No abstract

Light absorption in semiconductors due to interserial transitions of excitons has been investigated. Analytic expressions for the spectral and temperature dependence of the absorption coefficient have been obtained for the allowed and forbidden transitions of the exciton from one series into arbitrary discrete states of the other series, for various ratios of the translational masses of the excitons in these series. The absorption of light has a threshold or boundary frequency coo, depending on the mass of the excitons before and after the transition. With the increase of Iw -cool, the absorption coefficient increases and then decreases. For the allowed transition from the Is-exciton state of one series into the nl-state in the other series, the oscillator strength is proportional to TI, whereas the maximum value of the absorption coefficient is proportional to TI-1. The temperature ignition of the absorption bands at 1 > 1 has been predicted, which is not related to the change of the level population.

A quantum mechanical theory is developed for infrared absorption by excitons due to photoionization and intraband lattice scattering. The theory involves the interaction of the excitons with the acoustic and optical phonons. The Maxwellian and Bose‐Einstein distribution functions and the possible locations of the simple exciton band extremum are taken into account. The effect of the exciton photoionization is observable at the threshold frequency at comparatively low exciton concentrations.