0.07 eV for strain-free material was deduced. It is consistent with the ab initio calculated band-gap-dependence for uniform (not clustered) InGaN alloys. The bowing parameters for the highenergy inter-band transitions were found to be close to $1 eV.

In order to optimize the growth conditions, the effect of the most important growth parameters such as growth temperature, pressure and V/III ratio on MOCVD‐grown InN was investigated. A series of samples were grown by changing the growth temperature from 500 °C to 550 °C at fixed growth pressure of 800 mbar and V/III ratio of 145000. An improvement of electrical properties with temperature increment was noted. The highest mobility of 1200 cm2/Vs was achieved at 550 °C with a bulk carrier concentration of 4.32 x 1018 cm‐3. The effect of V/III ratio on In droplet formation and on carrier concentration was also studied. At fixed temperature of 520 °C, reactor pressure of 200 mbar and at fixed NH3 flow of 3 slm, a rising TMIn flow from 1.2 µmol/min to 2.0 µmol/min results in a carrier concentration increment from 6.06 x 1018 cm‐3 to 1.33 x 1019 cm‐3and a decrement of the mobility from 430 cm2/Vs to 348 cm2/Vs. X‐ray diffraction measurements show that the intensity associated with In droplets on the surface is rising with increasing TMIn flow. The effect of reactor pressure on InN growth was also examined. A high sensitivity to growth pressure for crystalline quality of InN was observed. The full width at half maximum (FWHM) values of InN (0002) reflexes decreased with increasing reactor pressure. With increasing growth pressure above 200 mbar, FWHM of around 275 arcsec of InN (0002) was achieved. This FWHM value is the lowest reported in literature for MOCVD‐grown InN so far. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The trench defects in InGaN/GaN multiple quantum well structures are studied using confocal photoluminescence (PL) spectroscopy and atomic force microscopy. A strong blueshift (up to ∼280 meV) and an intensity increase (by up to a factor of 700) of the emission are demonstrated for regions enclosed by trench loops. The influence of the difference in the well width inside and outside the trench loops observed by transmission electron microscopy, the compositional pulling effect, the strain relaxation inside the loop, and corresponding reduction in the built-in field on the PL band peak position and intensity were estimated. The competition of these effects is mainly governed by the width of the quantum wells in the structure. It is shown that the PL band blueshift observed within the trench defect loops in the InGaN structures with wide quantum wells is mainly caused by the reduction in efficiency of the quantum-confined Stark effect due to strain relaxation.

No abstract