Enhanced infrared absorption of spatially ordered quantum dot arrays

We have investigated the intersubband absorption for spatially ordered and non-ordered quantum dots (QDs). It is found that the intersubband absorption of spatially ordered QDs is much stronger than that of non-ordered QDs. The enhanced absorption is attributed to the improved size uniformity concurrent with the spatial ordering for the growth condition employed. For the FTIR measurement under normal incidence geometry, using a undoped sample as reference can remove the interference effect due to multiple reflections. (c) 2006 Elsevier B.V. All rights reserved.

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.

Optimization of mechanically induced long-period fibre grating transmission spectrum

A new double-layer grating template is designed to reduce the out-of-band loss as much as 1.8dB when the loss of LP03 reaches 10.2 dB. Meanwhile, we propose a method to remove the sidelobes in the transmission spectra by the adjustment of the thickness of pressure plates. The plate-thickness-induced shift of resonant wavelength and the attenuation of loss peak intensity when removing sidelobes can be modified by the fibre distance and contact point on the pressure plates.

Enhanced near-infrared photoluminescence from isoelectronic luminescent centers in sulfur-implanted silicon with copper or silver coimplantation

Enhanced near-infrared photoluminescence (PL) from sulfur-related isoelectronic luminescent centers in silicon was observed from thermally quenched sulfur-implanted silicon in which additional copper or silver ions had been coimplanted. The PL from the sulfur and copper coimplanted silicon peaked between 70 and 100 K and persisted to 260 K. This result strongly supports the original conjecture from the optical detection of magnetic resonance studies that the strong PL from sulfur-doped silicon comes from S-Cu isoelectronic complexes [Frens , Phys. Rev. B 46, 12316 (1992); Mason , ibid. 58, 7007 (1998).]. (c) 2007 American Institute of Physics.

Near infrared photoluminescence from Yb,Al Co-implanted SiO2 films on silicon

Intense room-temperature near infrared (NIR) photoluminescence (980 nm and 1032 nm) is observed from Yb,Al co-implanted SiO2 films on silicon. The optical transitions occur between the F-2(5/2) and F-2(7/2) levels of Yb3+ in SiO2. The additional Al-implantation into SiO2 films can effectively improve the concentration quenching effect of Yb3+ in SiO2. Photoluminescence exitation sprectroscopy shows that the NIR photoluminescence is due to the non-radiative energy transfer from Al-implantation-induced non-bridging oxygen hole defects in SiO2 to Yb3+ in the Yb-related luminescent complexes. It is believed that the defect-mediated luminscence of rare-earth ions in SiO2 is very effective.

Study on Raman spectra of GaMnAs

Raman spectra of diluted magnetic semiconductor GaMnAs alloy were reported. The coupled plamon-LO-phonon ( CPLP) mode has LO-like polarization properties. With increasing Mn concentration, the CPLP mode shifts to low frequency. The hole density in the alloy was determined from the ratio of the intensity of the CPLP mode to that of the unscreened LO mode in the depletion layer. The hole density increases with the increase of the Mn composition. The Raman spectra of GaMnAs alloy were measured at different temperature. It is confirmed that the hole density in the alloy increases with the increase of the temperature.

Biaxial stress dependence of the electrostimulated near-band-gap spectrum of GaN epitaxial film grown on (0001) sapphire substrate

The biaxial piezospectroscopic coefficient (i.e., the rate of spectral shift with stress) of the electrostimulated near-band-gap luminescence of gallium nitride (GaN) was determined as Pi=-25.8 +/- 0.2 meV/GPa. A controlled biaxial stress field was applied on a hexagonal GaN film, epitaxially grown on (0001) sapphire using a ball-on-ring biaxial bending jig, and the spectral shift of the electrostimulated near-band-gap was measured in situ in the scanning electron microscope. This calibration method can be useful to overcome the lack of a bulk crystal of relatively large size for more conventional uniaxial bending calibrations, which has so far hampered the precise determination of the piezospectroscopic coefficient of GaN. The main source of error involved with the present calibration method is represented by the selection of appropriate values for the elastic stiffness constants of both film and substrate. The ball-on-ring calibration method can be generally applied to directly determine the biaxial-stress dependence of selected cathodoluminescence bands of epilayer/substrate materials without requiring separation of the film from the substrate. (c) 2006 American Institute of Physics.

Liquid-phase-epitaxy-grown InAsxSb1-x/GaAs for room-temperature 8-12 mu m infrared detectors

High-quality InAsxSb1-x (0 < x <= 0.3) films are grown on GaAs substrates by liquid phase epitaxy and electrical and optical properties of the films are investigated, revealing that the films exhibit Hall mobilities higher than 2x10(4) cm(2) V-1 s(-1) and cutoff wavelengths longer than 10 mu m at room temperature (RT). Photoconductors are fabricated from the films, and notable photoresponses beyond 8 mu m are observed at RT. In particular, for an InAs0.3Sb0.7 film, a photoresponse of up to 13 mu m with a maximum responsivity of 0.26 V/W is obtained at RT. Hence, the InAsxSb1-x films demonstrate attractive properties suitable for room-temperature, long-wavelength infrared detectors. (c) 2006 American Institute of Physics.

Comparison of valence band x-ray photoelectron spectrum between Al-N-codoped and N-doped ZnO films

The valence band structures of Al-N-codoped [ZnO:(Al, N)] and N-doped (ZnO:N) ZnO films were studied by normal and soft x-ray photoelectron spectroscopy. The valence-band maximum of ZnO:(Al, N) shifts up to Fermi energy level by about 300 meV compared with that of ZnO:N. Such a shift can be attributed to the existence of a kind of Al-N in ZnO:(Al, N), as supported by core level XPS spectra and comparison of modified Auger parameters. Al-N increased the relative quantity of Zn-N in ZnO:(Al, N), while N-N decreased that of Zn-N in ZnO:N. (c) 2006 American Institute of Physics.

Measurement of gain spectrum for semiconductor lasers utilizing integrations of product of emission spectrum and a phase function over one mode interval

A technique based on the integrations of the product of amplified spontaneous emission spectrum and a phase function over one mode interval is proposed for measuring gain spectrum for Fabry-Perot semiconductor lasers, and a gain correction factor related to the response function of the optical spectrum analyzer (OSA) is obtained for improving the accuracy of measured gain spectrum. The gain spectra with a difference less than 1.3 cm(-1) from 1500 to 1600 nm are obtained for a 250-mum-long semiconductor laser at the OSA resolution of 0.06, 0.1, 0.2, and 0.5 nm. The corresponding gain correction factor is about 9 cm(-1) at the resolution of 0.5 nm. The gain spectrum measured at the resolution of 0.5 nm has the same accuracy as that obtained by the Hakki-Paoli method at the resolution of 0.06 nm for the laser with the mode interval of 1.3 nm.

Measurement of gain spectrum for Fabry-Perot semiconductor lasers by the Fourier transform method with a deconvolution process

To improve the accuracy of measured gain spectra, which is usually limited by the resolution of the optical spectrum analyzer (OSA), a deconvolution process based on the measured spectrum of a narrow linewidth semiconductor laser is applied in the Fourier transform method. The numerical simulation shows that practical gain spectra can be resumed by the Fourier transform method with the deconvolution process. Taking the OSA resolution to be 0.06, 0.1, and 0.2 nm, the gain-reflectivity product spectra with the difference of about 2% are obtained for a 1550-nm semiconductor laser with the cavity length of 720 pm. The spectra obtained by the Fourier transform method without the deconvolution process and the Hakki-Paoli method are presented and compared. The simulation also shows that the Fourier transform method has less sensitivity to noise than the Hakki-Paoli method.

The mechanism of blueshift in excitation-intensity-dependent photo luminescence spectrum of nitride multiple quantum wells

(1 1 (2) over bar 0) GaN/InGaN multiple quantum wells (MQWs) were grown on (1 (2) over bar 0 2) sapphire by metal-organic vapor phase epitaxy. The excitation-intensity-dependent photoluminescence (PL) spectrum of these samples was measured, and no peak shift was observed. This phenomenon was attributed to the absence of piezoelectric field (PEF) along the growth orientation of the (1 1 (2) over bar 0) face MQWs. Our experimental results showed that PEF was the main reason causing peak blueshift in excitation-intensity-dependent PL spectrum of (0 0 0 1) InGaN/GaN NIQWs. It was expected that fabricating (1 1 (2) over bar 0) face nitride device should be a method to avoid PEF and get low-threshold, high-quantum-efficiency and stable-emission-wavelength light-emission devices. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of rapid thermal annealing and hydrogen plasma treatment on the microstructure and light-emission of silicon-rich oxide film

Silicon-rich silicon oxide (SRSO) films are prepared by plasma-enhanced chemical vapor deposition method at the substrate temperature of 200degreesC. The effect of rapid thermal annealing and hydrogen plasma treatment on tire microstructure and light-emission of SRSO films are investigated in detail using micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and photoluminescence (PL) spectra. It is found that the phase-separation degree of the films decreases with increasing annealing temperature from 300 to 600degreesC, while it increases with increasing annealing temperature from 600 to 900degreesC. The light-emission of the films are enhanced with increasing annealing temperature up to 500degreesC, while it is rapidly reduced when the annealing temperature exceeds 600degreesC. The peak position of the PL spectrum blueshifts by annealing at the temperature of 300degreesC, then it red-shifts with further raising annealing temperature. The following hydrogen plasma treatment results in a disproportionate increase of the PL intensity and a blueshift or redshift of the peak positions, depending on the pristine annealing temperature. It is thought that the size of amorphous silicon clusters, surface structure of the clusters and the distribution of hydrogen in the films can be changed during the annealing procedure. The results indicate that not only cluster size but also surface state of the clusters plays an important role in the determination of electronic structure of the amorphous silicon cluster and recombination process of light-generated carriers.

Structural evaluation of polycrystalline silicon thin films by hot-wire-assisted PECVD

Tungsten wires were introduced into a plasma-enhanced chemical vapor deposition (PECVD) system as a catalyzer: we name this technique 'hot-wire-assisted PECVD' (HW-PECVD). Under constant deposition pressure (p(g)), gas flow ratio and catalyzer position, the effects of the hot wire temperature (T-f) on the structural properties of the poly-Si films have been characterized by X-ray diffraction (XRD), Raman scattering and Fourier-transform infrared (FTIR) spectroscopy. Compared with conventional PECVD, the grain size, crystalline volume fraction (X-e) and deposition rate were all enhanced when a high T-f was used. The best poly-Si film exhibits a preferential (220) orientation, with a full width at half-maximum (FWHM) of 0.2 degrees. The Si-Si TO peak of the Raman scattering spectrum is located at 519.8 cm(-1) with a FWHM of 7.1 cm(-1). The X-c is 0.93. These improvements are mainly the result of promotion of the dissociation of SiH4 and an increase in the atomic H concentration in the gas phase. (C) 2001 Elsevier Science B.V. All rights reserved.

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength infrared detectors

InxGa1-xAs/AlyGa1-yAs/AlzGa1-zAs asymmetric step quantum-well middle wavelength (3-5 mum) infrared detectors are fabricated. The components display photovoltaic-type photocurrent response as well as the bias-controlled modulation of the peak wavelength of the main response, which is ascribed to the Stark shifts of the intersubband transitions from the local ground states to the extended first excited states in the quantum wells, at the 3-5.3 mum infrared atmospheric transmission window. The blackbody detectivity (D-bb*) of the detectors reaches to about 1.0x10(10) cm Hz(1/2)/W at 77 K under bias of +/-7 V. By expanding the electron wave function in terms of normalized plane wave basis within the framework of the effective-mass envelope-function theory, the linear Stark effects of the intersubband transitions between the ground and first excited states in the asymmetric step well are calculated. The obtained results agree well with the corresponding experimental measurements. (C) 2001 American Institute of Physics.