A Wet Etching Technique to Reveal Threading Dislocations in Thin Germanium Layers

A defect selective wet chemical etching technique that allows accurate determination of etch pit density (EPD) in thin Germanium (Ge) layers is described. The effect is achieved by using chromium (Cr VI) based solution. Such a solution, in combination with other chemicals, exhibits mild oxidation power which provides low etch rates (ER) and excellent selectivity towards threading dislocations. The etching technique is able to delineate threading dislocations in layers with thickness in the range of 80 – 1500 nm within the resolution of scanning electron microscopy (SEM). Different types of Ge layers were analyzed (doping levels, defect density, degree of relaxation). The ER is shown to depend on several characteristics of the layer and is in the range of 7 to 100 nm/min.