The kinetics of conductivity type conversion in HgCdTe by ion beam milling

It is well established that dry etching of HgCdTe by Ar ion-beam milling (IBM) converts vacancy-doped p-type HgCdTe to n-type. Less well established is the understanding of the observed rate of conversion. This paper shows that the observed variations of the depth of conversion with milling time can be accounted for in terms of two rate processes operating in tandem. The first process is the diffusion of Hg interstitials from the surface to the conversion boundary followed by the second, or conversion, process that is the capture of the Hg interstitials by cation vacancies. Assuming steady-state conditions exist a quadratic equation is derived for the conversion depth and its milling-time dependence for two cases: when the initial p-type layer is electrically intrinsic at the milling temperature and when it is extrinsic. Good agreement is found with the available experimental Ar-ion-milling data. Good agreement is also found for type conversion due to etching with a radio-frequency Ar plasma. The effect of capture of Hg interstitials by traps, in addition to capture by cation vacancies, is also considered.