Carrier concentration and shallow electron states in In-doped hydrothermally grown ZnO

Abstract

Single-crystal ZnO has been hydrothermally grown with additional In 2O 3 in the solution. Schottky barrier contacts have been deposited by electron beam evaporation of Pd onto the ( 000 1 ̄ ) face. Capacitance–voltage measurements have been performed to reveal the carrier concentration as a function of the In 2O 3 content in the solution, and secondary-ion mass spectrometry was used to measure the resulting In concentration in the samples. For an In 2O 3 content of 2×10 19 cm −3, the average free electron concentration increased to 5×10 18 cm −3 compared to 4×10 17 cm −3 for the non-doped material. An increase of the In 2O 3 content to 4×10 19 cm −3 leads to a measured carrier concentration of approximately 1×10 19 cm −3; however, only up to a quarter of the incorporated In became electrically active. From thermal admittance spectroscopy measurements two prominent electronic levels are found, and compared with to the non-doped material case, the freeze-out of the shallow doping in the In-doped samples takes place at lower temperatures (below 80 K).