PURPOSE: To further increase operation speed by improving the electron mobility within a channel in a negative differential resistance FET. ;CONSTITUTION: A quantum well structure 9 where the sub-band of electrode is generated is laminated at a buffer layer 2, a channel layer 3, an electron supply layer 4, a gate electrode 5, and a second cap layer 6-2 of selective dope FET with first and second cap layers 6-1 and 6-2 while holding the gate electrode. By setting the impurity concentration of the cap layers to 1× 1018/cm or higher, the contact resistivity between the cap layer and a channel can be reduced to the order of 10-7Ωcm2 and achieving ohmic contact without providing an alloy region.;COPYRIGHT: (C)1996,JPO
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