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Politics : Formerly About Advanced Micro Devices

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To: Bill Jackson who wrote (92039)	2/8/2000 11:56:00 AM
From: Pravin Kamdar	Read Replies (1) of 1576627

Bill, GaAs wafers in themselves are very expensive. The higher carrier mobilities and saturation velocities of GaAs, wrt silicon, in conventional FET structures (such as those used in microprocessors) are not enough to outweigh the extra cost and the immaturity of FET processing technology (larger sized devices). A real speed benefit comes by using expensive MBE and special CVD techniques to build super high speed bipolar devices, such as HBTs, by carefully introducing Al into the lattice to "bandgap engineer" junction potential barriers. But I haven't researched this area for about 10 years, so a lot may have improved in terms of GaAs FETs. Pravin These energy discontinuities at the junctions limit the reverse injection of minority carriers, thus allowing the base region to be extremely highly doped while maintaining gain (the device's ability to amplify). The highly doped base (at solid solubility limits) can then be made very thin for fast carrier transit times (high frequency) while maintaining low base resistance.

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