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Nominally undoped n-type Gallium Nitride (GaN) layers grown by metalorganic chemical vapor deposition (MOCVD) on silicon substrates were studied. Thermal Admittance Spectroscopy (TAS) and Optical Admittance Spectroscopy (OAS) techniques were used to characterize these layers. Using Thermal Admittance Spectroscopy (TAS), a defect level was observed at Ec – 0.051 eV and this defect is correlated with the nitrogen vacancy (Nv) in GaN. The samples were illuminated with a monochromatic light with wavelengths (λ) ranging from 200 nm to 450 nm. The OAS spectrum was measured at different temperatures and with different excitation light intensities. The spectrum shows a maximum photoconductance (G) peak at λ = 365nm (E = 3.40eV). This peak is attributed to transitions from the valence band to the donor level at Ec – 0.051 eV. The analysis of the results shows that the saturation level (Gm) of the photoconductance is a function of both light intensity and temperature. The photoconductance decay, after illumination has been terminated, is adequately described by a stretched exponential function. This photoconductance decay is attributed to the thermal emissions of photo-excited carriers from the donor level to the conduction band.

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Independent Research

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Andrew Evwaraye

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Stander Symposium poster


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