Monolithic integration of InAlAs-InGaAs-InP HEMTs and InAs-AlSb-GaSb resonant interband tunneling diodes (RITDs) for high speed integrated circuits

Abstract

We report for the first time the monolithic integration of high-speed submicron gate length InAlAs-InGaAs-InP HEMTs with InAs-AlSb-GaSb resonant interband tunneling diodes (RITDs) for ultra-high-speed IC applications. The epitaxial layers for the integrated RITD/HEMT device process were deposited by molecular beam epitaxy (MBE) on 2 semi-insulating InP substrates. Critical aspects of MBE growth process development include: (1) nucleation of a smooth, strain-relaxed InAs n/sup +/ buffer layer on top of the InGaAs-InAlAs HEMT device layers to provide a growth template and bottom contact for the InAs-AlSb-GaSb RITD active layers, and (2) two AlAs etch stop layers to allow uniform removal of the RITD layers for HEMT processing and uniform gate recess etching. In situ substrate temperature control using an absorption edge spectroscopy sensor was used to nucleate the strain-relaxed InAs buffer at a substrate temperature of 400/spl deg/C followed by heating to 480/spl deg/C for growth of a 150 nm buffer layer. A smooth, thin buffer layer is advantageous for integration of the RITD and HEMT devices in that the RITD device mesas can be short (0.4 /spl mu/m), yielding a relatively planar process geometry. A 50 nm-thick lattice-matched InGaAs layer was deposited between the RITD/HEMT isolation AlAs etch stop layer and the strain-relaxed InAs buffer layer to ensure the structural integrity of the etch stop layer. A carrier concentration of 2.7 10/sup 12/ cm/sup -2/ and mobility of 9500 cm/sup 2//Vs in the HEMT channel were measured. These values are comparable to a control HEMT-only heterostructure.