Electronic consequences of lateral composition modulation in semiconductoralloys

Lateral composition modulation (CM) is a periodic, position-dependent varia tion in alloy composition occurring in the substrate plane, perpendicular t o the growth direction. It can be induced by growing size-mismatched short- period AC/BC superlattices (SL). Hers we study the electronic structure ind uced by such lateral composition modulation in GaAs/InAs, GaP/InP, and AlP/ GaP, in search of optical properties relative to the corresponding random a lloys. We investigate in detail the properties of (a) pure CM without any S L, (b) pure SL without any CM, and (c) the combined CM+SL system. The syste ms are modeled by constructing a large supercell where the cation sublattic e sites are randomly occupied in the lateral (vertical) direction according to the composition variation induced by CM (SL). The atomic structure and strain induced by CM and SL are explicitly taken into account using an atom istic force field. This approach is found to be crucial for an accurate des cription of the microscopic strain in CM+SL systems. The electronic structu re is solved using specially constructed empirical pseudopotentials and pla ne-wave expansion of the wave functions. We find that (i) CM in GaAs/InAs a nd GaP/InP systems induces type-I band alignment (electrons and holes local ized in the same spatial region), while CM in AlP/GaP is shown as an exampl e exhibiting type-II band alignment. (ii) Ch? and SL both induce significan t contributions (which add up nearly linearly) to band-gap redshift with re spect to random alloy. CM in GaP/InP is found to induce larger band-gap red shifts than in GaAs/InAs due to larger band offsets in the former system. ( iii) The symmetry of electronic states at the valence band maximum is sensi tively affected by CM: the lowest energy optical transitions exhibit strong polarization where transitions polarized perpendicular to the CM are favor ed, while transitions polarized parallel to the CM are surpressed by bring shifted to higher energy. These observations, as well as the magnitude of t he predicted band-gap redshift, agree with available experimental data, and suggest that control of composition modulation during growth might be used to tailor band gaps, carrier localization, and transition polarizations re lative to random alloys. [S0163-1829(99)02824-6].