Comparison of the Electronic Band Formation and Band Structure of GaNAs and GaNP

III—N—As as well as III—N—P materials have been successfully employed in optoelectronic devices. Nitrogen impurities in the dilute range have been investigated in the indirect gap semiconductor GaP since the 1960s, where they were used to produce green light-emitting diodes. In recent years new developments in molecular beam epitaxy and metalorganic vapour phase epitaxy growth methods have made it possible to introduce up to a few percent of nitrogen into direct gap GaAs and indirect gap GaP. GaInNAs with N concentrations of about 1% has been used as the active material in vertical cavity surface emitting laser (VCSEL) devices operating at telecommunication wavelengths. However, GaAs:N and GaP:N differ considerably in terms of their electronic structure. In GaNAs the nitrogen impurity states in the doping regime lie resonantly in the conduction band. With increasing N-content a strong redshift of the GaAs-like fundamental band gap (referred to as E ₋) occurs. It is accompanied by the formation of an N-induced E ₊ band, which blueshifts with increasing N. This repulsion behaviour of E ₋ and E ₊ can be well parameterized by a simple two-level band-anticrossing model, which forms the basis of the 10 band k·p model successfully employed for describing the electronic states of III—N—As layers in laser structures in the vicinity of the GaAs-like E ₋ band gap. The situation in GaP is somewhat different because the N levels in the doping regime are situated in the band gap close to the X conduction band states (corresponding to the indirect gap), i.e. well below the Г conduction-band states of GaP (corresponding to the direct gap). In other words, the order of the N states and the Г conduction band states is reversed. With increasing N content, the lowest conduction band must then evolve from the N-like states in GaNP. The question then arises as to whether the bandanticrossing model yields a good description of the lowest conduction band E ₋ in this case. If so, the lowest band gap will in a two-level band-anticrossing model acquire a large Г-like density of states comparable to a direct semiconductor, which is a prerequisite for employing GaNP based heterostructures in the active region of laser devices. In this review, we compare the electronic structure of GaNAs and GaNP, demonstrating that, in GaNP, the Г character in the energy range of the N localized states is spread over a broad variety of transitions. This situation cannot be properly parameterized by the simple band-anticrossing model and indicates that, in contrast to GaNAs, the lowest conduction band states are not suitable to promote laser action in GaNP alloys.