Huo Chong-Ru

Influence of the interface kinetics of crystallization and dissolution on the scaling laws in solution system for crystal growth

The influence of interface kinetics on scaling laws in a solution system for cry stal growth is studied. Because the variation of the solution density caused by the solute concentration change can be omitted and only that caused by the temperature change is taken into account, the interface kinetics does not affect the scaling laws of the fluid velocity and the temperature distribution index S-theta. By taking the interface kinetics into account, the curves of the concentration distribution index S-phi versus the Rayleigh number Ra, the Prandtl number Pr or the Schmidt number Sc are changed. When Ra and Sc are small. S-phi approaches a constant S-phi(0) independent of Ra, Sc and lambda. When Ra and Sc are large, the influence of the interface kinetics on the curves of S-phi is negligible. The interface kinetics affects the curves of the average dimensionless crystal growth rate (V) over bar(cg) versus Ra, Sc or Pr only when Ra and Sc are large. In this case, (V) over bar(cg) is still a power function of Ra, Pr or Sc in certain regions of the parameter (Ra, Pr and Sc) space, but the exponents and coefficients of power functions are varied.

Computational Analysis of the Vertical Bridgman Growth of Te Doped GaSb Under Microgravity

A transient analysis of Te doped GaSb melt growth process is performed using finite element method. The solute concentration at the growth interface increases with time because of k < 1. The growth interface shape becomes a little flat at the beginning of the growth compared with the initial shape. Radial segregation occurs even under the μg condition. This segregation increases with the increase of gravity when gravity is small, and reaches a maximum at g = 10-3 for our system.

Interface shape and concentration distribution in crystallization from solution under microgravity

The Kerr rotation of MnBixAl0.5(0.4 less than or equal to x 0.9) thin films with and Al protective layer as a function of the Bi concentration, x, has been investigated. Compared with MnBix thin films, it is found that a large enhancement of Kerr rotation appears in the MnBixAl0.15 thin films with 0.4 less than or equal to x less than or equal to 0.7, but no enhancement of Kerr rotation appears when x is greater than 0.7. When x = 0.5, a maximum Kerr rotation of 2.75 degrees is observed at 633 nm for the MnBi0.5Al0.15 thin film, which is much larger than that of 1.56 degrees for the MnBi0.5 thin film. For the MnBixAl0.15 thin films with 0.4 less than or equal to x less than or equal to 0.7, the c lattice shrinking may result in a stronger hybridization between Bi 6p and Mn 3d states, which also should be responsible for the large enhancement of Kerr rotation. In addition, the saturation magnetization M-s is reduced from 4 x 10(5) A/m for the MnBi0.5Al0.15 thin film to 3 x 10(5) A/m for the MnBi0.5Al0.15 thin film, suggesting that some of Al may also substitute for Mn at the octahedrtal sites.

Calculation of Binding Energies of the Ground and Excited States of a Donor in GaAs-AlxGa1-xAs Step Quantum Wells*

In this paper we present for the first time completely analytical variational expressions for calculating the binding energies of the low-lying bound states of a hydrogenic donor in a quantum well (QW). These expressions can be used for the problem of the binding energy of an impurity in a general manner, e.g. for calculating the binding energies of a donor associated with subband states of any order in the QW with any arbitrary potential profile. To demonstrate the utilization of these expressions we have theoretically studied the binding energies for the ground and a few low-lying excited states of a hydrogenic donor in a stepped quantam well (SQW). The variations of the binding energies for these donor etates with impurity positions are investigated for different heights of the step potential. The numerical calculation results show that the binding-energy curves in the SQW, in contrast to the case of the flat quantum wells (FQWs), exhibit a non-symmetrical structure relative to the center of the QW and depend on the sub-barrier potential. The peak position in the binding energy curves shifts away from the region occupied by the sub-barrier as increasing sub-barrier height. The maximum in the binding energies increases as the step potential increaaes. These effects can be interpreted by referring to the variation of the electron probability-density distribution and of the lowest subband in the SQW. The shape of the binding-energy curves related to the 2p0like state is different from the other states. It is associated with the particular feature of the wave function of the 2p0 state in the QW.