Two-dimensional electron gas field effect transistor including an improved InGaAs channel layer

摘要

The invention provides a compound semiconductor multilayer structure having a two-dimensional electron gas, which is applicable to field effect transistors. A ternary compound InGaAs planar channel layer serving as a quantum well has a variation of an In (indium) fraction in a perpendicular direction to a heterojunction interface. The variation has a step-graded profile with taking a maximum value at or in the vicinity of a portion where the two-dimensional electron gas takes a maximum density. Such quantum well has most large depth at a portion except for adjacent portions to the heterojunction interfaces. Such multilayer structure provides a great electron mobility and a strong electron confinement to major electrons at a high electron density portion. Such multilayer structure provides the large effective electron mobility and the large sheet electron density to the two-dimensional electron gas without a gain of the average of the In (indium) fractions, thereby suppressing the enlargement of the lattice mismatch which causes misfit dislocations in crystals.