Improvement of performance characteristics of deep violet InGaN DQW lasers using a strip DQW active region

The effect of the laser ridge width on the performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) has been numerically investigated. Simulation results indicated that threshold current of LDs is decreased and slope efficiency and differential quantum efficiency (DQE) are increased by decreasing ridge width, whereas output power is decreased. The results also showed that a decrease of more than 1 μm in the ridge width reduces the threshold current, whereas the slope efficiency, output power, and DQE are decreased. A new DQW LD structure with a strip active region has been proposed to obtain a lower current threshold and higher output power, slope efficiency, and DQE. The results showed the InGaN DQW LD with a strip DQW active region has the highest output power, slope efficiency, and DQE; it also has a lower threshold current compared with that of the original LD. The comparative study conducted for the LDs with output emission wavelengths of 390, 414 and 436 nm has also confirmed the enhancement in LD performance using the strip DQW active region structure.     

Photoluminescence of n-doped double quantum well—electron subbands under influence of in-plane magnetic fields

We report on photoluminescence (PL) measurements of a GaAs/AlGaAs double quantum well (DQW) in high magnetic fields. Measurements were carried out on a selectively contacted symmetric p-δn-DQW-δn-p structure, which allows a variation of the electron density in DQW by a p–n bias and simultaneously a tilting of DQW, when a p–p bias is applied. Attention was paid to phenomena in in-plane magnetic fields, theoretically studied by Huang and Lyo (HL), [Phys. Rev. B 59, (1999) 7600]. In this paper, we compare our results for both symmetric and asymmetric DQWs with the theoretical model made by HL. Whereas the spectra from a symmetric DQW fully confirmed the theoretical predictions, the results gained from DQW with an electric-field-induced asymmetry did not allow a proper study of anticipated effects. The reasons for that are discussed.     

Analysis and improvement of optical frequency response in a long wavelength transistor laser

Charge control model and rate equations have been exploited for the first time in order to glean the optical frequency response of a long-wavelength heterojunction bipolar transistor laser. For a 1.56 μm N-InP/p-InAlGaAs/N-InP fabricated transistor laser with a single quantum well, the optical bandwidth is estimated using this model. All parameters of the mentioned model have been computed for this new type of long wavelength transistor laser. It has been found that frequency response of this optoelectronic device has a 29 dB resonance peak which is not very desirable and is so higher than traditional GaAs transistor lasers. Furthermore, we have illustrated that the resonance peak will decrease and the optical bandwidth will increase, if we increase the width of the quantum well. Finally, we have analyzed that how base width affects on the optical bandwidth and resonance peak of frequency response. It has been proved that, there is a trade-off between larger bandwidth and lower resonance peak for base width effect.     

Numerical study of performance characteristics of deep violet InGaN DQW laser diodes with AlInGaN quaternary multi quantum barrier electron blocking layer

The performance characteristics of deep violet In_0.082Ga_0.918N/GaN double quantum well (DQW) laser diodes (LDs) with different electron blocking layer (EBL) including a ternary AlGaN bulk EBL, a quaternary AlInGaN bulk EBL and ternary AlGaN multi quantum barrier (MQB) EBL has been numerically investigated. Inspired by the abovementioned structures, a new LD structure with a quaternary AlInGaN MQB EBL has been proposed to improve the performance characteristics of the deep violet InGaN DQW LDs. Simulation results indicated that the LD structure with the quaternary AlInGaN MQB EBL present the highest output power, slope efficiency and differential quantum efficiency (DQE) and lowest threshold current compared with the above mentioned structures. They also indicated that choosing an appropriate aluminum (Al) and indium (In) composition in the quaternary AlInGaN MQB layers could control both piezoelectric and spontaneous polarizations. It will decrease the electron overflow from the active region to p-side and increased the contribution of electron and hole carriers to the radiative recombination effectively. Enhancing radiative recombination in the well using the quaternary AlInGaN MQB EBL also increased the optical output power and optical intensity.     

Simulation of quantum-well slipping effect on optical bandwidth in transistor laser

An optical bandwidth analysis of a quantum-well （16 nm） transistor laser with 150-μm cavity length using a charge control model is reported in order to modify the quantum-well location through the base region. At constant bias current, the simulation shows significant enhancement in optical bandwidth due to moving the quantum well in the direction of collector-base junction. No remarkable resonance peak, limiting factor in laser diodes, is observed during this modification in transistor laser structure. The method can be utilized for transistor laser structure design.     

Invited Paper: Design and modeling of a transistor vertical-cavity surface-emitting laser

A multiple quantum well (MQW) transistor vertical-cavity surface-emitting laser (T-VCSEL) is designed and numerically modeled. The important physical models and parameters are discussed and validated by modeling a conventional VCSEL and comparing the results with the experiment. The quantum capture/escape process is simulated using the quantum-trap model and shows a significant effect on the electrical output of the T-VCSEL. The parameters extracted from the numerical simulation are imported into the analytic modeling to predict the frequency response and simulate the large-signal modulation up to 40 Gbps.     

Exciton transport by surface acoustic waves

Long-range acoustic transport of excitons in GaAs quantum wells (QWs) is demonstrated. The mobile strain field of a surface acoustic wave creates a dynamic lateral type I modulation of the conduction and valence bands in a double-quantum-well (DQW) structure. This mobile potential modulation transports long-living indirect excitons in the DQW over several hundreds of μm.     

半导体量子电子和光电子器件

本文阐述了半导体异质结构电子的量子特性 ,如电子波输运、库仑阻塞效应等。介绍了几种新颖、典型的量子电子器件和量子光电子器件的物理模型和基本原理。这些器件包括了单电子晶体管、共振隧穿二极管、高电子迁移率晶体管、δ掺杂场效应晶体管、量子点元胞自动机、量子阱红外探测器、埋沟异质结半导体激光器、量子级联激光器等。给出了作者在半导体量子器件物理方面的最新研究结果。     

Effect of the light on MESFETs application to optically controlled devices

Light has some influence on static and dynamic characteristics of MESFETs illuminated by an optical fiber connected at the output of a laser diode (=845nm). They are first described from a theoretical point of view with a new unidimensional model for the component. An equivalent scheme extraction software gives the elements of the transistor scheme, using the results of the network analyzer measurements. A good agreement between the theoretical and experimental results exists. It is thus possible to design optically controlled devices such as amplifiers or oscillators. Good results have been obtained with both.     

Plasmons in asymmetric double quantum well structures

We investigate the effects of spatial asymmetry, tunneling coupling, and exchange-correlation correction on the plasmon modes in asymmetric double quantum well (DQW) structures in a time-dependent local-density approximation. Special attention is paid to the properties of the ω _- mode which is always damped in symmetric DQW systems. In addition, the results on the spectral weight of the excitations are also presented. In general, all the modes carry finite spectral weights and should be observable in resonant inelastic light scattering experiments for the specified values of the parameters. Received 2 July 2002 Published online 19 December 2002 RID="a" ID="a"e-mail: c412-1@aphy.iphy.ac.cn     

Modelling of optical Kerr effects on the static and dynamic behaviors of quantum cascade laser

The effect of optical Kerr nonlinearity on the static and dynamic behaviors of quantum cascade laser operating in the mid-infrared is theoretically investigated. Our model is based on three-level rate equations including the dependence of the loss on photon number in the cavity. The optical stability domain that allows for the determination of current injection is derived within the premises of our model. The analytical solutions of eigenvalue equation allowing the investigation of stability analysis are obtained. Furthermore, nonlinear effects influence significantly the dynamics of photons in cavity and electrons in the upper laser level.     

Entanglement via tunable Fano-type interference in asymmetric semiconductor quantum wells

Entanglement is realized in asymmetric coupled double quantum wells (DQWs) trapped in a doubly resonant cavity by means of Fano-type interference through a tunneling barrier, which is different from the previous studies on entanglement induced by strong external driven fields in atomic media. We investigate the generation and evolution of entanglement and show that the strength of Fano interference can influence effectively the degree of the entanglement between two cavity modes and the enhanced entanglement can be generated in this DQW system. The present investigation may provide research opportunities in quantum entangled experiments in the DQW solid-state nanostructures and may result in a substantial impact on the technology for entanglement engineering in quantum information processing.     

Intersubband transitions and refractive index changes in coupled double quantum well with different well shapes

In this study, both the linear intersubband transitions and the refractive index changes in coupled double quantum well (DQW) with different well shapes for different electric fields are theoretically calculated within framework of the effective mass approximation. Results obtained show that intersubband transitions and the energy levels in coupled DQW can importantly be modified and controlled by the electric field strength and direction. By considering the variation of the energy differences, it should point out that by varying electric field we can obtain a blue or red shift in the intersubband optical transitions. The modulation of the absorption coefficients and the refractive index changes which can be suitable for good performance optical modulators and various infrared optical device applications can be easy obtained by tuning applied electric field strength and direction.     

量子力学基本概念教学探讨

用一维无限深势阱中粒子的动态量子模型讨论了态叠加原理和时间与能量的不确定关系原理的意义,指出量子隧穿效应静态模型的疑难,建立了一个隧穿效应动态模型,并讨论了隧穿效应的微观机制.     

The low-frequency electrical noise as reliability estimation for high power semiconductor lasers

The low-frequency electrical noise of 980 nm InGaAsP/InGaAs/GaAlAs double quantum well (DQW) high power semiconductor lasers (LDs) is measured when the devices are in conducting state and in unconducting state. The correlation between the noise and device reliability is discussed. The results indicate that there is a good relation between the noise and device reliability for most devices. The devices with higher noise are usually unreliable whether the device is in conducting state or in unconducting state.     

The polarization sensitivity of optical absorption in tensile strained GaAs/InAlAs double quantum wells

The electric field dependence of the polarization sensitivity of optical absorption in tensile-strained GaAs/InAlAs double quantum wells (DQWs) was investigated theoretically. The coupling effects and electric-field-induced change of eigenstates in various DQW structures were analysed within the framework of the Bastard envelope function approximation using the transfer matrix method (TMM). The absorption coefficient was calculated with excitonic effects included. The simulation results show that it is possible to change the polarization characteristics in the DQW structures by adjusting the applied electric field.     

Simulations of Differential Gain and Linewidth Enhancement Factor of Quantum Dot Semiconductor Lasers

We present a multi-population rate equation model for the analysis of the static and dynamic characteristics of a quantum dot (QD) semiconductor laser. The model is applied to the extraction of the differential gain and linewidth enhancement factor of the QD laser simulating the same kind of experiments usually done in the laboratory. Coherently with the experimental results, we show the difference between the values of the differential parameters extracted in below and above threshold characterizations. We demonstrate that such discrepancy is due the complex dynamics of the carriers in those energy states, whose carrier concentration is not clamped by the stimulated emission process above threshold.     

Asymmetric Evolution of Two Two-Level Atoms Induced by Position-Dependent Excitation Phase

We report a phenomenon of asymmetric evolution of two two-level atoms which results from pump laser phase based on the model of[Phys.Rev.Lett.101(2008) 153601].Other than investigating the dynamical behavior of whole system,in this paper we investigate the effects of the pump laser phase on dynamic behavior of each atom.We find that two atoms show asymmetry both in time evolution of(population) excitation probability and quantum correlation with environment due to the quantum interference induced by pump laser phase as well as the dipole-dipole interaction.These phenomena are deeply related to the dynamical behavior of the whole system,therefore we can understand the dynamical behavior of whole system caused by pump laser phase from this point of view.     

Carrier transport effects in quantum well lasers: an overview

Early theoretical predictions and later experimental work have shown that lasers with quantum well active areas have enhanced differential gain over bulk lasers. The resonance frequency in a semiconductor laser is proportional to the square root of the differential gain. The resonance frequency is directly related to the modulation bandwidth, and the enhancement in the intrinsic differential gain led to theoretical predictions of increased modulation bandwidth in quantum well lasers. This enhancement in the modulation bandwidth proved to be elusive initially, and later it was realized that other factors, namely carrier transport effects, played a more dominant role in the high-speed properties of quantum well lasers. Carrier transport effects, in addition to bandfilling, affect a wide range of static and dynamic properties of the quantum well lasers. This paper will present an overview of our present understanding of the carrier transport processes and their effects in quantum well lasers.     

Luminescence from Si-Si1−xGex/Si1−yCy-Si structures

Near band edge photoluminescence has been obtained from Si_1−yC_y quantum well (QW) and neighboring Si_1−xGe_x/Si_1−yC_y double QW (DQW) structures. Enhanced no-phonon recombination is observed from the DQW structures and it is attributed to a breaking of the k-selection rule in the presence of the heterointerface. The luminescence persists for measurement temperatures up to 30–50 K and the intensity exhibits a quenching behavior with an activation energy equal to 8–20 meV. In electroluminescence only recombination in the Si_1−xGe_x layer has been observed from neighboring Si_1−xGe_x and Si_1−yC_y DQW structures.