Modulation of absorption and refractive index in Er3 -doped fibers

Modulation of the absorption and refractive index in Er³⁺-doped fibers for a signal wavelength in the 1550-nm band and a pump wavelength of 980 nm is investigated. The experimental results are compared with a model that takes into account optical transitions between the ground state and the metastable state in Er³⁺. Good agreement between the experiment and the model is obtained apart from a wavelength-independent constant in the refractive index modulation, which is discussed.     

用于高功率激光装置中的电脉冲整形系统

采用射频GaAs场效应管和微带传输线技术,研制出用于高功率激光装置中的电脉冲整形系统.该系统电脉冲整形宽度为3.5 ns,幅度在0~5 V范围内调节,时域调整精度200 ps.整形后的方波,前沿383 ps,后沿642 ps,顶部不平坦度4~5%,波形幅度稳定性4~5%（p-p).利用该系统产生的整形电脉冲驱动电光波导调制器进行激光脉冲整形,得到了理想的整形激光脉冲.     

The oxidation of GaAs(1 0 0) surfaces under atmospheric pressure conditions studied in real time using dynamic reflectance anisotropy spectroscopy at 2.6 and 4 eV

Using real-time, dynamic reflectance anisotropy spectroscopy (RAS) at both 2.6 eV and 4.0 eV, we demonstrate that an anisotropic oxide will form on As rich c(4 × 4)/d(4 × 4) GaAs surfaces when exposed to moisture- free air diluted in inert gases in a metal organic chemical vapour deposition (MOCVD) reactor, and that the initial c(4 × 4)/d(4 × 4) structure effects the resulting optical anisotropy of the oxide. This was achieved by investigating how the RA signals at 2.6 eV and 4 eV of annealed GaAs (1 0 0) surfaces evolve relative to the as-etched and as-annealed signals when exposed to oxygen. It is found that while the 2.6 eV response, which is known to be associated with the As dimers, degrades to pre-process levels indicating their destruction, the 4 eV signal, stabilizes at an intermediate, permanent level, suggesting the formation of an anisotropic oxide film whose structure is determined at least in part, by the initial c(4 × 4)/d(4 × 4) surface.     

Accurate Small-Signal Model Extraction for pHEMT on GaAs

An accurate small-signal modeling approach applied to GaAs-based pHEMT devices is presented. The procedure for extracting equivalent-circuit model parameters is illustrated in detail. A genetic algorithm (GA) program is developed to optimize the model parameters in order to improve the modeling accuracy. The validity of modeling approach is verified by comparing the simulated and measured result of two pHEMTs and a fabricated ka-band power amplifier. The conclusion can be drawn that the proposed modeling method is rather accurate and efficient.     

砷化镓探测器的镉上中子辐照改性

介绍反应堆镉上中子辐照改性的掺铬砷化镓（ＧａＡｓ：Ｃｒ）和本征砷化镓（ＧａＡｓ）光电导探测器，研究了探测器的响应时间、粒子灵敏度及输出电流随镉上中子辐照改性注量和施加偏压的变化关系。     

Study into the shape of oxide lines formed by LAO - Influence of an oxidized material

Linear oxide patterns were formed by local anodic oxidation (LAO) using an atomic force microscope (AFM) on an n-doped GaAs substrate, a 10-nm-thick titanium layer, and on shallow GaAs/AlGaAs-based heterostructures capped either with a 5-nm-thick undoped GaAs layer or a 2-nm-thick undoped InGaP layer. Each heterostructures had a 2DEG buried at a specific depth between 22 and 45 nm. LAO was performed in contact and non-contact AFM modes with the aim to explain the phenomenon of single and double line formation depending on material oxidized. The occurrence of the phenomenon was also simulated. The results showed that the occurrence of the double lines is linked with the thickness of native oxides.     

Effects of Si-doped GaAs layer on optical properties of InAs quantum dots

We have investigated the optical properties of InAs self-assembled quantum dots (SAQDs) with the Si-doped GaAs barrier layer. Two types of samples are fabricated according to the position of the Si-doped GaAs layer. For type A samples the Si-doped GaAs layer is grown below the QDs, whereas for type B samples the Si-doped GaAs layer is grown above the QDs. For both types of samples the excited-state emissions caused by state filling are observed in photoluminescence (PL) spectra at high excitation power densities. The bandgap renormalization of QDs can be found from the shift of the PL peak energy. Particularly, for type A samples the Si atoms act as nucleation centers during the growth of InAs QDs on the Si-doped GaAs layer and affect the density and the size of the QDs. The Si-doped GaAs layer in type A samples has more effects on the properties of QDs, such as state filling and bandgap renormalization than those of type B samples.     

Transport properties of a lateral semiconductor quantum dot defined by a single connected metallic front-gate

We present studies on the electric transport in a lateral GaAs/AlGaAs quantum dot defined by a patterned single connected metallic front-gate. This gate design allows to easily couple a large number of quantum dots and therefore holds high potential in the design of new materials with tailor-made band structures based on quantum dot superlattices of controlled shape. Clear Coulomb diamond structures and well pronounced tunneling peaks observed in experiment indicate that single-electron control has been achieved. However, the dependence on electron density in the heterostructure embedding the dot, which is controlled by an additional back-gate, reveals that transport characteristics are strongly influenced supposedly by potential fluctuations in the dot and lead regions.     

半绝缘GaAs光电导开关的超线性时间响应分析

报道了用1064nm激光脉冲触发电极间隙为3mm的横向半绝缘GaAs 光导开关的实验结果.对半绝缘GaAs光电导开关的超线性时间响应特性做了分析,表明半绝缘GaAs材料EL2能级对电子和空穴的俘获截面有较大的差异,这种较大的差异造成开关对激光脉冲的超快响应.     

Diffusion process of electrons injected from STM tip into AlGaAs/GaAs quantum wells

We have investigated the electron diffusion process in Al_0.3Ga_0.7As/GaAs quantum well (QW) structures by means of scanning tunneling microscope light emission (STM-LE) spectroscopy. The optical measurements were performed on a cleaved (1 1 0) surface at room temperature. The STM-LE spectra were measured by injecting hot electrons from the tip positioned at different distances from the QWs. The emission intensity from individual wells as a function of the tip-well distance was found to decay with two distinct decay constants. From comparison with Monte Carlo simulations for hot electron relaxation, we found that the intervalley scattering from the Γ valley to the L and X valleys has the most significant effect on the diffusion process of the injected electrons.