On selenium p–n heterojunctions and Schottky contacts

Experimental capacitance–voltage data of selenium p – n heterojunctions on n -type Ge, Si, and GaN and flat-band barrier heights of selenium Schottky contacts are reanalyzed. The resulting built-in potentials of the p – n heterojunctions as well as the flat-band barrier heights of the Schottky contacts are explained by the well established concept of interface-induced gap states (IFIGS) where the interfacial electric dipoles are estimated by using the differences of the respective electronegativities. The analysis of the built-in potentials of the heterojunctions between crystalline p -Se films and n -Si and n -GaN substrates give an energy distance of 0.06 eV between the bulk Fermi level and the branch point of the IFIGS. The evaluation of the Schottky barrier heights reveals the IFIGS branch point of crystalline selenium to lie 0.03 ± 0.15 eV above the valence-band maximum. In summary, the valence-band offsets of c -Se/Si and c -Se/GaN heterostructures are estimated as 0.29 and 2.22 eV, respectively.