bandalignment

Band alignment refers to the relative energy positioning of electronic bands between two different materials when they are in contact with each other, particularly in semiconductor heterostructures, interfaces, and quantum wells. This concept is fundamental in understanding the electronic properties of layered materials, such as those used in semiconductor devices like transistors, solar cells, and optoelectronic components. The alignment of bands—specifically the conduction band minimum (CBM) and valence band maximum (VBM)—determines how charge carriers (electrons and holes) behave at the interface, influencing phenomena like carrier injection, recombination, and transport.

Band alignment is typically categorized into three primary types: type-I (straddling), type-II (staggered), and type-III (broken-gap). In type-I alignment, both the CBM and VBM of one material lie within the bandgap of the other, confining carriers within the same material. Type-II alignment occurs when either the CBM or VBM of one material lies within the bandgap of the other, leading to spatial separation of electrons and holes, which can enhance carrier collection in devices like photodetectors. Type-III alignment, where the bandgaps overlap such that the CBM of one material is above the VBM of the other, is less common but can result in unique electronic properties.

The determination of band alignment relies on factors such as material composition, crystal structure, and the presence of interfacial defects or strain. Experimental techniques like photoemission spectroscopy and theoretical methods, including density functional theory (DFT), are commonly employed to analyze and predict band offsets. Understanding band alignment is crucial for optimizing device performance, as it directly impacts efficiency, stability, and functionality in semiconductor-based technologies.