M. Schenk

New defect etchants for CdTe and Hg1-xCdxTe

For the comparative investigations of the structural perfection of both CdTe and (Hg,Cd)Te, new versatile etchants have been developed and are reported in the presented paper. The etching solutions have a similar composition - two components are identical, but one acid is changed. The new etchants are suitable to produce etch pits on {111}A, {111}B, {110}, and other surface orientations of (Hg,Cd)Te and on {111}A surface of CdTe and Cd-rich (Cd,Zn)Te, respectively. The etch pits originate from grown-in dislocations as well as from dislocations produced by mechanical deformations. The etchants detect dislocations with high density (EPD up to 107 cm−2), subgrain boundaries, twins, and inclusions. It is possible to use the etchants both for bulk material and for epitaxial layers with suitable orientations. Furthermore, etching of Hg1-xCdxTe with variable mole fraction x(0⩽x⩽0.75) is possible by varying the dilutions of the etching solutions.

Native point defects in CdTe and its stability region

The main charged native point defects in CdTe are tellurium vacancies in cadmium-rich CdTe and cadmium vacancies in tellurium-rich CdTe. The stability region seems to be much broader than that measured by methods which are sensitive to electrically charged native defects.

Microhardness of (Hg,Cd)Te

Abstract The microhardness of (Hg,Cd)Te has been investigated by means of Vickers measurements. The measured hardening effect, dependent on composition, is discussed as a function of mutual changes of the binding properties of the solid solution and, additionally, as a function of a favoured formation of (3Cd:1Hg)Te tetrahedrons.

Eg versus x relation from photoluminescence and electron microprobe investigations in p-type Hg1−xCdxTe (0.35 ⩽ x ⩽ 0.7)

Abstract Combined photoluminescence (at 10 ⩽ T ⩽ 300 K) and electron microprobe investigations have been carried out with HgCdTe samples grown from the melt or from solution. By exciting the samples through metallic masks with 200 μm diameter holes fixed with respect to the sample care was taken to pick-up both characteristic X-ray radiation as well as the photoluminescence from the same sample area. The E g versus x relation determined in this way at T = 30 K has been compared with data from the interband absorption edge by other authors.

Study of Hg vacancies in (Hg,Cd)Te after THM growth and post-growth annealing by positron annihilation

Positron lifetime measurements have been performed to study vacancy defects in Hg0.78Cd0.22Te. Post-growth annealing under various Hg vapour pressure conditions have been used to create a well-defined number of Hg vacancies. The sensitivity range of the positron annihilation method was found to be 1015 < cHgvac<1018 cm-3. The obtained experience has been used to investigate THM-grown single crystals. The measured longitudinal and radial dependence of the vacancy concentration can be explained by the temperature profile in the grown (Hg,Cd)Te ingots.

Axially linear slopes of composition for “delta” crystals

Abstract “Delta” crystals are solid solutions of miscible materials with large lattice parameter differences which contain high concentration gradients in one direction (parallel to a lattice plane strongly diffracting X-rays). The system GaSb-InSb has been chosen as suitable for study. By means of a “gradient projection method”, the growth of nearly linear composition profiles with relatively steep slopes of the lattice parameter (up to (Δa/ā) / Δz = 8.3% cm-1), adjustable by the temperature gradient, have been performed. However, the grown ingots were not monocrystalline due to the use of too high a growth rate.

Native point defects in Te-rich p-type Hg1-xCdxTe

The stability regions of Te-rich p-conducting Hg1-xCdxTe with x=0.20, 0.28 and 0.38 were investigated by means of high-temperature in situ Hall and conductivity measurements. The Te-rich limits of the p-side stability regions, measured in situ, correspond to higher electrically active native point defect concentrations than reported in the literature for quenched samples. In the temperature range 300<or=T<or=900 K, there is a linear relationship between the reciprocal temperature and the logarithm of electrically active native acceptor concentrations. The authors conclude that only one predominant kind of native point defect exists probably the mercury vacancy VHg. Its defect formation energies are calculated. The assumption of Hg vacancies as the predominant kind of defects is supported by precision measurements of lattice parameters, which decrease with increasing defect concentration. From these investigations the authors conclude that a considerably greater number of defects exist than are electrically measurable, especially at higher Cd contents.

The influence of interdiffusion on the lattice misfit of epitaxial structures

Abstract The concept of lattice misfit and strain distribution at a heterointerface is reconsidered, taking into account the interdiffusion of substrate and layer components. Based on calculated compositional profiles for multicomponent solid solutions, the respective lattice-parameter profiles and stress profiles in the interface region of an epilayer system have been derived. For different diffusion coefficients and different influences of substrate and layer components on the lattice parameters, stresses develop due to interdiffusion during growth although the natural lattice matching is perfect. The stresses are formed both in the substrate and the layer and change their sign near the interface. Depending on the diffusion of substrate and layer components and on the sign of the natural misfit more than one stress-free plane can occur. They are shifted away from the interface either into the substrate or into the layer, the distance depending on the diffusion time. The model was applied to LPE-grown (Hg,Cd)Te on different substrates.

Non-abruptness of heterointerfaces during LPE growth of (Hg,Cd)Te on (Cd,Zn)Te and Cd(Te,Se) substrates

Abstract Interdiffusion of isoelectronic constituents across heterointerfaces during LPE growth of Hg 1− x Cd x Te on Cd 1− y Zn y Te and CdTe 1− y Se y substrates ( x = 0.2 and 0.5; y = 0, ∼ 0.04, and ∼ 0.07) has been measured by means of EDXS and SIMS. The interdiffusion coefficients of the constituent cation components Cd and Hg have been found to be dependent on the concentration x as well as on y , for growth temperatures of 450 to 460°C. Their asymmetric concentration profiles show steep drops in the Cd-rich substrate and long tails in the Hg-rich layer. The concentration profiles of Zn and Se can be described by means of constant diffusion coefficients, the values of which are identically to D Zn = D Se ≈ 1 × 10 (−13.0±0.5) cm 2 /s (at 450–460°C).

Effect of interdiffusion on dislocation generation in epitaxial layers on CdTe, (Cd,Zn)Te and Cd(Te,Se) substrates

Diffusion modifies the interfacial strain field induced by the composition difference and temperature changes. The strain field is estimated theoretically for liquid-phase epitaxial-grown (Hg,Cd)Te layers on different substrates. The effect on the generation of misfit dislocations is compared with etch pit density profiles.