Electrochemical sulfur doping of GaAs grown by molecular beam epitaxy

Abstract

A novel method of intentionally doping molecular beam epitaxy grown GaAs n- type is described. The donor atoms are sulfur, from a beam of S2, generated in a low temperature (200 °C), electrochemical Knudsen cell. The galvanic cell is Pt/Ag/AgI/Ag2S/Pt, where the flow of current through the cell, with the positive pole at the Ag2S is a measure of the sulfur flux effusing from the cell. Net carrier concentrations n between ∼1015 and ∼1018 cm−3 have been obtained. There is no detectable accumulation of S at the surface for high donor concentrations (∼1018 cm−3) in the bulk. This novel method of sulfur generation has a particularly fast (<1 sec) response time—much faster than the thermal equilibration times of conventional thermal Knudsen sources. Complicated doping profiles are shown to be produced relatively easily with a single doping source using this technique. Free-electron mobilities μ300 K = 6000 cm2/V sec and μ77 K = 17 000 cm2/V sec have been obtained for sulfur doped layers with n = 1.1016 cm−3.