Cryogenic, whole wafer imaging of semi-insulating GaAs
The authors have developed a whole wafer, cryogenic imaging system for making rapid absorption and photoluminescence maps of semiconductor wafers up to 100 mm in diameter. The cryostat requires no cryogens and can maintain a temperature of 15 K indefinitely. Its design facilitates the rapid (15 min) exchange of samples. Furthermore, the transmitted or emitted light from the sample is imaged onto a cooled Si CCD array rather than by using raster scanning. The net result is a system ideally suited for the routine characterisation of numerous wafers. This system has been used to map the EL2 concentration and donor-acceptor pair band photoluminescence intensity for a number of semi-insulating GaAs wafers.