Heterojunction field effect transistor with non-alloy ohmic contact electrodes

摘要

An InAlAs/InGaAs type heterojunction FET is provided which can reduce the source and drain contact resistance through the InAlAs layer without lowering the sheet carrier concentration so as to form an ohmic contact without alloying. A laminated structure of an undoped InAlAs buffer layer, an undoped InGaAs channel layer which accumulates two- dimensional electron gas, InAlAs electron supply layers containing an n- type layer, an undoped InAlAs Schottky layer, a first cap layer of n-type InAlAs, a second cap layer, and a third cap layer of n-type InGaAs are sequentially formed on a semi-insulating InP substrate. When undoped InGaAs or n-type IN(AlGa)As is employed as the second cap layer, the potential barrier at the interfaces between the cap layers are reduced so that the contact resistivity between the cap layer and the channel layer can be reduced to as low as 10.sup.-7 &OHgr;cm.sup.2.