A self-aligned gate lightly doped drain (Al, Ga)As/GaAs MODFET

An asymmetrical lightly doped drain (LDD) (Al, Ga)As/GaAs modulation-doped FET (MODFET) structure with high drain-to-source and drain-to-gate breakdown voltages was fabricated. The LDD structure has a self-aligned lightly doped n/sup -/ region between the channel and a heavily doped n/sup +/ region at the drain, to reduce the electric field and impact ionization. The length of the lightly doped n/sup -/ region on the drain side was varied from 0 to 1 mu m. Drain-to-source breakdown voltage BV/sub ds/ improved from 4.6 to >10 V while the transconductance g/sub m/ remained unchanged. The drain-to-gate reverse breakdown voltage BV/sub dg/ increased from approximately=7 to >20 V. The two breakdown mechanisms are believed to be independent. The LDD MODFET should find widespread application in circuits requiring high breakdown voltage such as high-speed analog-to-digital converters (ADCs) and microwave power amplifiers.<
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