A 10-GHz Bandwidth Electroabsorption Modulated Laser by Ultra-Low-Pressure Selective Area Growth

A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multiquantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0-30μm). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19mA, over 24 dB extinction ratio when coupled into a single mode fibre. More than 10 GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.

Application of step-scan FTIR to the research of quantum cascade lasers

The principle of step-scan Fourier transform infrared （FTIR） spectroscopy is introduced. Double modulation step-scan FTIR technique is used to obtain the quantum cascade laser＇s stacked emission spectra in the time domain. Optical property and thermal accumulation of devices due to large drive current are analyzed.

LPCVD Growth of 3C-SiC on Si Mesas and SiO2/Si Substrates for MEMS Applications

This paper presents the development of LPCVD growth of 3C-SiC thin films grown on Si mesas and thermally oxidized SiO2 masks over Si with an area of 150 × 100μm^2 and SiO2/Si substrates. The growth has been performed via chemical vapor deposition using SiH4 and C2H4 precursor gases with carrier gas of H2. 3C-SiC films on these substrates were characterized by optical microscopy, X-ray diffraction （ XRD ）, X-ray photoelectron spectroscopy （ XPS ）, scanning electron microscopy （SEM） and room temperature Hall effect measurements. It is shown that there were no voids at the interface between 3C-SiC and SiO2.

Optical Pr operties of GaNAs and GaAsSb Semiconductors

Under short pulse laser excitation, it has been observed, for the first time, a new high-energy photoluminescence emission from GaNx As1- x/GaAs SQWs. This new emission has totally different optical properties compared with the localized exciton transition in GaNx As1-x, and is attributed to the recombination of delocalized excitons in QWs. At the same time, a competition process between localized and delocalized exciton emissions in GaNx As1-x/GaAs quantum wells is observed in the temperaturedependent PL spectra under the short pulse excitation. This competition process for the first time, reveals the physical origin of the temperature-induced S-shaped PL peak shift, which was often reported in the disordered alloy semiconductor system under continuous-wave excitation and puzzled people for a long time. We have also investigated a set of GaNx As1- x samples with small nitrogen composition( x ＜ 1% )by PL, and time-resolved PL. After the PL dependence on temperature and excitation power and PL dynamics were measured, the new PL peak was identified as an intrinsic transition of alloy, rather than N-related bound states. This is the first observation in PL, showing that alloy state exists in GaNx As1- x materials even when N composition is smaller than 0.1%. Finally by selective excitation,both type-Ⅰ and type-Ⅱ transitions were observed simultaneously in GaAs1-xSbx/GaAs SQWs for the first time.

Effect of Annealing on Structural and Magnetic Properties of a Thick (Ga,Mn)As Layer

We investigate effects of annealing on magnetic properties of a thick (Ga,Mn)As layer, and find a dramatic increase of the Curie temperature from 65 to 115 K by postgrowth annealing for a 500-nm (Ga,Mn)As layer. Auger electron spectroscopy measurements suggest that the increase of the Curie temperature is mainly due to diffusion of Mn interstitial to the free surface. The double-crystal x-ray diffraction patterns show that the lattice constant of (Ga,Mn)As decreases with increasing annealing temperature. As a result, the annealing induced reduction of the lattice constant is mainly attributed to removal of Mn interstitial.

Raman Investigatins of 3C-SiC Films Grown on Si (100) and Sapphire (0001) by LPCVD

The Raman measurements have been performed with the back-scattering geometry on the SiC films grown on Si(100) and sapphire (0001) by LPCVD. Typical TO and LO phonon peaks of 3C-SiC were observed for all the samples grown on Si and apphire substrates, indicating the epilayers are 3C-SiC polytype. Using a free-standing 3C-SiC film removed from Si(100) as a free-stress sample, the stresses of 3C-SiC on Si(100) and sapphire (0001) were estimated according to the shift of TO and LO phonons.

Origin of flat-band voltage sharp roll-off in metal gate/high-k/ultrathin- SiO2/Si p-channel metal-oxide-semiconductor stacks

The origin of the flat band voltage roll-off (V-FB roll-off) in metal gate/high-k/ultrathin-SiO2/Si metal-oxide-semiconductor stacks is analyzed and a model describing the role of the dipoles at the SiO2/Si interface on the V-FB sharp roll-off is proposed. The V-FB sharp roll-off appears when the thickness of the SiO2 interlayer diminishes to below the oxygen diffusion depth. The results derived using our model agree well with experimental data and provide insights to the mechanism of the V-FB sharp roll-off.

The role of zinc dopant and the temperature effect on the controlled growth of InNnanorods in metal-organic chemical vapor deposition system

This work was supported by the National Science Foundation of China (60976008 and 60776015), the Special Funds for Major State Basic Research Project (973 program) of China (2006CB604907), and the 863 High Technology R&D Program of China (2007AA03Z402 and 2007AA03Z451). The authors express their appreciations to Prof. Yongliang Li (Analytical and Testing Center, Beijing Normal University) for FE-SEM measurements, to DrTieying Yang and Prof. Huanhua Wang (Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences) for XRD measurements and helpful discussions.

Fermi-Level Pinning at Metal/High-k Interface Influenced by Electron State Density of Metal Gate

The Fermi-level pinning (FLP) at the metal/high-k interface and its dependence on the electron state density of the metal gate are investigated. It is found that the FLP is largely determined by the distortion of the vacuum level of the metal which is quantitatively ruled by the electron state density of the metal. The physical origin of the vacuum level distortion of the metal is attributed to an image charge of the interface charge in the metal. Such results indicate that the effective work function of the metal/high-k stack is also governed by the electron state density of the metal.

The growth of ZnO on bcc-In2O3 buffer layers and the valence band offset determined by X-ray photoemission spectroscopy

This work was supported by the 863 High Technology R&D Program of China (Grant Nos. 2007AA03Z402 and 2007AA03Z451), the Special Funds for Major State Basic Research Project (973 program) of China (Grant No. 2006CB604907), and the National Science Foundation of China (Grant Nos. 60506002 and 60776015). The authors express their appreciation to Dr. Tieying Yang and Prof. Huanhua Wang (Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences) for XRD measurements and helpful discussions.

Intersubband absorption energy shifts in 3-level system for asymmetric quantum well terahertz emitters

Intersubband absorption energy shifts in 3-level system stemming from depolarization and excitonlike effects are investigated. Analytically, the expressions we derive present good explanations to the conventional 2-level results and bare potential transition energy results; and numerical results show that they are more exact than the previous studies to describe the 3-level system depolarization and excitonlike shift (DES) character especially for higher carrier density (more than 8 x 10(11) cm(-2)). One interesting detail we find is that the "large blue" DES becomes "slight redshift" in the low doping limit (less than 1.9 x 10(11) cm(-2)), which may be neglected by the previous studies of intersubband transitions. Temperature character of DES in the step well structure is also numerically studied. Finally the above are applied to calculate asymmetric step quantum well structures. The two main functional aspects of terahertz (THz) emitters are discussed and several basic optimizing conditions are considered. By adjusting the well geometry parameters and material composition systematically, some optimized structures which satisfy all of the six conditions are recommended in tables. These optimizations may provide useful references to the design of 3-level-based optically pumping THz emitters.

Numerical Study on the Distribution Characteristics of TP in Taihu Lake, China

A depth-averaged two-dimensional hydrodynamics model and a two-dimensional water quality model, bases on the alternating direction implicit (ADI) method, is developed to study the distribution characteristics of total phosphorus (TP) in Taihu Lake. Wind stress, the pollution source from the inflow rivers, releasing rate of TP from the bottom sediment and water diversion from Yangtze River are the effecting factors of TP distribution. By using the model proposed in this paper, the concentration field of the total phosphorus was simulated, which leads to the conclusion that the flow field has a great influence on the spatial and temporal distribution of TP in the Taihu Lake.

Isospin effects of the Skyrme potential and the momentum dependent interaction at intermediate energy heavy ion collisions

We improve the isospin dependent quantum molecular dynamical model by including isospin effects in the Skyrme potential and the momentum dependent interaction to obtain an isospin dependent Skyrme potential and an isospin dependent momentum interaction. We investigate the isospin effects of Skyrme potential and momentum dependent interaction on the isospin fractionation ratio and the dynamical mechanism in intermediate energy heavy ion collisions. It is found that the isospin dependent Skyrme potential and the isospin dependent momentum interaction produce some important isospin effects in the isospin fractionation ratio

Measurements of bremsstrahlung spectra on SECRAL

The axial emitted bremsstrahlung spectra were measured on SECRAL (Superconducting ECR ion source with Advanced design in Lanzhou) using an HPGe detector. The spectral temperature T-spe was obtained from the linear fit of the spectra in the semi-log present. The evolution of T-spe with microwave power and magnetic field configuration is investigated in this paper.

Production of EUV power with SECRAL

The high power EUV source is one of key issues in the development of EUV lithography which is considered to be the most promising technology among the next generation lithography. However neither DPP nor LPP seems to meet the requirements of the commercial high-volume product. Insufficiency of DPP and LPP motivate the investigation of other means to produce the EUV radiation required in lithography. ECR plasma seems to be one of the alternatives. In order to investigate the feasibility of ECR plasma as a EUV light source, the EUV power emitted by SECRAL was measured. A EUV power of 1.03W in 4 pi sr solid angle was obtained when 2000W 18GHz rf power was launched, and the corresponding CE was 0.5%. Considering that SECRAL is designed to produce very high charge state ions, this very preliminary result is inspiring. Room-temperature ECR plasma and Sn plasma are both in the planned schedule.