Details of Grant 

EPSRC Reference:	GR/J76422/01
Title:	SILICON LIGHT EMITTING STRUCTURES UTILIZING RARE EARTH LUMINESCENCE
Principal Investigator:	Evans-Freeman, Professor J
Other Investigators:	Peaker, Professor AR Dawson, Professor P
Researcher Co-Investigators:
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Department:	Centre for Electronic Materials
Organisation:	UMIST
Scheme:	Standard Research (Pre-FEC)
Starts:	30 September 1994	Ends:	29 October 1996	Value (£):	122,646
EPSRC Research Topic Classifications:	Optoelect. Devices & Circuits
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Summary on Grant Application Form
To realise a light emitting device fabricated from silicon doped with erbium, using and all-implant technology. The ultimate aim is that the device should be able to be integrated in to ULSI for applications in low cost fibre communications technology and to provide a starting point for inter and intra chip communications. Progress:A key factor in this project is the increase of power output from the Si:Er LED. This depends on three factors: the efficiency of the device, the amount (volume concentration) of erbium present in the silicon host and the percentage of erbium that is in the optically active Er3+ state. In order to increase the amount of erbium in the lattice, high doses of the element have been implanted which, when the wafer is annealed, have resulted in peak volume concentrations of erbium of the 5 x 1019 cm-3, two orders of magnitude greater than the solid solubility at the anneal temperature. To achieve this, we have used a two stage anneal. The first stage recrystallizes the layer, while the second, at a much higher temperature enhances the optical activity of the erbium and removes competing non-radiative centres. All wafers have been co-implanted with oxygen which enhances the luminescence efficiency, because of the change in ligand field due to the formation of Er-O complexes.We have succeeded in recrystallising layers which have been implanted with Er and O, and have characterised the erbium-related emission by photo luminescence (PL) experiments. The PL spectra reveal sharp emission lines in the 1.54-m region, resulting from intra-f-shell radiative transitions at the erbium atoms. Several sharp lines exist which are due to crystal field splitting. We have investigated the decay time of the erbium-related emission; this is an essential prerequisite in analysing the competing non-radiative routes in the material system. Preliminary investigations show that the integrated low temperature PL decay time is slow, of the order of 1ms, comparable with the value observed in erbium doped glasses. During the course of the anneal/re-growth studies, we established that the erbium doses were not sufficient to fully amorphise the layer, and that during re-crystallization, growth appeared to proceed from two interfaces. This has resulted in the higher erbium concentration samples, in a region of extended defects (observed by TEM) that coincides with the peak of the erbium distribution. The implant process for this device has consequently been modified to include a post-amorphization implant, using silicon. This will ensure full amorphization of the layer, and also ensure that re-growth commences from an interface deeper than the original amorphous/crystalline boundary. The next phase of work will be to assess the effect of this extra process on the optical quality of the Si:Er system.
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