An electronic phase diagram of hole-doped BiCuSeO crystals determined by transport characterization under various growth conditions

Abstract

The layered compound BiCuSeO is a narrow-band-gap semiconductor that demonstrates superior thermoelectric properties. However, the electrical properties of BiCuSeO with varied hole concentrations have not been characterized systematically, and this is explored in this work. Through delicately adjusting the growth conditions via a chemical-vapor-transport method, we successfully grew a series of BiCuSeO crystals with hole-concentration (n_h) values that varied from 1.0 × 10¹⁷ to 2.0 × 10²⁰ cm⁻³. Our systematic characterization of electrical properties shows that when n_h is around 1.0 × 10¹⁷ cm⁻³, BiCuSeO is an Anderson insulator when the temperature (T) is lower than 50 K, and it then transitions to a degenerate semiconductor (metal-like behavior); when n_h is around 3.0 × 10¹⁸ cm⁻³, BiCuSeO shows the features of a degenerate semiconductor at high temperature (T > 15 K), but there is non-Fermi liquid resistance features at low-temperature (T < 15 K); while when n_h is higher than 2.0 × 10²⁰ cm⁻³, BiCuSeO crystals show the fingerprint of a degenerate semiconductor. In the degenerate semiconductor regime, the electron–phonon interaction strength of BiCuSeO changes from 36.1 × 10⁻³ to 3.6 × 10⁻³ when n_h is increased from 1.0 × 10¹⁷ to 2.0 × 10²⁰ cm⁻³, which can be semi-quantitatively explained based on the enhanced screening of Coulomb interactions with an increased hole concentration. Based on these results, a temperature-hole-concentration dependent electronic phase-diagram of BiCuSeO is proposed. This work may be referenced to modify the electrical properties of layered-compounds similar to BiCuSeO.