Analysis of closely-spaced index-guided semiconductor lasers. II. Single-stripe channel-guide structures

Calculations of the properties of double-channel injection lasers are presented. The dependence of the device characteristics upon a number of material parameters is found. Near-field and carrier concentration profiles are compared for devices of different dimensions at two output power values.     

Conductance of small semiconductor devices

We calculate low field conductivity and mobility as a function of a sample length for small semiconductor samples. When the sample length is much smaller than the mean free path the current density is proportional to the applied voltage so that the apparent low field mobility is proportional to the device length. Calculation of the apparent low field mobility for high mobility GaAs devices shows that the size effects may be important for sample lengths smaller than 2 μm.     

Analysis of characteristics of long-wavelength semiconductor laser diode amplifiers

The effects of amplifier facet reflectivities, cavity length, input signal frequency, amplifier cavity resonant mode, modulation frequency and bias current on various semiconductor laser diode amplifier characteristics have been investigated for both 1.3m- and 1.55m-wavelength amplifiers. The analysis is based on a parabolic relationship between the amplifier peak-gain coefficient and injected carrier density, which improves the accuracy and range of applicability.     

Materials issues underlying compound semiconductor devices

In this paper we review the special properties of compound semiconductors which make them attractive for device applications and discuss current research issues concerning the propessing of III–V compounds and heterojunction multilayers. The novel electronic properties available in III–V alloys are discussed, including special new phenomena observed in heterostructure multilayers and strained-layer superlattices. Device-related processing issues are outlined, including novel growth technique, insulator interfaces, Schottky barrier and ohmic contact formation, sample preparation, and implantation and annealing.     

Analysis of the spectral linewidth of three-cavity semiconductor laser diodes

The spectral linewidth for a semiconductor laser diode coupled to two external cavities (known as a three-cavity laser diode) is studied in the article. A closed-form expression for the linewidth of this laser is derived by analyzing the number of photons in the laser cavity. It is found that, because of the optical feedback provided by the external cavities, the photon lifetime becomes longer than that of a solitary Fabry-Perot (FP) laser, hence reducing the value of the spectral linewidth. Our theoretical investigations reveal that the linewidth of a three-cavity laser can be reduced further by using external mirrors with high reflectivities and using anti-refection (AR) coatings on the laser diode facets. We have also studied the effects of uncertainties in the linewidth enhancement factor a due to optical feedback and found that such uncertainties have negligible effects on the validity of our results.     

Quantum fluctuations in atomistic semiconductor devices

Atomistic Green function simulations of model 25 nm×25 nm Si MOSFETs predict strong fluctuation effects derived from mode fluctuations in the quantum transport through the inhomogeneous 2DEG channel caused by the spatial distribution of non-self-averaged discrete dopants.     

Quantitative electron holography of biased semiconductor devices

Electron holography is used to measure electrostatic potential profiles across reverse-biased Si p-n junctions in situ in the transmission electron microscope. A novel sample geometry based on focused ion-beam milling is developed, and results are obtained for a range of sample thicknesses and bias voltages to allow the holographic contrast to be interpreted. The physical and electrical nature of the sample surface, which is affected by sample preparation and electron beam irradiation, is discussed.     

Below-band-gap waveguiding behaviors of a weakly index-guided GaAs/AlGaAs quantum well laser

We report the reduced waveguiding efficiency for the signals around 1560 nm as the injection current of an GaAs/AlGaAs multiple quantum well laser diode (lasing wavelength at 840 nm) with a ridge-loading waveguide configuration increased. This reduction trend stopped when the injection current reached the threshold condition of the laser diode. The decreased waveguide transmission and the more expanded mode profile indicated the variation of the effective refractive index gradient in the lateral dimension with injection current. This variation was due to the refractive index decrease with increasing carrier density even below band gap. A slab waveguide model was used to simulate the lateral mode profile variation with injection current. The refractive index differences between the guiding layer and claddings in the slab waveguide model provided estimates of refractive index contrasts of the laser diode at a concerned wavelength under various injection conditions.     

Micro-Raman spectroscopy for characterization of semiconductor devices

Selected examples of the usefulness of micro-Raman spectroscopy for the analysis of semiconductor devices are discussed. This includes the determination of local temperatures in devices under operational conditions, built-in strain in processed silicon, and local crystal orientation.     

列阵半导体激光器的噪声

重点报道列阵GaAs-AlGaAs激光器相对强度噪声的测量结果,并和单元器件作了比较.实验测量包括相对强度噪声和驱动电流、调制频率以及温度的关系,并验证了在这些情况下相对强度噪声在激光器处于阈值时具有最大值的理论予言.     

大功率半导体激光器光谱合束光栅热效应分析

提出了一种大功率半导体激光器光谱合束光栅仿真模型。该模型针对光谱合束中的核心器件光栅的光-热-应力变化特性进行了分析。数值分析结果表明,当激光巴条功率为200 W,自然对流系数为10 W·(m2·K)?1时,衍射光栅上温度最高点可升高至346.52 K,应力最高点可升高至0.4825 Pa,光栅表面变量最高为52.28 nm/mm,这将会使得反馈光束中心位置发生0.25～0.3 mm的偏移,从而影响激光功率以及合束效率。减少衍射光栅基底厚度,在相同激光光源条件下工作,温度、应力、面形以及应变的变化均能有效抑制,这与实验结果具有较高的一致性。该方法为大功率半导体激光器的结构设计和光学器件的测试分析提供了有效的多物理场分析,为激光器设计和测试提供了综合分析数值模型。     

Phase transitions in a ferromagnetic semiconductor. I

An analysis is given of the conditions for ferromagnetic phase transitions in an idealised semiconductor model containing magnetic ions. The system is described by a constant interaction — 2J/N between the magnetic ions (Spin I) and the electrons, by the energy gapΔ between two infinitely narrow bands and by the concentrationc of the magnetic ions. We find a great variety of ferromagnetic behavior. In particular there exists the possibility for the magnetization to disappear with a first or second order transition as the temperature decreases or increases. Some magnetization curves are evaluated numerically.     

Optimization of semiconductor quantum devices by evolutionary search

A novel simulation strategy is proposed for searching for semiconductor quantum devices that are optimized with respect to required performances. Based on evolutionary programming, a technique that implements the paradigm of genetic algorithms in more-complex data structures than strings of bits, the proposed algorithm is able to deal with quantum devices with preset nontrivial constraints (e.g., transition energies, geometric requirements). Therefore our approach allows for automatic design, thus avoiding costly by-hand optimizations. We demonstrate the advantages of the proposed algorithm through a relevant and nontrivial application, the optimization of a second-harmonic-generation device working in resonance conditions.     

Nonlinearities in semiconductor laser amplifiers

This review discusses the physical mechanisms of absorptive and dispersive nonlinearity in amplifiers resulting from interband and intraband electron transitions, with an assessment of the relative strengths and response times of these nonlinearities. Where appropriate, the potential applications of these nonlinearities in optical networks are also indicated.     

相干长度可连续调谐的半导体激光器

实验利用光反馈的方法获得了相干长度连续可调的半导体激光光源.通过调节反馈强度及抽运电流,有效控制了光反馈半导体激光器的相干长度.其相干长度可由无反馈时的几米连续调至100 μm.同时,利用光反馈半导体激光器速率方程,数值模拟了反馈强度及抽运电流对半导体激光器相干长度的影响.实验及数值模拟均表明：通过调节反馈强度的大小可以有效控制半导体激光器的相干长度,光反馈半导体激光器的相干长度随反馈强度的增大而减小,而偏置电流对相干长度无明显影响.模拟结果与实验结果符合. 关键词： 光反馈半导体激光器 相干长度 反馈 混沌     

Tapered waveguide semiconductor raman laser

Semiconductor Raman laser can act as a heterodyne demodulator of terahertz-band modulated light wave signals in wideband optical communication systems. We have been developing the semiconductor Raman laser with a waveguide structure composed of a GaP core and Al_xGa_1–xP cladding layers. The tapered waveguide structure can reduce the threshold pump power by increasing the internal pump power density. Fabricated tapered waveguide semiconductor Raman laser have shown the threshold pump power of 160 mW. Discussion is made on the origin of losses as well as the limit of the low pump power operation.     

Study on external-cavity semiconductor laser

In this paper, a narrow-band tunable external-cavity semiconductor laser with the Littman set-up is reported. The laser system consists of a semiconductor laser, a blazed grating and an external mirror. Its sideband suppression ratio over 20 dB was obtained. Conveniently tuning in wavelength region of 797.38 - 807.26 nm was achieved. The laser is operating in single frequency with narrow linewidth smaller than 0.06 nm. The output beam has good directional stability when tuned.     

Optical switching of semiconductor laser amplifiers

The underlying physics of optical switching in bistable diode-laser amplifiers is reviewed. The importance of minimizing the switching energy of optical bistable devices is emphasized. It is shown that conventional diode-laser amplifiers are switched with only thousands of photons in less than a nanosecond. Recent developments in single quantumwell lasers allow switching with total energy (including electronic) less than a picojoule.