Intersubband Transitions In Quantum Dots Research Articles

Quantum selection rule dependent plasmonic enhancement in quantum dot infrared photodetectors

In this paper, we analyze quantum selection rules of intersubband transitions in quantum dots (QDs) and determine their impact on plasmonic enhancement in quantum dot infrared photodetectors (QDIPs). Photoluminescence and photocurrent spectrum measurement were performed on QD samples with different doping levels to identify the QD energy levels and associate the photodetection peaks with the intersubband transitions. The quantum selection rules of the intersubband transitions are determined by the electric-dipole interaction. To determine the impact of quantum selection rules on the plasmonic enhancement, we fabricated metallic two-dimensional subwavelength hole array (2DSHA) plasmonic structures with different periods on QDIPs for specific plasmonic enhancement of individual intersubband transitions. We found that the plasmonic enhancement ratios of different intersubband transitions are not the same. The unequal enhancement ratios are attributed to the quantum selection rules in the intersubband transitions and the dominant electric field (E-field E→) vectors induced by the 2DSHA plasmonic structure.

The nonlinear optical rectification coefficient of quantum dots and rings with a repulsive scattering center

By using the matrix diagonalization method within the effective-mass approximation, we have investigated the second-order nonlinear optical rectification coefficient associated with intersubband transitions in quantum dots and rings which include a repulsive scattering centre and are subjected to a perpendicular magnetic field. Based on the computed energies and wave functions, we have studied the effects of impurity and magnetic field in quantum dots and rings on this coefficient. The results show that the nonlinear optical properties of quantum dots and rings are strongly affected by the external magnetic field, the quantum size and the impurity. Also we find that the second-order nonlinear optical rectification coefficient of quantum rings shows the Aharonov–Bohm oscillation as the external magnetic field is increased.

Photovoltaic quantum dot quantum cascade infrared photodetector

Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared photodetection (λpeak = 5.5 μm) is demonstrated. The quantum cascade barrier region provides the internal electric field to transfer photoexcited electrons into quantum dots of the next stack, enabling zero bias operation. Increased carrier relaxation time for intersubband transitions in quantum dots provides a distinct advantage for the carrier transport. Responsivity of 10 mA/W and detectivity of 9 × 109 cm Hz1/2 W−1 at 77 K for f/2 optics has been obtained at zero bias. Dark current density is 6.5 × 10−7A cm−2, at 80 K at zero bias.

Magnetic field effects on intersubband transitions in a quantum nanostructure

We report on our theoretical studies of the magnetic field effects on intersubband transitions in quantum dots (QDs) embedded in a quantum cascade structure subjected to a strong magnetic field applied perpendicular to the QD plane. The peaks of the emission spectra calculated for QDs containing a few interacting electrons indicate that there is a correlation between the non-monotonic behavior of the maximum value of the emission spectrum as a function of the applied magnetic field and the field dependence of the low-lying energy spectra of the dots.

Carrier dynamics in self-organized quantum dots and their application to long-wavelength sources and detectors

Carrier dynamics in self-organized quantum dots have been studied using temperature-dependent differential transmission spectroscopy and room temperature high-frequency electrical impedance measurements on quantum dot lasers. These results suggest the existence of a long relaxation time (∼100 ps) for the excited state carriers at higher temperatures with the dominant scattering mechanism being electron–hole scattering. The long relaxation time is exploited to realize far-infrared sources and detectors based on intersubband transitions in quantum dots. Quantum dot detectors with large detectivity ( D ∗ =(9–10) ×10 9 cm Hz 1/2/W) and responsivity ( R =100 mA/W ) have been reported at T =40 K . A unique unipolar intersubband quantum dot laser (13.3 μm) has also been reported at T =283 K , using the long intersubband relaxation time and the short interband recombination time to achieve population inversion between the ground and the excited states.