Research
MBE Growth of Nitrides and 2D Materials
In Sheffield I will be setting up a new activity in the MBE growth of 2d TMD materials such as MoSe2 and WSe2.
MBE growth of high mobility quantum devices
The primary focus of my work in the Semiconductor Physics Group is to provide a wide range of MBE grown samples for the research group as a whole. This includes production of two dimensional electron gases (2DEGs) with both GaAs and InGaAs channel materials as well as more complex layer structures involving multiple conducting channels for investigation of bilayer effects. These wafer structures are then patterned using a combination of electron beam and optical lithography to produce structures with lower dimensions 1D conduction, Bi-layers are just two examples.
Self Assembled Quantum Dots
Indium Arsenide quantum dots grown at the Cavendish have been successfully used for both single photon detection and emission experiments in collaboration with the Quantum Information Group at the Cambridge Research Laboratory of Toshiba Research Europe ltd. Dr. Christine Nicoll is heavily involved in this work along with several researchers at the QIG. Currently our efforts are concentrating on improving the properties of InAs QDs for photonic crystal and pillar microcavity structures. In order to improve the yield in such devices it will become increasingly important to be able to place individual QDs at known locations on the substrate to make subsequent ebeam and optical lithography stages
Optical Microcavities, VECSELs and Quantum Wells
The MBE facilities are accessible to other research groups and institutions from the UK and throughout the world. As such we are involved in external collaborations with Prof Anne Tropper, Prof Pavlos Lagoudakis and others at Southampton on the growth of Semiconductor Microcavities for optical excitation. This work requires careful calibration of the individual growth rates of several effusion sources in order to achieve the accurate control over both composition and thicknesses which are crucial in order to obtain the required characteristics. As is the case with Quantum Cascade Lasers these structures are extremely thick by MBE standards and generally require more than 10 hours to grow.
MBE Growth Fundamentals
With such thick structures being requested with increasing regularity it is important that we continually look at our methods of calibrating and measuring growth rate and temperature so that we can try to achieve reproducibility in our sample growths. In work with RTA Instruments ltd. and k-Space Associates, Inc. we have been using the BandiT system for monitoring temperatures during growth on all of our MBE systems and have recently trialled the Rate Rat Pro reflectivity system on our Veeco Gen-III system. In the future we hope to revisit optical flux monitoring as a technique for measuring the individual fluxes of the Group III elements during the growth of cavity structures. The final aim would be closed loop control of growth where the shutter actuation is triggered by measurements of reflectivity changes during the growth of multilayers.
