Impact ionization suppression by quantum confinement: Effects on the DC and microwave performance of narrow-gap channel InAs/AlSb HFET's

InAs/AISb heterostructure field-effect transistors (HFET's) are subject to impact ionization induced short channel effects because of the narrow InAs channel energy gap. In principle, the effective energy gap to overcome for impact ionization can be increased by quantum confinement (channel quantiza tion) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of qua ntum well thickness on the de and microwave performance of narrow-gap InAs/ AISb HFET's fabricated on nominally identical epitaxial layers which differ only by their quantum well thickness, We show that a thinner quantum well postpones the onset of impact ionization and suppresses short-channel effec ts. As expected, the output conductance go, and the gate leakage current ar e reduced, The f(MAX)/fT ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 Angstrom. The use of the thinner well reduces the cutoff frequency f(T) the transconductance g(m) and the cu rrent drive because of the reduced low-held mobility due to interface rough ness scattering in thin InAs/AISb channel layers: the low-held mobilitiy wa s mu = 21 000 and 9000 cm(2)/Vs for the 100- and 50-Angstrom quantum wells, respectively, To our knowledge, the present work is the first study of the link between channel quantization, in-plane impact ionization, and device performance in narrow-gap channel HFET's.