Grown ZnSe Crystal Research Articles

The crystal growth of ZnSe by the traveling heater method with the accelerated crucible rotation technique

The accelerated crucible rotation technique (ACRT) was employed in the traveling heater method (THM) growth of ZnSe crystals to manage the convection in the melt. Considering the large solubility, the PbCl2 was chosen as a solvent. During the growth, the growth interface changed from concave to slightly convex depending on the ACRT parameters. The ZnSe single crystals were obtained, when the ACRT with the maximum rotation of 15 rpm at the suitable growth rate (2.4 mm/day) was used. Furthermore, the chemical mappings of the energy-dispersive X-ray spectroscopy (EDS) show that there are two kinds of the solvent inclusions existed in the grown ZnSe crystals, i.e. PbCl2 and ZnCl2. And the PbCl2 inclusions are homogeneous with a total concentration of 7.03 × 102 cm−2. In addition, the FWHM on X-ray rocking curve of the (220) diffraction planes is 22 arcsec. The chemical etch pit density on the (110) cleavage plane is (1–2) × 105 cm−2 and the average infrared transmittance is over 68% in the range from 650 cm−1 to 4000 cm−1. All of these indicate that the grown ZnSe single crystals have good crystalline quality.

Studies on structural and optical properties of ZnSe and ZnSSe single crystals grown by CVT method

The ZnSe and ZnSSe single crystals have been grown by chemical vapour transport (CVT) with iodine as a transporting agent. The source and growth temperatures of the reactor are maintained at 850°C and 900°C respectively using the two zone horizontal resistive heating furnace. The grown crystals are characterised by structural, surface morphological and optical properties. The XRD pattern shows that the peaks due to reflection from (111), (220) and (311) planes belong to the cubic zinc-blend structure. The composition of grown ZnSe crystal has been determined by EDXRF analysis as Zn (52.5%) and Se (47.5%). The XPS study of grown ZnSe single crystal has been studied. The HRSEM images reveal the step, spiral and triangular patterns. The optical absorption study reveals the absorption cut off wavelength as 483nm (2.57eV) for ZnSe and 441nm (2.81eV) for ZnSSe crystals. The photoluminescence studies reveal the band edge emission and defect level emissions of ZnSe and ZnSSe single crystals.

Effect of N5+ ion implantation in CVT grown ZnSe single crystals

The ZnSe single crystals were grown by chemical vapor transport (CVT) technique using iodine as a transporting agent. As grown ZnSe single crystals have been implanted by N5+ ion at 45keV energy in room temperature with various fluences of 1×1015, 5×1015, 1×1016 and 5×1016 ions/cm2. The lattice constants of the as grown and implanted ZnSe single crystals are 5.57 and 5.45Å respectively. The photoluminescence studies reveal that N5+ implanted ZnSe has the band edge emission at 468nm (2.64eV) and broad luminescence peak due to defect level green emission at 551nm (2.25eV) and yellow emission 592nm (2.09eV). The as grown ZnSe crystal has the absorption cut off at 483nm whereas the cut off increases from 489 to 524nm with an increase in ion fluences. The frequency of vibration for as grown ZnSe crystal is 504cm−1 and for implanted ZnSe samples, the frequencies are 657–677cm−1 (NZn bending mode) and 2337–2353cm−1 (NSe stretching mode) which are due to bond formation of N.

Temperature-Dependent Defect-Induced New Emission in ZnSe Crystal

The temperature-dependent photoluminescence behaviour of chemical vapour transport (CVT)-grown ZnSe crystal is investigated. A new emission band appears when temperature is reduced to 155 K. It is shown that the new emission band is strongly related to defect emission peaked at around 2.1 eV. The emergence of the new emission band is accompanied by decreasing emission intensity of free exciton, as well as redshift of defect emission with temperature decreases. The activated energy of the defect state is estimated to be 60.6 meV, which is approximately equal to the energy difference between the new emission and the free exciton emission at 155 K.

Thermal Conductivity of ZnSe by Molecular Dynamics Simulation.

Molecular dynamics simulation using the new fit of the empirical Tersoff Potential is applied to study the thermal properties of ZnSe at and below the room temperature. The resulting diffusivity and thermal conductivity are compared with the photoacoustic measurements on the grown ZnSe crystal. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal conductivity of ZnSe by molecular dynamics simulation

AbstractMolecular dynamics simulation using the new fit of the empirical Tersoff Potential is applied to study the thermal properties of ZnSe at and below the room temperature. The resulting diffusivity and thermal conductivity are compared with the photoacoustic measurements on the grown ZnSe crystal. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Al diffused conductive ZnSe substrates grown by physical vapor transport method

ZnSe single crystals of 30 mm diameter and about 20 mm length were grown by the semi-open free-growth physical vapor transport method. The area of the dislocation density less than 1×10 4 cm −2 is more than 90% of the (1 0 0) substrate, about 28 mm×20 mm in size, cut from the grown ZnSe crystal. Al was diffused by annealing into (1 0 0) substrates. Al concentration and carrier concentration over the region between the surface and 400 μm in depth of the substrate were higher than 4×10 18 cm −3 and 5×10 17 cm −3, respectively. The dislocation density did not increase after Al diffusion and was kept below 1×10 4 cm −2. The full-width at half maximum of the X-ray rocking curve was maintained below 10 arcsec. The Al concentration dependence of the Al diffusion coefficient in ZnSe was estimated.

Growth of dislocation-free ZnSe single crystal by CVT method

ZnSe single crystals with a diameter of 12 mm and a length of 28 mm were grown by the CVT method using iodine as a transport agent. The ampoule wall, which has direct contact with the crystal during growth, was formed of pBN. The seed crystal, which was the CVT grown ZnSe single crystal with a reduced dislocation density (EPD) of less than 1×10 4 cm −2, was used. The seed crystal was protected against thermal stress from the ampoule end wall by inserting the undoped polycrystalline ZnSe between the back of the seed crystal and the ampoule end wall. The EPD of the grown ZnSe crystal was less than 1×10 4 cm −2 even near the seed crystal, and reduced to 0 at the tail part of the crystal. The shallow pits were found to exist on the etched surface of dislocation-free part. The dislocation-free part was annealed in Zn atmosphere, and crystallographic, electrical and optical characterizations were evaluated in relation to the annealing conditions.

Growth of ZnSe single crystal by CVT method with self-moving convection shield

The self-moving convection shield was used in the growth of ZnSe single crystal by chemical vapor transport method using iodine as a transport agent. The reduction of the convection enables the growth of a 1-in diameter ZnSe single crystal. The incorporation efficiency of iodine on (1 1 1)B facet was proved to be larger than that on (1 0 0) facet. Impurity-hardening effect of incorporated iodine in the grown ZnSe crystal is also suggested.

Stoichiometry control of ZnSe crystals

The stoichiometry of grown ZnSe crystals was controlled by using the source crystal pre-annealed under an optimum Zn vapor pressure for Se Te solvent, or an optimum Se vapor pressure for Zn solvent. The full width at half maximum (FWHM) value of the X-ray rocking curve of the crystal grown from the Se Te solvent by using a source annealed under an optimum Zn pressure was three times narrower than that of the one grown from an unannealed source. In the crystal grown from a Zn solvent, the Hall mobility of the crystal obtained from the pre-annealed source under the optimum Se pressure was one and a half times as high as that of the crystal using an unannealed source. The original idea of a stoichiometry control of the II–VI compound semiconductors using a pre-annealed source is proposed.

Observation of the morphology and displacement of dislocations in vapour phase grown ZnSe crystals

Abstract Dislocation walls on {111} and {110) planes in vapour phase grown ZnSe crystals were studied by light scattering tomography (LST), the cathodoluminescence mode of scanning electron microscopy (CL-SEM) and molten KOH etching. Many Y shaped nodes and hexagonal nets of dislocation lines caused by reactions between the lines were clearly observed on (111) planes by LST, although many dislocations of irregular shape and some parallel arrangements of dislocations were also found. Slip lines on (111) planes were clearly observed as dark lines by CL-SEM which allowed the determination of dislocation glide planes. Undecorated dislocations and slip lines were difficult to observe by LST in these crystals of high refactive index. The dislocations constituting the main part of the dislocation walls and Y shaped nodes were immobile even when the stress was increased sufficiently to fracture the specimen, while some of the other dislocations were displaced.

Seeded melt growth of ZnSe crystals under Zn partial pressure

We have successfully grown ZnSe crystals on a seed by a modified Bridgman method under an argon pressure of 6 MPa. A definite Zn partial pressure is maintained during growth by heating Zn in a reservoir. We have grown [111]Zn-, [111]Se-, and [011̄]-oriented crystals by using heavily twinned seeds. The oriented grown crystals contain numerous (111) twin planes.

Investigation of the transition range in seeded vapour grown ZnSe crystals

Prerequisite for the growth of large area single crystals are exactly (111)Se orientated seeds. For both used growth methods, seeded physical vapour transport (SPVT) and seeded chemical vapour transport (SCVT), an improved crystal quality can be achieved. In SCVT crystals, optically active deep level (DL) defects dominate mainly due to the self activated (SA)-centre. The transition range width was more than three times that of SPVT material, but in the bulk the concentration of linear defects is lower. Strong exciton luminescence and decreasing DL emission were found in the bulk of SPVT crystals. The decision what method should be used for optimal substrate performance has to be drawn after manufacturing light emitting devices by epitaxial methods.

Co Impurity Effect in Zn1-xCoxSe Crystals Grown under Equilibrium Condition

The influences of Co impurity in the Zn1-xCoxSe crystal were investigated by X-ray diffractometry (XRD) and Raman spectroscopy using melt grown Zn1-xCoxSe polycrystals. The solid solubility of Co atom in melt grown ZnSe crystal is about x=0.02±0.0015. The solid solubility of magmetic ions may depend on the electronegativity and covalent radius. It was found that the lattice constant of the crystal increases linearly up to x=0.0086 and then saturates as the amount of Co impurity increases. It is also observed that the TO2 and LO1 Raman modes in Zn1-xCoxSe grown under equilibrium condition soften in the value of x<0.0086 by the addition of Co atoms. There is a linear relationship between the ionicity and the oscillator strength which is calculated using the energies of TO2 and LO1 phonon modes with the slope of -7.02×1025 (s-2). From these observations it is clear that the instability of Zn1-xCoxSe crystal is mainly due to the ionicity difference between Zn and Co atoms since both covalent radii are almost the same.

Optically pumped stimulated emission in ZnSe

Stimulated emission in optically pumped ZnSe is reported. The emission at 4580 Å is observed at temperatures up to 250 K in solution grown ZnSe crystals with improved near band edge luminescence.