Micro-PL analysis of high current density resonant tunneling diodes for THz applications

Abstract

Low-temperature micro-photoluminescence (μPL) is used to evaluate wafer structural uniformity of current densities >5mA/µm 2 InGaAs/AlAs/InP resonant tunnelling diode (RTD) structures on different length scales. Thin, highly strained quantum wells (QWs) are subject to monolayer fluctuations, leading to a large statistical distribution in their electrical properties. This has an important impact on the RTD device performance and manufacturability. The PL spot size is reduced using a common photolithography mask to reach a typical high Jpeak for a given RTD mesa size (1 ~ 100 µm 2 ). We observe that for lower strain-budget samples, that the PL line-shape is essentially identical for all excitation/collection areas. For higher strain-budget samples, there is a variation in the PL line-shape that is discussed in terms of a variation in long-range disorder brought about by strain relaxation processes. The RTD operating characteristics are discussed in light of these findings, and we conclude that strain model limits overestimate the strain budget that can be incorporated in these devices. We also highlight μPL as a powerful non-destructive characterization method for RTD structures.There is a lack of efficient high-speed technology able to satisfy the ever-growing wireless datademand [1,2]. As a consequence, the THz frequency range (0.1-10THz)[3] has attracted considerable interest as it offers the wide bandwidth required for high data-rate communications. Resonant tunneling diodes (RTDs ) have been demonstrated to be the fastest solid-state device with oscillation near 2 THz [4] with highly attractive characteristics: tunability, compact dimensions, and room temperature operation [5] . As for all quantum-effect devices [6], the RTD performance is critically dependent on crystal purity and heterointerface perfection. We previously demonstrated how ~80% of the parasitic valley current is associated with non-thermal inelastic scattering [7], and as a consequence, the RTD output power is limited by crystal-related imperfections.RTDs are composed of a single double-barrier QW generally growth by molecular beam epitaxy (MBE) or metal-organic vapor-phase epitaxy (MOVPE), despite the outstanding precision offered by these technologies, wafer characterization remains a difficult process, leading to knowledge barriers in