Band offsets at the crystalline/amorphous silicon interface from first-principles

TL;DR

This study uses first-principles computational methods to accurately determine the band offsets at the crystalline/amorphous silicon interface, providing results consistent with recent experimental data.

Contribution

It introduces a detailed atomistic and DFT-based approach to model the silicon interface and compute band offsets, addressing conflicting experimental results.

Findings

Valence band offset of 0.30 eV

Conduction band offset of 0.17 eV

Agreement with recent XPS measurements

Abstract

The band offsets between crystalline and hydrogenated amorphous silicon (a-Si:H) are key parameters governing the charge transport in modern silicon hetrojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics (MD) runs at an elevated temperature on 30 statistically independent samples. In order to obtain a realistic conduction band position the electronic structure of the interface is calculated with a hybrid functional. We find a slight asymmetry in the band offsets, where the offset in the valence band (0.30 eV) is larger than in the conduction band (0.17 eV). Our results are in agreement with the latest XPS measurements that report a valence band offset of 0.3 eV [M. Liebhaber et al., Appl. Phys. Lett. 106, 031601 (2015)].