n-type doping of the wide gap ternary alloy (CdMg)Te during molecular beam epitaxy

Abstract

We report on the n-type doping of the wide gap II-VI semiconductor CdMgTe. Bromine and chlorine have been used as dopants during molecular beam epitaxy. For the CdTe base material both bromine and chlorine give shallow donors, and free carrier concentrations of up to 2.8×1018 cm−3 have been reached. For increasing Mg concentration, however, deep donors are created, limiting the free carrier concentration at room temperature. This is demonstrated by Hall effect measurements at different temperature. The deep donors can be converted to metastable shallow donors by light illumination at temperatures below about 180 K, which results in persistent photoconductivity. We interpret our results in terms of a DX-like state, which is introduced by both the chlorine and bromine doping, and which moves into the band gap with increasing Mg concentration. We conclude that the limit in the n-type doping of CdMgTe, the band gap of which can easily be tuned through the whole visible range, is an intrinsic property of the dopants used, and not due to self-compensation caused by nonideal growth conditions.

Iodine doping of CdTe and CdZnTe layers grown by molecular beam epitaxy

“…The existence of such DX-like levels has been proposed to explain the decrease of n-type doping efficiency in CdMgTe for halogens. 11 The reason why a higher doping level can be reached with iodine than with indium in the case of CdZnTe is not fully understood at this stage. A possible reason is that the iodine covalent radius ͑1.405 Å͒ is identical to that of tellurium whereas indium ͑1.405 Å͒ which substitutes for Cd or Zn atoms has a covalent radius identical to that of Cd but much larger than that of Zn ͑1.225 Å͒.…”

DX centers in CdTe: A density functional study

“…Such donor related lattice defects are called DX centers, which can cause the saturation of the free-electron carriers in the n-type semiconductors. [7][8][9][10][11][12][13][14][15] Structural models for DX centers associated with both group-III and group-VII donors in CdTe have been proposed, [16][17][18][19] which is similar to the brokenbond DX ͑BB-DX͒ model that was initially proposed for the DX centers in Si-doped AlGaAs alloys. However, the reverse structural transformation is subject to a thermal activation barrier, which gives rise to the persistent photoconductivity at low temperatures.…”

Structural and optoelectronic properties of Mg substituted ZTe (Z=Zn, Cd and Hg)

“…These Table 2. The calculated band gap of the ternaries MgZnTe are also compared with the theoretical results of Yang et al [22] using LDA and…”

“…The mixed crystals of CdTe-MgTe are grown using BridgmanStockbarger technique and the Hall coefficient and resistivity of Al doped and undoped Mg x Cd 1-x Te mixed crystals (0 ≤ x ≤ 0.35) have been measured between 60 and 300K [21]. Another interesting aspect of Mg x Cd 1−x Te as reported by Waag et al [22] is that it can be doped by either p or n-type carriers. Baîdullaeva et al [23] investigated the band gap energy of Mg x Cd 1-x Te at x = 0.15 using the photoconductivity technique.…”