The ageing of Li implants in cadmium mercury telluride

Secondary ion mass spectrometry (SIMS) requires the preparation and measurement of standard samples in order to be considered a quantitative technique. This normally can be achieved by the production of ion‐implanted specimens in the matrix to be studied. The measured SIMS depth profile then can be integrated and compared with the known implanted dose in order to produce quantitative results. This paper reports a potential source of error in this method, discovered by studying the ageing of a lithium‐implanted cadmium mercury telluride (CMT) specimen over a six‐year period. Lithium has been shown to be a mobile impurity in CMT. It is shown that the original implant produced a satisfactory profile shape, but that room‐temperature diffusion subsequently degraded its shape over a period of five years. This finding is confirmed by the further action of annealing the implanted specimen at 250°C and studying the resulting profile. The change in the shape of the implant profile is discussed in relation to diffusion theory. SIMS images are shown to demonstrate the spatial inhomogeneity of the sample.