The role of transport processes of nonequilibrium charge carriers in radiative properties of arrays of InAs/GaAs quantum
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DIMENSIONAL SYSTEMS
The Role of Transport Processes of Nonequilibrium Charge Carriers in Radiative Properties of Arrays of InAs/GaAs Quantum Dots A. S. Shkolnika^, A. V. Savelyevb, L. Ya. Karachinskya, N. Yu. Gordeeva, R. P. Seisyana, G. G. Zegryaa, S. Pellegrinic, G. S. Bullerc, and V. P. Evtikhieva aIoffe
Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] bSt. Petersburg State Polytechnical University, Politekhnicheskaya ul. 29, St. Petersburg, 195251 Russia cSchool of Engineering and Physical Science, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, United Kingdom Submitted June 21, 2007; accepted for publication July 25, 2007
Abstract—The results of time-resolved photoluminescence studies of heterostructures containing monolayer arrays of InAs/GaAs quantum dots are presented. A two-component time dependence of intensity of photoluminescence from the ground state of quantum dots, with characteristic times of the slow component up to hundreds of nanoseconds and those of rapid one several nanoseconds, is studied. It is shown that the slow component is determined by the transport of nonequilibrium charge carriers between the quantum dots. At low temperatures, the time of the slow component is determined by tunneling, and at high temperatures by thermal escape of nonequilibrium charge carriers. The ratio of the contributions of tunneling and thermal escape is determined by the degree of isolation of quantum dots. A theoretical model is constructed that describes the effect of the dynamics of carrier transport on the emergence and decay of the slow component of photoluminescence. PACS numbers: 73.21.La, 73.63.-b DOI: 10.1134/S1063782608030093
1. INTRODUCTION Semiconductor quantum dots (QDs) have for many years attracted great interest from researchers due to a series of new properties caused by a δ-like function of density of energy states [1–3]. Despite large progress in the study and fabrication of QD heterostructures and devices based on them, some of their fundamental properties remain poorly understood [4]. One of the most important parameters of QDs is the lifetime of nonequilibrium charge carriers. We previously studied the lifetime of nonequilibrium charge carriers in QDs depending on the size, occupancy, and temperature [5–7]. It was shown that the time dependence of intensity of luminescence from the ground state of the QD has a two-component character, where the characteristic time of the slow component is tens or even hundreds of nanoseconds. Savelyev et al. [8] independently determined the charged states of the QD array with characteristics relaxation times longer than 100 ns while studying 1.3-µm InAs/InGaAs/GaAs QDs by the method of time-resolved pump-probe spectroscopy. Later, this effect was used by some researchers for fabrication of prototypes of QD-based memory cells [9, 10]. The purpose of this study is to carry out a complex analysis of the obtained experimental data and to develop a theoretical m
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