Showing papers by "David W Parent published in 1997"

Structural properties of ZnS y Se 1−y /ZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

Abstract: ZnSySe1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSyySe1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is hc ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnSySe1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnSySe1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.

A comparison of ethyl iodide and hydrogen chloride for doping ZnSe grown by photoassisted MOVPE

Abstract: We have conducted a study of the electrical and photoluminescence properties of ZnSe films grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) (250 Torr, 400°C) with ethyl iodide and hydrogen chloride as n-type dopant sources. A higher peak electron concentration and a lower minimum resistivity were observed using hydrogen chloride (5.4 × 1018 cm−3, and .0070 ohm-cm, respectively), as opposed to ethyl iodide (1.55 × 1017 cm −3, and 0.067 ohm-cm, respectively). We show that the higher electron concentrations observed in the chlorine doped layers are due to a higher incorporation of chlorine atoms than that of iodine atoms, and that this may be a result of the different tetrahedral misfit factors for these atoms. Our photoluminescence and 77K Hall effect data support this conclusion. Growth rate depression was observed to be more severe for iodine doped layers than for chlorine doped layers. Thus, it appears that hydrogen chloride is a superior dopant source for low-temperature photoassisted MOVPE ZnSe growth of n-type layers for blue-green laser diodes in the pressure-temperature regime investigated.

Multiple quantum well in-line optical modulators using tunable distributed Bragg gratings photonically controlled active array

Abstract: The integration of photonic technology into phased array radar systems promises to reduce aperture, weight, size, transmit/receive (T/R) module complexity, mitigate EMI, and accommodate wider signal bandwidth with frequency independent beam steering. One of the photonic control methodology is to employ true time delays which have been incorporated in a variety of ways in the realization of phased array radar. We have proposed a technique using wavelength division multiplexing (WDM) to address a large number of elements, with each clement carrying the phase information on one channel/wavelength. This architecture is optically non-coherent and achieves a reduction in hardware complexity via sharing of various devices. As part of the Office of Naval Research's Accelerated Capabilities initiative, Raytheon/University of Connecticut team is developing and implementing this methodology. This paper focuses on the devices, including novel waveguide amplitude modulators and tunable filters, required to implement such an architecture. In particular, we propose to employ the quantum confined Stark effect in 1.55 micron InGaAsP/InP multiple quantum well (MQWs) for these components. We intend to use the quadratic electrorefractive effect in InGaAsP (1.5 /spl mu/m)/InGaAsP (1.3 /spl mu/m) and/or InGaAsP (1.5 /spl mu/m)/InP multiple quantum well (MQW) structures to achieve intensity modulation with the applied signal voltage. The investigation focuses on MQW devices which exhibit the quantum confined Stark effect since these devices yield large changes of refractive index with low insertion loss and are capable of being modulated at the required frequencies. The details of modulator structures are described.