Electroabsorption in laminatedGaSexS1−x semiconductors in the fundamental-absorption edge region

Electroabsorption spectra at 300 K and 77K and under fields of 2·103V/cm and 4·104V/cm have been studied in the fundamental-absorption edge region of single-crystal solid solutions GaSe x S1−x obtained by the Bridgman method. The characteristic of GaSe x S1−x electroabsorption spectra at 300 K and 77 K is the presence of a strong negative peak associated with the ground state of the exciton, the amplitude of which grows with the field according to a power law (Δα∼Em, wherem>1). Exciton ground-state lines have been observed for the first time in GaSe x S1−x (1≥x≥0.4) at 300 K. The exciton groud-state line in GaSe x S1−x was analysed, due regard being given to its broadening in the electric field as a result of phonon-exciton interaction. The parameters of the band structure have been determined in GaSe x S1−x (energy of allowed interband transitions Γ 4 − →Γ 3 + , exciton binding energy, reduced effective mass of an electron-hole pair, exciton Bohr radius, etc.). With GaSe0.5S0.5 a jump of 50 meV, which is attributed to a phase transition, is observed in the dependences ofEx andEgon composition. The compounds of GaSe x S1−x (0.6≤x≤1) crystallize mainly in the e-modification, whereas those of GaSe x S1−x (0≤x≤0.4) crystallize primarily in the β-modification.