Miniband quantum transport in semiconductor nanodevices under broadband illumination

A general theoretical framework for the modelling of miniband transport in semiconductor nanostructures under broadband illumination is presented. Our approach is based on the multi-subband three-dimensional Boltzmann transport equation and allows to investigate both the steady-state and the time-dependent dynamics. The model has been succesfully applied to the problem of the design and optimization of Terahertz quantum well infrared photodetectors and is now applied to a more generic superlattice system. We consider the carrier dynamics in multi-miniband superlattices under black-body illumination showing the existence of regimes in which the current in some minibands is inverted, eventually leading to absolute negative resistance. Electron dynamics in photoexcited nanostructures has been a matter of intense study for a long time both for the fundamental physical insights that this kind of systems can give and for potential technological applications. Among others, semiconductor superlattices has received considerable attention as they provide a relatively simple way to build systems in which the band structure of electrons can be precisely determined. This ability, along with the use of optically-active materials, allows to study interesting phenomena regarding the interactions between electrons and light. In particular, superlattices subject to coherent electromagnetic fields, like those typically provided by lasers, have been shown to give rise to a number of interesting phenomena including lightinduced absolute negative resistance [1, 2, 3]. On the other hand superlattices subject to an incoherent and broadband photoexcitation rather than a laser source are also interesting as they can be used as a model for state-ofthe-art quantum well infrared photodetectors (QWIPs) which basically consist in a sequence of quantum-wells and barriers (comprising many tens of periods) which are then exposed to background blackbody radiation and infrared light emitted by objects. The incoming photons will then promote bound electrons into the continuum which in turn will give rise to a current once the system is properly biased. In the past we have focused our attention on the development of a general theoretical framework for the simulation of carrier transport photoexcited weakly-coupled superlattices and we have applied it to the simulation and design of a new architecture for THz QWIPs with improved temperature performance [4, 5]. The model is based on the multi-subband threedimensional Boltzmann transport equation describing the dynamics of the electron population EDISON 16 IOP Publishing Journal of Physics: Conference Series 193 (2009) 012089 doi:10.1088/1742-6596/193/1/012089 c © 2009 IOP Publishing Ltd 1 0 10 20 30 40 50 −5 0 5 10 15 20 Temperature (K) C ur re nt d en si ty ( a. u. ) Figure 1. Total current as a function of temperature when the device is subject to a positive bias and irradiated with a 300K blackbody. The device shows absolute negative resistance between 5 and 40 K.