Selective area growth of InAs on InP with dielectric mask

Abstract

Low resistance ohmic contacts are important for high frequency applications of InP-based heterojunction bipolar transistors and high electron mobility transistors. In this paper, the authors investigate the use of an InAs layer as the low-resistance ohmic contact to these heterostructure devices. Selective area crystal growth of InAs on a dielectric [benzocyclobutene (BCB) polymer] covered InP(100) was carried out by molecular beam epitaxy (MBE). Additionally, direct growth of InAs on InP substrates was performed to allow comparisons with InAs grown on BCB-covered InP. Different growth temperatures were tested to optimize the crystal quality of the InAs layer, which was characterized by scanning electron microscope and x-ray diffraction. Heavy doping of InAs using Te was carried out to determine the lowest sheet resistance. As the substrate temperature was increased from 210 to 350 °C, the crystallinity improved from a polycrystal layer to a single crystal layer with corresponding improvement of surface morphology. Moreover, sharp x-ray diffraction indicated the 3.3% lattice-mismatch was fully relaxed without misorientation. However, a trade off was reached around 290 °C between crystallinity and optimized dopant incorporation of Te into InAs for lowest sheet resistance. The results indicate the potential of Te-doped InAs as emitter contact for high frequency devices by MBE.