Dilute bismide alloys

Dilute bismide alloys are III-V semiconductor alloys containing small fractions of substitutional bismuth (Bi) atoms. Similar to the incorporation of nitrogen (N) to form the dilute nitride alloys described in Chapter 9, dilute bismide alloys are characterized by the fact that Bi acts as an isovalent impurity when incorporated into, e.g. (In)GaAs, to form the (In)GaBi _x As_1-x alloy. Similar to the case of dilute nitride alloys, it is the large differences in size (covalent radius) and chemical properties (electronegativity) between Bi atoms and the group-V atoms they replace that brings about this impurity-like behavior, which in practice means that incorporating Bi at dilute concentrations has a significant impact on the material properties. Dilute bismide alloys, like dilute nitrides, are considered to be highly mismatched semiconductor materials. However, while N incorporation primarily affects the conduction band (CB) structure of the material into which it is incorporated, Bi, being significantly larger and more electropositive than N, primarily affects the valence band (VB). Since several general aspects of the physics of dilute bismide alloys are qualitatively similar to those of dilute nitrides, dilute bismide alloys can be considered a naturally complementary material system to the dilute nitrides.