Extended X-ray Absorption Fine Structure Investigation of Arsenic in HgCdTe: the Effect of the Activation Anneal

Abstract

Extended x-ray absorption fine structure (EXAFS) investigation was carried out on two arsenic-doped HgCdTe samples. Arsenic incorporation was achieved with a non-conventional radiofrequency plasma source in a molecular beam epitaxy reactor. Both samples were taken from the same epitaxial run. One of these samples followed a 400°C activation anneal under Hg pressure. EXAFS was used here to probe the local environment around arsenic, and the experimental data were fit through first-principle calculations to extract a quantitative description of the arsenic site transfer upon annealing. Arsenic neighbors are described in terms of chemical nature, numbers and distances. Arsenic was found to be involved mostly in noncrystalline structures, either an As 2 Te 3 glass or an AsHg compact structure. The effect of annealing is to break down the chalcogenide glass, thus favoring the compact AsHg structure. EXAFS results were compared to 77 K Halleffect measurements, and a very good correlation was found. These findings were compared to the commonly admitted scenario for arsenic site incorporation and transfer upon annealing and provided a new picture and the first experimental evidence of the site transfer.

Photoluminescence Studies of HgCdTe Epilayers

“…Those changes can be explained considering the extended x-ray absorption fine structure (EXAFS) results of Ballet et al 7 obtained on similar As-doped samples. In fact, it was shown by EXAFS measurements that, before p-type activation annealing, incorporated As atoms are shared between two structures: the donor complex As 2 Te 3 and an AsHg acceptor complex.…”

“…7 In our case, after MBE growth, annealing at 400°C for 1 h under saturated Hg pressure in a closed-space quartz ampoule was performed after growth. 7 This treatment is called ''p-annealing'' herein. Three samples were studied: Sample A is an unintentionally doped Hg 1Àx Cd x Te layer with a cadmium content x of 0.32.…”

Photoluminescence studies of HgCdTe epilayers

“…The middle energy peak is shifted by 2.3 meV towards lower energy. Those changes can be explained considering the EXAFS results reported by Ballet et al [7] obtained on similar As doped samples. Indeed, it was shown by EXAFS measurements that before p-type activation annealing, As incorporated atoms are shared between two structures: the donor complex As 2 Te 3 and an acceptor complex: AsHg.…”

“…This treatment is called the "n annealing". In the case of As-doped samples, in order to control the ptype doping, a high temperature annealing cycle is needed to transfer the incorporated As onto the proper sites [7]. In our case, after MBE growth annealing at 400 °C for 1 h under saturated Hg pressure in a closed-space quartz ampoule is performed after growth [7].…”

High operating temperature MWIR detectors

“…It has generally been argued that the arsenic resides on the metal sublattice under tellurium-rich conditions 4 , but there have been some recent suggestions that the true situation is more complex 5 . In order to place the arsenic on the tellurium sublattice thereby activating it, an anneal under mercury rich conditions at a suitably high temperature must be performed 6,7 .…”