Impact of nitrogen annealing on the electrical properties of HgCdTe epitaxial films

The nitrogen annealing of HgCdTe materials grown by molecular beam epitaxy (MBE) was carried out to manipulate their electrical properties. The results show that the annealing temperature, annealing time and cooling process all have significant influences on the electrical properties of HgCdTe materials. Excessive annealing temperature or long annealing time can make voids emerge on the surface of the CdTe passivation layer. Carrier concentration and mobility vary exponentially with annealing time and they reach an equilibrium value determined by annealing temperature over a long annealing duration. Moreover, time constants are given and a longer time is needed for mobility to reach an equilibrium value than carrier concentration. The relationship between equilibrium carrier concentration and annealing temperature is given and the activation energy under nitrogen annealing is calculated as 0.63 eV. For a long cooling duration, Hg vacancies are annihilated by Hg atoms diffusion, which makes carrier concentration lower and mobility higher. In addition, some outlier data were found in this experiment and explained by the combination between Te antisites and Hg vacancies.