K. Böttcher

Zinc selenide single crystal growth by chemical transport reactions

ZnSe single crystals were grown by closed-tube chemical vapour transport at temperatures below 800 o C. In the ZnSe-I 2 transport system studies have been performed to elaborate the influence of different heat and mass transport mechanisms on effects of nucleation and crystal growth. The transport of ZnSe, which is assumed to be composed of diffusion, Stefan flow and convection, was calculated by a numerical model. In the total pressure range between 0.5 and 2 atm, qualitative agreement has been found between the experimental transport rates and the theoretical ones. Experimental variables were the system pressure, temperature conditions, the concentration of the transport agent, and the aspect ratio of the ampoule. In contrast to convection controlled systems, mainly diffusion-limited mass transport reduces nucleation density and favours the growth of large ZnSe crystals of good crystallographic perfection

Influence of convection on zinc selenide single crystal growth by chemical vapour transport

Abstract Substrate-quality ZnSe single crystals have been grown by process optimized chemical vapour transport. In this connection, a computational procedure is used as an engineering tool to design a series of experiments targeting at the same total transport rate while every experiment exhibits another share of the convective transport modus. By evaluating experiments with a definite share of convective mass transport between 10 and 80%, a tendency to progressive deterioration of morphological stability and crystal perfection has been stated. In order to reduce kinetic limitations at the growing interface, constant values of total growth rate (3.5 × 10−8mol cm−2s−1) and growth temperature (750°C) were adjusted for all these experiments. For this, special data pairs of iodine charge and temperature difference have been determined via mass transport calculations taking into consideration diffusion, Stefan flow and convection. Diffusion-dominated transport conditions reduce the nucleation density and favour the growth of highly perfect ZnSe single crystals.

Global temperature field simulation of the vapour pressure controlled Czochralski (VCZ) growth of 3-4' gallium arsenide crystals

Abstract The vapour pressure controlled Czochralski (VCZ) method belongs to the new methods to provide low-gradient temperature fields during the growth of III–V crystals. For the first time a global two-dimensional model of the VCZ growth of 3″ and 4″ GaAs crystals is presented. The finite volume code CrysVUN++ was used to simulate heat transfer taking into account conduction and radiation in the whole equipment. Thermoelastic stresses are analysed in terms of the von-Mises stress. There is a good agreement between measured and calculated values, e.g., of the convexity of the crystal-melt interface.

Computational study on the CVT of the ZnSe–I2 material system

Abstract For the crystal growth of ZnSe from the gas phase by chemical vapour transport (CVT), the fluid flow and the temperature and species concentration fields are calculated with the finite element code FIDAP TM . The problem is treated in three dimensions. The transport rate of the crystal building species is analysed at the vapour–crystal interface and compared with experimental values.

Computational study on the SiC sublimation growth

Abstract Using a global two-dimensional model of SiC crystal growth by the Modified Lely method the temperature field of the furnace, the multi-species fluid flow between source and crystal, and the transport rate of the crystal building species at the gas–crystal interface are analysed. Finite element codes are used for the field computations while a free energy minimizing software is used to determine the thermodynamic equilibrium composition of the gas phase. The computed species transport rates meet the range of experimental values.

Crystal growth of zinc selenide under μg-conditions

The CVT growth of ZnSe single crystals under micro-gravity (μg)-conditions was investigated in comparison with the corresponding ground-based (1g) experiments. The transport rates have been found to be considerably higher than the computed values accounting mainly for diffusion and Stefan flow. Different types of convection may be masked or superimposed by thermal convection when under 1g-conditions. The quality of μg-grown crystals was improved even at such high mass transport rates that arise at 1g-experiments.

Silicon on glass grown from indium and tin solutions

A two-step process is used to grow crystalline silicon (c-Si) on glass at low temperatures. In the first step, nanocrystalline seed layers are formed at temperatures in the range of 230 to 400°C by either metal-induced crystallization or by direct deposition on heated substrates. In the second step, c-Si is grown on the seed layer by steady-state liquid phase epitaxy at a temperature range of 580 to 710°C. Microcrystalline Si layers with grain sizes of up to several tens of micrometers are grown from In and Sn solutions. Three-dimensional simulations of heat and convective flow in the crucible have been conducted and give valuable insights into the growth process. The experimental results are promising with regard to the designated use of the material in photovoltaics.