What causes high resistivity in CdTe

Abstract

Shallow donors are often introduced into semiconductor materials to enhance n-type conductivity. However, they can sometimes also be used to obtain compensation between donors and acceptors, resulting in high resistivity in semiconductors. For example, CdTe can be made semi-insulating by shallow donor doping. This is routinely done to obtain high resistivity in CdTe-based radiation detectors. However, it is widely believed that the shallow donor alone cannot be responsible for the high resistivity in CdTe. This is based on the argument that it is practically impossible to control the shallow donor doping level so precisely that the free carrier density can be brought below the desired value suitable for radiation detection applications. Therefore, a deep native donor is usually assumed to exist in CdTe and pin the Fermi level near midgap. In this paper, we present our calculations on carrier statistics and energetics of shallow donors and native defects in CdTe and illustrate different donorspecific mechanisms for achieving carrier compensation. Our results show that the shallow donor can be used to reliably obtain high resistivity in CdTe without requiring additional deep donors. Since radiation detection applications require both high resistivity and good carrier transport, one should generally use shallow donors and shallow acceptors for carrier compensation and avoid deep centers that are effective carrier traps. This study highlights how the interaction between impurities and native defects intricately affects the Fermi level pinning in the semiconductor band gap and the associated resistivity of the material.

First-principles DFT +GW study of the Te antisite in CdTe

“…Yang and co-workers 22 , Lordi 37 , and Lindström et al 38 have found a negative-U behavior in (Te Cd ). In contrast, Biswas and Du 39 have pointed out that (Te Cd ) is a deep donor with (+2/+) and (+/0) transition levels at VBM + 0.38 eV and VBM + 0.58 eV, respectively.…”

Cl-doping of Te-rich CdTe: Complex formation, self-compensation and self-purification from first principles

“…The (0/-1) charge transfer level is located at 0.07 eV above the valence band (see Fig.2(a), red lines). Biswas et al 19 reports this charge transfer level to be about 0.2 eV above the valence band. One difference between Biswas et al and our work is they do not consider the polaronic nature of the V −1 C d .…”

“…Two recent reviews highlight possibilities and challenges of first-principles calculations of point defects in solids. 16,17 We are aware of three earlier firstprinciples calculations of the (Cl T e -V C d ) −1 complex: [18][19][20] Chang et al 18 and Zhu et al 20 both use the Local density approximation (LDA) which we earlier have shown is insufficient to describe especially the properties of the V In the field of CdTe production, the self-compensation and self-purification effects of Cl T e are well known and widely used. 21,22 Despite this, the physics behind these two effects is still unsettled.…”

Stoichiometric effects in polycrystalline CdTe

“…At a specific temperature, the higher vapor pressure of Cd than that of Tez causes loss of Cd during deposition. The deposited CdTe can be Te-rich even if the source material is stoichiometric [2]. The p-type conductivity of Te-rich CdTe is due to the presence of cadmium vacancies (V Cd).…”