Characterisation of thin-layer resonant tunnelling diodes grown by MOVPE

Abstract

Resonant tunneling diodes (RTDs) are next-generation candidates for core THz generation technologies, with proven quasi-optical tunable emission capability, with centre frequencies of 0.1 - 1.98 THz at cca. 1mW, when coupled into a suitable monolithically integrated antenna. For this purpose, the strained InGaAs/AlAs/InP material system is approaching technological maturity, with its offering of high electron mobility, suitable conduction band offsets, and very low resistance contacts. However, the epitaxially thin layers used for RTDs, realise devices with current densities in excess of 10 mAμm^-2 and electric fields approaching that of the breakdown of the material. As a high current density is a traditional indicator of performance for these oscillators, it is now increasingly important to grow crystalline layers with near-atomic perfection. In previous work, we showed how the inclusion of a nominally identical, un-doped electrically neutral copy of the RTD double barrier - quantum well (QW) system, leads to the observance of a type-II QW emission in addition to the type-I emission from the active region QW. This could be used to establish the quasi-bound elastic energy, whose level is directly correlated to the peak voltage of the N-shape I-V characteristic. Here we extend this approach with the addition of high-resolution X-ray diffractometry and low-temperature photoluminescence spectroscopy. Through a step-by-step process of curve fitting, comparing to simulation and results, we can comment on the quality and thickness of the ternary InGaAs alloy interfaces surrounding the AlAs barriers. These findings are confirmed with scanning transmission electron microscopy