Ab Initio Studies of Hydrogen Defects in CdTe

Using first-principles calculations based on density functional theory, we have investigated the nature of H defects in CdTe. The formation energy calculations indicate that the ground state position of the H inside the CdTe lattice depends on charge state: the lowest energy position for H-0 and H+ is at the bond center site, while H- prefers the tetrahedral interstitial site with Cd nearest neighbors (T-Cd). We find that H in CdTe acts as an amphoteric impurity. In p-type samples, H is in a positive charge state, acting as a donor to neutralize the free holes in the valence band, and in n-type samples H acquires an electron, compensating the donors in the sample.