Depth profiling of defects in epilayer semiconductor materials by using synchrotron x-radiation topography

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Abstract
Depth profiling of defect structures can be accomplished by taking advantage of the increased penetration of x rays with decreasing wavelength. Topographs can then be taken at various integrated depths giving a nondestructive profile of the microstructure. This is usually accomplished via a monochromator, which is a slow and expensive procedure, even at a synchrotron source. Appropriate filters can be used in white beam synchrotron topography which reduce fluorescence while at the same time giving a limited, though not monochromatic, bandpass. This allows observations of the microstructure over a narrow energy range, diminishing the complications arising from harmonics in interpreting white beam images. In studies of GaAs crystals it was found possible to use GaAs or Cu prefilters in conjunction with deliberate air attenuation of the long wavelength components of the synchrotron spectrum. Studies were made on GaAs crystals that had been processed in a variety of ways. Examples will be shown for GaAs substrates with low grown-in dislocation density and with Zn-doped GaAs epilayers. This selective energy filtering provides a simple, rapid method of recording reflections varying from approximately 0.2 to 1.6 Å. The combination of this technique with a precision goniometer tilt stage permitted observations of the specimen defect structure from a few microns below the surface to 0.3 mm depth, thus presenting a visual profile of the effect of processing on the defect structure of the sample.