Barrier tuning of atomic layer deposited Ta2O5 and Al2O3 in resonant tunnelling diodes for terahertz applications

The performance of double dielectric (MIIM) resonant tunneling diodes using atomic layer deposited oxides of low (Al2O3) and high (Ta2O5) electron affinity (χ) is investigated. Varying the individual layer thickness of Ta2O5 with a 1 nm thick Al2O3, evidence for resonant tunneling is observed and related to the bound states in the quantum well established between the oxide layers. The results show good rectifying capability of resonant tunneling diodes at low turn-on voltage enabling their potential use for terahertz applications

Enhanced low voltage nonlinearity in resonant tunneling metal–insulator–insulator–metal nanostructures

The electrical properties of bi-layer Ta2O5/Al2O3 and Nb2O5/Al2O3 metal–insulator–insulator–metal nanostructures as rectifiers have been investigated. The ultra-thin (1–6 nm) insulator layers were deposited by atomic-layer deposition or rf magnetron sputtering with Al as metal contacts. Variable angle spectroscopic ellipsometry was performed to extract the optical properties and band gap of narrow band gap insulator layers while the surface roughness of the metal contacts was measured by atomic force microscopy. Superior low voltage large signal and small signal nonlinearities such as asymmetry of 18 at 0.35 V, rate of change of non-linearity of 7.5 V�1, and responsivity of 9 A/W at 0.2 V were observed from the current–voltage characteristics. A sharp increase in current at �2 V on Ta2O5/Al2O3 device can be ascribed to resonant tunneling