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GaAs-based Devices: How To Choose A Suitable Substrate

There are a number of companies that sell GaAs substrates grown by LEC or VGF, but what is the difference? Russ Kremer and Steffen Teichert provide some answers.
One of the more interesting questions that arises when considering the production of GaAs-based devices relates to the proper choice of substrate. Today s substrate suppliers currently mass-produce two types of wafer. These are based on two different crystal growth principles: the Czochralski process and the Bridgman process. With both methods it is possible to grow large-diameter, semi-insulating (as well as semiconducting) crystals for applications in micro- and optoelectronics.

The material is usually classified according to the crystal growth technology used in its manufacture. For the user, it is more meaningful to designate materials by their properties rather than by the production technology used. The two available substrate types are often called "low EPD" and "high EPD" material. The etch pit density (EPD) measures the dislocation density of the substrate. For semi-insulating GaAs, typical EPDs for material specified as high or low EPD are

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