Measurement of Minority Carrier Lifetime and Surface Effects in Junction Devices

The characteristics of junction devices are influenced to a considerable degree by the lifetime of the minority carriers. Accordingly, methods for the measurement of this quantity are of considerable importance. Methods have been described for the measurement of the lifetime of minority carriers when these carriers are produced within the volume of a semiconductor. When the minority carriers are introduced near the surface of a semiconductor the resulting effective lifetime may be determined to a large extent by the nature of the surface. For most junction devices, it is the effective lifetime that is of primary importance. This paper describes a simple method for the measurement of effective lifetimes of injected minority carriers. The measurements may be applied to practical junction structures as, for example, an alloyed junction transistor. Measurements may be made on either completed or partially completed devices. The resulting data are potentially of value as quality controls during the fabrication of transistors and similar devices. In many cases, the effective lifetime is a good indication of the surface conditions, and immediate evaluation of these conditions may be obtained at various stages of device processing. With selected geometries, the measurement method may be applied to determine absolute values of surface recombination velocities and should therefore be in studying surface conditions and treatments. The measurement method is described in terms of junction devices using germanium as the semiconductor. However, the method is equally applicable to junction devices made with other semiconductor materials.