Variation of minority-carrier diffusion length with carrier concentration in GaAs liquid-phase epitaxial layers

Abstract

Minority-carrier diffusion lengths in GaAs at 298 K were determined in Ge-doped p-type layers and Sn-doped n-type layers by short-circuit photocurrent measurements. The layers were grown by liquid-phase epitaxy and utilized a 1- to 2-μ top layer of Al0.5Ga0.5As to eliminate surface recombination. Electron diffusion lengths Ln of 7–8 μ were obtained at concentrations less than 1×1018 holes/cm3 with a decrease to 0.8 μ at 1×1019 holes/cm3. Hole diffusion lengths Lp of 2–4μ were obtained at concentrations less than 1×1018 electrons/cm3 with a decrease to 0.3 μ at 6×1018 electrons/cm3. The relatively constant diffusion length in p- and n-type layers below concentrations of 1×1018 cm−3 is determined by nonradiative recombination. At hole concentrations above 1×1018 cm−3, the radiative recombination contributes to the decrease in Ln. For the n-type layers, the rapid decrease in Lp above concentrations of 1×1018 cm−3 results from an increase of nonradiative recombination at high donor concentrations.