ERBIUM DOPING OF MOLECULAR-BEAM EPITAXIALLY GROWN INSB ON INP

The transport properties of molecular-beam epitaxially grown InSb films doped with Er (atom densities N(Er) from 4.3 x 10(16) cm-3 to 3.6 x 10(20) cm-3) are reported at temperatures between 40 and 400 K. Er is a donor in InSb films grown under Sb to In flux ratios smaller than 1.1. At a flux ratio Sb/In = 1.06, 25 atoms of Er give one extrinsic electron. The maximum extrinsic electron concentration achievable is approximately 1.8 x 10(17) cm-3, obtained for N(Er) > 4 x 10(18) cm-3. Magnetoresistance measurements at 4.2 K show evidence for spin-disorder scattering of the electron. The low-temperature (T < 150 K) electron mobility increases with doping concentration up to rare-earth densities of 1 x 10(18) cm-3, at higher rare-earth concentrations, mobility decreases again. At room temperature, the mobility decreases monotonically with increasing Er concentration. We note the analogy between these results and the observations made on HgSe:Fe, a system in which the carrier mobilities might be enhanced by impurity charge ordering.