The electronic activity of boron and phosphorus impurities in a-Si and a-Si:H

TL;DR

This study investigates how boron and phosphorus impurities affect the electronic properties of amorphous silicon and hydrogenated amorphous silicon through simulations, revealing effective doping configurations and the impact of hydrogen passivation.

Contribution

It provides detailed insights into doping mechanisms and the role of hydrogen in passivating impurities in amorphous silicon materials, which was not fully understood before.

Findings

Tetrahedral B and P are effective dopants in a-Si.

High impurity concentrations create defect states.

Hydrogen passivation can neutralize doping effects.

Abstract

In amorphous materials, acceptor and donor impurities rarely dope the system (shift the Fermi level). We find out why in a-Si:H. We report simulations on B and P doping of a-Si:H and a-Si. We analyze the Electronic Density of States (EDOS) with concentrations ranging from 1.6% to 12.5% of B or P in a-Si. The results indicate that tetrahedral B and P are effective doping configurations in a-Si, but high impurity concentrations introduce defect states. Clustered B or P also introduced mid-gap states. For a-Si:H, we report that both B(3,1) and P(3,1) (B or P atom bonded with three Si atoms and one H atom) are effective doping configurations. We investigate H passivation in both cases. There exists a "hydrogen poison range" for which H can modify the dopant configuration and suppress doping. For B doping, nearby H prefers to stay at the bond-center of Si-Si, leaves B four-fold and neutralizes the doping configuration; for P doping, nearby H spoils the doping by making tetrahedral P three-fold.