AVS 62nd International Symposium & Exhibition
    Electronic Materials and Processing Monday Sessions
       Session EM+AS+SS-MoA

Paper EM+AS+SS-MoA1
Engineered Tunnel-Barrier Terahertz Rectifiers for Optical Nantennas

Monday, October 19, 2015, 2:20 pm, Room 211A

Session: MIM Diodes, Functional Oxides, and TFTs
Presenter: Ivona Mitrovic, University of Liverpool, UK
Authors: I.Z. Mitrovic, University of Liverpool, UK
N. Sedghi, University of Liverpool, UK
A.D. Weerakkody, University of Liverpool, UK
J.F. Ralph, University of Liverpool, UK
S. Hall, University of Liverpool, UK
J.S. Wrench, University of Liverpool, UK
P.R. Chalker, University of Liverpool, UK
Z. Luo, University of Southampton, UK
S. Beeby, University of Southampton, UK
Correspondent: Click to Email
Thin film metal-insulator-metal rectifying devices using double, triple or quadruple insulator layers are currently the focus of attention for the development of next-generation optical nantennas for infrared energy harvesting. The interest is driven by their distinctive attributes, such as nanoscale footprint, room temperature operation, zero bias voltage requirement, and ease of integration with Complementary Metal Oxide Semiconductor technology. Highly asymmetric and nonlinear current-voltage (IV) behaviour at low applied voltages is critical for this application. In this paper, we present comprehensive experimental and theoretical work on tunnel-barrier rectifiers comprising double (Ta2O5/Al2O3 and Nb2O5/Al2O3) and triple (Ta2O5/Nb2O5/Al2O3) insulator configurations engineered to enhance low voltage nonlinearity. There are two mechanisms that allow metal-insulator-insulator-metal (MIIM) rectifiers to have a high nonlinearity while keeping the resistance low: (i) resonant tunnelling, and (ii) step tunnelling. This paper focuses on the former approach. A modified multi-layer Tsu-Esaki method has been used for IV calculations from the transmission coefficient by the transmission matrix method. The theoretical work indicates that the onset of resonant tunneling in MIIM and MIIIM rectifiers can be adjusted to be close to zero volts by appropriate choice of work function difference of the metal contacts, the thickness of insulator layers, and the depth of the quantum well. The double and triple insulator rectifiers were fabricated using atomic layer deposition (ALD) and rf magnetron sputtering, while different metal contacts including Al, Ta, W, Nb, Cr and Ag were defined by photolithography or shadow mask and deposited by e-beam and thermal evaporation. The thickness, band gap, surface roughness, band offsets and work functions have been extracted from variable angle spectroscopic ellipsometry, atomic force microscopy, x-ray and inverse photoelectron spectroscopy on fabricated devices to ascertain the quality of the interfaces and to measure barriers. The key rectifier properties, asymmetry, nonlinearity and responsivity have been assessed from current voltage measurements performed in the range 293-370 K. A superior low voltage asymmetry (18 at 0.35 V) and responsivity (9 A/W at 0.2 V) has been observed for fabricated bilayer Ta2O5/Al2O3 and Nb2O5/Al2O3 MIIM devices respectively, in advance of state-of-the-art experimental values. The results demonstrate ALD and rf sputtered tunnel-barrier rectifiers which enhance low voltage nonlinearity and have the potential to be employed in optical nantennas for infrared energy harvesting.