P.V. Shapkin

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.

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.

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.

Spectroscopic investigations of semiconductor solid solutions with structural phase transition (ZnxCd1-txSe system)

Abstract Low temperature (T = 2 K) spectra features of exciton reflection and luminescence of monocrystals of semiconductor solid solutions ZnxCd1−xSe with structural phase transition have been investigated.

ZnSe/ZnMgSSe QW Structures grown by MOVPE on ZnSe(1 0 0), ZnSe(5 1 1) and GaAs(1 0 0) substrates

Abstract Both ZnMgSSe epilayers and ZnSe/ZnMgSSe QW structures with mirror-like surfaces were grown on ZnSe(1 0 0), ZnSe(5 1 1) and GaAs(1 0 0) by LP-MOVPE using DTBSe, DTBS, DMZn(TEN), (MeCp) 2 Mg as precursors and H 2 as carrier gas. The ZnSe substrates were cut from single crystals grown by seeded chemical vapour transport (SCVT) in hydrogen. A comparative study of the structures by photoluminescence (PL), cathodoluminescence (CL), X-ray diffraction and microanalysis was performed. Using a 5 QW ZnSe/ZnMgSSe structure grown on ZnSe(5 1 1), a cleaved-face laser was realized under pulsed e-beam excitation at room temperature (RT).

ZnSe/ZnMgSSe QW structures grown by MOVPE on transparent ZnSSe substrates

Abstract ZnSSe substrates transparent for ZnSe QW emissions were used for the growth of ZnSe/ZnMgSSe structures. The FWHM of X-ray rocking curve of a substrate with a sulfur content of 8% was 38 arcsec. Effectively emitting ZnSe/ZnMgSSe QW structures of different specifications were grown by LP MOVPE. It was confirmed that etching the substrate surface in diluted HCl before growth improves the radiative properties of the grown structures due to a removal of oxide layers. For a QW structure with well thicknesses of 4 nm, 6 nm and 12 nm, well-resolved peaks of all QWs were observed in the low temperature PL spectra.

Study of ZnCdSe/ZnSe quantum-wells grown by molecular-beam epitaxy on ZnSe substrates

Abstract ZnCdSe/ZnSe multiple quantum-well (MQW) structures were grown by MBE on ZnSe(0 0 1) substrates prepared by seeded chemical-vapour transport (SCVT) in hydrogen. Scanning force microscopy (SFM) analysis of these structures was performed. A method for the preparation of the substrate surface was found that resulted in a decrease of the root-mean-square (RMS) roughness of the MQW structure surfaces, down to 1 nm. For these structures intense cathodoluminescence (CL) from the QWs was observed. By e-beam pumping a microcavity, pulse lasing was achieved at room temperature (RT).