Browsing by Author "Schaff, W. J."

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    Compensating point defects in 4He+ -irradiated InN
    (American Physical Society (APS), 2007) Tuomisto, Filip; Pelli, A.; Yu, K. M.; Walukiewicz, W.; Schaff, W. J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    We use positron annihilation spectroscopy to study 2 MeV 4He+ -irradiated InN grown by molecular-beam epitaxy and GaN grown by metal-organic chemical-vapor deposition. In GaN, the Ga vacancies act as important compensating centers in the irradiated material, introduced at a rate of 3600 cm exp −1. The In vacancies are introduced at a significantly lower rate of 100cm−1, making them negligible in the compensation of the irradiation-induced additional n-type conductivity in InN. On the other hand, negative non-open volume defects are introduced at a rate higher than 2000cm exp −1. These defects are tentatively attributed to interstitial nitrogen and may ultimately limit the free-electron concentration at high irradiation fluences.
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    Self-compensation in highly n-type InN
    (AIP Publishing, 2012) Rauch, C.; Tuomisto, Filip; King, P. D. C.; Veal, T. D.; Lu, H.; Schaff, W. J.; Teknillisen fysiikan laitos; Department of Applied Physics; Perustieteiden korkeakoulu; School of Science
    Acceptor-type defects in highly n-type InN are probed using positron annihilation spectroscopy. Results are compared to Hall effect measurements and calculated electron mobilities. Based on this, self-compensation in n-type InN is studied, and the microscopic origin of compensating and scattering centers in irradiated and Si-doped InN is discussed. We find significant compensation through negatively charged indium vacancy complexes as well as additional acceptor-type defects with no or small effective open volume, which act as scattering centers in highly n-type InN samples.