High (p,T) properties of wide band-gap semiconductors from second harmonic generation measurements

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We propose to measure the phase boundaries and the melting curves of the wide band-gap semiconductors ZnO and AlN at high pressures and high temperatures (up to 50 GPa and 3500 K). These measurements are necessary to obtain data to improve the synthesis of doped compounds, which in turn are needed to optimise device performances. We will determine the onset of melting and the slope of the phase boundaries by measuring the intensity of the optical second harmonic generation signal and from the change in the emitted radiation. These measurements will allow to test predictions based on molecular dynamics simulations using empirical potentials. Laser heating experiments with nitrogen as the pressure medium will provide insight into the possibility of doping in the high pressure phase of ZnO and AlN. The e_ect of high pressure on the refractive indices and on the second harmonic generation will be studied using a new approach based on Maker fringe measurements.