RADIATION OF DRESSED EXCITONS IN THE SEMICONDUCTOR MICROCAVITY

于2010-11-23批量导入

Design of spectrometer based on volume phase grating for near infrared range

In order to design and fabricate a spectrometer for the infrared range widely used in the different applications, Volume Phase Grating (VPG) with. low Polarization Dependence Loss (PDL) and high efficiency has been adopted as the dispersion element. VPG is constructed by coating an optical substrate with a thin film of dichromated. gelatin and exposing the film to two mutually coherent laser beams to form index modulation. The diffraction efficiency for a VPG is governed by Bragg effects. The depth (d) and index modulation contrast of the grating structure control the efficiency at which the light is diffracted when the Bragg condition is satisfied. Gradient index lens with high performance and low aberration are used as collimating system instead of standard lens. The spot diagrams and MTF curve of the collimating lens are shown in the paper. The receive system is InCaAs photodiode (PD) array including 512 pixels with 25 mum pitch. The spectrum resolution of the spectrometer reaches to 0.2nm and wavelength accuracy is 40pm.

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.

Asymmetric dark current in double barrier quantum well infrared photodetectors

Asymmetric dark current and photocurrent versus voltage characteristic in the Double Barrier Quantum Wells (DBQWs) photovoltaic infrared photodetector has been studied. A model based on asymmetric potential barriers was proposed. The asymmetric potential thick barrier, which due to the Si dopant segregation during growth makes a major contribution to the asymmetrical I-V characteristic, calculations based on our model agree well with experimental results. This work also confirms the potential use of this DBQWs for infrared photodetector with large responsivity and little dark current under negative bias.

JFET SOS devices: Processing and gamma radiation effects

A process for fabricating n channel JFET/SOS (junction field-effect transistors on silicon-on-sapphire) has been researched. The gate p(+)n junction was obtained by diffusion, and the conductive channel was gotten by a double ion implantation. Both enhancement and depletion mode transistors were fabricated in different processing conditions. From the results of the Co-50 gamma ray irradiation experimental we found that the devices had a good total dose radiation-hardness. When the tot;ll dose was 5Mrad(Si), their threshold voltages shift was less than 0.1V. The variation of transconductance and the channel leakage current were also little.

Twin and grain boundary in InP: A synchrotron radiation study

Experimentally observed X-ray reflectivity curves show bi-crystal(twin) characteristics. The study revealed that there was defect segregation at the twin boundary. Stress was relaxed at the edge of the boundary. Relaxation of the stress resulted in formation of twin and other defects. As a result of formation of such defects, a defect-free and stress-free zone or low defect density and small stress zone is created around the defects. So a twin model was proposed to explain the experimental results. Stress(mainly thermal stress), chemical stoichiometry deviation and impurities nonhomogeneous distributions are the key factors that cause twins in LEC InP crystal growth. Twins on (111) face in LEC InP crystal were studied. Experimental evidence of above mentioned twin model and suggestions on how to get twin-free LEC InP single crystals will be discussed.

Study of infrared luminescence from Er-implanted GaN films

In this study, we report the dependences of infrared luminescence properties of Er-implanted GaN thin films (GaN:Er) on the kinds of substrates used to grow GaN, the growth techniques of GaN, the implantation parameters and annealing procedures. The experimental results showed that the photoluminescence (PL) intensity at 1.54 mum was severely influenced by different kinds of substrates. The integrated PL peak intensity from GaN:Er /Al2O3 (00001) was three and five times stronger than that from GaN:Er /Si (111) grown by molecular beam epitaxy (MBE) and by metalorganic chemical vapor deposition (MOCVD), respectively. The PL spectra observed from GaN:Er/Al2O3 (0001) grown by MOCVD and by MBE displayed a similar feature, but those samples grown by MOCVD exhibited a stronger 1.54 mum PL. It was also found that there was a strong correlation between the PL intensity with ion implantation parameters and annealing procedures. Ion implantation induced damage in host material could be only partly recovered by an appropriate annealing temperature procedure. The thermal quenching of PL from 15 to 300 K was also estimated. In comparison with the integrated PL intensity at 15 K, it is reduced by only about 30 % when going up to 300 K for GaN:Er/Al2O3 sample grown by MOCVD. Our results also show that the strongest PL intensity comes from GaN:Er grown on Al2O3 substrate by MOCVD. (C) 2004 Elsevier B.V. All rights reserved.

Improved neutron radiation hardness for Si detectors: Application of low resistivity starting material and or manipulation of N-eff by selective filling of radiation-induced traps at low temperatures

Radiation-induced electrical changes in both space charge region (SCR) of Si detectors and bulk material (BM) have been studied for samples of diodes and resistors made on Si materials with different initial resistivities. The space charge sign inversion fluence (Phi(inv)) has been found to increase linearly with the initial doping concentration (the reciprocal of the resistivity), which gives improved radiation hardness to Si detectors fabricated from low resistivity material. The resistivity of the BM, on the other hand, has been observed to increase with the neutron fluence and approach a saturation value in the order of hundreds k Omega cm at high fluences, independent of the initial resistivity and material type. However, the fluence (Phi(s)), at which the resistivity saturation starts, increases with the initial doping concentrations and the value of Phi(s) is in the same order of that of Phi(inv) for all resistivity samples. Improved radiation hardness can also be achieved by the manipulation of the space charge concentration (N-eff) in SCR, by selective filling and/or freezing at cryogenic temperatures the charge state of radiation-induced traps, to values that will give a much smaller full depletion voltage. Models have been proposed to explain the experimental data.

Structural and infrared absorption properties of self-organized InGaAs GaAs quantum dots multilayers

Self-organized InGaAs/GaAs quantum dots (QDs) stacked multilayers have been prepared by solid source molecular beam epitaxy. Cross-sectional transmission electron microscopy shows that the InGaAs QDs are nearly perfectly vertically aligned in the growth direction [100]. The filtering effect on the QDs distribution is found to be the dominant mechanism leading to vertical alignment and a highly uniform size distribution. Moreover, we observe a distinct infrared absorption from the sample in the range of 8.6-10.7 mu m. This indicates the potential of QDs multilayer structure for use as infrared photodetector.

Ultrasensitive Detection of Infrared Photon Using Microcantilever: Theoretical Analysis

We present a new method for detecting near-infrared, mid-infrared, and far-infrared photons with an ultra-high sensitivity. The infrared photon detection was carried out by monitoring the displacement change of a vibrating microcantilever under light pressure using a laser Doppler vibrometer. Ultrathin silicon cantilevers with high sensitivity were produced using micro/nano-fabrication technology. The photon detection system was set up. The response of the microcantilever to the photon illumination is theoretically estimated, and a nanowatt resolution for the infrared photon detection is expected at room temperature with this method.

Sequential coupling transport for the dark current of quantum dots-in-well infrared photodetectors

The dark current characteristics and temperature dependence for quantum dot infrared photodetectors have been investigated by comparing the dark current activation energies between two samples with identical structure of the dots-in-well in nanoscale but different microscale n-i-n environments. A sequential coupling transport mechanism for the dark current between the nanoscale and the microscale processes is proposed. The dark current is determined by the additive mode of two activation energies: E-a,E-micro from the built-in potential in the microscale and E-a,E-nano related to the thermally assisted tunneling in nanoscale. The activation energies E-a,E-micro and E-a,E-nano decrease exponentially and linearly with increasing applied electric field, respectively.