Persistent IR photoconductivity in InAs/GaAs structures with QD layers
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ENSIONAL SYSTEMS
Persistent IR Photoconductivity in InAs/GaAs Structures with QD Layers V. A. Kul’bachinskiœ*^, V. A. Rogozin*, V. G. Kytin*, R. A. Lunin*, B. N. Zvonkov*, Z. M. Dashevsky**, and V. A. Casian** *Moscow State University, Moscow, 119992 Russia ^e-mail: [email protected] **Department of Materials Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva, 84105 Israel Submitted May 6, 2005; accepted for publication May 20, 2005
Abstract—Persistent IR photoconductivity in InAs/GaAs structures with layers of QDs with a p- and n-type conductivity was studied. At the initial stage, after the illumination is switched off, the relaxation of photoconductivity follows a logarithmic law. The relaxation time depends on temperature; it decreases as temperature increases. A simple model of photoconductivity relaxation, based on thermal activation of carriers from the QD layer, is proposed. The model is consistent with the experimental data. PACS numbers: 73.63.Kv, 73.21.La DOI: 10.1134/S1063782606020187
1. INTRODUCTION Studies of structures with quantum dot (QD) layers are of much academic interest; at the same time, these structures offer wide prospects for light-emitting devices [1–5]. A large number of studies have been devoted to QD InAs/GaAs structures. Of special interest are the structures where QDs, with high density, form a 2D conducting layer due to the overlapping of states in the neighboring QDs [6–8]. Owing to strong localization of carriers at low concentration, hopping conductivity is observed at low temperatures [9, 10]. Currently, IR detectors based on quantum wells are successfully used. However, they have some limitations, such as the angle of incidence and narrow range of wavelengths. For QDs, the direction of the incidence of light is insignificant, because the electron motion is confined in all three directions. In addition, self-assembled QDs on the surface can have a set of levels and, what is more, a scatter in size; this leads to photosensitivity in a wide range of wavelengths [11–13]. QD-based photodetectors are expected to have a very low dark current. The growth processes of self-assembled QDs have been studied thoroughly, and QD layers with well-resolved lines in the photoluminescence spectra can be produced [14]. Information on the transitions between QD states and the quantum-well band in the wetting layer is obtained from data on the lateral photocurrent. In this case, the charge is transported by photoexcited electrons in the quantum-well band in the wetting layer, or, in the case of subsequent thermal excitation, in the GaAs bulk [15, 16]. The conductivity change under IR illumination and its subsequent relaxation are especially important for
doped QD layers. In this case, the mechanisms of photoconductivity relaxation at different temperatures are highly important. These processes were studied mainly in the QD layers with n-type conductivity [8, 11–17]. We studied the conductivity along the QD layer in InAs/GaAs structures with n- and p-type conduction in a r
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