Theory of optical properties and carrier transport of mid-infrared quantum-dot devices

 

P. Vogl 

 

 

The main goal of this theory project is to study, optimize, and design novel device geometries of THz quantum cascade laser structures that incorporate quantum dot layers within the quantum wells. We will (i) calculate optical properties of InGaAs quantum dots with focus on the shape and charge dependence of absorption and emission, and (ii) study DC current through two coupled layers of quantum dots that form a resonant tunneling diode, and (iii) design and optimize quantum dot based THz QCLs. We will focus our studies on self-assembled quantum dot layers embedded in QCL type multi quantum wells and investigate situations where both laser level lie within (adjacent) quantum dot layers, as well as situations where only one level is a quantum dot state and the other one is an adjacent quantum well state. In addition, nanowire based quantum dot QCL structures may be studied theoretically, depending on their experimental realization in this collaborative project.

 

The theoretical methods used are based on two schemes. First, we employ a newly developed C++ version of nextnano. This software implements an 8-band k.p Schrodinger-Poisson solver with open quantum boundary conditions, including strain effects and can be used to calculate optical absorption and emission of nanostructures. Secondly, we have developed a fully self-consistent nonequilibrium Green’s function (NEGF) method for open quantum systems that includes optical and acoustic phonon scattering, interface roughness, impurity and alloy scattering, and electron-electron scattering in a local density functional approach. The full energy and momentum dependence of all self energies is taken into account and particular care is taken to ensure charge and current conservation which is not automatically fulfilled in this approach. We have demonstrated that this scheme can predict I-V characteristics of THz QCL structures quantitatively and without any fitting parameters. However, a major task in this project will be the generalization of this method to fully three-dimensional structures.

 

Since nextnano is a very versatile tool for studying, interpreting and predicting a wide range of semiconductor nanostructures, we will support several experimental groups by studying the electronic and optical properties of the planned novel nanostructures such as IV/III-V nanowires, antimonide based nanostructures, ballistic currents through quantum dots, and the shape and alloy composition of quantum dot structures.

 

 

Report 2005-2009 (.pdf)

 

Report 2009-2012 (.pdf)

 

 

This project part was merged for the third funding period with project part P09 and continued within the new project part P14.