Details of Grant 

EPSRC Reference:	GR/J67710/01
Title:	MANUFACTURABILITY OF MICROWAVE TUNNEL DEVICES
Principal Investigator:	Kelly, Emeritus Professor MJ
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Physics
Organisation:	University of Surrey
Scheme:	Standard Research (Pre-FEC)
Starts:	01 April 1994	Ends:	30 June 1996	Value (£):	172,571
EPSRC Research Topic Classifications:	Electronic Devices & Subsys.
EPSRC Industrial Sector Classifications:
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Panel History:
Summary on Grant Application Form
(1) To demonstrate that multilayer semiconductor tunnel structures, suitable for device manufacture, i.e. meeting the design specifications with an adequate reproducibility from wafer to wafer and high uniformity across a wafer, can be procured from MBE and MOCVD crystal growers. All physics and device results reported on tunnel structures to date seem to be one-offs. (2) To establish suitable analytical techniques for qualifying wafers prior to processing. These techniques should be non-destructive and wafer-mapping.Progress:For the first year we are concentrating on the asymmetric spacer layer tunnel (ASPAT) diode, consisting of a 2.85nm layer of AlAs in a tightly controlled but asymmetric doping environment in GaAs. The structure has previously been demonstrated to be a suitable microwave detector at X-band. The current mechanism is tunnelling through a barrier, rather than thermionic emission over the barrier, as occurs in Schottky and planar-doped-barrier diodes, and so the ASPAT has a very low dependence on ambient temperature. A simple simulation package (r) GEC Marconi Ltd) has been used to design a structure and to establish the tight tolerances required, especially of the height and thickness of the tunnel barrier, for a suitable I-V diode characteristic. A total of 13 crystal growth organisations were approached, with about half being willing to try to meet the specifications. One source each of MOCVD and MBE were chosen (both commercial suppliers) to provide five wafers to the same specification. In both cases the suppliers had to regrow the layers to meet the agreed specification and tolerances. Two wafers from each batch are being examined by transmission electron microscopy, x-ray racking curves, secondary ion mass spectroscopy and dc I-V measurements. So far the MOCVD wafers seem to be meeting the specification from the SIMS and x-ray data, but TEM suggests that the tunnel barrier might be too thin. Establishing the need for MBE regrowth has introduced a delay in progress with MBE material, which has been delivered. Material meeting the specification is being processed into microwave and dc diodes by GEC Plessey Semiconductors, for evaluation by both GPS and ourselves. In the second year, we will repeat this exercise with the ASPAT diode, if necessary, but otherwise we shall progress to the study of double barrier diodes suitable for sources and self-oscillating mixers. The PDRA on this project is Dr V Wilkinson.
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