Dependence of “Reststrahlen” bands in far-infrared reflectivity on configuration of GaAs/AlAs multiple quantum well heterostructures

Far infrared reflectivity measurements are performed on a series of GaAs/AlAs multiple quantum well (MQW) heterostructures with systematically varied thicknesses of the constituent layers. In addition to the artificial anisotropy we observe two distinct bulk-like Reststrahlen regions. The widths of the GaAs-like and the AlAs-like Reststrahlen bands strongly depend on the relative thicknesses of the constituent layers of the MQW heterostructures, in excellent agreement with the predictions of the effective-medium theory.Prof. Aldo Cingolani passed away just before the publication of this article. We would like to dedicate this paper to his memory     

Tensile-strained 1.3 μm InGaAs/InGaAlAs quantum well structure of high temperature characteristics

A new tensile strained InGaAs/InGaAlAs quantum well structure in the 1.3 μm wavelength region is proposed for high temperature characteristics via quantum well band structure and optical gain calculations. To obtain such features, a tensile-strained InGaAs/InGaAlAs quantum well structure, which emits light dominated by TM polarization, is considered. This proposed structure has very high temperature characteristics (T ₀ > 130 K) due to its high density of state at the first transition edge. This results clearly show the potential of tensile strained quantum well structure usage for the high temperature operation of quantum well semiconductor lasers.     

1.3-μm InAs/GaAs quantum dots grown on Si substrates

We compare the effect of InGaAs/GaAs strained-layer superlattice(SLS) with that of GaAs thick buffer layer(TBL)serving as a dislocation filter layer. The InGaAs/GaAs SLS is found to be more effective than GaAs TBL in blocking the propagation of threading dislocations, which are generated at the interface between the GaAs buffer layer and the Si substrate. Through testing and analysis, we conclude that the weaker photoluminescence for quantum dots(QDs) on Si substrate is caused by the quality of capping In_(0.15)Ga_(0.85)As and upper GaAs. We also find that the periodic misfits at the interface are related to the initial stress release of GaAs islands, which guarantees that the upper layers are stress-free.     

Nonlinear properties of quantum dot semiconductor optical amplifiers at 1.3μm Invited Paper

The dynamics of nonlinear processes in quantum dot(QD)semiconductor optical amplifiers(SOAs)are investigated.Using small-signal measurements,the suitabilities of cross-gain and cross-phase modulation as well as four wave mixing(FWM)for wavelength conversion are examined.The cross-gain modulation is found to be suitable for wavelength conversion up to a frequency of 40 GHz.     

Influences of quantum noises on direct-modulated properties of 1.3-μm InGaAsP/InP laser diodes

Due to the zero dispersion point at 1.3μm in optical fibres, 1.3-μm InGaAsP/InP laser diodes have become main light sources in fibre communication systems recently. Influences of quantum noises on direct-modulated properties of single-mode 1.3-μm InGaAsP/InP laser diodes are investigated in this article. Considering the carrier and photon noises and the cross-correlation between the two noises, the power spectrum of the photon density and the signal-to-noise ratio (SNR) of the direct-modulated single-mode laser system are calculated using the linear approximation method. We find that the stochastic resonance (SR) always appears in the dependence of the SNR on the bias current density, and is strongly affected by the cross-correlation coefficient between the carrier and photon noises, the frequency of modulation signal, and the photon lifetime in the laser cavity. Hence, it is promising to use the SR mechanism to enhance the SNR of direct-modulated InGaAsP/InP laser diodes and improve the quality of optical fibre communication systems.     

Design considerations to improve high temperature characteristics of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers: Strain in barriers

Uncooled multiple quantum well lasers have great attraction because of their lower power dissipation and smaller size than traditional semiconductor lasers. In this study we will investigate the strain effect in barriers of 1.3 μm AlGaInAs-InP uncooled multiple quantum well lasers. We simulate a laser structure using a band-to-band transition approach. Single effective mass theory has been used for conduction band and Kohn-Luttinger Hamiltonian has been solved for valance band to obtain quantum states and envelope wave functions in the structure. In the case of unstrained barriers, the results have good agreement with a real device fabricated and presented in one of the references. Our main work is proposal of 0.2% compressive strain in the structure Barriers that cause 20% improvement in mode gain-current density characteristic. Significant reduction in leakage current density and Auger current density characteristics is also obtained at 85 °C. Optical gain-photon energy spectrum is increased more than 3% proportional to unstrained barriers.     

InP-based InGaAs/InA1GaAs digital alloy quantum well laser structure at 2μm

The structural and optical characteristics of InP-based compressively strained InGaAs quantum wells have been significantly improved by using gas source molecular beam epitaxy grown InAs/Ino.53Ga0.47As digital alloy triangular well layers and tensile Ino.53Ga0.47As/InAiGaAs digital alloy barrier layers. The x-ray diffraction and transmission electron microscope characterisations indicate that the digital alloy structures present favourable lattice quality. Photo- luminescence （PL） and electroluminescence （EL） measurements show that the use of digital alloy barriers offers better optical characteristics than that of conventional random alloy barriers. A significantly improved PL signal of around 2.1μm at 300 K and an EL signal of around 1.95μm at 100 K have been obtained.     

Photoluminescence response of a quantum well to a change in the magnetic field of the Mn δ Layer in InGaAs/GaAs heterostructures

Ferromagnetic ordering of two types (depending on the sample geometry) is found to occur in a thin Ga_{1 − x} Mn _x As alloy layer (Mn δ layer) in heterostructures containing an InGaAs/GaAs quantum well. Singular samples in which the δ Mn layer is parallel to the (001) GaAs plane exhibit the “3/2” Bloch temperature dependence of magnetization, and vicinal samples in which the δ Mn layer deviates from the (001) GaAs plane exhibit a “percolation” ferromagnetic transition. The photoluminescence polarization of the quantum well is shown to follow changes in the magnetization of the Mn δ layer as a function of temperature according to the Bloch law in the singular samples and to a percolation law in the vicinal samples.     

Nonlinear change in refractive index and transmission coefficient of silicon at long-pulse,mJ-range, 1.54-μm excitation

An experimental study and theoretical modeling of the nonlinear changes in transmission coefficient and refractive index of mono-crystalline Silicon (Si) at long-pulse, mJ-range, single-beam Z-scan probing at 1.54 μm wavelength are reported. It is shown experimentally that at increasing pulse energy density the photo-induced darkening permanently increases in Si while its photo refraction properties demonstrate a more complicate character, being a product of various type nonlinearities. A theoretical analysis based on simple assumptions of a square-shape pulse in the time domain and Gaussian spatial distribution of the probe beam allows fitting of a whole of the experimentally measured open- and closed-aperture Z-scans through an account of the main contributions in the light-induced absorption and refractive index nonlinearities. These are revealed to originate from non-direct two-photon absorption and Kerr effect, induced absorption and dispersion of light-generated free carriers, and light-induced thermal lensing.     

Investigation on achieving the diode-pumped weak line laser at 1.3 μm

In this paper, a continuous-wave (CW) diode-side-pumped Nd:YAlO₃ (Nd:YAP) laser operating at the weak line of 1339 nm has been achieved and investigated. The output of the 1339 nm laser was realized based on the polarization selection and reasonable transmittance design. The relationship between the output powers and resonator lengths of the 1339 nm Nd:YAP laser has been studied and the optimum resonator length was adopted to improve the output power. As high as 31.3 W output power of the a-axis polarized 1339 nm laser has been obtained at the pumping power of 555 W with the optical-optical and slope efficiencies to be 5.6% and 13%, respectively. This work will provide an effective way to obtain the weak line lasers for potential applications in spectroscopy, coherent terahertz generation, etc.     

Four-wave mixing reflectivity of silicon at 1.06 μm: Influence of free-carrier absorption

The phase-conjugate reflectivity obtainable by degenerate four-wave mixing in silicon at a 1.06 m is calculated including free-carrier absorption. A maximum reflectivity of more than 100% is possible. The dependence of the reflectivity on the signal and pump energy densities up to 70 mJ/cm² is measured and found to agree with theory. The wave-front-correction property of DFWM is demonstrated with a lens in the signal beam.     

Two-Mode Converters at 1.3μm Based on Multimode Interference Couplers on InP Substrates

Two-mode converters at 1.3μm,aiming at applications in mode-division multiplexing in Ethernet systems,are proposed and experimentally demonstrated.Based on multimode interference couplers,the two-mode converters with 50%and 66%mode conversion efficiencies are designed and fabricated on fnP substrates.Mode conversion from the fundamental mode(TEo) to the first order mode(TE_1) is successfully demonstrated within the wavelength range of 1280-1320 nm.The 1.3-μm mode converters should be important devices in mode-division multiplexing systems in Ethernet systems.     

Photoluminescence properties of exciton–exciton scattering in a GaAs/AlAs multiple quantum well

We report on the photoluminescence (PL) properties of a GaAs (20 nm)/AlAs (20 nm) multiple quantum well under high-density-excitation conditions at excitation energies near the fundamental exciton energies. The biexciton-PL band is dominant in a relatively low-excitation-power region. The PL originating from exciton–exciton scattering, the so-called P emission, suddenly appears with an increase in excitation power. The excitation-energy dependence of the intensity of the P-PL band indicates that the excitation energy higher than the fundamental heavy-hole exciton by the energy of the longitudinal optical (LO) phonon is the most efficient for the P PL. This suggests that the LO-phonon scattering plays an important role in the relaxation process of excitons leading to the P PL. The appearance of the P-PL band remarkably suppresses the intensity of the biexciton-PL band; namely, the exciton–exciton scattering process prevents the formation of biexcitons. Furthermore, we have confirmed the existence of optical gain due to the exciton–exciton scattering process with use of a variable-stripe-length method.     

Optical spectra and Auger recombination in SiGe/Si heterostructures in 10 μm range of wavelengths

We discuss the possibility of usingp-type SiGe/Si multiple quantum well structures for infrared detection. We calculated the miniband dispersion in these structures using an empirical pseudopotential method including the effects of spin and strain. The absorption spectra of these structures is discussed and the microscopic origin of the absorption peaks identified. We present comparisons between our calculated absorption response and the experimental spectra obtained in recent experiments for both parallel and normal incidence light. We also report full-scale pseudopotential calculations of the Auger recombination in these structures and present a fresh discussion of the conditions which could help to minimize this recombination.     

Nature of the temperature dependence of the absorption coefficient in the remote wing of the 4.3 μm CO2 band

The complex nature of the temperature dependence of the absorption coefficient beyond the edge of the CO₂ 4.3 m band — the change of the sign of the derivative of the absorption coefficient with respect to the temperature near the edge and in the remote wing of the band — is explained on the basis of the theory of spectrum line wings. The first change in the sign is due to the temperature dependence of the classical potential of intermolecular interaction; the second depends mainly on the difference in the quantum energies of molecule interaction. Therefore, a study of the dependence of the absorption coefficient on the temperature in the band wings provides information about the nature of the terms of the interacting molecules.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 42–45, December, 1987.     

Molecular beam epitaxial growth of high quality InAs/GaAs quantum dots for 1.3-μm quantum dot lasers

Systematic investigation of InAs quantum dot(QD) growth using molecular beam epitaxy has been carried out, focusing mainly on the InAs growth rate and its effects on the quality of the InAs/GaAs quantum dots.By optimizing the growth rate, high quality InAs/GaAs quantum dots have been achieved.The areal quantum dot density is 5.9× 10~(10) cm~(-2), almost double the conventional density(3.0 × 1010 cm~(-2)).Meanwhile, the linewidth is reduced to 29 meV at room temperature without changing the areal dot density.These improved QDs are of great significance for fabricating high performance quantum dot lasers on various substrates.     

All-optical modulation at 1.3 μm wavelength in the inGaAsP/InP system

All-optical, normal-to-surface modulation in InGaAsP epitaxial layers, lattice matched to InP, is investigated. Close to the gap wavelength of 1.3 m a transmission increase under optical excitation is observed. A modulation depth of 34% is achieved for 0.8 mW pump power at 790 nm wavelength. The modulation frequency is limited by excess carrier lifetime. A 3 dB frequency of 80 MHz is achieved with a 10 dB decrease at 400 MHz. A lateral electric field enlarges the bandwidth but decreases the modulation depth. For weak excitation the experiments are well described in terms of direct electronic transitions between parabolic bands or in terms of simple band filling. The devices are well suited for parallel optical data processing.     

Effect of the δ-shaped quantum well at the one-dimensional lattice boundary on properties of Tamm-type surface electronic states

The Tamm-type surface electronic states at the boundary of the one-dimensional structure with periodically potential profile have been theoretically studied under the condition that the δ-shaped quantum well is at this boundary. The properties of surface electronic states in such a structure have been compared with Tamm electronic states in the absence of a quantum well at the lattice boundary and with electronic states localized near the δ-shaped potential well deep in the lattice. In particular, it has been shown that the existence of the δ-shaped potential well at the lattice boundary facilitates a significant increase in the degree of localization of Tamm-type surface electronic states and makes possible the appearance of these states at arbitrarily small heights of lattice potential barriers.     

Numerical study of strained InGaAs quantum well lasers emitting at 2.33 μm using the eight-band model

We investigate the band structure of a compressively strained In(Ga)As/In 0.53 Ga 0.47 As quantum well (QW) on an InP substrate using the eight-band k · p theory.Aiming at the emission wavelength around 2.33 μm,we discuss the influences of temperature,strain and well width on the band structure and on the emission wavelength of the QW.The wavelength increases with the increase of temperature,strain and well width.Furthermore,we design an InAs /In 0.53 Ga 0.47 As QW with a well width of 4.1 nm emitting at 2.33 μm by optimizing the strain and the well width.