A SELF-ALIGNED GATE GAAS-MESFET WITH P-POCKET LAYERS FOR HIGH-EFFICIENCY LINEAR POWER-AMPLIFIERS

This paper describes a newly developed GaAs metal semiconductor field- effect transistor (MESFET)-termed p-pocket MESFET-for use as a linear power amplifier in personal handy-phone systems. Conventional buried p -layer technology, the primary technology for microwave GaAs power MES FET's, has a drawback of low power efficiency for linear power applica tions. The low power efficiency of the buried p-lager MESFET is ascrib ed to the I-V kink which is caused by holes collected in the buried p- layer under the channel. In order to overcome this problem, we have de veloped the self-aligned gate p-pocket MESFET which incorporates p-lay ers not under the channel but under the source and drain regions. This new MESFET exhibited high transconductance and uniform threshold volt age. The problematic I-V kink was successfully removed and an improved power efficiency of 48% was achieved under bias conditions, which res ulted in adjacent channel leakage power at 600-kHz offset as low as -5 9 dBc for 1.9-GHz pi/4-shift QPSK modulated input.