bluuebunny/crossref_metadata_2025 huggingface dataset:
Large, Low Voltage Absorption Changes and Absorption Bistability in Novel, Three-Step Asymmetric Quantum Wells
Authors: Trezza J. A. , Larson M. C. , Lord S. M. , Harris J. S.
Published: February 2023

Optoelectronic devices which use large absorption changes in quantum wells typically use the Quantum Confined Stark Effect (QCSE).1 Negative differential absorption modulation (NDAM), which entails high absorption at zero field and lower absorption at large bias, is limited by the shifting of light hole excitons. Although the excitons are quenched with high bias, the devices require very high electric fields to produce any substantial absorption drop. Here we demonstrate a method for obtaining a higher degree of NDAM than is obtainable through the QCSE and at a far lower voltage than is typically required by the QCSE. In addition, at other wavelengths the same device displays positive differential absorption modulation (PDAM). Finally, the devices can display absorptive bistability. These characteristics make it uniquely suited for use in vertical cavity modulators2, self electro-optic effect devices (SEEDs)3, and waveguide devices, as well as a whole host of new devices.
Mixing of Electronic States and Control of Optical Transitions in Asymmetric Triple Quantum Well Structures
Authors: Sawaki N. , Fukuta S. , Goto H. , Suzuki T. , Ito H. , Hara K.
Published: February 2023

The resonance of electronic states, or the mixing of wave functions in semiconductor coupled quantum wells has attracted much attention, because of the physical interest as well as a possibility attaining novel functional devices in electro-optical applications [1,2]. In this paper, we will study the mixing of the electronic states in coupled triple quantum well structures(TQW’s). The coupling of the electronic states is a strong function of the external field applied perpendicular to the heterointerface, which enables us to control the optical oscillator strength.
High Contrast Reflection Electro-Absorption Modulator With Zero Phase Change
Authors: Trezza J. A. , Pezeshki B. , Larson M. C. , Lord S. M. , Harris J. S.
Published: February 2023

Vertical cavity quantum-well optical modulators utilizing the quantum-confined Stark effect (QCSE) are being increasingly investigated for use in optical communication and computing.1 Reflection modulators based upon large absorption changes in quantum wells have shown high contrast ratios2 while exhibiting lower parasitic phase modulation than conventional waveguide modulators.3 Since quantum wells are capable of large absorption changes (Δα), they also exhibit large refractive index changes (Δn).4-5 Understanding the role of quantum well excitons and phase is crucial for high speed optical switching since such switching will be critically limited by Δn induced pulse broadening. The ratio of phase shift to absorption is typically reported through the chirp parameter where a low chirp parameter is desirable for low-dispersion amplitude modulation. Here we describe how parasitic Δn can be eliminated in a novel, optimized structure thus yielding a pure reflection modulator with a zero chirp parameter. At the operating wavelength, such a device would exhibit a high reflectivity change and zero phase change when switched between two bias points. We have designed and developed such devices by analyzing excitonic lineshapes, numerically simulating our structures including quantum well absorption and dispersion effects, and creating a flexible modulator design which allows for optimization after growth. We note that our theory also applies to eliminating Δn in waveguide modulators which rely upon the QCSE.
Quantum Mechanical Oscillations of the Electron Capture Time in Quantum Wells
Authors: Deveaud B. , Morris D. , Regreny A. , Barros M. , Becker P.
Published: February 2023

When a quantum well is surrounded by large barriers (i.e. larger than the mean free path of the electrons) the capture mechanisms are dominated by diffusive motion of the electrons in the banders. This is the situation governing the capture process for example in a separate confinement heterostucture laser [1]. In working conditions, the limiting times correspond to the slow diffusion of holes.
Responsivity and Excitonic Electroabsorption in Proton-Implanted GaAs/AlGaAs Multiple Quantum Well Modulators
Authors: Woodward T. K. , Tell B. , Knox W. H. , Stark J. B. , Asom M. T.
Published: February 2023

Heavily implanted MQW structures have not been examined as a function of applied bias in a pin geometry. Such studies address the interesting physical question of whether phenomena such as sharp excitons and quantum confined stark effect (QCSE), normally associated with ultra-clean material can persist amid the controlled introduction of defects.[1] We have studied several such MQW pin samples, each of which was grown on a quarter-wave dielectric reflecting stack mirror consisting of Al0.11Ga0.89As and AlAs layers. Devices contained 60 periods of GaAs quantum wells 100 Å thick with 60 Å Al
x
Ga1-
x
As barriers having mole fractions of x=0.3, 0.45, and 1.0. Devices were implanted with roughly 130 keV protons, focusing the damage into the intrinsic regions, to dose levels of 1 × 1012cm−2, 1 × 1013cm−2, and 1 × 1014cm−2. Large-area mesa devices were then fabricated from these structures via standard lithographic techniques. We have previously reported the behavior of x=0.3 barrier samples.[2]
Nonlinear optical properties in infrared region in quantum well ---- an application of intersubband transitions
Authors: Khurgin J. B. , Li Shaozhong
Published: February 2023

Substantial effort has been recently dedicated to the study of the
infrared nonlinear optical properties of the intersubband transitions
(IST) in different quantum well structures. The large oscillator
strength of 1ST gives it a great potential application in infrared
nonlinear optical devices, such as detection and frequency conversion.
In this work, we extensively investigated the nonlinear optical
susceptibilities due to the IST’s in different bands and the
comparison with band-to-band transition is also made.
Intersubband Transitions in High Indium Content InGaAs / AlGaAs Quantum Wells Grown on GaAs with a Graded InGaAs Buffer
Authors: Chui H. C. , Lord S. M. , Harris J. S. , Fejer M. M.
Published: February 2023

Large intersubband transition energies are interesting for applications in quantum well infrared photodetectors (QWIPs) and nonlinear optical frequency conversion devices. QWIPs have recently been a topic of interest for applications in high speed detector arrays.1 By using large energy intersubband transitions in quantum wells, the useful range of these QWIPs can be extended to the 3-5μm atmospheric window. With the demonstration of large nonlinear optical susceptibilities in quantum wells,2 application of large intersubband transition energies to frequency conversion devices is also of interest. Large intersubband transition energies have been observed in GaAs / AlAs (E16 = 434meV)3 as well as InGaAs / InAlAs on InP quantum wells (E12 = 400meV for strained, E12 = 295meV for unstrained).4,5,6 By using pseudomorphic InGaAs / AlGaAs quantum wells, the conduction band offset AEC is further extended.7 However, the lattice mismatch of InGaAs and AlGaAs typically limits the range of indium content available. By using a compositionally graded buffer, Lord, et. al.8 have demonstrated that high quality In(0.5)Ga(0.5)As / AlGaAs quantum wells can be grown on a GaAs substrate. Using this novel growth technique, we report the first observation of intersubband transitions in high indium content InGaAs / AlGaAs quantum wells.
Quantum Non-Demolition Measurement of Photon Number using a Mesoscopic Electron Interferometer
Authors: Shimizu Akira
Published: February 2023

Quantum phenomena in low-dimensional electron systems have been attracting much attention of semiconductor physicists and engineers for the last few decades. However, most discussions concern either electron transport or responses to classical electromagnetic fields. On the other hand, non-classical effects of light are a subject of growing interest in quantum optics. In this case, however, electronic systems are usually limited to either atoms or effective media (which are phenomenologically described to induce photon-photon couplings). The purpose of this talk is to give a brief introduction to “fully-quantum optoelectronics,” in which electrons confined in low-dimensional semiconductors are assumed to interact with quantized electromagnetic fields.
Multi-Quantum Barrier (MQB); — Is It a Good Spice for Semiconductor Laser Performances ? —
Authors: Iga K.
Published: February 2023

We use the double heterostructure (DH) in most of current semiconductor lasers for the purpose of confinement of both optical field and carriers as well1. In order to prevent electrons from leaking over the hetero-barrier of a p-type cladding, it is known that more than 300 meV of built-in potential difference is usually required2. But in some cases such as high power and high temperature operations, much higher barrier height is preferable. However, enough barrier height is not sometimes available due to the material limitation, e.g., in short wavelength GaAlInP based red-orange lasers and II-VI based blue-green ZnCdSSe or blue ZnMgSSe systems3.
Ultrafast All-Optical Switch with Switch-Off Time Unlimited by Carrier Lifetime
Authors: Tajima K. , Nakamura S.
Published: February 2023

All-optical switches are expected to become one of key elements in future ultrafast and flexible all-optical communication networks. And it has been generally believed that such all-optical devices would require very fast, as well as very efficient, nonlinear optical material (or phenomena). In fact, the well-known and often discussed figure of merit for nonlinear materials [n2/(ατ), where n2 is the nonlinear refractive index change coefficient, α is the linear absorbance, and τ is the relaxation time] implies that it is the chosen nonlinear material that determines the basic device performance such as the switching speed and energy. In this paper, we show that this is not necessarily the case; the speed of a nonlinear optical switch proposed by the authors1,2 not restricted by the slow relaxation time of high efficiency incoherent nonlinearities.
Exciton Dynamics in InGaAs/GaAs Quantum Dots
Authors: Wang G. , Sun C-K , Leonard D. , Riberio G. M. , Bowers J. E. , Petroff P. M. , Oshinowo J. , Arakawa Y.
Published: February 2023

Photoluminescence lifetimes of InGaAs quantum dots and monolayers are compared. The dynamics of localized and free excitons in quantum structures are measured under different pump intensity.
Squeezed Light Generation in Semiconductors
Authors: Fox A.M. , Baumberg J. J. , Dabbicco M. , Huttner B. , Ryan J.F.
Published: February 2023

The signal to noise ratio of optical systems is ultimately limited by the shot noise due to the Poissonian statistics of the light field. In recent years there has been a considerable effort to find ways to overcome this limitation by generating non-classical light with sub-shot noise statistics. Several groups have demonstrated non-classical light generation in diode lasers or light emitting diodes, and the amplitude fluctuations have been reduced substantially below the shot noise level [1,2]. However, for phase-sensitive measurements it is necessary to generate the more general quadrature squeezed states. Such quadrature squeezed light can be generated either by second-order or third-order nonlinear processes provided the nonlinear material has very low losses at the optical wavelength. To date, the successful generation schemes for quadrature squeezed light have been restricted to atomic vapours, optical fibres, or second-order nonlinear crystals [3]. The possibility of using the large χ(3) nonlinearities of semiconductors at frequencies below the band gap where the optical absorption is small has been discussed in the literature, but so far there have been no successful experiments [4-6]. In this paper we report measurements on GaAs/Al0.3Ga0.7As multiple quantum well waveguides and bulk ZnS in the wavelength range 750 - 890nm. Although we measure much larger nonlinearities in the quantum wells, the strong two-photon absorption is detrimental for squeezed light generation. However, in the ZnS where the laser frequency is below the two- photon absorption edge, we have succeeded in generating quadrature squeezed light in a semiconductor for the first time. On the basis of our results, we would expect that squeezed light could be generated in many other semiconductor systems provided the photon energy is less than half the band-gap energy.
Cavity Characteristics of Selectively Oxidized Vertical-Cavity Lasers
Authors: Choquette K. D. , Lear K. L. , Schneider R. P. , Hadley G. R. , Geib K. M. , Kilcoyne S. P.
Published: February 2023

Vertical-cavity surface emitting lasers (VCSELs) are of interest from both scientific and technological points of view. For example, distributed Bragg reflector (DBR) mirrors used to produce microcavities with a single longitudinal mode have been employed to study novel optical phenomena and are critical to VCSEL performance. Optical and electrical confinement in the transverse direction has been commonly achieved using etched post index-guided structures, or ion implanted "gain-guided" devices. We report the optical and electrical properties of VCSEL diodes fabricated using a buried oxide layer with a current aperture within an all semiconductor DBR mirror. We show this oxide layer has profound implications, leading to new transverse optical effects in the cavity as well as significant advances in VCSEL performance.
Optical Properties and Transport Properties of Self Assembled Quantum Dots
Authors: Petroff P.M. , Schmidt K. , Meideiros-Ribeiro G. , Leonard D.
Published: February 2023

We will discuss the photoluminescence, modulated photoluminescence and transport properties in InAs and InAlAs self assembled quantum dots. We will also show evidence of three dimensional carrier confinement above 77K.
Excitonic spin-flip dynamics under resonant two-photon excitation in quantum wells
Authors: Lohner A. , Michler P. , Rühle W. W. , Köhler K.
Published: February 2023

The detailed dynamics of resonantly excited nonthermal excitons in quantum wells has been investigated recently [1,2]. Various fit parameters were necessary to describe the time evolution of the heavy-hole exciton luminescence. Comparable and therefore not easily distinguishable rates for the radiative recombination, the spin relaxation, and the momentum relaxation of excitons were obtained. In particular, the flip of the spin of optically active (J=±1) into optically inactive (J=±2), ”dark” excitons plays an important role in the analysis since these dark excitons serve as a huge, invisible reservoir in the overall dynamics.
Anizotropy and dispersion of the optical rectification in the symmetric quantum wells
Authors: Khurgin J. B.
Published: February 2023

Generation of the far-infrared light by the optically excited semiconductors have been reported by numerous groups of researchers [1,2] While such various mechanisms as current surge and the depletion field-induced optical rectification (OR) have been proposed, recent results [3] have shown that the bulk OR accounts for a major portion of the observed teraherz signal. Recently [4] we have evaluated the OR coefficients of the bulk zinc-blende semiconductors excited above the bandgap and obtained the results in agreement with the experimental data. We have shown that the OR has its origin in the asymmetry of bonding orbitals in the valence band.
Pulse Propagation and Many-body Effects in Semiconductor Four Wave Mixing
Authors: Schulze A. , Knorr A. , Koch S.W.
Published: February 2023

The simultaneous influence of pulse propagation and Coulomb many-body interaction in Four Wave Mixing experiments is theoretically studied using the Semiconductor-Maxwell-Bloch equations. In this framework, the propagation of the optical fields and the microscopic interaction of the light with the semiconductor are treated consistently. The Maxwell equation is used as a reduced wave equation and the many-body Coulomb interaction are treated at the level of a screened Hartree-Fock approximation including phenomenological decay terms. We have analyzed the interplay of the propagation and Coulomb effects by calculating the Four Wave Mixing signal (FWMS) for different sample lengths and various excitation conditions, i.e, for pulses with different intensities at the exciton and in the continuum.
Generation of Far Infrared Radiation Using Compositionally-Asymmetric Multiple Quantum Well Waveguides
Authors: Saif Babak N. , Seery Bernard D. , Khurgin Jacob , Wood Colin
Published: February 2023

NASA's Earth and space science missions have motivated the investigation of methods to produce coherent radiation in the 1-3 terahertz (THz) spectral region, corresponding to 100-150 μm wavelength, for use as local oscillator sources in high resolution laser heterodyne spectrometers. Scientific applications of this technology include measurements of the hydroxyl radical (OH) at 2.5 THz in Earth's upper atmosphere, which is important because of its role in the destruction of ozone. In addition, astrophysicists are interested in spectroscopy of the interstellar molecular cloud in this previously unexplored region of the electromagnetic spectrum. However, these measurements nessitate a space-based instrument because the lower atmosphere is largely opaque in this spectral region.
Equal Pulse Correlation in GaAs thin films with Near-field Microscopy
Authors: Smith S. , Orr B.G. , Kopelman R. , Norris T.
Published: February 2023

We are developing a femtosecond Near-field Scanning Optical Microscope (NSOM) with the aim of probing ultrafast optoelectronic processes in semiconductor materials and devices with sub-wavelength spatial resolution. Here we present preliminary results from an Equal Pulse Correlation^) (EPC) measurement in GaAs thin films (1 |im thick) taken using our near-field microscope. These results demonstrate the possibility of making highly localized, femtosecond carrier relaxation and/or carrier diffusion measurements in a semiconductor thin film.
Fast Coherent Vertical Exciton Transport in Multiple Quantum Wells
Authors: Citrin D. S.
Published: February 2023

In superlattices in which the barriers are sufficiently narrow and low, the low-temperature vertical transport of excitons is due to quantum-mechanical tunneling between successive quantum wells (QW).[1] For structures with wide and high barriers [multiple QW’s (MQW)], the interwell coupling is due to the dipole-dipole interaction.[2] The context for treating coherent effects of this sort is exciton-polariton theory.[3] Exciton transport has been of interest in various molecular systems,[4] where the picture is of incoherent Förster transport.[5]. The MQW provides a tailor-made system of which an individual structure can be studied, while data on molecular systems must be frequently interpreted in terms of ensembles. There has been little experimental or theoretical[6] work on this type of vertical transport in MQW’s, although incoherent transport in such structures has been the subject of one study.[7]
Femtosecond Near-field Spin Spectroscopy in Digital Magnetic Heterostructures
Authors: Levy J. , Nikitin V. , Kikkawa J. M. , Awschalom D. D. , Garcia R. , Samarath N.
Published: February 2023

The nature of electronic spin-scattering is central to a wide class of condensed matter systems, ranging from semiconductor quantum wells, magnetic multilayers and granular materials, high-Tc superconductors, Kondo insulators, and magnetic semiconductor quantum structures. The latter class of systems is particularly appealing because one can tailor both the electronic and magnetic properties using MBE techniques. Time-resolved spectroscopies allow one to probe both the electronic and magnetic dynamics within ultrafast timescales, but spatial information is typically diffraction-limited to the wavelength of light. Near-field scanning optical microscopy (NSOM) [1] overcomes this limit, and when combined with femtosecond time resolution and polarization analysis, provides direct information regarding carrier and spin dynamics in both space and time.
Effects Of Two-Photon Absorption In Saturable Bragg Reflectors In Femtosecond Solid State Lasers
Authors: Obeidat Amjad T. , Knox Wayne H. , Khurgin Jacob B.
Published: February 2023

The process of two-photon absorption (TPA) in semiconductors plays an important role at frequencies below the bandgap where it can dominate other absorption processes. TPA has been observed and studied in semiconductor materials of different composition and dimensionality1-3, and, while TPA may have useful applications in such devices as optical memories and switches, more often than not it can severely limit the performance of electro-optic devices, especially at high intensities. For example, due to TPA, the insertion loss of saturable absorbers and other optical switches can become prohibitively high for intracavity applications requiring minimal losses. In this paper we will discuss TPA in a saturable distributed Bragg reflectors (DBR) recently used for mode-locking in a femtosecond, a diode-pumped Cr:LiSAF laser4. The focused intensity on the DBR is about 5 GW/cm2, well into the regime for strong TPA. Yet the DBR exhibits a reflectivity in excess of 99%. Clearly, the DBR structure itself must be minimizing the effects of tpa.The saturable DBR used in ref.(4) is simply a DBR with a single quantum well in the first quarter-wavelength layer. However, we will study TPA in a simple DBR structure since the quantum well is very thin. The DBR is made of GaAs/AlAs, a material with a TPA coefficient of β = 0.05cm/MW1. Thus, one expects to see absorption in excess of α = 104 cm-1 (i.e 45% per round trip through reflector) which would certainly degrade the reflectivity of the saturable DBR.
Fabrication and Characterization of Si Dots Prepared by Self-Organized Recrystallization
Authors: Tsybeskov L. , Hirschman K. D. , Duttagupta S. P. , Hall D. G. , Fauchet P. M.
Published: February 2023

The photoluminescence (PL) in crystalline silicon (c-Si) has been investigated during the last decades. Interest has focused on the visible PL that is observed in Si nanoclusters and in porous Si (PSi), the infrared PL in silicon-germanium superlattices, and the subgap PL due to impurities in c-Si [1]. Whereas strong room-temperature PL has been demonstrated in the visible with porous silicon, band edge PL in bulk Si is inefficient and usually observed only at low temperatures. The electroluminescence (EL) is as inefficient as the PL, and, in addition, the EL is quenched by an electric field E ≥ 104V/cm due to field-induced dissociation of the exciton [2]. A result of the indirect bandgap of Si, bandgap luminescence is extremely weakly reabsorbed by Si. It follows that the light generated, propagated, and detected at the Si bandgap would not disturb the Si microelectronic circuitry with which it shares a chip, a situation that is very desirable for systems applications.
Reflection Properties and Defect Formation in Metallic Photonic Crystals
Authors: Özbay Ekmel , Temelkuran Burak , Sigalas M. , Tuttle G. , Soukoulis C.M. , Ho K.M.
Published: February 2023

Photonic crystals are three-dimensional periodic dielectric structures where the propagation of electromagnetic (EM) waves can be forbidden for a certain range of frequencies.1-2 Early attempts to use these structures in applications like thresholdless semiconductor lasers and single-mode light-emitting diodes have suffered from the difficulties associated with fabricating sub-micron features needed to achieve a band gap at optical frequencies. On the other hand, fabricating photonic band gap (PBG) structures at microwave and millimeter-wave scales3 have been more successful, with numerous demonstrations of PBG-based applications like high directivity millimeter wave antennas, high-quality resonators, microwave cavities for accelerators, and efficient microwave reflectors.
Observation of Photonic Bandgap in GaInAsP/InP 2D Photonic Crystals by Equivalent Transmission Measurement
Authors: Baba T. , Ikeda M. , Kamizawa N.
Published: February 2023

Semiconductor photonic crystals are promising candidates for realizing spontaneous emission control, i.e., enhancement of spontaneous emission rate (SER) and spontaneous emission factor. Schematic structure of various dimensions of photonic crystal and corresponding wave vector space inhibited by photonic bandgaps (PBGs) are summarized in Fig. 1. Due to the almost perfect PBG and single mode localized state, 3D structures are ideal. However, structures for optical wavelength range are still difficult to fabricate. We have studied 2D structures1,2) to confirm preliminary effects of photonic crystals. In this study, we simply predict the spontaneous emission control in 2D structures, and report the experiment to observe PBG in GaInAsP/InP 2D photonic crystals.
Relaxation dynamics of excitons and electron-hole pairs studied by spatiotemporal pump and probe experiments
Authors: Grosse S. , Arnold R. , Kriele A. , von Plessen G. , Kotthaus J.P. , Feldmann J. , Rettig R. , Marschner T. , Stolz W.
Published: February 2023

Ultrafast laser spectroscopy has been used extensively to study carrier relaxation phenomena in semiconductors and semiconductor nanostructures. Accordingly, several physical issues of the carrier thermalization and recombination scenario after optical excitation are well understood. This is particularly true for many III-V quantum well structures. However, there is a basic problem when using light-matter interaction to study carrier relaxation in crystals. As a consequence of (i) the conservation law for the total momentum and (ii) the vanishing momentum of visible light as compared to the extension of the Brillouin-zone only electron-hole (e-h) pair transitions with vanishing total wavevector
(K→=0) can be excited and detected, provided no other quasi-particle carrying momentum is involved in the optical transition.
Picosecond Switching using Resonant Nonlinearities in a Quantum Well Device
Authors: LiKamWa Patrick , Kan’an Ayman
Published: February 2023

Resonant nonlinearities in quantum well structures arise from exciton saturation and band-filling due to photogeneration of free carriers. Through the Kramers-Kronig’s relation, a corresponding change in refractive index occurs close to the bandgap energy where the absorption change occurs. The change in refractive index can effectively be used to produce optical switching in devices that can convert phase changes into intensity changes or directional switching1. Although the turn-on of carrier induced nonlinearities is effectively an instantaneous effect which follows the photon pulse, these photogenerated carriers tend to linger on well after the photon pulse has passed. The recovery time is usually governed by carrier relaxation times2,3 or carrier removal rates4. In this work, we demonstrate all-optical switching in a Y-junction device in which two control optical pulses are used for each switching event. The first control pulse flips the state of the switch while the second control pulse turns the switch back to its initial state. The switch dynamics is related to other carrier induced devices demonstrated by other independent researchers5,6.
Laser Annealing of Trap States in ZnSe Quantum Dots
Authors: Smith Christine A. , Risbud Subhash H. , Cooke J. Diane , Lee Howard W. H.
Published: February 2023

Our study of ZnSe quantum dots is motivated by the inherent interest in quantum confined systems and by the potential for shorter wavelength laser operation enabled by blue-shifted quantum confined energy levels. The optical and electronic properties of these nanocrystals as a function of the fabrication process were investigated with various optical techniques including photoluminescence (PL) lifetimes, and absorption, PL , and excitation spectroscopy.
Quantum Devices Using Multi-Dots Structures
Authors: Fagotto E. A. M. , Rossi S. M. , Moschim E.
Published: February 2023

Nowadays, due to the advances in nanolithography technology it is possible to fabricate structures whose electronic properties correspond to that of a quasi-one-dimensional electron gas. Such structures allow us to observe ballistic quantum transport at low temperatures, and remarkable experimental observations have resulted1. Many theoretical studies have investigated conductance fluctuations2 and voltage controlled defects. Cahay et al3 studied the problem of localization associated with the conductance fluctuations of an array of elastic scatterers. Joe et al4 discussed the effects of a voltage controlled impurity for the conductance of a single open quantum box. As the impurity size is changed, it causes conductance oscillations due to the interference of circulating and bound states of the quantum box. In this paper we analyze how changes in geometry of a structure with three open dots affect its electronic properties.
Observation of Quantum Confined Stark Effect in Strain Compensated GaInAsSb/AlGaAsSb Multiple Quantum Well Structures
Authors: Shi Yan , Zhao Jian H. , Sarathy Jiten , Olsen Greg , Lee Hao
Published: February 2023

The quantum confined Stark effect (QCSE) has been observed in quantum well structures of many different material systems, such as GaAs/AlGaAs [1]-[3] and InGaAs/InP [4]. Because of the steep rise at the absorption edge, coupled with the very high excitonic resonance peak, and its shift with the applied electric field, the QCSE has many applications in optoelectronics.
Computational Modeling of Ultrashort Pulse Propagation in Semiconductor Materials
Authors: Goorjian Peter M. , Agrawal Govind P.
Published: February 2023

An algorithm has been developed that solves the semiconductor Maxwell-Bloch [1], without making the standard slowly-varying envelope (SVEA) and rotating-wave (RWA) approximations. This more exact formulation is applied to simulations of the propagation of ultrashort pulses for which the standard approximations reach their limits. This development was motivated by the generation of optical pulses as short as 8 fs, which has become possible due to recent progress in ultrafast technology.
Vertical cavity surface emitting laser with self-assembled quantum dots
Authors: Nishi Kenichi , Saito Hideaki , Sugou Shigeo
Published: February 2023

Recently, low-dimensional quantum structures such as quantum dots (QDs) and quantum wires (QWIs), has been attracting much interest due to their novel physical properties and consequent improvements in device performances.1) When the ideal QD or QWI structures are achieved, higher gain and lower threshold current in laser diodes are expected.2) Among the many fabrication methods reported for such structures, self-assembled quantum-dot (SAQD) growth techniques3-5) are particularly notable. They positively utilize the islanding growth in highly strained heteroepitaxial systems, such as InGaAs on GaAs. The SAQDs can be simply fabricated by molecular beam epitaxy (MBE)3) or metal-organic vapor phase epitaxy (MOVPE)4),5) and they have high crystal quality and uniform size distributions of within 10% as well as high surface densities of more than about 1011cm-2. Using these SAQDs, low-threshold QD edge-emitting lasers have been fabricated.6-8) We expect to make even more advanced lasers, such as QD vertical-cavity surface-emitting lasers (VCSELs) using QDs in the active region.9) The QD-VCSEL is especially attractive for controlling both the electron and photon modes in a microcavity structure.10) When the cavity mode coincides with the narrow bandwidth light emission that originates from the delta-function-like density of states in uniform QDs, a high-performance light source with very low threshold current can be realized. On the other hand, the gain width, which critically determines the temperature characteristics of the VCSEL,11) can be designated in QD-VCSELs by controlling the dot size distribution. Therefore, for improving and modifying device performances, we believe that the QD-VCSEL is the optimum optical device utilizing the QD structure. In this article, we report the fabrication of a QD-VCSEL and the observation of lasing oscillation at room temperature.
Quantum Coherence of Hole Continuum States in GaAs Quantum Wells
Authors: Dekorsy T. , Kim A.M.T. , Cho G.C. , Hunsche S. , Bakker H.J. , Kurz H. , Chuang S.L. , Köhler K.
Published: February 2023

The investigation of quantum coherence excited by femtosecond laser pulses is one of the central topics in quantum optoelectronics. Up to now, most investigations in semiconductors and semiconductor quantum structures deal with quantum coherence of excitonic states. For two reasons the quantum coherence of continuum states has not been anticipated for a long time due to i) the expected high momentum scattering rates of continuum states and ii) the dispersion of the valence and conduction bands, which gives rise to a strong "inhomogeneous" broadening of the band-to-band transitions. Recently, optically excited quantum coherence has been observed, which was attributed to the phase coherence of continuum states in the conduction band. These observations include Bloch oscillations in superlattices [1,2] and free-electrons in Landau levels [3]. Most recently, quantum coherence in the valence band has been observed in GaAs quantum wells [4] and bulk GaAs [5]. Here, we report on the observation of quantum coherence of the first heavy and light hole subbands in a GaAs quantum well under excitation above the fundamental excitonic transitions [4].
Interferometrie Four-Wave-Mixing Spectroscopy on Semiconductors
Authors: Wehner M. U. , Hetzler J. , Wegener M.
Published: February 2023

In ultrafast nonlinear spectroscopy interferometric techniques can be applied both for heterodyne detection of the signal and for the excitation of the sample by phase-locked pulses, thus delivering coherent control [1] over the system. Such techniques have been predicted to be extremely sensitive with respect to the dynamics of elementary excitation [2] and have been applied to the study of non-Markovian dynamics of molecules [3, 4]. For the case of semiconductors, interferometric sensitivity has been employed for detection purposes [5] and the use of phase-locked pulses has been reported quite recently [6]. In this paper we report the observation of a novel interference phenomenon in interferometric four-wave-mixing due to contributions beyond the third order perturbational limit. An analysis of the observed interferences allows for an estimation of the importance of these higher order contributions.
Coherent Control Of Semiconductor Optoelectronic Properties
Authors: Haché A. , Kostoulas Y. , Atanasov R. , Fraser J. , Sipe J. , van Driel H.M.
Published: February 2023

Historically, phase has received little attention as a parameter which can be used to control the properties of matter. Recently, however, coherence control of physical and chemical properties of simple systems using two or more laser beams has been demonstrated [1-3]. The possibility of influencing the phase of matter by controlling the phase of light arises from the fact that two or more phased perturbations which can connect the same initial and final states in a system can lead to interference effects between the different quantum mechanical pathways and therefore influence the final state of matter. In this talk we report two manifestations of this effect in bulk semiconductors, namely the generation and control of carrier density and electrical currents [3] in a bulk, unbiased semiconductor when both initial and final states are in the continuum (valence and conduction bands). The observations of such effects is not only intellectually appealing but may point the way to novel device applications. In initial experiments, control has been achieved in GaAs at room temperature using picosecond and 100 fs optical pulses at 1550 and 775 nm. The talk will focus on the description of these phenomena in terms of quantum mechanics as well as nonlinear optics. The influence of beam parameters and sample characteristics will be discussed.
Stark Localization and Optical Properties of Superlattices Under an Electric Field
Authors: Mendez E. E.
Published: February 2023

Optical experiments in GaAs-GaAlAs superlattices under electric fields show the formation of a Stark ladder and the gradual localization of the electronic states, which at very high fields become confined to individual quantum wells.
Van Hove Type M1 Exciton and Stark Localization Exciton in GaAs-AlGaAs Superlattices under an Electric Field
Authors: Yan R. H. , Simes R. J. , Ribot H. , Coldren L. A. , Gossard A. C.
Published: February 2023

A field-dependent two-dimensional exciton due to a Van Hove type M1 singularity at the top of superlattice minibands has been observed in MBE grown superlattices for the first time at room temperature. The largest ever-reported room temperature two-dimensional heavy hole exciton shift up to ~30meV was observed by field-dependent photocurrent measurements.
Dynamic Switching Characteristics of Light Emission in Quantum Confined Field-Effect Light Emitters
Authors: Kan Y. , Yamanishi M. , Mukaiyama K. , Okuda M. , Ohnishi T. , Obata K. , Kawamoto M. , Suemune I.
Published: February 2023

Recently, field-induced modulations of optical properties of quantum well (QW) structures are of great interest because of their high speed switching capability. We have proposed a light emitting device1) which makes use of the field effect, instead of the change in carrier density, to result in a fast emission switching free from life time limitation. One of the key points to realize the proposed device was how to design a possible device structure which has the functions of carrier injection and of field control. In this paper, we report the dynamic switching characteristics of the practical field-effect light emitter2), demonstrating a life time free switching.
The Effects of Confinement on the Be-Acceptor in Narrow GaAs/AlGaAs Quantum Wells
Authors: Holtz P.O. , Doughty K. , Sundaram M. , Merz J.L. , Gossard A.C.
Published: February 2023

Electronic properties such as the binding energy of the ground state and the excited states of impurities confined in quantum wells (QWs) have been predicted in several theoretical papers. In the original calculation by G. Bastard [1] hydrogenic impurity potentials and infinite barrier heights were used, which resulted in continuously increasing binding energies with decreasing QW width. When more realistic finite heights for the barriers were used in the calculations, it was shown that the binding energy goes through a maximum at a non-zero QW width [2,3]. Thus, there has been recent progress with respect to the theoretical aspect of this subject, but there have been few experimental demonstrations of the properties of confined impurities.
Photoluminescence Studies of overgrown GaAs/AlGaAs MOCVD and MBE Quantum Dots..
Authors: Arnot H E G , Sotomayor-Torres C M , Cusco R , Watt M , Glew R , Beaumont S P
Published: February 2023

A comparison of the photoluminescence emission from MOCVD overgrown quantum dots (QDs) patterned in MOCVD and MBE grown starting material has been made. Before overgrowth luminescence was obtained from the QDs down to 750Å in diameter fabricated in MBE material whereas after overgrowth only the larger 3000Å QDs luminesce. However when MOCVD material is used the largest dots (3500Å) only luminesce after regrowth. With both types of material the QW emission shifts to higher energies after regrowth.
Fabrication and Optical High Speed Characterization of Phase-Shifted InGaAs/InP Multi Quantum Well DFB Structures
Authors: Korn M. , Forchel A. , Germann R. , Streubel K. , Cebulla U.
Published: February 2023

We have fabricated 1st order phase shifted DFB-gratings for the 1.5 µm wavelength range on MOCVD grown InGaAs/InP-multi quantum well (MQW) layers. The dynamic properties were investigated by a new optical method which allows to test the high frequency behaviour of the devices far into the GHz range.
Physics and Applications of Enhanced Quantum Size Effects in (111)-Oriented Quantum Wells
Authors: Suyama Takahiro , Hayakawa Toshiro , Hijikata Toshiki
Published: February 2023

Semiconductor superlattices and quantum wells (QWs) are very important as new man-made materials for novel electronic and photonic devices. These modulated semiconductor structures have been extensively investigated for the past decade; however, they have been prepared almost exclusively on (100)–oriented substrates. The recent progress in molecular beam epitaxy (MBE) has made it possible to grow "device-quality" AlGaAs layers on (111)- and (110)–oriented GaAs substrates.1-3 As a result of comparing several properties of QWs grown on both (111)- and (100)-oriented substrates, we have discovered that a variety of quantum size effects (QSEs) depend upon the quantization direction, that is, the growth axis. In this paper, the experimentally confirmed orientation-dependent QSEs are overviewed, and application to the QW laser is presented.
Tunable Quantum-Well Infrared Detector
Authors: Doughty K.L. , Holtz P.O. , Simes R.J. , Gossard A.C. , Maseijian J. , Merz J.L.
Published: February 2023

Infrared detectors (2-25 microns) have been a subject of much interest in recent years for defense and space exploration applications. Detectors built using II-VI compounds (for example, HgCdTe) have been investigated in depth, but suffer from the instability and nonuniformity of the materials, and from processing difficulties. Recently, quantum-well detectors using III-V compounds have been produced which demonstrate good detectivity in the 10 micron wavelength region 1,2. Their approach is based on inter-subband absorption in quantum-wells, or on confined-state to conduction-band transitions, and is limited to a fixed band of wavelengths for a given detector.
Photoluminscence and Photoluminescence Excitation Spectroscopy Study of Thin GaInAs/InP Quantum Wells
Authors: Reihlen E.H. , Persson A. , Wang T.Y. , Fry K.L. , Stringfellow G.B.
Published: February 2023

Photoluminescence excitation spectroscopy (PLE) has been widely applied to reveal information about the subband structure of quantum wells (QWs). PLE essentially probes the intersubband absorption in the well, which cannot be probed in transmission because of the low absorbances of single QWs. PLE is a standard characterization technique for AIGaAs/GaAs QWs due to the availability of tunable dye lasers as excitation sources in the AIGaAs/GaAs spectral regime (e.g. ref.[1]). There have been very few PLE studies on GaInAs/InP QWs because in this spectral regime there are no laser dyes commercially available. Kodama et al. [2] and Sauer et al. [3] have studied GaInAs/InP multiple QWs and observed transitions from the first three heavy and the first two light hole subbands to the respective electron subbands. Skolnick et al.[4,5], Sauer et al.[6,7], Razeghi et al. [8,9], and Temkin et al.[10] have studied GaInAs/InP single QWs, and observed transitions from the first five heavy and the first three light hole subbands to the respective electron subbands. Skolnick et al. [5] have tentatively assigned a feature in their spectra to absorption involving the first heavy hole subband and the InP (barrier) conduction band. In this study PLE spectra from extremely thin Gag0 47ln0 53AS /InP single QWs are investigated. The PL spectra from these samples exhibit narrow, intense multiplets, which have been attributed to recombination in regions of the wells, differing in width by single monolayers [11].
Time-Resolved Observation of Luminescence from a Charge-Transfer State in Double Quantum Wells
Authors: Norris T.B. , Vodjdani N. , Vinter B. , Weisbuch C. , Mourou G.A.
Published: February 2023

Time-resolved techniques have lately been applied to the study of the dynamics of tunneling in semiconductor quantum well (QW) structures.1,2 The physics of tunneling in coupled QW structures has also been a topic of much recent interest.2,3 We have applied the technique of time-resolved photoluminescence (PL) spectroscopy to investigate tunneling in a novel asymmetric GaAs/AlGaAs double QW structure. We report in this paper the direct observation of PL from a charge-transfer" (CT) state, which is built up by electron and hole tunneling in opposite directions between the QW's.
Effect of Numerical Aperture on Light Injection from Sources at the Core/Cladding Interface of a Fiber Optic Fluorosensor
Authors: Bryant Alvin , Albin Sacharia , Egalon C. O. , Rogowski R. S.
Published: February 2023

The fluorosensor discussed here is a fluorescent cladding optical fiber sensor. The sensitivity of such a sensor depends on the amount of light injected into the fiber core due to a fluorescent cladding. Conditions necessary for high injection, were experimentally determined for side excitation. Previous theoretical work has predicted that, for a side excited fiber, the refractive index difference between the core and cladding, ncore−nclad, must be maximized to achieve high sensitivity. This prediction has used the exact field solution of an optical fiber and was qualitatively verified in the present work. This shows that standard optical fibers used for communication, which are weakly guiding, are not suitable for fluorosensor applications. Another result shows that the light injection increases with the fiber diameter.
Thermally Induced Optical Effects in End-Pumped Lasers: A Discussion
Authors: Farrukh Usamah O.
Published: February 2023

Birefringence and thermally induced lensing in end-pumped laser rods and blocks are function of position. The temperature distribution is a function of the transverse and longitudinal coordinates and of time. The picture becomes more complicated when the pump beam is non symmetric. A discussion and data on the non symmetric temperature distribution is included.
Femtosecond Exciton Dynamics of II-VI Semiconductor Multiple Quantum Wells (Invited)
Authors: Johnson Anthony M.
Published: February 2023

Room temperature excitonic absorption peaks have been difficult to observe in II-VI semiconductors and has been attributed to strong exciton-phonon interactions. The first well-defined room temperature excitonic absorption peaks were measured in CdZnTe/ZnTe multiple quantum wells (MQWs), grown by molecular beam epitaxy on GaAs substrates. We report the first direct measurement of the relative bleaching strength of room temperature excitonic absorption by "cool" free or ionized electron-hole (e-h) pairs and "cold" excitons. In these II-VI MQWs, the exciton binding energy
(E
b

x
≈23meV), the longitudinal-optic (LO) phonon energy
(ℏωLO≈25 meV), and the thermal energy (kT ≈ 26 meV) are all comparable and thus the ionized e-h pairs are "cool" (ΔE ≈ 2 meV), in contrast to the "hot" ionized e-h pairs (ΔE ≈ 27 meV) generated in GaAs/AlGaAs MQWs
Ebx≈9 meV,ℏωLO≈36 meV. Utilizing 80 fs duration pump pulses to resonantly create a distribution of "cold" excitons followed by a broad band 14 fs probe pulse to measure the induced transmission, we found that the bleaching effect of "cold" neutral excitons on the excitonic absorption was nearly twice as strong as the same density of "cool" uncorrelated e-h pairs, in contrast to theoretical estimates. We have measured a very fast exciton ionization time, τion ≈ 110 fs, which agrees well with the measured homogeneous exciton linewidth broadening, supporting a model of thermal broadening due to the ionization of excitons through LO-phonon scattering. These are the first reported room temperature experiments on femtosecond exciton dynamics in II-VI semiconductor MQWs.
New Energy Levels Calculational Method Applicable to Biased Far Infrared GaAs Detectors
Authors: Farrukh Usamah O. , Jenkinson Howard A.
Published: February 2023

There is an interest in the technical community to develop efficient 10 µm detectors for the focal plane arrays. GaAs-AlGaAs quantum well detectors are one of these candidates. The detection principle in these systems is based on the concept of intersubband transitions. These far infrared detectors are normally biased. The energy levels in biased quantum wells shift downward and the peak of the electron positional probability shifts toward the deeper side of the quantum well potential. This paper presents an exact method to calculate the energy levels and positional probability in biased quantum wells.