Stable and metastable (Al,Ga)As/(In,Ga)As n-channel strained quantum well field-effect transistors

It is demonstrated that FETs with excellent electrical properties can be generated in metastable (Al,Ga)As/(In,Ga)As SQW (strained quantum well) material if processing approaches which do not substantially exceed the growth temperature are utilized. To demonstrate this effect an n-channel structure with a 15-nm In/sub 0.15/Ga/sub 0.85/As SQW, capped by 38 nm of Al/sub 0.1/Ga/sub 0.83/As and 40 nm of GaAs, was fabricated into FETs. It is further demonstrated that significant spatially nonuniform relaxation occurs after high-temperature annealing in structures which were not recognized until recently as being metastable. The dislocations associated with this relaxation modify transistor characteristics in gross, uncontrolled ways.<
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