Electronic structure of GaP/Si(001) heterojunctions and the role of hydrogen passivation

Abstract

Epitaxially grown single crystal GaP on Si is of considerable interest due to being nearly lattice matched to Si, making it attractive for III‐V/Si solar cells. GaP has been used as a buffer layer for III‐V/Si solar cells and also in selective contact Si solar cells. The performance and functionality of such devices are strongly influenced by the presence of localized states at the GaP/Si interface. Here, we examine the electronic structure of GaP/Si(001) heterojunctions and the effect of hydrogen (H) passivation at the interface, in contrast to interface mixing, through density functional theory calculations. Our calculations show that due to the heterovalent mismatch nature of the GaP/Si interface, there is a high density of localized states at the abrupt GaP/Si interface due to the excess charge associated with heterovalent bonding, as reported elsewhere. We find that the addition of H leads to additional bonding at the interface, which mitigates the charge imbalance, and greatly reduces the density of localized states, leading to a nearly ideal heterojunction. A similar result is found with a completely intermixed interface (alternating cation and anion bonding) in terms of low interface state density. However, when the intermixing occurs through single‐layer or double‐layer terraces, the benefits of intermixing are lost and the interface state density reverts more to the abrupt interface case.

Hard X‐ray photoelectron spectroscopy study of core level shifts at buried GaP/Si(001) interfaces

“…12 Suggested interface types involve abrupt heterovalent interfaces with Ga-polarity or P-polarity, mixed (compensated) interfaces with Si/Ga/P atomic intermixture in interfacial layers, and hydrogen passivated interfaces. 13 The charge due to formation of Si-Ga or Si-P heterovalent bonds can be compensated by atomic intermixing 12,14 or by interface passivation by hydrogen. 13 Hard X-ray photoelectron spectroscopy (HAXPES) represents a highly attractive tool for studying buried interfaces and for determining VBOs.…”

“…13 The charge due to formation of Si-Ga or Si-P heterovalent bonds can be compensated by atomic intermixing 12,14 or by interface passivation by hydrogen. 13 Hard X-ray photoelectron spectroscopy (HAXPES) represents a highly attractive tool for studying buried interfaces and for determining VBOs. 15 Due to higher kinetic energies of the photoemitted electrons, the information depth is larger than in case of highly surface-sensitive soft X-ray PES, which limits its application to samples with very thin overlayers.…”

“…Recent theoretical studies have shown a VBO dependence on the atomic structure of the heterointerface 12 . Suggested interface types involve abrupt heterovalent interfaces with Ga‐polarity or P‐polarity, mixed (compensated) interfaces with Si/Ga/P atomic intermixture in interfacial layers, and hydrogen passivated interfaces 13 . The charge due to formation of Si–Ga or Si–P heterovalent bonds can be compensated by atomic intermixing 12,14 or by interface passivation by hydrogen 13 …”