Numerical simulation of CdZnTe single crystalline growth by the Bridgman method

MARTINEZ NAGY, A.M.; MARIO ROBERTO ROSENBERGER; TRIGUBO, A.B.; SCHVEZOV, C. E.; WALSÖE DE RECA, N.E.

Puerto Madryn. Chubut. Argentina

Congreso; Second Meeting of the Asociación Argentina de Cristalografía (Miembro de la Internacional Union of Crystallography); 2006

The semiconductor Cd(1-y)Zn(y)Te (0 £ y £ 0,1) is grown in single crystalline ingots by the Bridgman method. This consists in the fractional solidification of the melted alloy when going through a temperature gradient. The crystalline material has to be grown with an excellent structural and electric quality so it can be used in detecting x and gamma rays and a substrates for epitaxial films that can be employed for the manufacture of IR devices: Hg(1-x)Cd(x)Te, Hg(1-x-y)Cd(x)Zn(y)Te.  The numerical simulation of the single crystalline growth, using the Finite Element Method, allows to know which parameters can be controlled in the process to get the crystalline structure with the slightest microstructural defects. Mathematical modelling allows to make a smaller number of experimental tests, which also determines a smaller cost and time. The characterization results of the ingots compared to the simulation predictions allow to vary the growth conditions.   The furnace boundary conditions, that is to say the temperature on the walls of the cylindrical alumina tube, allow to carry out the simulation. The temperature profile measured on the axis of the furnace allows to make the validation of the calculation. The method sensitivity is analysed using different mesh densities to check the model convergence keeping in mind the best results with the smallest calculation time.  The simulation of the temperature profile is carried out on the quartz ampoule loaded with the material to grow. At first it is considered a stationary state followed afterwards by a transitory state. Once obtained the temperature profile on the ampoule, the simulation continues considering that the material to grow presents an interface solid-liquid. In this stage the simulation is carried out following the movement of the interface until reaching the complete solidification of the material. It is analyzed the form and position of the interface solid / liquid in function of the time. It is wished to get a single crystalline ingot that is to say a single grain. But it happens that it could arise more than a single grain according to the form of the interface (concave or convex) [1]. The emergence of possible nucleation of new grains is given in the intersection of the interface liquid solid with the wall of the ampoule. The control in the form of the interface depends on the relationship between the flow of the radial and axial heat. By means of the simulation it is determined which parameters affect the form of the interface.   [1] Parfeniuk, C. L., Mathematical Modelling of the vertical bridgman growth of cadmium telluride, Doctoral Thesis, Chapter 1, University of British Columbia, Vancouver, 1990.