Imaging semiconductor wafers using photoluminescence

A facility for producing photoluminescence (PL) images of semiconductor wafers at cryogenic temperatures is described. A custom-designed liquid helium cryostat capable of accepting 50-mm-diam wafers is used together with a scanning optical table for PL excitation and collection. Spectral analysis is achieved by the use of a CCD detector mounted on a standard grating spectrometer. The configuration used enables a full spectrum to be recorded for each point on a wafer with a spatial resolution of approximately 100 μm. The spectral information may be used to produce images of the total PL intensity, the peak PL intensity, and the wavelength at which the peak intensity occurs. Typical PL maps are presented to illustrate the quality of the information.