J. P. Prineas

Time-resolved optical measurements of minority carrier recombination in a mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice

Measurements of carrier recombination rates using time-resolved differential transmission are reported for an unintentionally doped mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice. Measurements at 77 K yield minority carrier lifetimes of 3 μs and 9 μs for the InAsSb alloy and InAs/InAsSb superlattice, respectively. The un-optimized InAsSb-based materials also exhibit long lifetimes (>850 ns) at temperatures up to 250 K, indicating the potential use for these materials as mid-wave infrared photodetectors with improved performance over current type-II superlattice photodetectors at both cryogenic and near-ambient operating temperatures.

Excitonic photoluminescence in semiconductor quantum wells: plasma versus excitons.

Time-resolved photoluminescence spectra after nonresonant excitation show a distinct 1s resonance, independent of the existence of bound excitons. A microscopic analysis identifies exciton and electron-hole plasma contributions. For low temperatures and low densities, the excitonic emission is extremely sensitive to details of the electron-hole-pair population making it possible to identify even minute fractions of optically active excitons.

Storage of ultrashort optical pulses in a resonantly absorbing Bragg reflector.

A practical method of slowing and stopping an incident ultrashort light pulse with a resonantly absorbing Bragg reflector is demonstrated numerically. It is shown that an incident laser pulse with suitable pulse area evolves from a given pulse waveform into a stable, spatially-localized oscillating or standing gap soliton. We show that multiple gap solitons can be simultaneously spatially localized, resulting in efficient optical energy conversion and storage in the resonantly absorbing Bragg structure as atomically coherent states.

All-optical spin-dependent polarization switching in Bragg-spaced quantum well structures

All-optical polarization switching is demonstrated in a resonant photonic band-gap structure consisting of Bragg-spaced quantum wells (BSQWs). The switch takes advantage of the large spin-dependent optical nonlinearities and the ultrafast recovery present in BSQWs to produce large throughputs (greater than 40%), high contrast ratios (greater than 40 dB), and large optical bandwidths (∼0.6THz), where both switching time and sample recovery time are control-pulse-width limited.

MBE-grown high-efficiency GaInAsSb mid-infrared detectors operating under back illumination

This paper describes molecular beam epitaxial growth, processing and room temperature characterization of lattice-matched GaInAsSb mid-infrared detectors on GaSb substrates for room temperature operation. For the first time, we demonstrate GaInAsSb detectors operating under back-illumination, a critically important geometry for flip-chip-mounted focal plane arrays, and achieve performance equal or superior to front-illuminated detectors. Very high quantum efficiency and flat spectral response are achieved for the back-illuminated detectors due to improved carrier collection efficiency, photon recycling and reduced carrier recombination. In situ RHEED intensity oscillations and post-growth XRD are used for coarse and fine tuning of GaInAsSb lattice matching, respectively.

Resonant photonic band gap structures realized from molecular-beam-epitaxially grown InGaAs/GaAs Bragg-spaced quantum wells

We present a comprehensive study of the growth and fabrication of Bragg-spaced quantum wells, a type of resonant photonic band gap structure. To begin, we considered the impact of disorder and drift in the periodicity of the quantum wells on the formation of the resonant photonic band gap. We found that steady decrease in the periodicity greater than a few percent leads to collapse of the resonant photonic band gap, while random disorder in the quantum well periodicity of several percent leads to extra peaks in the resonant photonic band gap due to coupling to “intermediate band” states. Next, we optimized the growth of low x (x⩽0.06) InxGa1−xAs∕GaAs quantum wells, the building block of Bragg-spaced quantum well structures. Growth parameters optimized include growth rate, modulation of substrate temperature for barrier/quantum well, and V/III flux ratio. Fast growth of quantum wells was achieved with some of the narrowest heavy-hole exciton linewidths (0.37meV) reported to date for quantum wells of these ...

Room-temperature normal-mode coupling in a semiconductor microcavity utilizing native-oxide AlAl/GaAs mirrors

A GaAs/AlAs microcavity containing six InGaAs quantum wells was grown, and the sample was then etched via chemically‐assisted ion‐beam etching to form 50‐μm‐diam cylindrical mesas. The formation of native oxides, accomplished by baking the samples at 400 °C in the presence of a pressurized N2/H2O vapor line, lowered the refractive index of the AlAs layers to 1.5. The higher refractive index contrast more effectively confined the intracavity field, leading to well‐resolved reflectivity dips with an exciton‐polariton splitting of 6.72 nm=9.44 meV at room temperature.

Cascaded Superlattice InAs/GaSb Light-Emitting Diodes for Operation in the Long-Wave Infrared

Superlattice InAs/GaSb light-emitting diodes with peak emission wavelength of 8.6 μm and output power approaching 190 μW at 77 K from a 120 × 120 μm2 mesa are demonstrated. Output power in excess of 600 μ.W was demonstrated from a 520 × 520 μm mesa at 1 A drive current and 50% duty cycle. Devices were grown by molecular beam epitaxy on lightly n-doped GaSb substrates and employed a 16-stage cascaded active region configuration to improve current efficiency and increase optical output. Emitting regions were coupled by semi-metallic tunnel junctions consisting of a p-GaSb layer and a thickness-graded InAs/GaSb superlattice stack.

Tunable slow light in Bragg-spaced quantum wells

The group velocity of light is continuously varied in the intermediate band of a Bragg-spaced quantum well structure by tuning the pulse frequency. Delays of 0–0.4bit, without significant pulse distortion, are measured. The high group index is found to lead to large Fresnel reflection coupling losses and Fabry-Perot fringing. Antireflection (AR) coatings deposited on both sides of the Bragg-spaced quantum well structure are shown to improve coupling of light into the intermediate band but to be sensitive to small errors (∼1%) in the AR coating layer thicknesses.

Theory of coherent effects in semiconductors

A microscopic theory is applied to discuss coherent excitation effects in semiconductors. The theory is evaluated to analyze ultrafast absorption changes around the exciton resonance in semiconductor quantum-well structures where the relative strength of the different many-body contributions can be manipulated by proper selection of pump and probe polarizations. For two-band systems and oppositely circular polarization it is shown that Coulombic correlation dynamics dominates the optical response. As a consequence, the optical Stark effect in this configuration corresponds to a red shift of the exciton resonance in striking contrast to the usual atomic-like blue shift. The predictions are confirmed by experiments using high-quality InGaAs quantum-well systems.