The Effect of Growth Rate and Temperature on the Incorporation of Sn in GaAs during LPE

Abstract

A growth rate dependence of the impurity incorporation .... has been measured for the first time: average carrier n, donor ND, and acceptor NA concentrations of heavily Sn-doped GaAs layers grown by liquid phase epitaxy (LPE) increase in the range 0.2 < V/~m/min < 6. At faster growth rates, the concentrations tend to be constant (1.4 9 1019 cm -a for donors, 3.5 9 10 is cm a for acceptors). Growth rates between 0.2 and 35 #m/rain have been adjusted by varying the cooling rates of the epitaxial processes_between__0.04 ~ and 100~It can be reported that the relation between I~D/A and V corresponds to the theoretical predictions under surface equilibrium conditions. The most important parameter is the barrier height of the system melt and semiconductor, modified by a concentration-dependent barrier lowering in the case of heavy doping. Based on the same assumptions, the temperature dependence of the measured incorporation ND/A (T) is explained. This results from a comparison of the possiole incorporation theories surface and bulk equilibrium.During epitaxial growth from the liquid phase, the interface between melt and semiconductor can be regarded as a metal semiconductor contact because of the great density of conduction electrons in the melt. The Schottky model is then applicable to the surface. Merten and Hatcher (1) have pointed this out.Later on Zschauer and Vogel (2) and Casey et aI. (3) used this model. As a consequence of such an electrical model, the thermodynamic equation for the impurity incorporation will have electrical properties like the Fermi level or the barrier height (3,4).According to the growth conditions, two aspects have to be distinguished: the bulk equilibrium and the surface equilibrium. If the growth rates of the crystal are slow compared with the impurity diffusion in the semiconductor, there exists a thermal equilibrium between the two phases, melt and semiconductor bulk (bulk equilibrium). This model explains the impurity incorporation of Zn (5, 6) and Cu (7) in GaAs. Where the ratio of the growth rate to the solid diffusion constant is large, the melt is in equilibrium with the surface of the growing crystal only. The important parameter of the surface equilibrium theory is represented by the height of the Schottky barrier. The validity of this theory has been shown for the incorporation of Te (8) and for the Sn donor (4,9). Panish has found that the incorporation of Sn in GaAs can be better explained if one also assumes a Sn acceptor complex SnAs2VGa using the surface equilibrium theory again (4). The concentration in the case of bulk equilibrium is almost proportional to the square root of the atomic fraction of tin Xs= in the melt, while in the case of surface equilibrium it is directly proportional to Xsn. In spite of the principal agreement Panish obtained with the surface equilibrium theory, for high Sn concentrations above 4 9 1017 cm -3 there exists a discrepancy between theory and experiment: Experimentally evaluated concentrations indicate a weaker slope with higher Xsn data t...

Studies on nucleation kinetics of In1−xGaxP/GaAs by Liquid-Phase Epitaxy

“…This alloy has also been used for fabrication of LED and laser material [9,10]. This effect was observed by many researchers [12][13][14][15][16][17][18] and is referred to as a composition-pulling effect or latticelatching effect. The lattice mismatch between the InGaP ternary alloy and GaAs substrate affects the crystalline qualities of the epilayers such as surface morphology, misfit dislocation density at the interface and emission intensity.…”