Electrooptic and electroabsorptive modulation properties ininterdiffusion-modified AlGaAs-GaAs quantum wells

The electric field induced refractive index change and absorption coefficient change in TE polarization are analyzed at room temperature for several interdiffusion modified Al_0.3Ga_0.7As-GaAs quantum-well structures. The results show that for the small and medium interdiffusion lengths with fields of 100 and 50 kV/cm, respectively, improved chirping and electroabsorption can be obtained. Further, in a selected set of interdiffusion lengths and fields, the material can be used for an electroabsorption modulator with reduced chirping in a wide range of operation wavelengths (758-874 nm)     

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.     

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.     

Potential chirpless DFB laser for InGaAs/InGaAsPcompressive-strained quantum wells using modulation doping

The effects of detuning on the linewidth enhancement factor α are theoretically investigated for InGaAs/InGaAsP compressive-strained QW lasers. The relationship among the material gain, the Kramers-Kronig transformed differential gain, and the linewidth enhancement factor is calculated taking into account the effect of compressive strain on the valence subband structure and of p-type modulation doping. It is shown that compressive strain and/or p-type doping significantly reduces the α factor. It is also demonstrated that chirpless operation wherein α=0 can be achieved in a modulation-doped compressive-strained structure by using detuning     

Optical investigations of strained InGaAs quantum wells

InGaAs/GaAs MOCVD-grown quantum wells have been investigated. Photoluminescence (PL) measurements have shown heavy-hole-related excitonic transitions within the temperature range from 10 to 100 K for all samples. In room-temperature photoreflectance (PR), sharp heavy- and light-hole excitonic transitions in the quantum wells have been observed. The transition energies obtained have been compared with values derived from theoretical considerations using the envelope function model including lattice-mismatch-related stress. The heavy- and light-hole transitions have been identified as excitonic transitions of types I and II respectively. © 1997 John Wiley & Sons, Ltd.     

131 ps optical modulation in semiconductor multiple quantum wells (MQW's)

A new optical modulator has been fabricated which uses the recently discovered electroabsorption effect in MQW's. Optical pulses 131 ps long were generated when the device was driven with 122 ps electrical pulses. The input-output characteristics of the device show that it has low insertion loss with reasonable modulation depth and drive voltage.     

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.<>     

InGaAs(P)应变补偿多量子阱结构激光器的理论研究

从理论上分析了应变补偿多量子阱激光器的阈值特性，并以ＩｎＧａＡｓ（Ｐ）体系为例，分别对应变补偿结构和普通应变多量子阱激光器进行了数值计算。结果表明，具有应变补偿结构的激光器可以获得较大的增益和较小的阈值电流密度。其中，阱材料能带结构的变化是使得应变补偿结构激光器具有上述优良特性的决定性因素。     

Strained-layer InGaAs(P) quantum well semiconductor lasers and semiconductor laser amplifiers

Progress in long-wavelength strained (compressive and tensile) InGaAs(P) quantum well semiconductor lasers and amplifiers for applications in optical fibre communication systems is reviewed. By the application of grown-in strain, device performance is considerably improved to such an extent that conventional bulk and unstrained quantum well active-layer devices are outperformed, while high reliability, similar to that of unstrained devices, is maintained.     

Time-resolved photoluminescence study of InGaAs/GaAs quantum wells on (111)B GaAs substrates

The exciton dynamics in In_0.15Ga_0.85As/GaAs quantum wells grown on (111)B and (100) GaAs substrates are studied by the time-resolved photoluminescence (PL). We have found that the piezoelectric fields in (111)B samples affect the transient behavior of PL spectra. Compared with the reference (100) samples, we have confirmed that the piezoelectric effect induces slower exciton relaxation in (111)B strained quantum wells.     

Intersubband dynamics in modulation doped quantum wells

A theoretical investigation of the dynamics of intersubband transitions in modulation doped multiple narrow GaAs / Al_xGa_1−xAs quantum well structures by emission of GaAs (well) and Al_xGa_1−xAs (barrier) slab and interface mode polar optical phonons is presented. Photo-excited carrier behavior is interpreted via Monte Carlo simulations which predict long time constants for electron relaxation.     

Atmospheric and low pressure shadow masked MOVPE growth of InGaAs(P)/InP and (In)GaAs/(Al)GaAs heterostructures and quantum wells

The shadow masked growth technique is presented as a tool to achieve thickness and bandgap variations laterally over the substrate during metalorganic vapor phase epitaxy. Lateral thickness and bandgap variations are very important for the fabrication of photonic integrated circuits, where several passive and active optical components need to be integrated on the same substrate. Several aspects of the shadow masked growth are characterized for InP based materials as well as for GaAs based materials. Thickness reductions are studied as a function of the mask dimensions, the reactor pressure, the orientation of the masked channels and the undercutting of the mask. The thickness reduction is strongly influenced by the mask dimensions and the reactor pressure, while the influence of the orientation of the channels and the amount of undercutting is only significant for narrow mask windows. During shadow masked growth, there are not only thickness variations but also compositional variations. Therefore, we studied the changes in In/Ga and As/P ratios for InGaAs and InGaAsP layers. It appears that mainly the In/Ga-ratio is responsible for compositional changes and that the As/P-ratio remains unchanged during shadow masked growth.     

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     

Characterizing electric fields in (111)B InGaAs quantum wells using electric field modulated photoluminescence and reflectance techniques

We have performed a series of electroreflectance, photoluminescence, and electric-field-modulated photoluminescence experiments to characterize the strain-induced electric fields in (111)B InGaAs/AlGaAs quantum well p-i-n diode structures. A 180° phase change in the lineshapes of electroreflectance spectra of these samples determines when the quantum well is biased to flatband. Using this bias and a depletion model for the diode, the polarization field in the quantum well can be determined. Contrary to expectations, this polarization field increases significantly with increasing temperature. In addition, at fixed temperature, the quantum well transition energies red-shift with increasing excitation intensity when excited by photons of energy higher than the lowest quantum well transition but lower than the AlGaAs diode's bandgap. When excited with photons of energy greater than the AlGaAs bandgap, the transition energy first red shifts then blue shifts with increasing excitation intensity.     

Interband-resonant light modulation by intersubband-resonant lightin undoped quantum wells

Interband-resonant light modulation by intersubband-resonant light in undoped quantum wells is investigated. Theoretical calculation for the modulation is carried out by considering not only the excitonic interband-transition but also the continuous level transition between the conduction and valence bands. The modulation characteristics are compared with those of the modulation using n-doped quantum wells. The possibility of the modulation using undoped quantum well is successfully shown by real-time single-shot experiment using Ti-Al₂O₃ and CO₂ lasers for interband- and intersubband-resonant lights at room temperature     

High-temperature excitons and enhanced electroabsorption in InGaAs/InAlAs multiple quantum wells

Sharp heavy-hole and light-hole excitons are clearly observed for the first time in InGaAs/InAlAs multiple-quantum-well (MQW) structures at temperatures ranging from ?190°C to 70°C. The halfwidth of the heavy-hole exciton line is as narrow as 6.2 meV at room temperature. InGaAs/InAlAs MQWs are prepared in a PIN doped configuration by molecular beam epitaxy. An enhanced electroabsorption effect is also clearly observed in long-wavelength-region MQWs.     

InGaAs（P）／InP应变量子阱和超晶格的光电性质

利用低压金属有机化合物化学汽相沉积（ＭＯＣＶＤ）生长技术在ＩｎＰ衬底上生长ＩｎＧａＡｓ／ＩｎＰ应变量子阱，超晶格和ＩｎＧａＡｓＰ／ＩｎＰ量子阱结构材料，利用７７Ｋ光荧光（ＰＬ）测量这一应变量了阱和量子阱的光学性质，利用双晶Ｘ光测量应变超晶格的性质。     

Segregation of indium in InGaAs/GaAs quantum wells grown by vapor-phase epitaxy

Distribution of indium atoms in structures which contained double InGaAs/GaAs quantum wells and were grown by vapor-phase epitaxy from metal-organic compounds was studied. Experimental indium-concentration profiles were obtained using Auger electron spectroscopy. A model of growth with allowance made for indium segregation and a model for the Auger profiling were used in the calculations of profiles. Fitting calculated profiles to experimental ones made it possible to estimate the activation energies for In-Ga exchange in the context of a kinetic model for segregation. These energies are found to be somewhat higher than those that are well known for molecular-beam epitaxy, which is related to stabilization of the growth surface by hydrogen atoms in a vapor-phase reactor.     

Phonon-assisted tunnelling of photoexcited carriers from InGaAs quantum wells in applied electric fields

We have measured photocurrent spectra and photoluminescnce decay times of InGaAs quantum well pin structures as a function of temperature under different conditions of illumination intensity and applied electric field. Our results give clear evidence that phonon-assisted tunnelling of carriers is the dominant escape mechanism. We have obtained direct evidence for the build up of holes and interpret the reduction of the hole concentration at high fields in terms of phonon-assisted tunnelling via the lowest light-hole subband.