Fabrication, Characterisation, and Epitaxial Optimisation of MOVPE-Grown Resonant Tunnelling Diode THz emitters

摘要

Resonant tunnelling diodes (RTDs) are a strong candidate for future wireless communications in the THz region, offering compact, room-temperature operation with Gb/s transfer rates. We employ the InGaAs/AlAs/InP material system, offering advantages due to high electron mobility, suitable band-offsets, and low resistance contacts. We describe an RTD emitter operating at 353GHz, radiating in this atmospheric transmittance window through a slot antenna. The fabrication scheme uses a dual-pass technique to achieve reproducible, very low resistivity, ohmic contacts, followed by accurate control of the etched device area. The top contact connects the device via the means of an air bridge. We then proceed to model ways to increase the resonator efficiency, in turn improving the radiative efficiency, by changing the epitaxial design. The optimization takes into account the accumulated stress limitations and realities of reactor growth. Due to the absence of useful in-situ monitoring in commercially-scalable metal-organic vapour phase epitaxy (MOVPE), we have developed a robust non-destructive epitaxial characterisation scheme to verify the quality of these mechanically shallow and atomically thin devices. A dummy copy of the active region element is grown to assist with low temperature photoluminescence spectroscopy (LTPL) characterisation. The resulting linewidths limits the number of possible solutions of quantum well (QW) width and depth pairs. In addition, the doping levels can be estimated with a sufficient degree of accuracy by measuring the Moss-Burstein shift of the bulk material. This analysis can then be combined with high resolution X-ray diffractometry (HRXRD) to increase its accuracy.