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Indium phosphide optoelectronic devices

Substrate defect structure, surface characteristics and purity are significant factors which determine the current quality of metal organic chemical vapour deposition (MOCVD) grown epitaxial layer structures used in the fabrication of long wavelength indium phosphide/indium galluim arsenic phosphide optoelectronic devices. Consequently this project directs significant effort at the development of improved bulk crystal growth and substrate finishing technology which addresses these problems.
Crystal growth in a large scale liquid encapulated Czochralski (LEC) system has been achieved and the ability to produce both longer (up to 300 mm) and large diameter (up to 80 mm) ingots demostrated. Thermal characterization and improved furnace design have led to reduced crystal dislocation content in this system.
Semiinsulating material requirements demand high background purity in the crystals. Low residual carrier levels and impurity content determined by secondary ion mass spectrometry (SIMS) analysis have been demonstrated. This has allowed control over the concentration of iron dopant to a minimum level. The possibility of undoped semiinsulating indium phosphide has been investigated by use of heat treatments combined with electrical and electron paramagnetic resonance (EPR) characterisation. Modifications in bulk properties by high temperature treatments have been shown and semiinsulating behaviour extended to lower iron dopant concentrations.
Microprecipitate bulk defects and their relationship with dislocations have been studied by a variety of techniques. New etching methods have allowed the study of the influence of these defects on epitaxy and their behaviour during expitaxial processing.
Substrate surface quality has been an important topic in the work. New techniques for chemomechanical polishing have been developed resulting in overall improved surface specifications on geometrical tolerance, surface defect density and chemical cleanliness. The overriding imp ortance of epitaxial ready quality was established for MOCVD processing. This has been achieved in demonstrator substrates of semiconducting tin doped and semiinsulating iron doped material. New optical surface characterisation tools have been developed based on phase stepping microscopy. These have been applied to the quantitative assessment of surface roughness and patterningdue to device processing, with vertical resolution at the nanometre scale. Assessment surveys of the demonstrator substrates against state of art wafers from other sources show these to be comparable in characteristics such as background purity, bulk defect density and surface physical properties.

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