Phase Shift Method of Carrier Lifetime Measurements in Semiconductors

Abstract
A direct reading instrument for lifetime measurements in semiconductors is described. It is based on the phase shift that exists between a sinusoidal modulation of carrier injection and the corresponding modulation of specimen conductance. Carrier injection is effected optically, a Kerr cell being used to modulate the intensity of the injecting light. The phase shift is determined by means of a compensating RC circuit which allows a direct reading of lifetime. The actual measurement is reduced to the setting of a variable resistor in such a way that an ellipse observed on the screen of a CRO degenerates into a straight line. The performance of the instrument is discussed for the case of a thin, rectangular filament illuminated on one of its large faces either homogeneously or in a narrow band.
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