We demonstrate mid-infrared electroluminescence from intersublevel transitions in self-assembled InAs quantum dots
coupled to surface plasmon modes on metal hole arrays. Subwavelength metal hole arrays with different periodicity are
patterned into the top contact of the broadband (9-15 μm) quantum dot material and the measured electroluminescence
is compared to devices without a metal hole array. The resulting normally directed emission is narrowed and a splitting
in the spectral structure is observed. By applying a coupled quantum electrodynamic model and using reasonable values
for quantum dot distributions and plasmon linewidths we are able to reproduce the experimentally measured spectral
characteristics of device emission when using strong coupling parameters.
We demonstrate room temperature electroluminescence from intersublevel transitions in self-assembled InAs quantum
dots in GaAs/AlGaAs heterostructures. The quantum dot devices are grown on GaAs substrates in a Varian Gen II
molecular beam epitaxy system. The device structure is designed specifically to inject carriers into excited conduction
band states in the dots and force an optical transition between the excited and ground states of the dots. A downstream
filter is designed to selectively extract carriers from the dot ground states. Electroluminescence measurements were
made by Fourier Transform Infrared Spectroscopy in amplitude modulation step scan mode. Current-Voltage
measurements of the devices are also reported. In addition, both single period and multi-period devices are grown,
fabricated, characterized, and compared to each other. Finally, we discuss the use of plasmonic output couplers for these
devices, and discuss the unique emission observed when the quantum dot layer sits in the near field of the plasmonic top
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.
Ultrashort electrical pulses were used to characterize the magnetoplasmon resonance of a two-dimensional electron gas formed in an AlGaAs/GaAs heterostructures at frequencies up to 400 gigahertz. This was accomplished by incorporating the sample into a guided wave probe operating in a dilution refrigerator. A bath temperature of 50mK was recorded during measurements, demonstrating the feasibility of this approach in other situations requiring high magnetic field and mK temperatures.
We have recently measured pulsed electron spin resonance (ESR) from electrons bound to donors in silicon. Measurements made in the late 1950's showed that these spins were long-lived, but we find coherence times that are about two orders of magnitude longer than previously seen. We have also measured the spin-decoherence of free, 2-
dimensional electrons in an ultra-high mobility Si/SiGe quantum well. The coherence time of the 2D electron spins is long in comparison to compound semiconductor systems, but several orders of magnitude shorter than that of the donorbound electrons. Spin-orbit coupling in the form of the Structural Inversion Asymmetry (Rashba effect) appears to be the cause of the increased decoherence rate of the 2D electrons' spin. For architectures employing quantum dots at a
heterointerface, the Rashba effect is not expected to cause a loss of spin coherence while the electron is in the ground state, but thermal excitation to upper dot levels could lead to decoherence. We discuss ways in which this Rashba term can be minimized in Si-based structures, as well as other physical systems (electrons on liquid helium, for example) in which much longer spin coherence times can be expected.