A perspective on Fermi levels and insights into the surface characteristics of S- and Fe-doped InP substrates

Abstract

As a pivotal substrate material in III-V compound semiconductors, indium phosphide (InP) plays a critical role in the development of optoelectronic and high-frequency devices. Although extensive research has been conducted on the Fermi levels of single crystals in bulk materials, studies have also explored how Fermi-level modifications induced by various dopants affect the surface characteristics and adsorption capacities of InP substrates. This study presents a comparative analysis of the significant disparities in surface attributes, including metal ions, absorbed particles, and oxide layer thickness, between sulfur-doped InP and iron-doped InP. Theoretical simulations based on first-principles density functional theory under the plane-wave pseudopotential method reveal that sulfur acts as a shallow donor when substituting phosphorus and as a deep donor in the sulfur gap, whereas iron serves as a deep donor when replacing indium. These substitutions engender variations in the Fermi energy levels, thereby altering the work functions of the substrate surfaces. Consequently, these changes manifest in the surface properties of the substrates, influencing factors such as the metal ion composition, particle dimensions, and oxide thickness.