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Program Manager
Prof Andrew Dzurak - University of New South Wales

Intergrated Quantum Computer Device Researchers
Dr Søren Andresen
Dr Rolf Brenner
Dr Eric Gauja
Dr Fay Hudson
Mr Frank Wright

Mrs Susan Angus (PhD), Mr Victor Chan (PhD), Mr Chris Escott (PhD), Mr Mladen Mitic (PhD),
Mr Lars Hansen (International Research Student), Mr Karl Petersson (Research Assistant),
Mr David Waterhouse (Research Assistant), Ms Maja Cassidy (Thesis), Ms Kitty Lo (Thesis),
Mr Graeme Lowe (Thesis)

Participating UNSW Researchers
Dr Andrew Ferguson
Prof Robert Clark
Mr Martin Brauhart (SNF Lab Manager)

Collaborating Centre Researchers
Prof David Jamieson - University of Melbourne
Prof Steven Prawer - University of Melbourne
Dr Jeff McCallum - University of Melbourne
A/Prof Lloyd Hollenberg - University of Melbourne
Dr Andrew Greentree - University of Melbourne
Dr Changyi Yang - University of Melbourne
Dr Chris Pakes - University of Melbourne
Prof Gerard Milburn - University of Queensland
Prof David McKenzie - University of Sydney

Other Collaborating Researchers
UNSW Electron Microscope Uni - Dr Marion Stevens-Kalceff
University of Notre Dame, USA - Prof Gregory Snider

Program Description
The Centre for Quantum Computer Technology is focused on realisation of spin-based qubits in silicon and also a charge-based qubit scheme (see Figure 1). The IQCD program develops 'top-down' fabrication strategies for producing fully-configured quantum computer devices including on-chip detectors for registration of single ion implants, control gates accurately aligned to implanted donors and integrated single electron transistors (SETs) for qubit state read-out. Longer term aims include process integration with the 'bottom-up' STM-fabrication approach of the Atomic Scale Fabrication and Crystal Growth Program for configuration of large-scale multi-qubit devices.

Figure 1: (Left) Spin qubits and (right) charge qubits

Prototype quantum computer test devices (as depicted in Figure 2) include on-chip detectors for registration of single ion implants, control gates accurately aligned to implanted donors and two single electron transistors (SETs) for qubit state read-out. A complex series of fabrication processes has been tailored for producing devices for critical charge transfer experiments on the path to charge and spin qubit devices.

Figure 2:(a) Schematic of a prototype two P-atom charge qubit device and associated energy level diagram. (b) Energy level diagram for buried P-atom cluster device.

Charge Based Si:P Qubits
We have fabricated many atom (100, 200 and 600) clusters implanted with either P or Si (control), few atom (5, 20) devices and two-atom devices implanted using single atom detection. Figures 3(a) and (b) show correlated SET data for 600-atom cluster devices. These data correspond to quasi-periodic charge transfer events detected by both surface SETs. The charge transfer loci can be seen to alter in angle with differing control gate sweeps. Figure 3(c) and (d) show equivalent data for control devices implanted with 600-atom Si clusters. These data show no clear transfer events suggesting that the implantation and annealing process produces no large numbers of significant charge traps or defects.

Our on-chip PIN detector structures are depicted in Figure 4. Figure 4(b) shows a scanning electron microscope image of the structure fabricated using optical lithography with carefully aligned p+ diffused regions, contact metal and a central thin oxide site for the finer device features. In Figure 4(c) a detection spectrum shows two 14 keV 31P+ ion impacts well above the noise threshold achieved with this structure. (Please refer to the Ion Beam Program page for further details.) Data in Figures 4(d) and (e) show correlated SET data for devices implanted with nominally 5 atoms in total. There is a small number of transfer events observed as might be expected for such a device.

Figure 3 (left) (a) and (b) ((c) and (d)) Schematic diagrams and correlated
SET data for buried P(Si)-atom cluster devices with different control gate sweeps.

Figure 4 (right) (a) Schematic diagram of PIN detector structures with real implant data for single 14 keV 31P+ ion impacts. (b) SEM image of PIN structure. (c) Detection spectrum showing two P atom strikes above the noise threshold. (d) and (e) Schematic and correlated SET data for few-P-atom and no atom (control) devices respectively.

Linux Cluster for ISE-TCAD Device Modelling
In 2004, a new high performance computer modelling cluster was installed at UNSW, equipped with ISE-TCAD 10.0 to facilitate efficient semiconductor device simulation. The cluster resources include three AMD Athlon XP 2800+ dual CPU machines each with 3 GB RAM and two Intel Xeon 2.4 GHz dual CPU machines each with 6 GB RAM. The individual sub-programs within ISE-TCAD are intricately linked together to provide a complete simulation flow, from fabrication process modelling, to device simulation, to integration into industrial applications. Various components of the TCAD platform have been evaluated and used to model various aspects of our device structures, including implantation simulation, capacitance extraction, PIN single ion detector and nanoMOSFET simulation (see Figure 5).

Figure 5: TCAD modelling of implanted Si:P nanoMOSFET device.
(a) 2D and 3D maps showing set-up of fine and coarse meshes for modelling.
(b) Dopant concentrations obtained from process simulation of 14 keV P+ implant,
showing localized clustering of P atoms in the nominally undoped barrier region.



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