A method of determining the distribution of photoconductivity and its relaxation time over the semiconductor wafer thickness

A noncontact method is proposed to determine the depth profiles of photoconductivity and its relaxation time in a high-resistance plane-parallel semiconductor wafer placed at the center of an open confocal cavity normally to its axis and exposed to intensity-modulated light. The method is based on measuring the cavity transmission modulation depth at several frequencies for which the wafer optical thickness equals an integer number of half-waves and the wafer positions in which the phase difference between the interfering waves on the wafer surfaces is a multiple of π/2. The effect of experimental errors on the accuracy of the method is studied by computer simulation.