Giant and zero electron g factors of dilute nitride semiconductor nanowires

The electronic structures and electron g factors of InSb1-sNs and GaAs1-sNs nanowires and bulk material under the magnetic and electric fields are investigated by using the ten-band k.p model. The nitrogen doping has direct and indirect effects on the g factors. A giant g factor with absolute value larger than 900 is found in InSb1-sNs bulk material. A transverse electric field can increase the g factors, which has obviously asymmetric effects on the g factors in different directions. An electric field tunable zero g factor is found in GaAs1-sNs nanowires. (C) 2007 American Institute of Physics.

Measurement of chirp parameter and modulation index of a semiconductor laser based on optical spectrum analysis

A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods.

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 x 10(12) cm(-2) was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

Rate-equation-based circuit model of high-speed semiconductor lasers

Based oil rare equations of semiconductor laser, a symbolically-defined model for optical transmission system performance evaluation and network characterization in both time- and frequency domains is presented. The steady-state and small-signal characteristics, such as current-photon density curve, current-voltage curve, and input impedance, call be predicted from this model. Two important dynamic characteristics, second-order harmonic distortion and two-tone third-order intermodulation products, are evaluated under different driving conditions. Experiments show that the simulated results agree well with the published data. (c) 2007 Wiley Periodicals, Inc.

Tunable giant Faraday rotation of exciton in semiconductor quantum wells embedded in a microcavity

The Faraday rotation of an exciton in a GaAs quantum well (QW) embedded in a microcavity is investigated theoretically. The authors find that the Faraday rotation is enhanced remarkably by the microcavity, with a magnitude about two orders of magnitude larger than that of a single QW without microcavity. The Faraday rotation can be tuned by changing the incident angle of the pump and probe lights, or by varying the temperature or an external electric field. With an appropriate detuning between the cavity mode of the pump and probe lights, the Faraday rotation spectrum displays a strongly asymmetric line shape, which can easily be detected experimentally.

Simultaneous Q switching and mode locking with narrow envelope width in a microchip Nd : YVO4 laser with a composite semiconductor absorber

By using a composite semiconductor absorber and an output coupler, we demonstrated a Q-switched and mode-locked diode-pumped microchip Nd:YVO4 laser. With a 350-mu m-thick crystal, the width of the Q-switched envelope was as short as 12 ns; the repetition rate of the mode-locked pulses inside the Q-switched pulse was more than 10 GHz. The average output power was 335 mW at a maximum pump power of 1.6 W. Q-switched envelope widths of 21 and 31 ns were also achieved with crystals 0.7 and 1.0 mm thick, respectively.

Fabrication of photonic crystal on semiconductor materials by using focued ion-beam

A method of manufacturing two-dimensional photonic crystals on several kinds of semiconductor materials in near infrared region by a focused ion beam is introduced, and the corresponding fabrication results are presented and show that the obtained parameters of fabricated photonic crystals are identical with the designed ones. Using the tunable laser source, the spectra of the fabricated passive photonic crystal and the active photonic crystal are measured. The experiment demonstrates that the focused ion-beam can be used to fabricate the perfect two-dimensional photonic crystals and their devices.

Broad-band semiconductor optical amplifiers

Broad-band semiconductor optical amplifiers (SOAs) with different thicknesses and thin bulk tensile-strained active layers were fabricated and studied. Amplified spontaneous emission (ASE) spectra and gain spectra of SOAs were measured and analyzed at different CW biases. A maximal 3 dB ASE bandwidth of 136 nm ranging from 1480 to 1616 nm, and a 3 dB optical amplifier gain bandwidth of about 90 nm ranging from 1510 to 1600 nm, were obtained for the very thin bulk active SOA. Other SOAs characteristics such as saturation output power and polarization sensitivity were measured and compared. (c) 2006 Elsevier B.V. All rights reserved.

XPS depth profiling study of n/TCO interfaces for p-i-n amorphous silicon solar cells

Detailed X-ray photoelectron spectroscopy (XPS) depth profiling measurements were performed across the back n-layer/transparent conducting oxide (n/TCO) inter-faces for superstrate p-i-n solar cells to examine differences between amorphous silicon (a-Si:H) and microcrystalline silicon (mu c-Si:H) n-layer materials as well as TCO materials ZnO and ITO in the chemical, microstructural and diffusion properties of the back interfaces. No chemical reduction of TCO was found for all variations of n-layer/TCO interfaces. We found that n-a-Si:H interfaces better with ITO, while n-mu c-Si:H, with ZnO. A cross-comparison shows that the n-a-Si:H/ITO interface is superior to the n-mu c-Si:H/ZnO interface, as evidenced by the absence of oxygen segregation and less oxidized Si atoms observed near the interface together with much less diffusion of TCO into the n-layer. The results suggest that the n/TCO interface properties are correlated with the characteristics of both the n-layer and the TCO layer. Combined with the results reported on the device performance using similar back n/TCO contacts, we found the overall device performance may depend on both interface and bulk effects related to the back n/TCO contacts. (c) 2006 Elsevier B.V. All rights reserved.

Electronic noise of diluted magnetic semiconductor (Ga,Mn)As around Curie point

National Natural Science Foundation of China 10674129

A comparison between contactless electroreflectance and photoreflectance spectra from n-doped GaAs on a semi-insulating GaAs substrate

Contactless electroreflectance (CER) and photoreflectance (PR) measurements have been performed on samples with the structure of an n-doped GaAs epitaxial layer on a semi- insulating GaAs substrate. Modulated reflectance signals from the n-GaAs surface and those from the n-GaAs/SI-GaAs interface are superposed in PR spectra. For the case of CER measurement, however, Franz-Keldysh oscillations (FKOs) from the interface, which are observed in PR spectra, cannot be detected. This discrepancy is attributed to different modulation mechanisms of CER and PR. In CER experiments, the electric field modulation cannot be added to the interfacial electric field because of the effective screening by the fast response of carriers across the interface. FKOs from the interface without any perturbation by the surface signals are extracted by subtracting CER spectra from PR spectra.

Semiconductor-metal transition in InSb nanowires and nanofilms under external electric field

The electronic structures, Rashba spin-orbit couplings, and transport properties of InSb nanowires and nanofilms are investigated theoretically. When both the radius of the wire (or the thickness of the film) and the electric field are large, the electron bands and hole bands overlap, and the Fermi level crosses with some bands, which means that the semiconductors transit into metals. Meanwhile, the Rashba coefficients behave in an abnormal way. The conductivities increase dramatically when the electric field is larger than a critical value. This semiconductor-metal transition is observable at the room temperature. (c) 2006 American Institute of Physics.

Passively mode-locked Nd : YVO4 laser using semiconductor saturable absorption mirrors of interface states relaxation region

Semiconductor saturable absorber mirrors (SESAMs) with GaAs/air interface relaxation region have less nonsaturable loss than those with low temperature grown In0.25Ga0.75As relaxation region. A thin layer Of SiO2 and a high reflectivity film Of Si/(SiO2/Si)(4) were coated on the SESAMs, respectively in order to improve the SESAM's threshold for damage. The passively continuous wave mode-locked lasers with two such SESAMs were demonstrated, and the SESAM with high reflectivity film of Si/(SiO2/Si)(4) is proved to be helpful for high output power. (c) 2006 Elsevier GmbH. All rights reserved.

Optical characteristics of DBR with inhomogeneous graded interfaces

Optical properties of Al0.9Ga0.1As/Al gamma Ga1-gamma As/GaAs/Al chi Ga1-chi As DBR with inhomogeneous graded interfaces has been investigated by using characteristic matrix method. The refractive index model and the analytic characteristic matrix of graded interfaces are obtained. The reflectance spectrum and the reflective phase shift are calculated for GaAs/Al-0.9 Ga-0.1 As DBR and graded interfaces DBR by using characteristic matrix method. The effect of graded interfaces on the optical properties of DBR is discussed. The result shows an extra graded phase matching layer must he added in front of the graded interfaces DBR to fulfil the conditions of phase matching at central wavelength. The accurate thickness of phase matching layer is calculated by optical thickness approximation method.

High-repetition rate Q-switched Nd : YVO4 laser with a composite semiconductor absorber

A diode-pumped Nd:YVO4 laser passively Q switched by a semiconductor absorber is demonstrated. The Q-switched operation of the laser has an average output power of 135 mW with a 1.6 W incident pump power. The minimum pulse width is measured to be about 8.3 ns with a repetition rate of 2 MHz. To our knowledge, this is the first demonstration of a solid-state laser passively Q-switched by such a composite semiconductor absorber. (c) 2006 Optical Society of America.