Single crystalline InN films with an absorption edge between 0.7 and 2 eV have been grown using a variety of different techniques, including conventional metal-organic vapor-phase epitaxy (MOVPE), ArF-laser assisted MOVPE (la-MOVPE), and plasma-assisted molecular-beam epitaxy (pa-MBE). Analysis of samples grown using different methods has led to important evidence for determining the actual band gap energy of InN. In an effort to find the origin of the change in absorption edge, this evaluation was focused on the la-MOVPE of InN. This deposition technique enables InN film deposition over a wide range of growth temperatures, ranging from room temperature to a very high temperature (700 °C). Characterization of InN films grown over a wide range of temperatures strongly suggests that oxygen contamination leads to a larger band gap absorption energy value than the actual value, even in the case of single crystalline films. In films grown at low temperatures, oxygen appeared to form an alloy, resulting in a larger absorption edge, whereas, in films grown at high temperatures oxygen was present as a donor, which resulted in a larger absorption edge due to a Burstein–Moss shift.

We have measured the resistive transition of molecular beam epitaxy prepared Bi 2 Sr 2 CaCu 2 O 8+x thin films in the presence of perpendicular low magnetic fields H (0 Oe < H < 1100 Oe) for different values of the bias current density J (10 2 A cm −2 < J < 10 5 A cm −2 ). The experimental data show two distinct dissipative behaviours. In the low-current region (J < 10 3 A cm −2 ) the electrical resistivity ρ is independent on J , changing only with H , while in the high-current region (J > 10 4 A cm −2 ) ρ is independent of both the bias current and the magnetic field. The result is considered in terms of thermally activated flux flow-flux creep-steady flux flow crossovers. The role of the statistical distribution of the pinning energy in the vortex dynamics is discussed.

No abstract

An InN film is grown using an ArF excimer laser assisted-MOVPE where a high NH 3 decomposition rate condition is realized because of the effective dissociation of NH 3 by the ArF laser. Grown films show unusual phenomena such that amount of metallic In involved in a grown InN film is increased with increasing NH 3 flow rate during the growth. Through the annealing of grown InN films in the NH 3 flow, it is revealed that the photolysis of NH 3 by the ArF laser irradiation causes the decomposition of InN and, as a result of it, the formation of In droplets. The direction of the source gases injection during the growth, perpendicular or parallel to the substrate surface, has a significant effect on the formation of metallic In. Compared with the perpendicular injection, the parallel injection can suppress the formation of In droplets and allow us to grow InN at a higher temperature. A high density of atomic hydrogen (H) generated by the photolysis of NH 3 seems to take nitrogen atoms away from InN, leaving metallic In on the surface..

In this paper, the employment of the ArF excimer‐laser assisted nitridation of sapphire substrate is studied in the ArF‐laser assisted MOVPE (la‐MOVPE) of InN. An ArF excimer laser with an energy 50 mJ/pulse and a repetition rate 20 Hz is introduced parallel to the substrate surface. The surface morphology of InN film grown on α‐Al2O3 (0001) is found to be markedly dependent on the nitridation conditions for the sapphire substrate. When no nitridation is made, the surface of grown InN film is very rough and many In droplets are found on it. A film with a mixture of rough‐surface region with In droplets and smooth‐surface region is grown on the thermally‐nitrided substrate (1000 °C for 30 min). By employing the ArF‐laser irradiation to the NH3 flow during the substrate nitridation at 1000 °C for 30 min (la‐nitridation), a smooth surface region is expanded to the entire surface of film. The smooth surface is found to be stable at growth temperature higher than 700 °C. The KOH etching of grown films reveals that the smooth surface has 5–10 time higher etching rate than the rough one. From these facts, it is concluded that the film with the smooth surface has N‐polarity. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)