Sputtering of ZnO buffer layer on Si for GaN blue light emitting materials

The preparation of high quality ZnO/Si substrates for the growth of GaN blue light emitting materials is considered. ZnO thin films have been deposited on Si(100) and Si(lll) substrates by conventional magnetron sputtering. Morphology, crystallinity and c-axis preferred orientation of ZnO thin films have been investigated by transmitting electron microscopy (TEM), X-ray diffraction (XRD) and X-ray rocking curve (XRC). It is proved that the ZnO thin films have perfect structure. The full-width-at-half-maximum (FWHM) of the ZnO(002) XRC of these films is about 1 degrees, while the minimum is 0.353 degrees. This result is better than the minimum FWHM (about 2 degrees) reported by other research groups. Moreover, comparison and discussion are given on film structure of ZnO/Si(100) and ZnO/Si(lll).

Arsenic clusters on the surface of vertically aligned InAs islands on GaAs substrate by annealing

The formation of arsenic clusters in a system of vertically aligned InAs quantum islands on GaAs during thermal annealing under As overpressure has been investigated by transmission electron microscopy (TEM) and Raman scattering. Semicoherent arsenic clusters, identified by TEM examination, have been formed on the surface of the GaAs capping layer. The existence of arsenic precipitates is also confirmed by Raman spectra, showing new peaks from the annealed specimen at 256 and 199 cm(-1). These peaks have been ascribed to A(1g) and E-g Raman active phonons of crystalline arsenic. The phenomenon can be understood by a model of strain-induced selected growth under As overpressure. (C) 1999 American Institute of Physics. [S0003-6951(99)02045-8].

A novel 1.3-mu m high T-0 AlGaInAs/InP strained-compensated multi-quantum well complex-coupled distributed feedback laser diode

A 1.3-mu m AlGaInAs/InP buried heterostructure (BH) stripe distributed feedback laser with a novel AlInAs/InP complex-coupled grating grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) is proposed and demonstrated. A high characteristic temperature (T-0 = 90K between 20-80 degrees C) and temperature-insensitive slope efficiency (0.25 dB drop from 20 to 80 degrees C) in 1.3 mu m AlGaInAs/InP DFB lasers was obtained by introducing AI(Ga)InAs graded-index separate-confinement heterostructure (GRINSCH) layers and a strained-compensated (SC) multi-quantum well (MQW).

Effect of defects on optical phonon Raman spectra in SiC nanorods

Fabricated one-dimensional (1D) materials often have abundant structural defects. Experimental observation and numerical calculation indicate that the broken translation symmetry due to structural defects may play a more important role than the quantum confinement effect in the Raman features of optical phonons in polar semiconductor quantum wires such as SiC nanorods, (C) 1999 Elsevier Science Ltd. All rights reserved.

Photocurrent derivative spectra of ZnCdSe-ZnSe double multi-quantum wells

Photocurrent (PC) spectra of ZnCdSe-ZnSe double multi-quantum wells are measured at different temperature. Its corresponding photocurrent derivative (PCD) spectra are obtained by computing, and the PCD spectra have greatly enhanced the sensitivity of the relative weak PC signals. The polarization dependence of the PC spectra shows that the transitions observed in the PC spectra are heavy-hole related, and the transition energy coincide well with the results obtained by envelope function approximation including strain. The temperature dependence of the photocurrent curves indicates that the thermal activation is the dominant transport mechanism of the carriers in our samples. The concept of saturation temperature region is introduced to explain why the PC spectra have different temperature dependence in the samples with different structure parameters. It is found to be very useful in designing photovoltaic devices.

Native-oxidized InAlAs blocking layer buried heterostructure InGaAsP-InP MQW laser for high-temperature operation

A novel idea of InAlAs native oxide utilized to replace the p-n-p-n thyristor blocking layer and improve the high-temperature performance of buried heterostructure InGaAsP-InP laser is first proposed and demonstrated. A characteristic temperature (T-0) of 50 K is achieved from an InA1As native oxide buried heterostructure (NOBH) InGaAsP-InP multiquantum-well laser with 1.5-mu m-wide diode leakage passage path. The threshold current and slope efficiency of NOBH laser changes from 5.6 mA, 0.23 mW/mA to 28 mA, 0.11 mW/mA with the operating temperature changing from 20 degrees C to 100 degrees C. It is comparable to conventional p-n reverse biased junction BH laser with minimized diode leakage current, and is much better than the buried ridge strip with proton implanted laterally confinement laser.

Effects of annealing on self-organized InAs quantum islands on GaAs (100)

Self-organized InAs islands on (001) GaAs grown by molecular beam epitaxy were annealed and characterized with photoluminescence (PL) and transmission electron microscopy (TEM). The PL spectra from the InAs islands demonstrated that annealing resulted in a blueshift in peak energy, a reduction in intensity, and a narrower linewidth in the PL peak. In addition, the TEM analysis revealed the relaxation of strain in some InAs islands with the introduction of the network of 90 degrees dislocations. The correlation between the changes in the PL spectra and the relaxation of strain in InAs islands was discussed. (C) 1998 American Institute of Physics. [S0003-6951(98)01850-6].

Asymmetry in the vertically aligned growth induced InAs islands in GaAs

A 10-InAs-island-layer vertically coupled quantum dot structure on (001) GaAs was grown and investigated by molecular beam epitaxy and transmission electron microscopy. The result shows that the vertically aligned InAs islands are asymmetrical along the two < 110 > directions on the (001) growth plane. Such an asymmetry in the vertically coupled quantum dot structure can be explained with the chemical polarity in the III-V compound semiconductors.

Characterization of strain relaxation in As ion implanted Si1-xGex epilayers grown by gas source molecular beam epitaxy

Strain relaxation in the As ion implanted Si0.57Ge0.43 epilayers was studied by double-crystal x-ray diffractometry and transmission electron microscopy, and was compared to that in the nonimplanted Si0.57Ge0.43 epilayers. Experimental results show that after rapid thermal annealing (RTA) the x-ray linewidth of the As+-implanted Si0.57Ge0.43 epilayers is narrower than that of the nonimplanted epilayers, and than that of the partially relaxed as-grown samples, which is due primarily to low density of misfit dislocations in the As+-implanted SiGe epilayers. RTA at higher than 950 degrees C results in the formation of misfit dislocations for the nonimplanted structures, and of combinations of dislocations and precipitates (tentatively identified as GeAs) for the As+-implanted epilayers. The results mean that the strain relaxation mechanism of the As+-implanted Si1-xGex epilayers may be different from that of the nonimplanted Si1-xGex epilayers. (C) 1998 American Institute of Physics.

Effects of growth temperature on highly mismatched InAs grown on GaAs substrates by MBE

InAs layers were grown on GaAs by molecular beam epitaxy (MBE) at substrate temperature 450 and 480 degrees C, and the surface morphology was studied with scanning electron microscopy (SEM). We have observed a high density of hexagonal deep pits for samples grown at 450 degrees C, however, the samples grown at 480 degrees C have smooth surface. The difference of morphology can be explained by different migration of cations which is temperature dependent. Cross-sectional transmission electron microscopy (XTEM) studies showed that the growth temperature also affect the distributions of threading dislocations in InAs layers because the motion of dislocations is kinetically limited at lower temperature. (C) 1998 Elsevier Science B.V. All rights reserved.

Alignment of misfit dislocations in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As/InP heterostructure

It was observed with transmission electron microscopy in the In0.52Al0.48As/InxGa1-xAs/In0.52Al0.48As system grown on the (001) InP substrate that misfit dislocation lines deviate [110] directions at an angle with its value depending on the gallium content. Such an abnormal alignment of misfit dislocations is explained in terms of an alloy effect on the formation of single jogs on misfit dislocations in the interface between the III-V ternary compounds. (C) 1998 American Institute of Physics.

The research of range-gated laser night vision system on cars - art. no. 68351V

The characteristic of several night imaging and display technologies on cars are introduced. Compared with the current night vision technologies on cars, Range-gated technology can eliminate backscattered light and increase the SNR of system. The theory of range-gated image technology is described. The plan of range-gated system on cars is designed; the divergence angle of laser can be designed to change automatically, this allows overfilling of the camera field of view to effectively attenuate the laser when necessary. Safety range of the driver is calculated according to the theory analysis. Observation distance of the designed system is about 500m which is satisfied with the need of safety driver range.

High Q microring resonator in silicon-on-insulator rib waveguides - art. no. 68380J

A high quality (Q) factor microring resonator in silicon-on-insulator rib waveguides was fabricated by electron beam lithography, followed by inductively coupled plasma etching. The waveguide dimensions were scaled down to submicron, for a low bending loss and compactness. Experimentally, the resonator has been realized with a quality factor as high as 21,200, as well as a large extinction ratio 12.5dB at telecommunication wavelength near 1550nm. From the measured results, propagation loss in the rib waveguide is determined as low as 6.900/cm. This high Q microring resonator is expected to lead to high speed optical modulators and bio-sensing devices.

Single-negative negative index metamaterials with broad bandwidth - art. no. 683109

The theoretical method to design negative refractive index metamaterials by single negative permittivity metamaterials is presented. By designing the electric and magnetic response metamaterials separately, the complexity of the design work can be simplified a lot. For the magnetic response metamaterials, the metallic post structure is adopted. Varying the height of the post, the response wavelength can be adjusted linearly. For electric metamaterials, wire-mesh structure is adopted. The effective material parameters, including refractive index, impedance, permittivity and permeability are given. Such a structure has negative refractive index during a broad frequency band and easy to design.

Accurate vibration detection of a rough surface - art. no. 683118

Based on the semiconductor laser whose spectral line with width is compressed to be less than 1.2Mhz, a system was designed to measure and improve the amplitude and frequency of the real-time microvibration with sinusoidal modulation. real-time microvibration measurement was executed without alignment problem in the interferometry; and low-frequency disturbance of environment could be eliminated. Suggestions were also given to consummate the system. The system also has resistance against the low frequency disturbance of the environment.