Theoretical modelling of electron transport in InAs/GaAs quantum dot superlattices

Abstract

A theoretical model describing the electron transport in InAs/GaAs quantum dot infrared photodetectors, modelled as ideal quantum dot superlattices, is presented. The carrier wave functions and energy levels were evaluated using the strain dependent 8-band k · p Hamiltonian and used to calculate all intra-and inter-period transition rates due to interaction with phonons and electromagnetic radiation. The interaction with longitudinal acoustic phonons and electromagnetic radiation was treated perturbatively within the framework of Fermi's golden rule, while the interaction with longitudinal optical phonons was considered taking into account their strong coupling to electrons. The populations of energy levels were then found from a system of rate equations, and the electron current in the superlattice was subsequently extracted.1 Introduction Considerable research effort has recently been put in the development of quantum dot infrared photodetectors [1][2][3][4][5][6][7] (QDIPs) to overcome the limitations of quantum well based devices, which has lead to a recent demonstration of QDIPs operating at room temperature [8]. On the other hand, there has been much less work on theoretical modelling of carrier transport in QDIPs [9,10]. In these models, the current is deduced from the analysis of the processes of carrier capture, thermal escape and photoexcitation. However, none of these models aims to predict the dependence of relevant QDIP output parameters, such as responsivity or dark current on the choice of material system used or on quantum dot size and composition, which it is highly desirable to know in order to optimize QDIP characteristics. Deeper understanding of underlying QDIP physics can also be achieved by obtaining information about carrier distribution among various quantum dot and continuum energy levels, which is hard to access experimentally. In this work, we therefore present a theoretical model of vertical electron transport in quantum dot infrared photodetectors, modelled as ideal quantum dot superlattices. The model being able to treat both the transport in dark and light conditions will be presented and the results of the simulation of the transport in dark conditions will be given.