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To confirm the actual effect of an exponential-doped structure on cathode performance, an exponential-doped structure was applied to the preparation of a transmission-mode GaAs photocathode, and spectral response curves after high-temperature activation, low-temperature activation, and the indium sealing process were separately measured by use of the on-line spectral response measurement system. The results show that, compared to the previously uniform-doped photocathode, the exponential-doped photocathode can obtain higher cathode performance and photoemission capability because of the built-in electric field. Nevertheless, cesium desorption and impurity of gas during the sealing process can cause the degeneration of spectral response in the entire response waveband, especially in the long-wavelength region, with the decrease in surface electron escape probability related to the adverse evolution of the surface potential barrier profile. OCIS codes: 160.2100, 250.0250.

We describe a microreflectance difference ([mu]RD) spectrometer based on a charge coupled device (CCD), in contrast to most common RD spectrometers that are based on a photomultiplier or a photodiode as a light detector. The advantage of our instrument over others is the possibility to isolate the RD spectrum of specific areas of the sample; thus topographic maps of the surface can be obtained. In our setup we have a maximum spatial resolution of approximately 2.50 [micro]m x 2.50 [micro]m and a spectral range from 1.2 to 5.5 eV. To illustrate the performance of the spectrometer, we have measured strains in mechanically polished GaAs (001) single crystals. OCIS codes: 120.2130, 120.6200, 300.6470, 110.0180.

Obtaining higher quantum efficiency and more stable GaAs photocathodes has been an important developmental direction in the investigation of GaAs photocathodes. One significant approach to this problem is to improve the electron diffusion length. We put forward and investigate an exponential doping mode GaAs photocathode. It was proved by theoretical and experimental results that, because the exponential doping structure is in favor of forming a directional constant built-in electric field, the electron diffusion and drift length of the cathode material can accordingly be enhanced. The mathematical expression of the electron diffusion and drift length [L.sub.DE] of an exponential doping photocathode was deduced, and the relationship between the doping coefficient and the electron diffusion and drift length is made certain. This investigation contributes to the understanding of varied doping GaAs photocathodes and provides guidance to optimize the doping structure of GaAs photocathodes for higher quantum efficiency. [c] 2009 Optical Society of America OCIS codes: 160.2100, 250.0250.

An InGaAlAs-based component and an InGaAsP-based component are integrated by using a butt-jointing process with in situ cleaning. The results have shown that InGaAlAs-InGaAsP hetero-material integrated devices can be used for next-generation high-speed data links.

The impact of a 2-D-charged carrier reservoir for high-speed optical amplification and modulated lasing in quantum dot (QD)-based devices is discussed by testing the amplification of short trains of high power, femtosecond optical pulses in an InGaAs QD-in-a-well-based semiconductor optical amplifier (SOA). The high optical pump power close to the device saturation regime has shown that the ultrafast SOA dynamics is governed by the overall injection current.

The [alpha]-parameters of both conventional and broadband semiconductor quantum dot (Qdot) lasers below and above threshold injection are analyzed by using a rate-equation model. The results have shown that the linewidth enhancement factor from the ground state of broadband Qdot lasers is larger but in the same order of magnitude as compared to that of conventional Qdot lasers.

The band-edge optical properties of highly strained In(Ga)As/InGaAs quantum wells (QWs) are analyzed by using 6- and 8-band k.p theory. The photoluminescence peak wavelength and absorption spectra of In(Ga)As/InGaAs quantum wells calculated by 8-band model have agreed with the experiment.

A theoretical model is used for explaining the quasi-supercontinuum interband emission from InGaAs/GaAs self-assembled semiconductor quantum dots lasers by accounting for both inhomogeneous and homogeneous optical gain broadening. The results have derived the optical gain broadening in the broadband lasers based on semiconductor quantum-confined nanostructure materials.

A study was conducted to evaluate the electrostatic potential profile across the p-n junction of an AlGaAs/GaAs light-emitting diode (LED) with linearly graded triangular AlGaAs barriers using off-axis electron holography. Results suggest that electron holography measurements shared with modeling present device designers a helpful tool for analyzing doping profiles in complex heterostructures.

A theoretical model is used for examining the lasing spectrum properties of InAs-InP(113)B quantum dot (QD) lasers emitting at 1.55 [micro]m. Unlike InAs-GaAs QD lasers emitting at 1.3 [micro]m, the studies have shown that a continuous transition from the GS to the excited state (ES) is displayed because of the large inhomogeneous broadening comparable to the GS and ES lasing energy difference.

Inductively coupled argon plasma (ICP)-enhanced quantum-well intermixing (QWI) on the quaternary materials InGaAs(P)-InP quantum-well structure is examined. The large blue and red shift is realized with p-InP and n-InGaAs caps by controlling the diffusion length ratio for interdiffusion on two sublattices.

An active quenching application-specific integrated circuit (ASIC) is described for use in conjunction with InGaAs-InP avalanche photodiodes (APDs) for detecting 1550-nm single-photon. The results have shown that the performance of APDs with an on-chip quenching circuit has surpassed the conventional quenching electrons and has made them suitable for quantum cryptography.

A set of dots with a bi-modal distribution is exploited and is used as a method for identifying two different groups of dots that are spatially independent of each other. The studies have confirmed that the minimum in the temperature dependence of threshold current seen in many quantum dot (QD) lasers is associated with the increased relative population of higher lying states as the temperature is reduced due to a transition to nonthermal behavior at low temperature.

A modulated bias measurement setup is used for examining the effect of modulated voltage on the nonlinear response of the InGaAs-InP charge-compensated modified uni-traveling carrier photodiode. A simple equivalent circuit model is used for explaining the frequency characteristics of the intermodulation distortions caused by the modulated bias.

The high-performance continuous-wave (CW) operation of 10-m-wide quantum-cascade lasers (QCLs) emitting at approximately 4.6[mu] m is discussed. Results suggest the achievement of the maximum wall-plug efficiencies of 8.6 percent in pulsed and 3.1percent in CW operations at 298 K.

InGaAs quantum wells and a Bragg mirror structure are grown on a GaAs substrate to simultaneously serve as a low-loss saturable absorber and an output coupler for highly efficient Q switching of a diode-pumped Nd:YAG laser operating at 946 nm. With an incident pump power of 9.2 W, the laser produces pulses of 38 ns duration with average pulse energy of as much as 20 [micro]J at a pulse repetition rate of 55 kHz. OCIS codes: 140.3480, 140.3540, 140.3580.

A doubly Q-switched laser with both an acousto-optic (AO) modulator and a GaAs saturable absorber can obtain a more symmetric and shorter pulse with high pulse peak power, which has been experimentally proved. The key parameters of an optimally coupled doubly Q-switched laser with both an AO modulator and a GaAs saturable absorber are determined, and a group of general curves are generated for what we believe is the first time, when the single-photon absorption (SPA) and two-photon absorption (TPA) processes of GaAs are combined, and the Gaussian spatial distributions of the intracavity photon density and the initial population-inversion density as well as the influence of the AO Q-switch are considered. These key parameters include the optimal normalized coupling parameter, the optimal normalized GaAs saturable absorber parameters, and the normalized parameters of the AO Q-switch, which can maximize the output energy. Meanwhile, the corresponding normalized energy, the normalized peak power, and the normalized pulse width are given. The curves clearly show the dependence of the optimal key parameters on the parameters of the gain medium, the GaAs saturable absorber, the AO Q-switch, and the resonator. Sample calculations for a diode-pumped [Nd.sup.3+]:[YVO.sub.4] laser with both an AO modulator and a GaAs saturable absorber are presented to demonstrate the use of the curves and the relevant formulas. [C] 2007 Optical Society of America OCIS codes: 140.0140, 140.3540, 140.5560.

An analysis on the application of resonant cavities to the photon-frequency-upconversion-based far-infrared (FIR) semiconductor imaging devices is performed. It suggested that applying bottom mirror (BM) for the GaAs homojunction interfacial work-function internal photoemission (HIWIP) FIR detector and distributed Bragg reflector(DBR) cavity for the near-infrared(NIR) light-emitting diodes (LEDs) .

The effects of the optically induced transition from the excitonic, insulating regime, to the plasma, metallic regime, on the spectra and on the photoluminescence dynamics of GaAs are examined. The critical density for transition is obtained with the unprecedented resolution through the study of characteristics of photoluminescence dynamics.

The polarization-resolved photoluminescence emitted from InGaAs/AlGaAs single quantum dots (QDs), which are grown in inverted tetrahedral pyramids, are studied. It is seen that the emitted light is detected for two mutually perpendicular linear polarization directions in the less conventional cleaved-edge geometry.

A systematic study of layered structures containing an InGaNAs/GaAs single quantum well (SQW) sandwiched between type-II AlAs/GaAs superlattices (SL) was carried out. The predominant optically detected cyclotron resonance (ODCR) peak was shown to be related to carriers with a 2D character and a cyclotron resonance effective mass.

The article details the technique of valence band splitting in epitaxial lift-off (ELO) GaAs film bonded to silicon. The ELO technique introduces strain in GaAs films, where the strain incorporated is due to the difference in the thermal expansion coefficients of GaAs and silicon.

The optical properties of InAs/GaAs quantum well (QW) structures were studied by photoreflectance (PR) modulation spectroscopy, photoluminescence (PL) and atomic force microscopy. The transitions connected with a thin InAs/GaAs QW are visible for all samples.

A Monte Carlo simulation of the electron transport incorporating the T-, as well as the X-valley states in various GaAs-based midinfrared quantum cascade lasers (QCLs) is presented. The analysis shows that the leakage current of the QCLs at the room temperature is extremely high, as the value of the leakage current highly depends on the temperature, as well as the occupation of the X-valley subbands.

The fabrication and characterization of the thermophotovoltaic converters based on [In.sub.0.69][Ga.sub.0.31]As/In[As.sub.0.34][P.sub.0.66] is presented. The recombination velocity for the InGaAs/InAsP interface is found to be below 2000 cm/s.