Estimation of interaction parameters in the Al-Ga-As-Sn-Bi system

The development of GaAs based high power side-input photovoltaic converters requires thick (50–100 μm) transparent gradient refraction layers that can be grown by liquid phase epitaxy. Such thick layers can also be used in LED structures. To solve the problem of Al(x)Ga(1-x)As conductivity reduction at the x∼40% point a five-component, Al-Ga-As-Sn-Bi system is proposed. The interaction parameters in the liquid phase (αij) in the Al-Ga-As-Sn-Bi system are determined within the framework of a quasi-regular solutions model. For an Al(x)Ga(1-x)As solid solution growing from a Ga-melt containing 10 at.% of Bi (as a neutral solvent) and 15 at.% of Sn (as an n-type dopant), liquidus and solidus isotherms for 900 °C are modeled based on the calculated αij. Satisfactory agreement between calculated and experimental data has been obtained. Hall data show that AlGaAs layers grown from Bi-containing melts have n-type conductivity. Doping by tin during growth from mixed Ga–Bi melts makes it possible to increase the electron concentration in the AlGaAs layer.