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Abstract
Firstly, we report on recent developments in the fabrication, simulation and demonstration of prototype silicon-on-insulator (SOI) microdosimeter arrays. The design, which is based upon 2500 planar cylindrically-shaped p-i-n detectors, incorporates two types of guard ring (GR): (i) Defined annular GR concentric to each sensitive volume (SV); and (ii) GR that is continuous everywhere between each SV. A comprehensive ion-beam-induced charge (IBICC) investigation into the charge collection characteristics of the microdosimeter arrays was performed. The results show that the SVs maintain well-defined cylindrical geometry and are successfully read out in a parallel mode. In addition, an ion-implanted structure has been modelled using Technology Computer Aided Design (TCAD) showing avalanche signal multiplication around the n+ region for improved detection.
Secondly, we describe the integration of p-i-n structures for single-ion implant detection with p-type channel-stop regions to eliminate parasitic leakage currents in n-MOS structures while maintaining a single-ion detection capability. The structures are configured for the assembly of a MOS spin-qubit architecture based on phosphorus donors in silicon. The detection method is based on charge collection in the sensitive region by generation of electron-hole pairs in the Si substrate following the impact of a single 14-keV P+ ion. We present the results of leakage current and ion-beam-induced charge collection (IBICC) tests which show that the structure is capable of providing almost 100% detection efficiency for implanted P ions, thus facilitating the construction of Si:P qubit devices.
Finally, we report on the observation of Pauli spin blockade in a silicon MOS double quantum dot system. We demonstrate independent gate control of each dot's electron occupancy (m, n) and gate-tunability of the inter-dot tunnel coupling. The device exhibits robust charge stability over a wide range of occupancy of the lithographically-defined dots. At weak inter-dot coupling we clearly observe Pauli spin blockade and measure a large intra-dot singlet-triplet splitting > 1 meV. The leakage current in spin blockade has a peculiar magnetic field dependence, unrelated to electron-nuclear effects and consistent with the effect of spin-flip cotunneling processes. The results obtained here provide excellent prospects for realizing singlet-triplet qubits in silicon.