BAND-EDGE ABSORPTION AND LUMINESCENCE OF NONSPHERICAL NANOMETER-SIZE CRYSTALS

The effect of nonspherical shape on the optical properties of semiconductor microcrystals with a degenerate valence band has been theoretically studied. The asymmetry of microcrystals leads to a splitting of the fourfold-degenerate ground hole state into two twofold-degenerate ones. The value of this splitting is proportional to the deviation from sphericity and inversely proportional to the square of the microcrystal size, and is the function of the ratio of light- to heavy-hole effective masses (beta). This splitting could lead to the formation of long-lived electron-hole pairs in the prolate microcrystals of semiconductors with small beta and in the oblate ones with beta > 0.14.