Yu. V. Korostelin

Vapour growth and characterization of bulk ZnSe single crystals

Large (up to 60 mm in diameter) untwinned ZnSe single crystals have been grown in sealed quartz ampoules by seeded physical vapour transport and seeded chemical vapour transport with hydrogen. The dependence of structure perfection on the seed quality and its orientation, the source design, the gas filling of the growth ampoule and the temperature regime was researched. Selective chemical etching topography, X-ray diffraction rocking curve and cathodoluminescence studies are presented to characterize grown crystals. The influence of oxygen impurity on crystal emission and weakening of this influence in crystals grown in hydrogen was found. The results of crystal annealing in Zn vapour and Zn melt are discussed.

Localization of excitons and Anderson transition in ZnSe1−xTex solid solutions

Abstract Low temperature luminescence spectra of ZnSe1-xTex mixed crystals with Te concentration up to 22 at % have been studied for the first time. Strong exciton localization by the aggregates composed by several Te atoms has been observed. The increase of Te concentration leads to the onset of energy migration through the localized states which can be considered as an analogue of the Anderson transition in the system of localized excitons.

Exciton luminescence in ideal solid solutions (ZnxCd1−xSe system,0 < x < 1)

The temperature and concentration dependences of exciton emission spectra in ZnxCd1−xSe solid solutions (0 < x < 1) have been studied. It has been shown: (1) high efficiency of the luminescence of localized exciton states (LES) produced by large-scale potential fluctuations, (2) absence of the energy gap between LES and exciton band bottom states. Results obtained have common meaning for ideal solid solutions, in which distribution of substitutional atoms is random.

Vapour growth and doping of ZnSe single crystals

The results of seeded vapour-phase free growth of ZnSe single crystals in both the and directions are presented and discussed. Optimum growth conditions were found to be essentially different for these two directions. The doping by In and Al from both vapour phase during the growth process at T = 1180-1240°C and liquid phase by means of annealing in liquid Zn with In or Al additions at T = 900-950°C was performed. To characterize grown crystals, selective chemical etching. X-ray diffraction rocking curve, cathodoluminescence study, atomic-emission analysis, specific resistance and Hall effect measurements were carried out.

MBE growth and characterization of ZnTe epilayers and ZnCdTe/ZnTe structures on GaAs(1 0 0) and ZnTe(1 0 0) substrates

Abstract Deposition of an amorphous ZnTe seed layer with a thickness of 10xa0nm followed by its solid-phase crystallization was done before the beginning of molecular beam epitaxy of ZnTe layers on GaAs(1xa00xa00) substrates. RHEED patterns have proved that a creation of three-dimensional formations is avoided, and two-dimensional growth occurs during the early stage of epitaxy. Cathodoluminescence (CL) and X-ray measurements have evidenced a higher quality of ZnTe layers grown with an amorphous ZnTe seed layer. ZnTe substrates made of ZnTe crystals grown from vapor phase have been used for the epitaxy of ZnTe layers and ZnCdTe/ZnTe structures also. CL comparison of homo- and heteroepitaxial layers and structures shows the superiority of epilayers and structures grown on ZnTe(1xa00xa00) substrates.

Seeded-vapour-phase free growth and characterization of ZnTe single crystals

Abstract A seeded-vapour-phase free growth (SVPFG) technique for obtaining large (40–50xa0mm in diameter) substrate-quality ZnTe single crystals is described. To provide high structural perfection of crystals, two main methods were applied. (i) The use of small area (1–2xa0cm 2 ) seeds in combination with a temperature regime that provides simultaneous tangential and normal growth of a crystal. This allowed to decrease an effect of seed quality on the structure of growing crystal. (ii) The use of a reverse temperature gradient between the seed and support pedestal. This allowed to avoid sticking a growing crystal to the pedestal and to decrease the contact area between them. The ZnTe crystals obtained were twin free. Ech pit density was about 10 4 xa0cm −2 . The full-width at half-maximum of the X-ray rocking curve was 18–22xa0arcsec. The specific resistance was 4–20xa0Ωxa0cm. To remove Te precipitates observed in as-grown crystals, annealing in liquid Zn or Zn vapour was used. The removal of the Te precipitates correlates with decrease of acceptor related emission and increase of free exciton emission in the low-temperature cathodoluminescence spectra.

Seeded vapour-phase free growth of ZnSe single crystals in the 〈1 0 0〉 direction

Abstract Seeded vapour-phase free growth of ZnSe single crystals at T g = 1100–1250°C in 〈1 0 0〉 direction was studied. The 〈1 0 0〉 growth process was found to be more sensitive to the temperature profile in a furnace than the 〈1 1 1〉 direction. The problem that seed attachment to a support pedestal is followed by a generation of high dislocation density was solved by use of a reverse temperature gradient along the axis of the furnace between the seed and the pedestal and by optical monitoring of the attachment process during the growth. Seeds with dislocation density of 10 4 –10 5 cm −2 and 2–4 cm 2 area selected from single crystals grown in 〈1 1 1〉 direction were used for the first growth processes in 〈1 0 0〉 direction. To increase the diameter of the grown crystals, a tangential growth regime was developed. Twin free ZnSe single crystals of 51 mm diameter and of 15 mm height were grown in helium. The average dislocation density was about 10 4 cm −2 and the full-width at half-maximum (FWHM) of the X-ray rocking curve was as small as 16 arcsec.

Vapour phase and liquid phase doping of ZnSe by group III elements

Abstract A vapour phase doping of ZnSe single crystals by In impurity during a growth process at T = 1180°C was developed. A liquid phase doping was performed by means of annealing of crystal wafers in liquid Zn with an addition of In or Al at T = 900°C. Atomic-emission analysis, cathodoluminescence study, specific resistance and Hall measurements were carried out. The concentration of the In and Al impurities in ZnSe single crystals were in a range from 10 17 to 10 19 cm −3 . High n-type conductivity in the ZnSe single crystals doped by In or Al impurities was achieved: the specific resistance was as low as 0.05 Ω cm for the Al liquid phase doping and about 1 Ω cm for the In vapour phase doping followed by annealing in the liquid Zn : In.

Localized exciton luminescence in ZnxCd1−xSe solid solutions

The reflection and luminescence spectra of ZnxCd1−xSe solid solutions (0.8 < x < 1.0) have been studied. The features of these spectra due to the influence of the composition large-scale fluctuations on the exciton states have been found, i.e. (1) disorder induced broadening of exciton reflection lines (2) observation of the IL photoluminescence line caused by localized exciton states.

Vapour Growth of ZnSxSe1—x Single Crystals

Seeded chemical and physical vapour transport with H 2 and He, respectively, was used to grow twin-free ZnS x Se 1-x (x < 0.15) single crystals with diameter of 50-55 mm and height up to 15 mm. Use of a source with polycrystalline ZnSSe having a composition gradient along the furnace axis, allowed to improve the homogeneity of alloy composition. The change of x per 1 cm along the growth direction in the grown crystals was as small as 1.5%. The etch pit density was (3-5) x 10 4 cm -2 . Specific resistance of ZnSSe wafers was decreased up to 0.06 Ω cm by annealing in liquid Zn:Al.