Scanning Microscopy


A procedure for the evaluation of the depletion region width of a Schottky barrier diode made on semi-insulating materials has been assessed and applied to gallium arsenide nuclear detectors. This procedure, which makes use of the optical beam induced current method of charge collection scanning microscopy, allows the direct measurement of the depletion layer width. By taking into account the high resistivity of the material under examination and measuring the diode reverse current, it is possible to evaluate the actual voltage applied at the depletion layer boundaries. It was found that, at low actual bias values, the voltage dependence of the depletion layer follows the usual square root power law, while at increasing voltages, it changes into a linear behavior. An explanation in terms of deep trap effect and trap field-enhanced capture cross-section is proposed even though further work must be done to explain the space charge width dependence on bias applied in terms of the deep trap influence.

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