Graphic script provides quick classification of GaAs wafers

Infrared transmission topography has long been used to detect variations in gallium arsenide wafers that can cause dark-line defects that limit lifetime of GaAs lasers and solar cells. In the past, infrared transmission was measured over a whole wafer by scanning a small spot mechanically. Absorption was calculated at each location across the surface of the wafer and used to produce colour-coded plots that allow the wafer's characteristics to be determined at a glance. The program ran on VAX/VMS computers, but these are being taken out of service due to obsolescence. To overcome these problems, the author developed a graphics script using a state-of-the-art data analysis program which provides quick classification of GaAs wafers based on traps and defects, but runs on inexpensive personal computers and, as a bonus, produces bit-map plots that can be cut and pasted into Windows word processing and presentation software.

Source: III-Vs Review

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Crystal growth of large-diameter bulk CdTe on GaAs wafer seed plates

We report here on some of the characteristics of CdTe bulk crystals grown on commercially available (2 1 1)B GaAs wafers by multitube physical vapour transport, a process analogous to vapour phase heteroepitaxy. Crystals several millimetres in thickness have been grown on 50 mm diameter seed plates with growth rates∼120 μm/h. Double- and triple-axis X-ray diffraction gave resolution-limited FWHM values of 34 arcsec. Maps across an as-grown surface showed the FWHM to be less than ∼80 arcsec over the majority of the surface. Infrared microscopy revealed there were comparatively low levels of Te inclusions in the central part of the crystal, but rather higher concentrations towards the edges. The use of GaAs substrates did not appear to produce the compensated material, and it was necessary to dope the material with Cl to render it semi-insulating.

Source: Journal of Crystal Growth

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Stress analysis and bending tests for GaAs wafers

Wafer made from single crystal gallium arsenide (GaAs) are used as substrate materials in micro- and opto-electronic devices. During the various processes of manufacturing, the wafers are subjected to mechanical loads which may lead to fracture. The characterization of the fracture strength of the wafers need bending tests and a theoretical calculation of various stress distributions within the wafers.

In this study we show that the nonlinear von Kármán theory may serve as an appropriate tool to calculate the stress distributions as functions of the external load, while the Kirchhoff theory has turned out to be completely inappropriate. Our main focus is devoted to (i) calculation of the contact area between the load sphere and the wafer, (ii) study of the influence of the anisotropic character of the material, (iii) study of the important geometric nonlinearity. Finally we compare the calculated and theoretical load–flexure relations in order to demonstrate the high accuracy of the von Kármán theory and its finite element implementation.

Source:Microelectronics Reliability

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State of the art 6″ SI GaAs wafers made of conventionally grown LEC-crystals

6″ SI GaAs single crystals are grown by the standard LEC-process in a new-generation multi-heater puller designed for charges up to 50 kg and crucibles up to 12″, applying the carbon controlled growth technology. It is demonstrated that the increasing requirements of device manufacturers with regard to macroscopic and mesoscopic homogeneity of electrical properties, mechanical strength, flatness and cleanliness of the wafers can be fully met by LEC grown 6″ crystals.

Source:Journal of Crystal Growth

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