Chan Hin Kam

Effects of arsenic beam equivalent pressure on InGaAsP grown by solid source molecular beam epitaxy with continuous white phosphorous production

Abstract We report the effects of arsenic beam equivalent pressure on lattice mismatch, electrical properties, surface roughness and morphology of InGaAsP grown by solid source molecular beam epitaxy using valve arsenic and phosphorous cracker cells with continuous white phosphorous production. Arsenic is found to have a higher sticking coefficient than phosphorous in almost all arsenic pressure employed in the growth. The incorporation of arsenic is found to fit a polynomial expression, Y =1.56 R −0.59 R 2 , with the beam equivalent pressure ratio R = f As /( f As + f P ). The incorporated arsenic elements significantly affect lattice mismatch and electrical properties. They also dominate surface construction of the quaternary material.

Physical properties of InGaAsP/InP grown by molecular beam epitaxy with valve phosphorous cracker cell

InGaAsP films grown on InP substrate by solid source molecular beam epitaxy (SSMBE) using a valve phosphorous cracker cell are investigated. It is found that the films grown at flux ratios f As /(f As + f p ) from 0.45 to 0.50 show a superior quality. It is also found that As pressure plays a crucial role in the scattering process; for the films grown at higher arsenic beam pressure (BEP), the Hall mobility μ is dominated by impurity scattering, polar phonon scattering and alloy scattering. For the films with high quality, optical scattering and alloy scattering dominate the mobility. The exponent of T for the films grown at low BEP is found to be as high as 2.54, which cannot be explained by impurity scattering alone. It is believed that, in addition to the impurity-related scattering, some defects associated with As vacancies also significantly contribute to the scattering, especially at low temperatures.

Sol-gel fabrication and properties of optical channel waveguides and gratings made from composites of titania and organically modified silane

Optical waveguide thin films have been prepared from composites of TiO2 and organically modified silane (ormosil) at low temperature by the sol-gel technique, using ?-glycidoxypropyltrimethoxysilane and tetrapropylorthotitanate as precursors. Atomic force microscopy and ellipsometry have been used to characterize the morphologies and properties of the waveguide thin films deposited on compound- semiconductor and silicon substrates. These results indicated that a dense and porosity-free waveguide film could be obtained at 100°C. The refractive index of the film could be varied from 1.44 to 1.55 at 633 nm by varying the titanium content. It was experimentally demonstrated that a channel waveguide and grating structures could easily be fabricated for these composite thin films by etching and embossing. It was found that this method is specifically useful for the fabrication of diffractive grating and optical planar waveguides on sol-gel-derived glass films coated on temperature-sensitive substrates such as III-V compound semiconductors. By this means, channel waveguides have been fabricated using laser writing and reactive ion etching or wet etching, and gratings with a period of 1.102 ?m and depth of 57.2 nm have also been obtained by embossing.

Second-harmonic generation using an a axis Nd:MgO:LiNbO3 single crystal fiber with Mg-ion indiffused cladding

We report the implementation of a low-loss core-cladding waveguide structure of an a axis Nd:MgO:LiNbO3 single-crystal fiber with a step refractive index profile and the demonstration of a frequency- doubled laser made from such a cladded crystal fiber. The laser-heated pedestal-grown a axis single-crystal fiber, with an elliptical crosssectional area of 200x 150?m, is further shown with a Mg ion indiffusion process. Electron probe microanalysis is used to measure the Mg ion concentration distribution in the Mg-diffused layer. After several trials, diffusion parameters suitable for achieving a core-cladding waveguide structure with a step refractive index profile are obtained. The optical and structural properties of the cladded crystal fibers are also characterized. Room-temperature second-harmonic generation with such a cladded crystal fiber is demonstrated. At room temperature, cw green laser output with a power of 10 ?W at the wavelength of 0.532 ?m is achieved. The origin of the relatively low conversion efficiency is discussed.

High-resolution X-ray diffraction study of strained InGaAsP/InP multiple quantum well structures grown using all solid sources

Abstract This paper reports characterization of n-type strained InGaAsP/InP multiple quantum well (MQW) structures, grown by solid source molecular beam epitaxy (MBE), using high-resolution X-ray diffraction. It was found that well-defined periodic satellite peaks up to 20 orders and the Pendellosung fringes appeared between the satellite peaks were observable, indicating a very high crystalline quality of the MQW structures. The data extracted from the rocking curves, including position and FWHM of the zero-order peak, the angle separation between diffraction peaks and the intensity of the first-order peak, indicate that high-quality InGaAsP/InP MQW structures with controllable well width and sharp interfaces can be successfully grown using all solid sources, and the well width has no significant effect on the quality of the interfaces. These observations are in good agreement with the simulated results using dynamical X-ray theory.

Effects of phosphorous beam equivalent pressure on GaInAsP/GaAs grown by solid source molecular beam epitaxy with a valve phosphorous cracker cell

Abstract We report the growth and characterization of GaInAsP films on GaAs substrates by solid source molecular beam epitaxy (SSMBE) using a valve phosphorous cracker cell at varied white phosphorous beam equivalent pressure (BEP). It is found that the GaInAsP/GaAs can be easily grown with the solid sources, and the incorporated phosphorous composition as a function of the beam equivalent pressure ratio, R=fP/(fP+fAs), can be well described by a parabolic relationship. With the increase of the incorporated phosphorous composition, the GaP-, InP-, InAs- and GaAs-like phonon modes shift towards opposite directions and their emission intensities also change. The first three modes shift to larger wave numbers while the last one shifts to smaller wave number. The lattice mismatch, Δa/a, of the materials grown with varied phosphorous BEP follows a linear relationship. Photoluminescence (PL) measurements reveal that as the phosphorous BEP ratio increases, the peak position or energy band gap of the material shifts towards higher energy; the full-width at half-maximum (FWHM) becomes narrower, and the luminescence intensity becomes higher. In addition, the materials also show smooth surfaces that do not change significantly with phosphorous beam equivalent pressure.

Optical amplification by two-wave mixing in lithium niobate waveguides

Photorefractive Fe:LiNbO3 planar waveguides have been fabricated by proton exchange method using Fe:LiNbO3 as substrate and benzoic acid as exchange medium. The waveguide has a much larger refractive index increment than a Ti diffused one. Through end-face coupling, a pump beam and a signal beam were injected into the waveguide and the optical amplification properties of the waveguide have been investigated experimentally. The results showed that a hundred fold amplification gain could be obtained in a wide range of grating periods and an amplification gain of 180 was achieved easily. This scheme has potential applications in optical signal processing at not very high incident intensity.

Structural, electrical, and optical properties of sol-gel-processed thin films of BaTiO3 on ITO glass

BaTiO3 thin films are prepared on ITO-coated Corning 1737 glass. The solution is prepared from a double metal ethoxide and the films are deposited by spin coating and annealing at 700°C for 2 hours in an O2 atmosphere. The films are characterized using x-ray diffraction, atomic force microscopy, micro-raman, UV-VIS spectroscopy, and Sawyer-Tower Bridge. The pure perovskite phase of BaTiO3 is identified by x-ray diffraction. The tetragonality is revealed from Raman study by identifying the symmetrical dependent Raman shift at about 306 cm-1. The ferroelectricity of the film is confirmed by the P-E hysteresis loop. The films are highly transparent, with an absorption edge at 3.73eV. These desirable features indicate that the films have potential in electronic display and electro-optical applications.

Preparation and optical properties of neodymium-doped sol-gel glasses using trimethylphosphate as P2O5 precursor

The Nd3+ ions doped bulk glasses and thin films with the trimethylphosphate (TMP) as the precursor of P2O5 were prepared by the sol-gel technique. Their optical properties have been investigated. The Fourier Transform IR (FTIR) of Nd3+ doped SiO2-TiO2-P2O5 films have been measured to study the influence of P2O5 content in the removal of hydroxyl group. Fluorescence spectral results show stronger fluorescence intensity along with the narrowing of the emission bands due to the availability of the co-dopant P2O5 in the sol-gel glasses compared with those of aluminum co-doped glasses. Our experimental results show that up to 6wt percent of Nd2O3 could be incorporated into the P2O5-SiO2 glass matrix without significant fluorescence quenching effect due to the usage of the TMP as a precursor. We have also found that the hydroxyl groups could easily be removed at lower temperatures, as we increase the P2O5 content. It indicates that the P2O5 co-doping has a great potentiality in reducing the process temperature.

Spectroscopic and photoluminescent studies of magnesium- and erbium-codoped lithium niobate crystal

A heavily magnesium (5.0 mol%) and erbium (2.0 mol%) codoped lithium niobate crystal has been grown using Czochralski method. The crystal is highly transparent and has strong resistance to photorefractive damage. Spectroscopic study showed that the crystal exhibits the typical f-f transitions of erbium ions. Photoluminescence at 1.54 micrometers was measured under excitations at 514 nm from an Ar+ laser and 980 nm from a GaAs laser diode. The temporal evolution of the 1.54 micrometers emission showed a single-exponential decay with a lifetime of approximately 5 ms. Upconversion property of the crystal under 980 nm excitation was also studied and the transient spectrum of the green emission at 548 nm also yields a single-exponential decay with a lifetime of approximately 35 microsecond(s) . The results have shown that clustering and pairing of Er ions could be effectively avoided by magnesium codoping.