Abstract
A high-transconductance AlGaAs/GaAs/AlGaAs selectively-doped double-heterojunction FET (SD-DH FET) with 1μm gate length has been fabricated by using high-quality epitaxial layer grown by MBE and Pd-buried gate structure. The double-heterojunction structure showed high sheet electron concentration of 2.5x10 12 /cm 2 and high electron mobility of 37000cm 2 /Vs at 77K. The sheet resistance at room temperature was 450 ohm/sq., which is about one half of that for a conventional high electron mobility transistor (HEMT). Systematic change of SD-DH FET characteristics with threshold voltage variation has been studied by gradually burying Pd into AlGaAs layer. It was found that transconductance of SD-DH FET monotonically increased for threshold voltage up to 0.1V, at which maximum extrinsic transconductance of 500mS/mm 7 was obtained. The estimated saturation velocity of electrons in SD-DH FET was 1.7 -2.0x10 7 cm/s, which is comparable to that of HEMT. The SD-DH FET has been shown to be superior to conventional HEMT fabricated at the same time in high current drivability, high transconductance and lower drain conductance.
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