Relaxation of persistent photoconductivity in Ga-doped Cd 1-x Mn x Te.

Abstract

Semiconductors containing so-called DX centers exhibit at low temperatures an ability to modify locally a refractive index under illumination. This modification persists due to the metastable character of the centers. As a result at low temperatures persistent photoeffects are observed for the materials. This property suggests the potential application of the materials in optoelectronic devices and an optical memory based on holography. It has been shown that at low temperatures the centers behave like deep defects whereas after photoionization they behave like shallow dopants. This twofold nature also accompanies different localization at the crystal lattice. As a result at low temperatures return to the dark ground state is not possible unless the system possesses enough energy. This energy is called the capture barrier. Changes in the refractive index depend on the height of the capture barrier and temperature. Estimation of the barrier is therefore of prime importance for materials possessing DX centers. It was found that a gallium dopant in Cd 1-x Mn x Te exhibits DX-like behaviour. In this paper we report on the capture barrier of gallium doped Cd 0.99 Mn 0.01 Te. In order to determine the barrier persistent photoconductivity (PPC) decay kinetics were investigated. The kinetics are governed by the transition from a shallow donor state to the deep DX state. The measurements were run within a temperature range from 77K<T<105K. The capture barrier was deduced from the decay time constants after switching off the light taken at different temperatures. Its value was found to be equal to 0.23eV.