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

Abstract

InAs/AlSb 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 quantization) to alleviate impact ionization related nonidealities such as the kink effect and a high gate leakage current. We have studied the effects of quantum well thickness on the dc and microwave performance of narrow-gap InAs/AlSb 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 effects. As expected, the output conductance g/sub DS/ and the gate leakage current are reduced. The f/sub MAX//f/sub T/ ratio is also significantly improved when the InAs well thickness is reduced from 100 to 50 /spl Aring/. The use of the thinner well reduces the cutoff frequency f/sub T/, the transconductance g/sub m/, and the current drive because of the reduced low-field mobility due to interface roughness scattering in thin InAs/AlSb channel layers: the low-field mobility was /spl mu/=21 000 and 9000 cm/sup 2//Vs for the 100- and 50-/spl Aring/ 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.