Detection and emission of infrared radiation based on group IV nanostructures

 

T. Fromherz

 

 

The setup and the methods developed during periods 1 and 2 of the IR-ON project for single dot spectroscopy in the 1.5 µm spectral range will be applied in order to get information about the energy level structures of CdTe/ZnTe quantum dots, solution-processed nanocrystals passivated with a silica shell and of SiGe islands. Since the first two material systems show large luminescence efficiency, they will be investigated by single island photoluminescence spectroscopy. The resulting data on the energy level structure and exciton interactions in these QDs will be important for the optimization and development of QD lasers as aimed at in P04 and P05. Room temperature PL efficiency of SiGe islands and quantum wells will be further increased by optimizing their coupling to the electromagnetic field in PhC structures. This strategy will also allow the reduction of the excitation intensity required for detection of PL from only a few SiGe islands. We will continue our efforts to utilize the expected large photoconductive gain due to type II band alignment in the SiGe islands for single island photocurrent spectroscopy. By combining these experiments with a structural characterization of the same island as performed in P07 and a subsequent energy level calculation, highly predictive quantum dot models will be developed.

By time correlated single PL photon experiments, the excited state lifetimes of nanostructures emitting in the 1.5 µm region will be determined. For these experiments, we will use a superconducting single photon detector that has a ~100 smaller dark count rate as state of the art photo-multipliers and avalanche diodes for this wavelength region (Goltsman 2009). These experiments will be performed for the PbTe/CdTe quantum dots, solution processed nanocrystals and SiGe islands integrated into PhC structures. For the first two material systems, the experiments aim at identifying and suppressing the dominant relaxation mechanisms especially at high excitation levels. For the SiGe system these measurements will allow a quantification of the radiative lifetime-reduction due to the integration of the islands into photonic structures.
The optoelectronic properties of novel group IV nanostructures grown in P02 will be investigated by PL experiments. For biaxially tensile strained GeC on Ge, GeSn, and nanostructures made thereof, an analysis of the PL-yield for various layer compositions and growth conditions will be performed. Here, we will use the methods developed in the previous IR-ON periods based on shallow concentration gradients across a substrate wafer. These activities aim at the demonstration of direct bandgaps and an improvement of the room temperature PL efficiency for group IV semiconductors.

The blocked impurity band (BIB) detectors will be further optimized with respect to single photon detection in the THz and MIR spectral region. These experiments will be based on the setup developed in phase II of the IR-ON project for BIB characterization under ultra-low background radiation.