Hall Effect Studies of AlGaAs Grown by Liquid-Phase Epitaxy for Tandem Solar Cell Applications

We report results from Hall effect studies on Al x Ga 1− x As ( x = 0.23–0.24) with bandgap energies of 1.76 ± 0.01 eV grown by liquid-phase epitaxy (LPE). Room-temperature Hall measurements on unintentionally doped AlGaAs revealed p -type background doping for concentrations in the range 3.7–5.2 × 10 16 cm −3 . Sn, Te, Ge, and Zn-doped AlGaAs were also characterized to study the relationship between doping concentrations and the atomic fractions of the dopants in the melt. Temperature-dependent Hall measurements were performed to determine the activation energies of the four dopants. Deep donor levels (DX centers) were dominant for Sn-doped Al 0.24 Ga 0.76 As, but not for Te-doped Al 0.24 Ga 0.76 As. Comparison of the temperature-dependent Hall effect results for unintentionally and intentionally doped Al 0.24 Ga 0.76 As indicated that the impurity contributing to the p -type background doping had the same activation energy as Mg. We thus suggest a Te-doped emitter and an undoped or Ge-doped base to maximize the efficiency of Al x Ga 1− x As ( x ∼ 0.23) solar cells grown by LPE.