Construction of Atomically Thin B Films on Si Heterojunctions Using a First Principles Approach

Deposition of amorphous B (a-B) onto Si substrates via chemical decomposition of B2H6 molecules produces a-B/Si heterojunctions which are the core parts of photodetectors used in vacuum ultraviolet (VUV) and potentially in extreme ultraviolet (EUV) lithog-raphy. However, fundamental questions regarding the limit on the thickness of the de-posited a-B thin-films and the intrinsic electronic nature of the B atoms adjacent to the Si substrate remain unanswered. Here we investigated the local structural and electronic properties of atomic-thin amorphous boron (a-B) layers at the Si{001} substrates using ab initio molecular dynamics (AIMD) techniques. The investigation revealed a rich variety of local chemical bonding and consequently interfacial electronic properties. For thin a-B layer(s)/Si systems, most of the a-B atoms at the interface formed (-B-Si-B-Si-) chains on the Si{001} surface, occupying the positions of the missing Si atoms and strongly hy-bridizing with the nearby Si atoms. Localized defect states at the Fermi level for the in-terfacial Si and B atoms were found in the pseudo-gap. These states have a major influ-ence on the electrical properties of the device. The predicted minimum thickness of the a-B films is 1nm, a useful metric for the manufacturing of a-B/Si devices. The information obtained here further helps understanding the working mechanisms of a-B/Si interfaces for photon detection, and constructing new core devices for potential applications in the field of metal/semiconductor heterojunctions for photodetection, photovoltaics, Schottky diodes and semiconductor devices.