Apr 21, 2014

Pulse plating of Pt on n-GaAs (100) wafer surfaces: Synchrotron induced photoelectron spectroscopy and XPS of wet fabrication processes

Preparation steps of Pt/n-GaAs Schottky contacts as applied in the fabrication process of varactor diode arrays for THz applications are analysed by photoelectron spectroscopy. Pulsed cathodic deposition of Pt onto GaAs (1 0 0) wafer surfaces from acidic solution has been studied by core level photoelectron spectroscopy using different excitation energies. A laboratory AlKα source as well as synchrotron radiation ofhν=130 and 645 eV at BESSY was used. Chemical analyses and semiquantitative estimates of layer thickness are given for the natural oxide of an untreated wafer surface, a surface conditioning NH3 etching step, and stepwise pulse plating of Pt. The structural arrangement of the detected species and interface potentials are considered.

Source: sciencedirect

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Residual strain in annealed GaAs single-crystal wafers as determined by scanning infrared polariscopy, X-ray diffraction and topography

We have compared the strain data in GaAs wafers, as-grown as well as annealed, determined by means of the scanning infrared polariscope (SIRP) with data of high-resolution X-ray diffraction (HRXD) and qualitative results of a synchrotron based, single-crystal X-ray transmission topography (SXRTT) study. The in-plane strain component |εr−εt| measured by SIRP throughout the wafer thickness was about 10−5, while it derived from the single components εxx, εyy, and εxy determined by HRXD at a penetrated layer close to the surface was above 10−4. Consequently, we assume that a strong strain gradient exists between the surface and the bulk.

Source: Journal of Crystal Growth

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Apr 9, 2014

Characterization of EL2 distribution on semi‐insulating GaAs wafer by optically assisted imperfection profile

An improved nondestructive characterization technique is developed to measure the relative density distribution of the EL2 level in undoped semiinsulating (SI) GaAs wafers at room temperature. Experimentally, the resistance of a small area of the wafer is measured twice, first with greater than bandgap illumination outside a small masked area and then with a narrowband optical filter centered at 1074 nm in place of the masked area. The difference of the two measured resistances is shown to be proportional to the density of the EL2 level. By moving the masked area across the wafer while taking resistance measurements, the relative density variation of EL2 can be determined. A theoretical discussion based on the commonly used compensation model for undoped SI GaAs materials is presented to interpret the experimental data. A technique for applying electrical contacts to SI GaAs materials by ultrasonic soldering has been developed to achieve reproducible measurements. Although only GaAs materials were investigated, this optically assisted imperfection profile can be applied to study other highresistivity semiconductors.

Source:IEEE

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GaAs wafer breakage: Causes and cures, growth and process

The impact of GaAs wafer breakage on processing facilities is discussed. Wafer strength and equipment assessment are detailed. The authors describe many of the improvements that have resulted in the virtual elimination of wafer breakage due to unassignable causes. When proper material and process control techniques are used, GaAs wafer breakage should not occur.

Source:IEEE

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