In this project part we focus on the investigation of optical transitions between quantized levels of III-V semiconductor nanostructures, which are in the infrared (IR) spectral region. The knowledge of the optical properties is essential for the deeper understanding of the physics of nanostructures as well as for the design of novel nano photonic devices. The third period will be structured in three work packages:

•    WP1 – THz QCLs: next generation of devices
•    WP2 – Time-domain-spectroscopy
•    WP3 – Quantum dot spectroscopy

WP1 – The further development of terahertz quantum cascade lasers, which are based on the novel, Al-free material combination InGaAs/GaAsSb (Deutsch 2010), is the main goal of this part. First we will focus on the classic optimization of the active region band structure and device processing. Subsequently we will address the improvement of the growth quality (in collaboration with P03) with special symmetric active regions for the investigation of interface qualities. The second approach is a nanowire-based terahertz quantum cascade laser. From the successful work of the theory group (P14), strong enhancement of the gain at THz frequencies in such lower dimensional active regions is expected. Finally the integration with photonic crystal cavities will be pursued also for these nanowire-based active regions.

WP2 – The goal is the study of the dynamics of intersubband systems. We will study the gain dynamics of terahertz quantum cascade lasers based on the InGaAs/GaAsSb material system as well as that of the lower dimensional systems using our successfully introduced coupling scheme for double metal resonators (Martl 2011). The type II alignment and the narrow band gap of InGaAs/GaAsSb allow us to study a different facet excitation and enable the direct use of stable fs-fibre lasers with telecommunications wavelengths.