Viscosity measurements of GaInSn eutectic alloys were performed in a homebuilt device for low (9%) and high (95%) relative humidity for shorter (450 min) and longer (1800 min) time periods. At constant exposure time a characteristic increase of viscosity is observed with increasing humidity. For high humidity, high viscosity is obtained after a short time.Assuming that the measured viscosity change is strongly related to the absorption of oxygen, XPS was applied to the chemical and quantitative analysis of differently prepared samples. In all cases, Ga is predominantly oxidized at the surface whereas Ga atoms in the metallic state are located deeper inside. Besides Ga 2 O 3 (the most stable oxide phase), the less stable Ga 2 O is detected. Indium and tin are almost stable in their metallic state. With increasing humidity the thickness of the oxide film increases in our case from about 19Å to 25Å, assuming a layer-by-layer model. The presented results confirm our assumption of the increase in viscosity of the GaInSn system as a consequence of the preferential oxidation of gallium in the near-surface region.
We report on the optical characterization of highly Si-doped AlN layers grown by plasma-assisted molecular-beam epitaxy. Cathodoluminescence spectra reveal a sharp band-edge line and two broadbands around 4.4eV and 3.6eV. Near-band-edge luminescence remains intense at room temperature, and shows a systematic redshift with increasing Si concentration. Regarding the low-energy bands, we observe a redshift of the emission around 3.6eV with increasing Si concentration accompanied by an increase in relative intensity compared to the 4.4eV band.
Electrical properties and deep traps spectra of N-polar and Ga-polar AlGaN films grown by molecular beam epitaxy in a wide composition range Electrical properties and photoresponse of AlGaN based photodetectors were studied demonstrating an adverse effect of the broad-band trap distribution on the spectral, electrical, and time-response characteristics. It was found that n-type conduction mechanism is space charge limited indicating a strong carrier trapping effect. In particular, we show that dark current, photoresponsivity, and response time are determined by the slow-varying energy distribution of traps located above the equilibrium Fermi level. We demonstrate also that both the deep recombination centers and the localized shallow states do not impact the response time of the photodetector, and the persistent photocurrent effect is directly connected to the voltage-induced injection and trapping of the excess carriers.
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