QUANTITATIVE INFRARED IMAGING FOR THE MEASUREMENT OF DOPANT DISTRIBUTION IN GALLIUM-ARSENIDE

This paper discusses a quantitative infrared imaging technique for mea surement of dopant distribution for n-type semiconductors such as sele nium-doped GaAs. It is demonstrated that the dopant distribution for a n entire axial slice may be found using this technique. The imaging ap paratus consists of a uniform light source, a narrow bandpass filter, a high resolution charged coupled divice (CCD) detector, and an image processor. Neutral density filters of known transmission are used to c alibrate the grey level output of the image processor to transmission. The absorption coefficient is calculated based on the transmission, r eflectance and thickness of the sample. The imaging is performed at 1. 05 mum. Free carrier concentration is then found from its relation to the absorption coefficient. Grey level intensity of the sample can be used as a measure of free carrier concentration. This calibration is d one assuming complete ionization of free carriers and that all absorpt ion is due to free carriers. An illustration of the dopant distributio n imaged for a longitudinal slice of a Czochralski grown bulk single c rystal is shown as an example of this technique and compared to theore tical results.