Photodiodes based on the Boron on Silicon junction (B-Si) show excellent responsivity to DUV and VUV photons, radiation hardness, and impressive electrical characteristics. However, the proposed models describing the junction formation mechanism do not sufficiently predict the junction's properties. We analyze two previously proposed models: the ultra-shallow p-n junction model and the charge transfer heterojunction model. We additionally apply the Schottky-Mott theory, a semiconductor-metal heterojunction model. Both the commonalities and incompatibilities between these models are discussed.

Metal-Semiconductor (M/S) heterojunctions, better known as Schottky junctions play a crucial role in modern electronics. At present, the mechanisms behind the M/S junctions are still a subject of discussion. In this work, we investigate the interfaces between semiconducting crystalline Si and amorphous metallic indium, Si{0 0 1}/a-In and Si{1 1 1}/a-In using both ab initio molecular dynamics simulations and a Schottky-Mott approach. The simulations reveal the formation of a distinct border between the Si substrates and amorphous In at the interfaces. The In atoms adjacent to the interfaces exhibit atomic ordering. Charge transfer occurs from In to Si, forming c-Si^−q/a-In^+q charge barriers at the interfaces. This indicates that a crystalline p-Si/a-In heterojunction will have rectifying properties, which agrees with an analysis using the Schottky-Mott model which predicts a Schottky barrier height of 1.3 eV for crystalline p-Si/a-In using the calculated work function for a-In (3.82 eV). We further discuss the interfacial charge transfer, related hole-depletion regions in Si adjacent to the interfaces and the Schottky-Mott approximations.

The discovery of the extremely shallow amorphous boron-crystalline silicon heterojunction occurred during the development of highly sensitive, hard and robust detectors for low-penetration-depth ionizing radiation, such as ultraviolet photons and low-energy electrons (below 1 keV). For many years it was believed that the junction created by the chemical vapor deposition of amorphous boron on n-type crystalline silicon was a shallow p-n junction, although experimental results could not provide evidence for such a conclusion. Only recently, quantum-mechanics based modelling revealed the unique nature and the formation mechanism of this new junction. Here, we review the initiation and the history of understanding the a-B/c-Si interface (henceforth called the “boron-silicon junction”), as well as its importance for the microelectronics industry, followed by the scientific perception of the new junctions. Future developments and possible research directions are also discussed.

The recently found crystalline silicon-amorphous boron (c-Si/a-B) heterojunction has been successfully applied in the detection of short-wave UV photons. These detectors play a decisive role in the progress of nanoelectronics fabrication. The c-Si/a-B heterojunction could not be explained using the existing 'instrumentarium' in semiconductor physics. We investigated the c-Si/a-B interfaces using ab initio molecular dynamics simulations. The simulations reveal atomic ordering of the a-B atoms adjacent to both the Si{0 0 1} and Si{1 1 1} substrates. Charge transfer occurs from the interfacial Si to B, thereby forming Si+/B- charge barriers, which induce an electric field in the nearby regions. The obtained information here is helpful in furthering our understanding of the physics behind the c-Si/a-B junctions, as well as driving the development of a new 'instrumentatrium' in solid state physics.