Electrical properties of Si films doped with 200-eV In+ ions during growth by molecular-beam epitaxy

Abstract

A single‐grid ultra‐high‐vacuum‐compatible ion source was used to provide accelerated In⁺‐dopant beams during Si(100) growth by molecular‐beam epitaxy. Indium incorporation probabilities σ, determined by secondary ion mass spectrometry, in films grown at T_s=800 °C were too low to be measured for thermal In (σ_In was 550 °C) . However, for accelerated In⁺ doping, σ_In⁺ at 800 °C ranged from 0.03 to ∼1 for In⁺ acceleration energies E_In⁺ between 50 and 400 eV. Temperature‐dependent Hall‐effect and resistivity measurements were carried out on In⁺‐doped Si films grown at T_s =800 °C with E_In⁺=200 eV . Indium was incorporated substitutionally into electrically active sites over a concentration ranging from 2×10¹⁵−2×10¹⁸ cm⁻³, which extends well above reported equilibrium solid‐solubility limits. The acceptor‐level ionization energy was 156 meV, consistent with previously published results for In‐doped bulk Si. Room‐temperature hole mobilities μ were in good agreement with the best reported data for B‐doped bulk Si and were higher than previously reported values for annealed In‐implanted Si. Temperature‐dependent (77–400 K) mobilities μ(T) were well described by theoretical calculations, with no adjustable parameters, including lattice, ionized‐impurity, neutral‐impurity, and hole‐hole scattering. Lattice scattering was found to dominate, although ionized‐impurity scattering was still significant, at temperatures above ∼150 K where μ varied approximately as T^−2.2 . Neutral‐impurity scattering dominated at lower temperatures. Plan‐view and cross‐sectional transmission electron microscopy observations showed no indications of dislocations or other extended defects. Considering the entire set of results, there was no evidence of residual ion‐bombardment‐induced lattice damage.