The fundamental relationship between radiative lifetime and spectral linewidth of free excitons is demonstrated theoretically experimentally for quasi 2D in GaAs/AlGaAs quantum wells.Received 24 August 1987DOI:https://doi.org/10.1103/PhysRevLett.59.2337©1987 American Physical Society

In this letter, we report the room-temperature operation of an electrically controlled THz modulator. The modulation is achieved by reducing electron density in a gated two-dimensional gas structure, which leads to increase transmitted intensity incident beam radiation. By depleting 1012 cm−2, maximum depth 3% for pulse terahertz radiation covering range frequencies from 0.1 2 THz.

We have studied the low-temperature (T=6K) optical properties of a series InGaN∕GaN single-quantum-well structures with varying indium fractions. With increasing fraction peak emission moves to lower energy and strength exciton–longitudinal-optical (LO)-phonon coupling increases. The Huang–Rhys factor extracted from Fabry–Pérot interference-free photoluminescence spectra has been compared results model calculation, yielding value approximately 2nm for in-plane localization length scale...

Localization lengths of the electrons and holes in InGaN/GaN quantum wells have been calculated using numerical solutions effective mass Schr\"odinger equation. We treated distribution indium atoms as random found that resultant fluctuations alloy concentration can localize carriers. By a locally varying function we contribution to potential energy carriers from band gap fluctuations, deformation potential, spontaneous piezoelectric fields. considered effect well width these contribute...

There is a great deal of interest in the underlying causes efficiency droop InGaN/GaN quantum well light emitting diodes, with several physical mechanisms being put forward to explain phenomenon. In this paper we report on observation reduction localization induced S-shape temperature dependence peak photoluminescence energy increasing excitation power density. This key fingerprint carrier localization. Over range density where depth S shape reduced, also observe integrated intensity per...

We have used anodization techniques to process porous surface regions in p-type Czochralski Si and Si0.85Ge0.15 epitaxial layers grown by molecular beam epitaxy. The SiGe were unrelaxed before processing. observed strong near-infrared visible light emission from both systems. Analysis of the radiative nonradiative recombination processes indicate that is consistent with decay excitons localized structures one or zero dimensions.

Discrete peaks are seen in the photoluminescence excitation spectra of GaAs-(AlGa)As multiple-quantum-well samples which we identify as excited $2s$ state $n=1$ heavy- and light-hole excitons. The $1s\ensuremath{-}2s$ splitting excitons is accurately determined combined with calculations heavy-hole exciton binding energy to give an accurate determination ground state.

The optically detected magnetic resonance of electrons and excitons in type-II GaAs/AlAs quantum wells has been studied as a function the orientation well with respect to direction field. An analysis anisotropy reveals that for AlAs layers thinner than \ensuremath{\sim}55 A\r{} ${X}_{z}$ conduction-band valley lowest energy while thicker ${X}_{x}$ ${X}_{y}$ valleys are energy. This is consequence lattice-mismatch strain splitting X conduction band which dominates confinement A\r{}.

Using a mixed type-I/type-II GaAs/AlAs multiple-quantum-well sample, we have demonstrated an optically controllable and tunable terahertz (THz) filter. Long-lived electron–hole pairs in the quantum wells allow for efficient THz attenuation over large spot size (2 mm) extremely low optical cw power. This sample can also be used as phase shifter. The induced change of GaAs from dielectric to conducting material leads observed shifting wave forms.

The first demonstration has been made of the transmission an audio signal via a THz communication channel using recently developed room temperature semiconductor modulator which is based on depletion two-dimensional electron gas. A standard time-domain spectroscopy setup modified to transmit signals up 25 kHz over 75 MHz train broadband pulses.

We report the results of low-temperature photoluminescence and excitation studies short-period, n=m, (GaAs${)}_{\mathrm{n}}$-(AlAs${)}_{\mathrm{m}}$ superlattices fabricated by molecular-beam epitaxy. Values n ranged between 2 8. find that smallest energy gap does not approximate to an ${\mathrm{Al}}_{0.5}$${\mathrm{Ga}}_{0.5}$As alloy until n+m\ensuremath{\le}4 monolayers. The limits a simple Kronig-Penney model electronic states are explored in relation our observations. For direct gap,...

A detailed experimental study of the real-space \ensuremath{\Gamma}-X transfer in type-II GaAs/AlAs short-period superlattices and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As/AlAs multiple-quantum-well structures is presented. Transfer times on a subpicosecond picosecond time scale are observed. The constants critically depend thickness (Al,Ga)As layers, but not AlAs-layer samples studied. rate determined by spatial overlap \ensuremath{\Gamma} X wave...

We have directly measured the real-space transfer times associated with \ensuremath{\Gamma}\ensuremath{\rightarrow}X intervalley scattering in type-II GaAs/AlAs superlattices by femtosecond optical pump and probe spectroscopy. domonstrate that rate for this unique process connecting electron states different slabs of superlattice is related to spatial overlap electronic envelope wave functions satellite minima.

We report the results of a systematic investigation effects decreasing AlAs layer thickness from 41 to 5 A\r{} on band alignment GaAs/AlAs quantum wells in which GaAs was kept constant at nominally 25 A\r{}. Combining techniques photoluminescence and excitation spectroscopy we have mapped out both direct \ensuremath{\Gamma}-related gap X-\ensuremath{\Gamma} as function thickness. observe reversal align- ment type-II type-I arrangement when is reduced below \ensuremath{\sim}13 In addition,...

Photoluminescence spectra from Al0.37Ga0.63As/AlAs multiple quantum well structures with staggered band alignments are presented which provide the first direct optical measure of valence-band offset at a semiconductor heterojunction. The experiment takes advantage crossover occurring critical aluminum concentration above indirect X minima in AlAs become lowest energy conduction bands system, and recombination occurs across interface. resulting emission fixes ΔEv =342±4 meV for this structure.

In this paper, we compare and contrast the experimental data theoretical predictions of low temperature optical properties polar nonpolar InGaN/GaN quantum well structures. both types structure, at temperatures are governed by effects carrier localisation. structures, effect in-built electric field leads to electrons being mainly localised width fluctuations, whereas holes regions within wells, where random distribution local minima in potential energy. This a system independently holes....

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, general, lower internal efficiencies than their blue-emitting counter parts, a phenomenon referred as “green gap.” One of main differences between green-emitting samples is that well growth temperature for structures at longer wavelengths, order reduce effects In desorption. this paper, we report on impact optical properties InGaN/GaN 460 nm 530 nm. It was found both sets...

Direct evidence for In-segregation in InGaN/GaN quantum-well structures is given via highly spatially resolved energy dispersive x-ray analysis performed a dedicated scanning transmission electron microscope. The In fluctuations become increasingly pronounced the vicinity of dislocations. latter assist diffusion and cause severe Ga/In intermixing.

We present the first high-resolution excitation spectra of (Al,Ga)As multiple-quantum-well structures grown on substrates with different orientations [(001), $(111)B$, and (310) planes]. The features in these can be consistently assigned by a single set effective masses sophisticated eight-bank $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ calculation. In this way, we obtain very directly anisotropy valence bands GaAs. $0.34{m}_{0}$ $0.094{m}_{0}$ for heavy hole light...

The impact of trench defects in blue InGaN/GaN light emitting diodes (LEDs) has been investigated. Two mechanisms responsible for the structural degradation multiple quantum well (MQW) active region were identified. It was found that during growth p-type GaN capping layer, loss part enclosed within a defect occurred, affecting top-most QWs MQW stack. Indium platelets and voids also to form preferentially at bottom presence high densities LEDs relate significant reduction photoluminescence...

In this paper we present a detailed analysis of the structural, electronic, and optical properties an $m$-plane (In,Ga)N/GaN quantum well structure grown by metal organic vapor phase epitaxy. The sample has been structurally characterized x-ray diffraction, scanning transmission electron microscopy, 3D atom probe tomography. have studied photoluminescence (PL), time-resolved PL spectroscopy, polarized excitation spectroscopy. spectrum consisted very broad line with high degree linear...

We present a detailed theoretical analysis of the electronic and optical properties $c$-plane $\mathrm{In}\mathrm{Ga}\mathrm{N}$/$\mathrm{Ga}\mathrm{N}$ quantum-well structures with $\mathrm{In}$ contents ranging from 5% to 25%. Special attention is paid relevance alloy-induced carrier-localization effects ``green gap'' problem. Studying localization length electron-hole overlaps at low elevated temperatures, we find are crucial for accurate description...

From room-temperature measurements of the photoluminescence decay time, values for sum interface recombination velocities in a series GaAs/AlGaAs double heterostructures have been obtained. The effects various combinations prelayers GaAs and AlGaAs investigated we show that it is possible to reduce as low 60 cm/s.

We report a room-temperature study of the photoluminescence observed from high-quality, molecular-beam-epitaxy grown GaAs-(AlGa)As multiple-quantum-well structure. The spectrum is dominated by free-exciton emission. This assignment inferred use excitation spectroscopy.