Saturable optical absorption of the deep Te-complex center inAl0.4Ga0.6As

Direct measurements of optical absorption by a deep complex in Te-doped ${\mathrm{Al}}_{0.4}$ ${\mathrm{Ga}}_{0.6}$As, referred to as the $\mathrm{DX}$ center, are reported. A novel double-waveguide configuration is employed to measure accurately the absorption coefficient ${\alpha }_{\mathrm{DX}}$ of this center. The results are in agreement with earlier photoconductivity and photocapacitance measurements on this center, and are consistent with most aspects of an anomalously large lattice relaxation model which has been proposed to explain these earlier optical results. The photoconductivity results for this center predict a saturable absorption which is directly measured in this paper, and its temperature dependence is described. For a Te concentration of ≈ 3×${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$, the absorption reaches a maximum of ∼18 ${\mathrm{cm}}^{-1\mathrm{}}$ for $100\le T\le 150$ K. At lower temperatures the absorption saturates; at higher temperatures it falls off due to thermal emission from the center. These effects are calculated using a simple rate equation. Also investigated is the dependence of ${\alpha }_{\mathrm{DX}}$ on photon energy. The results are in good agreement with the magnitude of the absorption cross section as measured by photocapacitance, although the absorption peaks at somewhat higher energy.