Quantum well

About: Quantum well is a research topic. Over the lifetime, 44627 publications have been published within this topic receiving 674023 citations. The topic is also known as: QW & quantum potential well.

Chirp reduction of directly modulated semiconductor lasers at 10 Gb/s by strong CW light injection

Abstract: The influence of strong light injection on the reduction of the dynamical linewidth broadening of directly current-modulated semiconductor lasers at high bit rates is theoretically investigated and experimentally verified for 10 Gb/s NRZ pseudorandom modulation with a large current swing of 40 mA pp. Significant chirp reduction and single-mode operation are observed for bulk DFB, quantum well DFB lasers at 10 Gb/s and a weakly coupled bulk DFB laser at 8 Gb/s, so that an improvement of the transmission performance using standard monomode fibers in the 1.55 /spl mu/m low-loss wavelength region can be achieved for all these laser types, where dispersion otherwise causes severe penalties for long-haul transmission. The properties of injection-locked bulk DFB and quantum well DFB lasers with respect to high bit rate modulation have been systematically studied by the use of the rate equation formalism. A dynamically stable locking range of more than 30 GHz under modulation has been found for both laser types with injection ratios higher than 0.5. >

Two-Dimensional Arsenene Oxide: A Realistic Large-gap Quantum Spin Hall Insulator

Abstract: Searching for two-dimensional (2D) realistic materials able to realize room-temperature quantum spin Hall (QSH) effects is currently a growing field. Here, we through ab initio calculations to identify arsenene oxide, AsO, as an excellent candidate, which demonstrates high stability, flexibility, and tunable spin-orbit coupling (SOC) gaps. In contrast to known pristine or functionalized arsenene, the maximum nontrivial band gap of AsO reaches 89 meV, and can be further enhanced to 130 meV under biaxial strain. By sandwiching 2D AsO between BN sheets, we propose a quantum well in which the band topology of AsO is preserved with a sizeable band gap. Considering that AsO having fully oxidized surfaces are naturally stable against surface oxidization and degradation, this functionality provides a viable strategy for designing topological quantum devices operating at room temperature.

Strong polarization-sensitive electroabsorption in GaAs/AlGaAs quantum well waveguides

Abstract: We report the first measurements of perpendicular field electroabsorption (quantum confined Stark effect) in GaAs/AlGaAs quantum wells for light propagating parallel to the plane of the layers. This geometry is well suited for integrated optics. The absorption edge shifts to longer wavelengths with increasing field by as much as 40 meV, giving a modulation depth>10 dB. The strong dichroism present in this geometry is retained even at high fields, making polarization‐sensitive electro‐optical devices possible. We also demonstrate in the waveguide geometry optical bistability due to the self‐electro‐optic effect with 20:1 on/off ratio.

Spontaneous formation of stacking faults in highly doped 4H–SiC during annealing

Abstract: 4H–SiC samples doped with nitrogen at ∼3×1019 cm−3 were annealed in Ar for 90 min at 1150 °C. Transmission electron microscopy revealed stacking faults at a density of approximately 80 μm−1 where faults were not found to exist prior to annealing. All faults examined were double layer Shockley faults formed by shear on two neighboring basal planes. The structural transformation was interpreted as due to quantum well action, a mechanism where electrons in highly n-type 4H–SiC enter stacking fault-induced quantum well states to lower the system energy. The net energy gain was calculated as a function of temperature and nitrogen doping concentration through solution of the charge neutrality equation. Calculations showed that doping levels in excess of ∼3×1019 cm−3 should result in double layer stacking faults forming spontaneously at device processing temperatures, in agreement with our observations. Single layer faults are not expected to be stable in 4H–SiC at concentrations below 1×1020 cm−3, but are expected to form at doping concentrations above ∼2×1019 cm−3 in 6H–SiC. Charge buildup in the stacking fault was shown to produce an electrostatic potential that exceeds 90% of the energy difference between the Fermi level position and lowest energy state in the fault-related quantum well. This potential barrier is one of the factors leading to increase of the forward voltage drop in SiC pin diodes.

Investigation of the Nonthermal Mechanism of Efficiency Rolloff in InGaN Light-Emitting Diodes

Abstract: We present a comparative study on the optical characteristics of InGaN-based multiple quantum well light-emitting diodes (LEDs) with peak emission ranging from green to ultraviolet (UV) over a wide injection range. It is found that by pulsing the LEDs with a duty cycle that is below 1%, thermally induced peak red shift and efficiency reduction are largely eliminated. The current dependence of both the quantum efficiency and peak shift appears to be a strong function of the indium content in the active region. The quantum efficiencies of the blue and green LEDs peak at very low currents and dramatically decrease at high currents, whereas the UV LED has a nearly constant quantum efficiency under high injection conditions. In contrast to the minimal current- induced energy shift in the UV LED, a monotonic blue shift of the peak energy, which has a total amount of ~110 meV-1 kA/cm2, is seen for the green LED. These results offer a strong support for the argument that the current overflow from localized states is the major nonthermal mechanism underlying the efficiency rolloff in InGaN-based visible LEDs.