W. Goodhue

Wafer-fused orientation-patterned GaAs

The fabrication of thick orientation-patterned GaAs (OP-GaAs) films is reported using a two-step process where an OP-GaAs template with the desired crystal domain pattern was prepared by wafer fusion bonding and then a thick film was grown over the template by low pressure hydride vapor phase epitaxy (HVPE). The OP template was fabricated using molecular beam epitaxy (MBE) followed by thermocompression wafer fusion, substrate removal, and lithographic patterning. On-axis (100) GaAs substrates were utilized for fabricating the template. An approximately 350 μm thick OP-GaAs film was grown on the template at an average rate of ~70 μm/hr by HVPE. The antiphase domain boundaries were observed to propagate vertically and with no defects visible by Nomarski microscopy in stain-etched cross sections. The optical loss at ~2 μm wavelength over an 8 mm long OP-GaAs grating was measured to be no more than that of the semi-insulating GaAs substrate. This template fabrication process can provide more flexibility in arranging the orientation of the crystal domains compared to the Ge growth process and is scalable to quasi-phase-matching (QPM) devices operating from the IR to terahertz frequencies utilizing existing industrial foundries.

Photoconductive optically driven deformable membrane under high-frequency bias: fabrication, characterization, and modeling

The fabrication and characterization of an optically addressable deformable mirror for a spatial light modulator are described. Device operation utilizes an electrostatically driven pixelated aluminized polymeric membrane mirror supported above an optically controlled photoconductive GaAs substrate. A 5 mum thick grid of patterned photoresist supports the 2 mum thick aluminized Mylar membrane. A conductive ZnO layer is placed on the backside of the GaAs wafer. Similar devices were also fabricated with InP. A standard Michelson interferometer is used to measure mirror deformation data as a function of illumination, applied voltage, and frequency. The device operates as an impedance distribution between two cascaded impedances of deformable membrane substrate, substrate, and electrode. An analysis of devices operation under several bias conditions, which relates membrane deformation to operating parameters, is presented.

Spectrally variable two-beam coupling nonlinear deconvolution

In previous work, we introduced a dynamic range compression-based technique for image correction using nonlinear deconvolution; the impulse response of the distortion function and the distorted image are jointly transformed to pump a clean reference beam in a photorefractive two-beam coupling arrangement. The Fourier transform of the pumped reference beam contains the deconvolved image and its conjugate. Here we extend our work to spectrally variable dynamic range compression. This approach allows the retrieval of distorted signals embedded in a very high noise environment and does not require one to work with a very high beam ratio as in our previous work. Resolution recovery of blurred noisy images is demonstrated for several different types of image blur.

Real-time holographic deconvolution techniques for one-way image transmission through an aberrating medium: characterization, modeling, and measurements

We propose and demonstrate a new photorefractive real-time holographic deconvolution technique for adaptive one-way image transmission through aberrating media by means of four-wave mixing. In contrast with earlier methods, which typically required various codings of the exact phase or two-way image transmission for correcting phase distortion, our technique relies on one-way image transmission through the use of exact phase information. Our technique can simultaneously correct both amplitude and phase distortions. We include several forms of image degradation, various test cases, and experimental results. We characterize the performance as a function of the input beam ratios for four metrics: signal-to-noise ratio, normalized root-mean-square error, edge restoration, and peak-to-total energy ratio. In our characterization we use false-color graphic images to display the best beam-intensity ratio two-dimensional region(s) for each of these metrics. Test cases are simulated at the optimal values of the beam-intensity ratios. We demonstrate our results through both experiment and computer simulation.

Gas Cluster Ion Beam Processing of GaSb and InSb Surfaces

Gas Cluster Ion Beam (GCIB) processing has recently emerged as a novel surface smoothing technique to improve the finish of chemical-mechanical polished (CMP) GaSb (100) and InSb (111) wafers. This technique is capable of improving the smoothness CMP surfaces and simultaneously producing a thin desorbable oxide layer for molecular beam epitaxial growth. By implementing recipes with specific gas mixtures, cluster energy sequences, and doses, an engineered oxide can be produced. Using GaSb wafers with a high quality CMP finish, we have demonstrated surface smoothing of GaSb by reducing the average roughness from 2.8A to 1.7A using a dual energy CF 4 /O 2 -GCIB process with a total charge fluence of 4×10 15 ions/cm 2 . For the first time, a GCIB grown oxide layer that is comprised of mostly gallium oxides which desorbed at 530°C in our molecular beam epitaxy system is reported, after which GaSb/AlGaSb epilayers have been successfully grown. Using InSb, we successfully demonstrated substrate smoothing by reducing the average roughness from 2.5A to 1.6A using a triple energy O 2 -GCIB process with a charge fluence 9×10 15 ions/cm 2 . In order to further demonstrate the ability of GCIB to smooth InSb surfaces, sharp ∼900nm high tips have been formed on a poorly mechanically polished InSb (111)A wafer and subsequently reduced to a height of ∼100nm, an improvement by a factor of eight, using a triple energy SF 6 /O 2 -GCIB process with a total charge fluence of 6×10 16 ions/cm 3 .

Recent progress in development orientation-patterned GaP for next-generation frequency conversion devices

Progress in developing a cost effective technique for fabrication of orientation patterned GaP templates and a reliable technology for thick epitaxial growth on them is described. First 350 μm thick device quality OPGaP is produced.

Micromechanical Characterization of Gasb by Microbeam Deflecion and Using Nanoprobe and Finite Element Analysis

The commercial development of low-power electronics and electro-optics based on antimonides demands a better understanding of the mechanical properties of ternary and quaternary thin-film alloys fabricated from the InGaAlAsSbP material system. Of particular importance is the determination of Youngs modulus of these materials. In this paper, a technique for studying the mechanical behavior of these thin films was developed by using microbeam bending and finite element modeling. The technique was successfully applied to investigate the mechanical properties of GaSb. A test structure consisting of an array of gallium antimonide microbeams was fabricated with lengths ranging from 50 to 500 μm long. The microbeams were deflected using a calibrated nanoprobe, thereby generating load-displacement curves. Youngs modulus was then extracted from the data using beam bending theory and a finite element simulation of the structures under load. A total of five microbeams with the same trapezoidal cross-section and lengths of 80, 85, 200, 250 and 500 μm were tested to study the technique applicability and size scaling effects on the mechanical properties. It was observed that the 80 and 85 μm beams exhibited linear elastic behavior and the 200, 250, and 500 μm microbeams exhibited non-linear elastic behavior.