Investigation of electrically active defects in undoped BaSi2 light absorber layers using deep-level transient spectroscopy

Abstract

We grow 500-nm-thick undoped n-BaSi2 epitaxial films on n-Si(111) substrates by molecular beam epitaxy with an optimized Ba-to-Si deposition rate ratio of approximately 2.2, and investigate defect levels and their densities by deep-level transient spectroscopy (DLTS). A hole trap level (H1) with a density NT = 1 × 1013 cm−3 is detected at 0.27 eV from the valence band maximum (VBM). It is suggested from a sharp rise in capacitance during trap filling processes that H1 is caused by point defects, which is interpreted to originate from Si vacancies. The leakage current of the diode under reverse-biased voltages increases significantly once the sample temperature exceeds approximately 200 °C during DLTS. Postannealing performed at 200 °C in N2 for 20 min gives rise to similar results. The measured value of NT is approximately two orders of magnitude smaller than those reported for undoped BaSi2 films. We also discuss the minimum lifetime of BaSi2 from the viewpoint of the Shockley–Read–Hall recombination model.