Showing papers on "Quantum well published in 1985"
TL;DR: In this paper, a dipole occurs between two envelope states of the conduction-band electron wave function, and is called a quantum well envelope state transition (QWEST).
Abstract: A new type of optical transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction‐band electron wave function, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption for two structures with 65‐A‐thick‐ and 82‐A‐thick wells. The transitions exhibit resonant energies of 152 and 121 meV respectively, full width at half‐maximum linewidths as narrow as 10 meV at room temperature, and an oscillator strength of 12.2. The material is anticipated to have subpicosecond relaxation times and be ideal for low‐power optical digital logic.
902 citations
TL;DR: In this article, the effects of an exciton gas and an electron-hole plasma on the excitonic optical absorption in a two-dimensional semiconductor and compare these with recent experimental results on absorption saturation in single and multiple-quantum-well structures.
Abstract: We present theoretical results for the effects of an exciton gas and an electron-hole plasma on the excitonic optical absorption in a two-dimensional semiconductor and compare these with recent experimental results on absorption saturation in single- and multiple-quantum-well structures. A simple theoretical description of the nonlinear optical properties of these microstructures is developed for the case of low-density optical excitation near and above the band edge. We argue that the effects of Coulomb screening of excitons by the plasma are relatively weak in these structures but that the consequences of phase-space filling and exchange are significant in each case. We are able to explain the recent unexpected experimental result that ``cold'' excitons are more effective than ``hot'' carriers in saturating the excitonic absorption. Good agreement with the experimental data is obtained without adjustable parameters.
658 citations
TL;DR: In this article, a comprehensive discussion of optical transitions in these microstructures is given, including excitonic effects and the specific features of room-temperature exciton resonances.
Abstract: We review the nonlinear-optical effects observed at room temperature in semiconductor quantum-well structures photoexcited near the band gap. A comprehensive discussion of optical transitions in these microstructures is given, including excitonic effects and the specific features of room-temperature exciton resonances. Experimental investigations using continuous-wave, picosecond-, and femtosecond-laser sources are presented. They show extremely efficient nonlinear processes. In the case of excitations that are long compared with the exciton-ionization time, the induced changes in absorption and refraction do not depend on the wavelength or on the duration of excitation. These changes depend only on the density of absorbed photons and are interpreted in terms of electron–hole plasma screening and band filling. In contrast, for ultrashort excitation, nonlinear processes depend critically on the excitation wavelength. The selective generation of excitons is found to produce effects larger than a plasma of the same density. This unexpected result is shown to arise from the low temperature of the exciton gas before it interacts with the lattice and from the decrease of screening that is the reduced dimensionality of quantum-well structures.
321 citations
TL;DR: In this article, a negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region is proposed.
Abstract: We propose a new negative conductance device consisting of a heterojunction bipolar transistor with a quantum well and a symmetric double barrier or a superlattice in the base region. The key difference compared to previously studied structures is that resonant tunneling is achieved by high‐energy minority carrier injection into the quantum state rather than by application of an electric field. Thus this novel geometry maintains the crucial, structural symmetry of the double barrier, allowing unity transmission at all resonance peaks and higher peak‐to‐valley ratios and currents compared to conventional resonant tunneling structures. Both tunneling and ballistic injection in the base are considered. These new functional devices have significant potential for a variety of signal processing and multiple‐valued logic applications and for the study of the physics of transport in superlattices.
314 citations
TL;DR: The first direct determination of carrier-energy-loss rates in a semiconductor is reported, providing fundamental insight into carrier-phonon interactions in semiconductors.
Abstract: We report the first direct determination of carrier-energy-loss rates in a semiconductor. These measurements provide fundamental insight into carrier-phonon interactions in semiconductors. Unexpectedly large differences are found in the energy-loss rates for electrons and holes in GaAs/AlGaAs quantum wells. This large difference results from an anomalously low electron-energy-loss rate, which we attribute to the presence of nonequilibrium optical phonons rather than the effects of reduced dimensionality or dynamic screening.
269 citations
TL;DR: In this article, the authors investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers, and reveal the existence of gain saturation with current in structures with a small number of wells, pointing to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
Abstract: We investigate theoretically a number of important issues related to the performance of AlGaAs quantum well (QW) semiconductor lasers. These include a basic derivation of the laser gain, the linewidth enhancement factor α, and the differential gain constant in single and multiple QW structures. The results reveal the existence of gain saturation with current in structures with a small number of wells. They also point to a possible two-fold increase in modulation bandwidth and a ten-fold decrease in the spectral laser linewidth in a thin QW laser compared to a conventional double heterostructure laser.
269 citations
TL;DR: In this article, the density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments, which is given theoretically by the k. p method and is calculated for various semiconductor materials.
Abstract: The density-matrix theory of semiconductor lasers with relaxation broadening model is finally established by introducing theoretical dipole moment into previously developed treatments. The dipole moment is given theoretically by the k . p method and is calculated for various semiconductor materials. As a result, gain and gain-suppression for a variety of crystals covering wide wavelength region are calculated. It is found that the linear gain is larger for longer wavelength lasers and that the gain-suppression is much larger for longer wavelength lasers, which results in that single-mode operation is more stable in long-wavelength lasers than in shorter-wavelength lasers, in good agreement with the experiments.
265 citations
TL;DR: In this article, the authors derived the gain/current curves for a single quantum well and the optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers.
Abstract: Gain/current curves for a single quantum well are calculated. The optimum well number, cavity length, threshold current, and current density of multi-quantum-well (MQW) lasers are derived in terms of this gain curve. The limiting performance of MQW lasers is found to be better than that of graded refractive index (GRIN) lasers, assuming comparable efficiencies and spontaneous emission linewidths. The optimum threshold current for an MQW laser with a 7 μm cavity and 90 percent facet reflectivity is \sim50 \mu A/μm.
253 citations
TL;DR: In this article, the crystal orientation dependence of n− and p−type Si doping in molecular beam epitaxial GaAs was investigated and high electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes were demonstrated for the first time.
Abstract: Results on crystal orientation dependence of n‐ and p‐type Si doping in molecular beam epitaxial GaAs are presented. High electron and hole mobilities in AlGaAs/GaAs heterostructures on high index planes are demonstrated for the first time. The doping results should prove useful for various transistor structures and complementary circuits. Also, due to the differences in the band structure for different orientations, quantum well heterostructures are likely to exhibit many interesting phenomena which are strongly orientation dependent.
207 citations
TL;DR: A substantial density of states between Landau levels is revealed, even in high-mobility single quantum wells, with no existing theoretical explanation for this anomaly.
Abstract: The density of states of two-dimensional electron systems in GaAs/AlGaAs single-layer and multilayer heterostructures has been determined through measurements of the high-field magnetization. Our results reveal a substantial density of states between Landau levels, even in high-mobility single quantum wells. There is no existing theoretical explanation for this anomaly.
197 citations
TL;DR: In this paper, a doubly resonant laser cavity driven by such atomic configurations can have vanishing diffusion coefficient for the relative phase angle for the Hanle effect in quantum beat and Hanleeffect experiments.
Abstract: In quantum-beat and Hanle-effect experiments, spontaneous-emission events from two coherently excited states are strongly correlated. A doubly resonant laser cavity driven by such atomic configurations can have vanishing diffusion coefficient for the relative phase angle.
TL;DR: In this article, the authors used molecular beam epitaxy to grow GaAs/AlGaAs on (100) oriented Ge and Si substrates, and showed that the antiphase disorder was contained within the 250-Athick initial layer which was grown at a 0.1-μ/h growth rate at a substrate temperature of 500 °C.
Abstract: Using molecular beam epitaxy, we have successfully grown device quality GaAs/AlGaAs on (100)‐oriented Ge and Si substrates. Modulation doped field effect transistors have been fabricated from these layers which exhibit room‐temperature transconductances as high as 160 and 170 mS/mm for layers on Ge and Si, respectively, and showed no looping in either case. At 77 K, these values rose to 345 and 275 mS/mm for Ge and Si, respectively. Analysis by transmission electron microscopy of layers grown on Ge showed that the antiphase disorder was contained within the 250‐A‐thick initial layer which was grown at a 0.1‐μ/h growth rate at a substrate temperature of 500 °C. For both the layers grown on Si and Ge specular surface morphologies were obtained. The photoluminescence of GaAs/AlGaAs quantum wells grown on Si and Ge was similar in intensity to the same quantum well structures grown on GaAs. In quantum wells grown on Ge, the luminescence was dominated by a donor‐acceptor recombination at 1.479 eV, which appears to be Ge0Ga ‐Ge0As. These results show that high‐quality GaAs/AlGaAs is obtainable on nonpolar substrates, which has important implications for the monolithic integration of III‐V’s with Si.
TL;DR: In this article, the optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation-doped heterojunctions at room temperature.
Abstract: The optical modulation technique of photoreflectance (PR) has been applied to characterize the interband transitions in GaAs/AlGaAs multiple quantum wells (MQW) and modulation‐doped heterojunctions at room temperature. The spectra of the MQW show ‘‘derivativelike’’ reflectance features due to allowed interband transitions from heavy and light hole subbands to conduction subbands, and the E0(Γ8,v→Γ6,c) transitions of the AlGaAs layers. Our data are consistent with a square well calculation using a conduction‐band offset of 60% of the band‐gap discontinuity. For modulation‐doped heterojunctions, a correlation is observed between a PR feature approximately 18 meV above the GaAs fundamental gap and the presence of a two‐dimensional electron gas.
TL;DR: In this article, the authors describe high electron mobility transistors (HEMT's) utilizing a conducting channel which is a single In 0.15 Ga 0.85 As/GaAs interface.
Abstract: This letter describes high electron mobility transistors (HEMT's) utilizing a conducting channel which is a single In 0.15 Ga 0.85 AS quantum well grown pseudomorphically on a GaAs substrate. A Hall mobility of 40 000 cm2/V.s has been observed at 77 K. Shubnikov-de Haas oscillations have been observed at 4.2 K which verify the existence of a two-dimensional electron gas at the In 0.15 Ga 0.85 As/GaAs interface. HEMT's fabricated with 2-µm gate lengths show an extrinsic transconductance of 90 and 140 mS/mm at 300 and 77 K, respectively-significantly larger than that previously reported for strained-layer superlattice In x Ga 1-x As structures which are nonpseudomorphic to GaAs substrates. HEMT's with 1-µm gate lengths have been fabricated, which show an extrinsic transconductance of 175 mS/mm at 300 K which is higher than previously reported values for both strained and unstrained In x Ga 1-x As FET's. The absence of Al x Ga 1-x As in these structures has eliminated both the persistent photoconductivity effect and drain current collapse at 77 K.
TL;DR: In this article, a formalism to study the effect of alloy disorder and interface roughness on the linewidths of excitonic emission spectra in quantum-well structures is developed.
Abstract: A formalism to study the effect of alloy disorder and interface roughness on the linewidths of excitonic emission spectra in quantum‐well structures is developed. The study includes the cases where the alloy forms (a) the barrier region, (b) the well region, and (c) both the barrier and well regions of the quantum‐well structures, and demonstrates the importance of alloy quality in all three cases. The relative importance of the effects of alloy disorder and interface roughness on the excitonic linewidths is discussed. As an illustration, the formalism is applied to AlGaAs/GaAs, InP/InGaAs, and InAlAs/InGaAs quantum‐well structures and the results compared with the available experimental data.
TL;DR: In this article, the authors summarize some of the salient properties of excitons in GaAs quantum wells and in doing so it will emphasize work at AT&T Bell Labs with which the authors have been associated.
TL;DR: In this article, the authors describe a novel concept that can lead to new quantum interference effects with potential applications in switching devices, where interference occurs between currents flowing in two parallel channels formed by contiguous GaAs quantum wells.
Abstract: This Letter describes a novel concept that can lead to new quantum interference effects with potential applications in switching devices. The interference occurs between currents flowing in two parallel channels formed by contiguous GaAs quantum wells. Preliminary experiments with a simple structure show oscillations in the conductance as a function of the magnetic field with a period close to $\frac{h}{e}$ indicating an Aharonov-Bohm effect.
TL;DR: In this paper, the authors examined the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth of 10 or more atomic layers and found that the growth interruption of 10−100 seconds prior to the interface formation is effective in achieving an atomically flat interface.
Abstract: Photoluminescence spectra of GaAs-AlAs quantum wells are studied to evaluate the flatness of heterointerfaces prepared by molecular beam epitaxy. We examine the correlation of the interface roughness with the measured intensity oscillations of reflective high energy electron diffraction (RHEED) during the growth. The crystal surface is found to roughen after the growth of 10 or more atomic layers. The growth interruption of 10–100 seconds prior to the interface formation is effective in achieving an atomically flat interface, leading to sharp photoluminescence with the linewidth <30 A at 77 K even when the quantum well width is reduced to 40 A.
TL;DR: In this article, the quantum-confined Stark effect on the photoluminescence of the lowest free exciton for electric fields perpendicular to the quantum well layers is investigated.
Abstract: We report on picosecond luminescence studies of GaAs/AlGaAs quantum wells in the regime of the quantum-confined Stark effect. A drastic increase of the recombination lifetime is accompanied by a Stark shift of the photoluminescence of the lowest free exciton for electric fields perpendicular to the quantum-well layers. A consistent picture of the quantum-confined Stark effect is presented.
TL;DR: In this article, the authors show that for a quantum-well wire perpendicular to light propagation, gain remains finite at subband edges due to the intraband relaxation, therefore, high gain can be obtained by reducing intraband scatterings.
Abstract: Gain is given theoretically for quantum-well wire lasers where electrons are confined one-dimensionally. Maximum gain is obtained for a quantum-well wire perpendicular to light propagation, due to anisotropy of the dipole moment. Although the density-of-states is infinite at subband edges, gain remains finite due to the intraband relaxation. Therefore, high gain can be obtained by reducing intraband scatterings. Gain in 100 A×100 A Ga0.47In0.53As/InP quantum-well wires is about twice that in 100 A thick conventional quantum-wells, and reduction of the laser threshold is expected.
01 Jun 1985
TL;DR: The basic concepts and first-order growth model derived from the RHEED intensity oscillation technique are described and the limitations imposed by the experimentally demonstrated multiple-scattering nature of the diffraction process are indicated.
IBM1
TL;DR: Luminescence data reveal large electronic energy shifts relative to bulk energy levels which can be used to calculate the confinement energy of the localized electrons in a simple borosilicate glass system.
Abstract: Finite size effects have been observed at low temperatures for electrons confined to semiconductor microcrystallites embedded in a simple borosilicate glass. Luminescence data reveal large electronic energy shifts relative to bulk energy levels which can be used to calculate the confinement energy of the localized electrons. This system provides an attractive alternative to quantum well heterostructures, permitting direct optical studies of electron-confinement effects over a wide range of temperatures.
TL;DR: The first observation of strong and well-resolved exciton peaks in the room-temperature absorption spectra of infrared band-gap multiple quantum well structures (MQW) was reported in this article.
Abstract: The first observation of strong and well‐resolved exciton peaks in the room‐temperature absorption spectra of infrared band‐gap multiple quantum well structures (MQW’s) is reported. Assignment of the optical resonances in the absorption spectra of GaInAs/AlInAs MQW’s yields the material parameters of this new heterojunction. The discontinuities of the conduction and valence bands are found to be ΔEc=0.44 eV and ΔEv=0.29 eV, respectively.
Patent•
08 Mar 1985TL;DR: In this article, a means responsive to light for generating a photocurrent, a structure having a semiconductor quantum well region, and a mean responsive to the photocurrent for electrically controlling an optical absorption of the semiconductor well region.
Abstract: The invention is a nonlinear or bistable optical device having a low switching energy. The invention uses a means responsive to light for generating a photocurrent, a structure having a semiconductor quantum well region, and means responsive to the photocurrent for electrically controlling an optical absorption of the semiconductor quantum well region. The optical absorption of the semiconductor quantum well region varies in response to variations in the photocurrent. A photodiode or phototransistor may be used as the means responsive to light, and may be made integral with the structure having the semiconductor quantum well region. An array of devices may be fabricated on a single chip for parallel logic processing.
TL;DR: In this article, the first measurements of the linear and nonlinear anisotropic absorption of light propagating along the plane of a single quantum well are reported and discussed in terms of the structure of the valence band in ultrathin semiconductor layers.
Abstract: The first measurements of the linear and nonlinear anisotropic absorption of light propagating along the plane of a single quantum well are reported and discussed in terms of the structure of the valence band in ultrathin semiconductor layers. Nonlinear optical effects are compared to those of multiple layer structures and to recent theory.
TL;DR: In this paper, 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 were reported.
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.
TL;DR: In this paper, the subband structure of a two-dimensional hole system at GaAs/AlGaAs heterojunctions and quantum wells is calculated in the selfconsistent Hartree approximation.
Abstract: The subband structure of a two-dimensional hole system at GaAs/AlGaAs heterojunctions and quantum wells is calculated in the self-consistent Hartree approximation. The subband dispersion is shown to be quite nonparabolic and anisotropic. The cyclotron effective mass is strongly dependent on the hole concentration. The spin splitting is extremely large due to the lack of inversion symmetry at single heterojunctions. Light-scattering spectra are calculated for quantum wells and the agreement with experiments is excellent for systems with low hole concentrations.
TL;DR: In this article, an infrared detector based on the excitation of carriers out of a modulation-doped quantum well is investigated, and the efficiency of the detector is increased by using a grating to enhance the fields in the well.
Abstract: An infrared detector based on the excitation of carriers out of a modulation‐doped quantum well is theoretically investigated. The efficiency of the detector is increased by using a grating to enhance the fields in the well. Scattering effects are taken into account by designing the quantum well so that upon excitation carriers will escape in a short time compared to the time it takes to scatter back into the well. Despite this constraint, a quantum efficiency of 90% is shown to be possible for a GaAs‐AlGaAs quantum well with a carrier density of 1012 cm−2.