Verification of EL2 electronic absorption effect on charge transfer in semi-insulating GaAs

The electronic absorption of EL2 centers has been clarified to be related to the electron acid hole photoionizations, and the transition from its ground state to metastable state, respectively. Under an illumination with a selected photon energy in the near infrared region, these three processes with different optical cross sections will show different kinetics against the illumination time. It has recently been shown that the photosensitivity (measured under 1.25 eV illumination) of the local vibrational mode absorption induced by some deep defect centers in SI-GaAs is a consequence of the electron and hole photoionizations of EL2. This paper directly measures the kinetics of the electronic transition associated with EL2 under 1.25 eV illumination, which implies the expected charge transfer among different charge states of the EL2 center. A calculation based on a simple rate equation model is in good agreement with the experimental results.

BROADENING OF THE EXCITONIC LINEWIDTH DUE TO SCATTERING OF 2-DIMENSIONAL FREE-CARRIERS

By photoluminescence measurements we find that at low temperature the linewidth of the excitonic luminescence broadens with increasing electron density in the wider well from a photoexcited type-I-type-II mixed GaAs/AlAs asymmetric double quantum well structure, which even makes the excitonic linewidth at 77 K larger than at 300 K above a certain excitation intensity. We verify that the broadening is due to the scattering of two-dimensional carriers to excitonic states. Based on the theory of the scattering of carriers to excitonic states, we calculate the broadening of the excitonic linewidth. Our experimental results are convincing for verifying the theoretical prediction. (C) 1995 American Institute of Physics.

INFRARED-ABSORPTION DUE TO 2-DIMENSIONAL-ELECTRON-GAS COLLECTIVE EXCITATION IN GAAS/ALXGA1-XAS MULTIPLE-QUANTUM-WELL STRUCTURES

Infrared absorption due to a collective excitation of a two-dimensional electronic gas was observed in GaAs/AlxGa1-xAs multiple-quantum wells when the incident light is polarized parallel to the quantum-well plane. We attribute this phenomenon to a plasma oscillation in the quantum wells. The measured wavelength of the absorption peak due to the plasma oscillation agrees with our theoretical analysis. In addition, in this study the plasma-phonon coupling effect is also fitted to the experimental result. We show that the absorption is not related to the intersubband transitions but to the intrasubband transition, which originates from a plasma oscillation.

A RESONANT RAMAN-STUDY ON PHONONS IN GAINAS/ALINAS MULTIPLE-QUANTUM WELLS

The LO phonon modes in the barrier layers of a GaInAs/AlInAs multiple quantum well structure are investigated by resonance Raman scattering (RRS), the excitation laser photon energy tuned to resonate with the above barrier interband transition energy. The resonance enhancement of LO phonon peaks are shown to be caused by Frohlich electron-phonon interaction. The pressure-dependent profiles for both AlAs-like (LO(2) mode) and InAs-like (LO(1) mode) Raman peak intensities are well fitted by the Gaussian lineshape. The shift between these two profiles can be explained by the outgoing RRS mechanism, providing information on the pressure-induced shift of the excitonic transition energy. The amplitude ratios of the two profiles are close to 1, showing a well defined two-mode behavior and the nearly equal polarizability for Al-As and In-As bonds in AlInAs alloy.

Wet etching and infrared absorption of AlN bulk single crystals

The defects and the lattice perfection of an AlN (0001) single crystal grown by the physical vapor transport (PVT) method were investigated by wet etching, X-ray diffraction (XRD), and infrared absorption, respectively. A regular hexagonal etch pit density (EPD) of about 4000 cm~(-2) is observed on the (0001) A1 surface of an AlN single crystal. The EPD exhibits a line array along the slip direction of the wurtzite structure, indicating a quite large thermal stress born by the crystal in the growth process. The XRD full width at half maximum (FWHM) of the single crystal is 35 arcsec, suggesting a good lattice perfection. Pronounced infrared absorption peaks are observed at wave numbers of 1790, 1850, 2000, and 3000 cm~(-1), respectively. These absorptions might relate to impurities O, C, Si and their complexes in AlN single crystals.

Offset quantum-well method for tunable distributed Bragg reflector lasers and electro-absorption modulated distributed feedback lasers

A two-section offset quantum-well structure tunable laser with a tuning range of 7 nm was fabricated using offset quantum-well inethod. The distributed Bragg reflector （DBR） was realized just by selectively wet etching the multiquantum-well （MQW） layer above the quaternary lower waveguide. A threshold current of 32 mA and an output power of 9 mW at 100 mA were achieved. Furthermore, with this offset structure method, a distributed feedback （DFB） laser was integrated with an electro-absorption modulator （EAM）, which was capable of producing 20 dB of optical extinction.

A Wavelength Tunable DBR Laser Integrated with an Electro Absorption Modulator by a Combined Method of SAG and QWI

We report a wavelength tunable electro-absorption modulated DBR laser based on a combined method of SAG and QWI. The threshold current is 37mA and the output power at 100mA gain current is 3.5mW. When coupled to a single-mode fiber with a coupling efficiency of 15% ,more than a 20dB extinction ratio is observed over the change of EAM bias from 0 to -2V. The 4.4nm continuous wavelength tuning range covers 6 channels on a 100GHz grid for WDM telecommunications.

Passively Mode Locked Diode-End-Pumped Yb∶YAB Laser with High Reflectivity Type Semiconductor Saturable Absorption Mirror

利用金属有机气相淀积方法生长了一种新型吸收体:高反射率半导体可饱和吸收镜.用这种吸收体兼作端镜,实现了1.044μm半导体端面泵浦Yb∶YAB激光器被动锁模,脉冲宽度为3.05ps,重复率为375MHz,输出功率为45mW.

Monolithic Integration of Electro-Absorption Modulators and DFB Lasers by Modified Double Stack Active Layer Approach

Monolithic electro-absorption modulated distributed-feedback(DFB) lasers are proposed and fabricated by using a modified double stack active layer.The 38mA threshold,9dB extinction ratio (from 0.5V to 3.0V),and about 5mW output power at the 100mA operation current are achieved.Compared with other reported results (only 1.5mW at the same operation current) of the traditional stack active structure,the proposed structure improves the output power of devices.

Nonlinear Absorption Properties of nc-Si∶H Thin Films

于2010-11-23批量导入

Raman scattering and infrared absorption of silicon nanocrystals in silicon oxide matrix

Structural dependence on annealing of a-SiOx:H was studied by using infrared absorption and Raman scattering. The appearance of Raman peaks in the range of 513-519cm(-1) after 1170 degreesC annealing was interpreted as the formation nanocrystalline silicon with the sizes from 3-10nm. The Raman spectra also show the existence of amorphous-like silicon phase, which is associated with Si-Si bond re-construction at boundaries of silicon nanocrystallites. The presence of the shoulder at 980cm(-1) of Si-O-Si stretching vibration at 1085cm(-1) in infrared spectra imply that except that SiO2 phase, there is silicon sub-oxide phase in the films annealed at 1170 degreesC. This sub-oxide phase is located at the interface between Si crystallites and SiO2, and thus support the shell model for the mixed structures of Si grains and SiO2 matrix.

Strained MQW electro-absorption modulators with high extinction ratio and low capacitance

We fabricate an electro-absorption modulator for optical network system using a new strategy, the improved modulation properties of the strained InGaAs/InAlAs MQW show it's polarization independent, high extinction ratio (> 40dB) and low capacitance (C <0.6pF) which can achieve an ultra-high frequency(> 10GHz). The device is be used in 10Gbps optical time division multiplex (OTDM) system as a signal generator.

Light-induced change of Si-H bond absorption in hydrogenated amorphous silicon

Device-quality a-Si:H films were prepared by glow discharge CVD with pure or H-diluted silane as well as by hot-wire CVD. The hydrogen content was varied from similar to 2 to 15 at. %. The Si-H bond absorption and its light-soaking-induced changes were studied by IR and differential IR absorption spectroscopes. The results indicate that the more stable sample exhibits an increase of the absorption at wave number similar to 2000 cm(-1), and the less stable one exhibits a decrease at similar to 2040 cm(-1) and an increase at similar to 1880 cm(-1).

The plasmon resonance absorption of Ag/SiO2 nanocomposite films

The plasmon resonance absorption of the Ag/SiO2 nanocomposite film is investigated. The measured absorption spectra are compared with those calculated by the Mie theory. The results indicate that the Mie theory on the basis of classical electrodynamics can only partially explain the optical absorption spectra of the Ag/SiO2 nanocomposite film. We believe that the plasmon resonance absorption is mainly an intrinsic quality of the metal particle, and can be explained only with the electronic structure of the metal particle. In the latter, surface resonance state is introduced to systematically discuss the optical absorption spectra of the Ag/SiO2 nanocomposite film. (C) 2003 Elsevier Science B.V. All rights reserved.