Photoionization cross-section of the DX center in Te-doped AlxGa1−xSb

Abstract

The photoionization of DX centers in Te-doped AlxGa1−xSb layers grown by molecular beam epitaxy is investigated by measuring the increase of the Hall free electron density after illumination by monochromatic light in the temperature range typical of the persistent photoconductivity (PPC) effect. The investigated samples have AlSb molar fractions in the 0.3⩽x⩽0.5 range and n-type doping in the 1017−1018 cm−3 range. An accurate investigation of the isothermal photoionization transients is performed to evidence features in the curve not directly related to the phenomenology of the DX center, the free electron density being influenced by the possible occupancy of other impurity levels. The transients show, in particular, an initial nonexponential behavior which is demonstrated as due to localization of a fraction of the photoexcited electrons into a nonmetastable impurity state which is responsible for the semiconductor-to-metal transition observed under the PPC regime. When this effect is accounted for, the dependence of the photoionization cross section of the DX center on the photon energy was obtained from the analysis of the linear part of the transients and analyzed through a model given in the literature. The analysis gives values of the optical ionization energy and of the Frank-Condon shift varying in the ranges of 0.84–0.95 and 0.70–0.74 eV, respectively, depending on the alloy composition. This confirms a large lattice relaxation for the DX center related to the Te-impurity in AlxGa1−xSb.

Photoionization cross-section analysis for a deep trap contributing to current collapse in GaN field-effect transistors

“…One is presently concerned with such lack of knowledge particularly in cases of traps responsible for current collapse phenomena in GaN metal-semiconductor field-effect transistors. This is in analogy to the analyses performed in a variety of earlier articles for cases of small 9,10,15 (DϽE T ) as well as large [32][33][34][35][36][37] This concerns in particular the thermal ionization ͑ϭelectron binding͒ energy, E T , the Franck-Condon ͑FC͒ shift, D, the corresponding classical optical ionization energy, E O ϭE T ϩD, as well as the effective ͑average͒ phonon energy, ប .…”

X-ray induced persistent photoconductivity in Si-doped Al0.35Ga0.65As

“…At temperatures below ∼ 80 K the induced photoconductivity is persistent [6]. Excitation of DX centers using visible light has been studied extensively in various semiconductor compounds over the last few decades [7][8][9][10]. Here, we demonstrate that irradiation by X-rays can also induce persistent photoconductivity in Si-doped Al 0.35 Ga 0.65 As.…”

“…6 Excitation of DX centers using visible light has been studied extensively in various semiconductor compounds over the last few decades. [7][8][9][10] Here, we demonstrate that irradiation by x rays can also induce persistent photoconductivity in Si-doped Al 0.35 Ga 0.65 As. While phenomenologically the persistent photoconductivity and its erasure upon annealing is similar to the x-ray induced metallization observed in a transition metal oxide, 11 the underlying mechanisms are quite different.…”