ABSTRACT The effect of annealing temperature on the structural properties of Al-N codoped ZnO films were studied by X-ray diffraction, photoluminescence and Raman spectroscopy. ZnO films were deposited by sputtering technique on silicon substrates at 20 ºC, Al-concentration was kept constant and N-flow was changed to 6, 12 and 15 sccm. A thermal treatment was performed by annealing the sample during 30 minutes at 300, 400, 500, 600 and 700 °C. Before annealing, Raman spectra shows two vibration modes located at 275 and 580 cm-1 associated to the nitrogen incorporation and the presence of point defects. Both Raman intensities of modes I275 and I580 decreases when the nitrogen flow increases from 6 to 12 and 15 sccm, which is originated by a decreasing interstitial defects density. The improving of the crystal quality was confirmed by x-ray diffraction and room temperature photoluminescence measurements. After annealing, in the Raman spectra it was observed that I275 increases as the temperature increase, reaches a maximum intensity between 500 and 600 °C, and decreases for higher temperatures. X-ray diffraction measurements show that after annealing the compressive stress decrease progressively as the annealing temperature increase. This study suggests that 275 Raman mode could be used to estimate the optimal thermal treatment in order to achieve p-doping ZnO.

ABSTRACT In this work a theoretical study of electrical behavior for a c-GaN/GaAs heterostructure as a photovoltaic device through a two-dimensional (2D) finite element numerical simulation is presented for a first time. I-V curves and electrical parameters like short circuit current (Isc), open circuit voltage (Voc), fill factor (FF) and efficiency (η) were obtained for n-i-p and n-p heterostructures with different thicknesses and doping of the layers by modeling heterostructures with characteristics parameters of this materials previously reported. As a result, an increment on Isc was observed by extending the thickness of i-GaAs layer from 12 mA/cm2 for thinner heterostructures to a maximum of ~32 mA/cm2 for heterostructures with i-GaAs layer >3000 nm and a decrease in Voc and FF in the range from ~1.06 V and 0.89 for n-p heterostructures to 0.75 V and 0.7 respectively for thicker i-GaAs layers allowing estimate maximum efficiencies between 23 and 25% for n-i-p and n-p configurations, respectively. This study allows demonstrating the potential of this type of heterostructures for solar cells applications, considering the possibility of using p-doping GaAs substrates for photovoltaics based in GaN.