Epitaxial lead salt nanostructures for mid-infrared lasers and detectors


G. Springholz



The goal of this project is to employ novel epitaxial lead salt nanostructures for realization of mid-infrared devices such as quantum dot lasers and detectors. For this purpose, lead salt quantum dots embedded in wide band gap II-VI matrices will be used, which were developed in the second IR-ON period. The quantum dots are formed by phase separation and nano-precipitation during molecular beam epitaxy and controlled post-growth annealing. The quantum dots exhibit unique properties such as nearly spherical shapes, atomically abrupt interfaces, very large confinement energies due to the large band gap difference between the narrow gap IV-VI and wide gap II-VI materials, as well as very bright and efficient emission in the mid-infrared region. The project will pursue three main research directions, namely,


Fabrication of novel mid-infrared nanodevices based on lead salt quantum dots in wide gap barrier materials grown on GaAs substrates. This includes microdisk lasers with advanced resonator designs for control of the emission characteristics, vertical external cavity surface emitting lasers (VECSELs) with high output powers and externally tunable emission wavelengths, and novel quantum dot detectors based on the high photoconductive gain observed in PbTe/CdTe structures.



Realization of novel types of lead salt nanostructures based on (a) new material combinations such as selenides and ternary alloys, including Sr and Sn-chalcogenides. This will allow to expand the wavelength coverage of quantum dots. (b) Hybrid colloidal lead salt nanocrystals embedded and overgrown by molecular beam epitaxy with wide gap II-VI materials, and (c) growth of nanowires and dot-in-nanowires structures by the VLS method. In addition, growth of lead salt nanostructures on Si substrates as well as on pre-pattern substrates for site-control will be developed.



Determination of the structural and electronic properties of the novel quantum dot systems in order to reveal the shape, composition, interface structure, band alignments, as well as quantum efficiencies and radiative and non-radiative carrier lifetimes.


The research will be performed in close collaboration with several IR-ON partners, including P02 for transmission electron microscopy and growth on Si substrates, P05 for realization of photo-detectors and fabrication of hybrid colloidal-epitaxial quantum dots, P07 for detailed structural analysis using advanced X-ray scattering techniques with synchrotron radiation, P12 for optical spectroscopy aiming at single dot experiments, and P14 for calculation of the electronic structure and modeling of advanced resonator designs for microdisk lasers. The final goal will be to realize a novel class of nanomaterials and to demonstrate sensitive mid-infrared quantum dot detectors and efficient quantum dot lasers with high operation temperatures and high output powers with tunable emission over a wide spectral region.


Report 2005-2009 (.pdf)


Report 2009-2012 (.pdf)