Impact of ultra-thin-layer material parameters on the suppression of carrier injection in rectifying junctions formed by interfacial charge layers

Pure amorphous boron (PureB) deposition on Si is used to fabricate ultrashallow low-saturation-current p⁺n-like diodes even at process temperatures where the boron is not expected to diffuse into the bulk Si. It has been proposed that the bonding of the B atoms to the Si creates a monolayer of fixed negative charge that attracts holes to the interface. In this paper, an investigation using semiconductor simulation tools is performed starting from an all-Si test structure where suppression of electron injection from an n-Si bulk was achieved by introducing a large concentration of negative fixed charge that attracts holes to the interface between a thin-film top-layer and the bulk. This introduces a barrier which lowers the electron saturation current density of the simulated diode to become comparable to or lower than the saturation current density of holes injected into the bulk. The material properties of the top-layer such as electron mobility and tunneling mass, bandgap and electron affinity are individually varied from default Si-values to values typical for amorphous boron layers indicating that a critical concentration of negative fixed charge is always needed for suppression of the electron injection.