Scanning Tunneling Spectroscopy of Cubic Boron Arsenide Single Crystals*

Recent theoretical and experimental studies have validated cubic boron arsenide (BAs) as the first known semiconductor with an unusual high lattice thermal conductivity comparable to those of graphite and diamond. Knowledge of the surface electronic structure of BAs is required for realizing its potential as both a heat spreading material and an active layer in future-generation electronic devices. Here, we report scanning tunneling spectroscopy (STS) measurements of the electronic structures of as-grown and in situ cleaved BAs single crystal surfaces. While the onset of tunneling from the conduction band cannot be identified clearly on the as-grown bare surface, the bandgap measured at several interior locations of the cleaved surface is close to 2.1 eV, in agreement with a recent optical measurement and theoretical calculation. However, the measured bandgap decreases to about 1.9 eV near the two edges of the cleaved surface due to tunneling from high-concentration shallow acceptors. The tunneling peaks observed by STS within the bandgap are compared with calculated energy levels for lattice defects and substitutional impurities.