Anisotropic electroabsorption and optical modulation in InGaAs/InAlAs multiple quantum well structures

The first measurements to be made of large anistropic electroabsorption and modulation of long-wavelength light propagating along the plane of InGaAs/InAlAs multiple quantum well (MQW) structures grown by molecular beam epitaxy (MBE) are reported. Photocurrent response of waveguide p-i-n diodes is studied for incident light polarization parallel and perpendicular to the MQW layers. Photocurrent increase with reverse bias throughout the entire photoresponse spectrum is observed for both polarizations. The MQW p-in optical modulator shows a capacitance-limited pulse response of 250 ps and the modulation depth is 14 percent.     

High-speed long-wavelength optical modulation in InGaAs/InAlAs multiple quantum wells

A long-wavelength optical modulator has been fabricated which makes use of an electroabsorption effect in multiple quantum wells (MQWs). Here, InGaAs/InAlAs MQWs are prepared in a PIN configuration using molecular beam epitaxy (MBE). The rise time of the detected pulse modulation signal has been measured at 190 ps. This response level has been attributed to the detecting system response and RC time constant, and not to such intrinsic effects as carrier lifetime.     

Strained-layer InGaAs/InAlAs multiple quantum wells for efficient optical waveguide modulation at 1.55 mu m

Strain is used to tailor the absorption edge of thick (100 AA) quantum wells. This allows efficient modulation at 1.55 mu m. An extinction ratio of 18 dB has been achieved by applying a reverse bias of 6 V to a 160 mu m long waveguide device.<>     

Compact low-voltage InGaAs/InAlAs multiple quantum well waveguide interferometers

Semiconductor waveguide interferometric intensity modulators are demonstrated with a voltage-length product for 180 degrees optical phase shift V/sub pi /*L=2.2 V mm. The device uses a Mach-Zehnder configuration fabricated by wet chemical etching.<>     

InP/InAlAs/InGaAs quantum wires

Single InGaAs quantum wires and stacked InGaAs quantum wires with InAIAs barriers have been fabricated on V-grooved InP substrates by low pressure metal-organic chemical vapour deposition (MOCVD). We have found growth conditions where the InAIAs barrier exhibits a resharpening effect, similar to that of AlGaAs utilized for growth on GaAs substrates. The existence of structural and electronic quantum wires in the bottom of the grooves is proven.     

Dynamic frequency response for InGaAs/InAlAs multiple quantum well optical modulators

The frequency response of InGaAs/InAlAs multiple-quantum-well (MQW) optical modulators and their dependence on incident light power are described. No decrease in small-signal modulation bandwidth was observed up to ten times the initial value of 1 mW. The mechanism of the frequency-response difference between InGaAs/InAlAs MQW modulators and InGaAs/InP modulators is discussed.<>     

Electron properties of surface InGaAs/InAlAs quantum wells with inverted doping on InP substrates

The electron-transport and optical properties of heterostructures with a surface InGaAs/InAlAs quantum well in the cases of inverted δ doping with Si atoms (below the quantum well) and of standard δ doping (above the quantum well) are compared. It is shown that, in the case of inverted doping, the two-dimensional electron density in the quantum well is increased in comparison with the case of the standard arrangement of the doping layer at identical compositions and thicknesses of other heterostructure layers. The experimentally observed features of low-temperature electron transport (Shubnikov–de Haas oscillations, Hall effect) and the photoluminescence spectra of heterostructures are interpreted by simulating the band structure.     

Strained InGaAs/InAlAs MQW electroabsorption modulators with largebandwidth and low driving voltage

We demonstrate the improved modulation properties of a new strained InGaAs/InAlAs MQW electro-absorption modulator. This tensile strained MQW modulator shows low driving voltage (V_{15 dB}=1.2 V), large modulation bandwidth (f_{3 dB}>20 GHz), and a 10 Gbit/s eye pattern with a clear eye opening and high extinction ratio. The effective α parameter determined from waveform deterioration is 0.6, which is low enough for multigigabit long-haul fiber transmission systems     

Highly sensitive InGaAs/InAlAs quantum wire photo-FET

An InGaAs/InAlAs quantum wire photo-FET has been fabricated on a V-grooved (311) InP substrate by atomic hydrogen assisted molecular beam epitaxy. The room-temperature photosensitivity of the quantum wire photo-FET reached 350 kA/W near a wavelength of 700 nm at a drain-source voltage of 1 V.     

Structural characterization of InGaAs/InAlAs quantum wells grown on 0 (111)-InP substrates

Recent studies on HEMT structures according to their growth orientation have attracted much interest from the viewpoint of physics and novel device applications. However, the optimization of their properties needs a high degree of crystalline quality. In this work, the structural characteristics of the layers present on InGaAs/InAlAs HEMT structures grown on (111)-InP substrates have been analyzed by atomic force and transmission electron microscopies. The presence of a strained quantum well induces a defect structure and surface morphology quite different from those observed in similar samples without the quamtum well. These results show that an accurate control of the growth conditions is necessary to obtain acceptable structural quality for (111) devices.     

Electroabsorption properties of InGaAs/InAlAs multiple quantum wellstructures at 1.5 μm

The electroabsorption properties of InGaAs/InAlAs MQW structures are characterised in terms of Δα, Δα/F and Δα/α₀, where Δα is the electroabsorption, α₀ is the residual absorption coefficient under zero bias, and F is the applied electric field. The limitations of these structures for 1.5 μm modulators are primarily due to the relatively small Δα/F values as a result of the small well width. The results are compared with the literature     

Impact ionization in InAlAs/InGaAs/InAlAs HEMT's

The kink effect and excess gate current in InAlAs/InGaAs/InAlAs HEMT's have been linked to impact ionization in the high field region of the channel. In this letter, a relationship is established between experimentally measured excess gate current and the tunneling of holes from the quantum well formed in the channel. The channel hole current is then obtained as the quotient of the excess gate current to the gate-voltage-dependent transmission probability. This channel hole current follows the exponential dependence of the ionization constant on the inverse electric field     

Large refractive index changes in tunable-electron-densityInGaAs/InAlAs quantum wells

Measurements of electrorefraction and electroabsorption in a multiple-quantum-well waveguide structure in which each InGaAs quantum well is provided with an individual electron reservoir are presented. External bias transfers electrons into the wells, thus quenching the absorption and producing a refractive index change at wavelengths below the bandedge which is linear in the applied voltage. It is shown that in this type of structure both the change in refractive index per applied field and the ratio of optical phase to intensity modulation can be significantly enhanced over those found in the quantum confined Stark effect     

Observation of heavy-hole and light-hole excitons in InGaAs/InAlAs MQW structures at room temperature

Heavy-hole and light-hole excitons were clearly observed at room temperature in the InGaAs/InAlAs MQW structure for the first time. The observed values of the exciton peak energy agree well with the calculated values. The halfwidth of the photoluminescence spectrum of MQW wafers is as narrow as 470 ? (25 meV) at room temperature, which is only 57% of that (970 ?, 44 meV) of the undoped bulk InGaAs layer.     

InGaAs/InAlAs RTD I-V特性的量子力学隧穿模拟

本文通过数值求解含时Schrodinger方程得到了InGaAs/InAlAs共振隧穿二极管 (RTD)的电流 偏压曲线 ,我们发现数值模拟的结果与实验符合得很好。     

Charge accumulation effects in InGaAs/GaAs [111]-oriented piezoelectric multiple quantum wells

We show that charge accumulation in piezoelectric [111]-oriented multiple quantum wells (MQWs), with average electric fields opposing the field in the barriers, inhibits the shift of optical transitions by externally applied electric fields. This effect is due to the screening of the average electric field as photogenerated electrons and holes drift towards the opposite edges in the MQW region due to this average field. The resulting dipole flattens the envelope potential and hence precludes the change of energy levels with variations of external voltage. This behavior has been observed in different device configurations employing InGaAs/GaAs MQW embedded in a p-i-n diode by low temperature photoluminescence (PL) and photocapacitance spectroscopies under different bias conditions. In addition to these ‘self-locked’ transitions we also observed other peaks in the PL spectra related to the charge accumulation effect and that are qualitatively explained using Hartree calculations.     

Ordering in InGaAs/InAlAs layers

The structure of InCaAs/InAlAs layers lattice matched to an InP substrate, grown on either (100) or on (110) with a 4° tilt toward [111] at 500 and 300°C has been investigated by transmission electron microscopy. High perfection resulted for the layers grown on [001] oriented substrates whereas growth on the near [110] substrates resulted in compositional nonuniformities, macrosteps formation, and ordering of the group III elements. This difference in structural perfection between the two sets of samples was also reflected in differences in electrical properties.     

Blue-chirp electroabsorption modulators with very thick quantum wells

Electroabsorption modulators operating at a wavelength of 1.55 /spl mu/m with very thick quantum wells of 19.6 mm were fabricated using InGaAlAs-InAlAs multiple quantum wells. Blue-chirp (/spl alpha/<0) operation for low applied bias was demonstrated with low insertion loss.     

Nearly chirp-free electroabsorption modulation usingInGaAs-InGaAlAs-InAlAs coupled quantum wells

We present an electroabsorption modulator based on slightly asymmetric InGaAs-InGaAlAs-InAlAs coupled quantum wells operated in the normally-off mode. The device exhibits a large change of the absorption coefficient in the vicinity of the zero-bias exciton peak wavelength with a very small change of the refractive index. The maximum excursion of the chirp parameter over the entire span of the bias voltage is less than ±0.1 for a specific wavelength or ±0.4 over a 12~14 -nm range. This structure is promising for low-chirp, high bit-rate electroabsorption modulators     

Electroabsorption on room-temperature excitons in InGaAs/InGaAlAs multiple quantum-well structures

Large optical absorption changes are observed in InGaAs/InGaAlAs multiple quantum wells when an electric field is applied perpendicular to the wells for incident light both parallel and perpendicular to the MQW layers. Polarisation-related absorption spectra are also investigated.