We report a semiconductor based mechanism for electrically controlling the frequency of light transmitted through extraordinary optical transmission gratings. In doing so, we demonstrate active control over the surface plasmon (SP) resonance at the metal/dielectric interface. The gratings, designed to operate in the midinfrared spectral range, are fabricated upon a doped GaAs epilayer. Tuning of over 25 cm{sup -1} is achieved, and the devices are modeled to investigate the physical origin of the tuning mechanism. Though our structures are designed for the midinfrared, the tuning mechanism demonstrated could be applied to other wavelength ranges, especially the visible and near infrared.
Electroluminescence from self-assembled InAs quantum dots in cascade-like unipolar heterostructures is demonstrated. Initial results show weak luminescence signals in the mid-infrared from such structures, though more recent designs exhibit significantly stronger luminescence with improved designs of the active region of these devices. Further studies of mid-infrared emitting quantum dot structures have shown anisotropically polarized emission at multiple wavelengths. A qualitative explanation of such luminescence is developed and used to understand the growth morphology of buried quantum dots grown on AlAs layers. Finally, a novel design for future mid-infrared quantum dot emitters, intended to increase excited state scattering times and, at the same time, more efficiently extract carriers from the lowest states of our quantum dots, is presented,.
The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.
The thermal interdiffusion of AlSb/GaSb multiquantum wells was measured and the intrinsic diffusivities of Al and Ga determined over a temperature range of 823-948 K for 30-9000 s. The 77-K photoluminescence (PL) was used to monitor the extent of interdiffusion through the shifts in the superlattice luminescence peaks. The chemical diffusion coefficient was quantitatively determined by fitting the observed PL peak shifts to the solution of the Schroedinger equation, using a potential derived from the solution of the diffusion equation. The value of the interdiffusion coefficient ranged from 5.2 x 10{sup -4} to 0.06 nm{sup 2}/s over the conditions studied and was characterized by an activation energy of 3.0 {+-} 0.1 eV. The intrinsic diffusion coefficients for Al and Ga were also determined with higher values for Al than for Ga, described by activation energies of 2.8 {+-} 0.4 and 1.1 {+-} 0.1 eV, respectively.
n-type GaSb has been prepared by metal-organic chemical vapour deposition with tellurium donors using diethyltelluride as the dopant precursor. The maximum carrier concentration achieved was 1.7 x 10{sup 18} cm{sup -3}, as measured by van der Pauw-Hall effect measurements, for an atomic tellurium concentration of 1.8 x 10{sup 19} cm{sup -3}. The apparent low activation of tellurium donors is explained by a model that considers the effect of electrons occupying both the {Lambda} and L bands in GaSb due to the small energy difference between the {Lambda} and L conduction band minima. The model also accounts for the apparent increase in the carrier concentration determined by van der Pauw-Hall effect measurements at cryogenic temperatures.
Quantum dot nanostructures were investigated experimentally and theoretically for potential applications for optoelectronic devices. We have developed the foundation to produce state-of-the-art compound semiconductor nanostructures in a variety of materials: In(AsSb) on GaAs, GaSb on GaAs, and In(AsSb) on GaSb. These materials cover a range of energies from 1.2 to 0.7 eV. We have observed a surfactant effect in InAsSb nanostructure growth. Our theoretical efforts have developed techniques to look at the optical effects induced by many-body Coulombic interactions of carriers in active regions composed of quantum dot nanostructures. Significant deviations of the optical properties from those predicted by the ''atom-like'' quantum dot picture were discovered. Some of these deviations, in particular, those relating to the real part of the optical susceptibility, have since been observed in experiments.