Aixtron takes HVPE vertical for cheap GaN substrates
Aixtron, the deposition apparatus manufacturer, has provided the latest details of its system for the production of low-defect, low-cost GaN using hydride vapor phase epitaxy (HVPE).
At the 2007 CS Mantech event in Austin, Texas, Bernd Schineller, manager of the company's development projects department, presented the vertically-aligned system, with the capacity to grow 2-inch diameter, 7cm depth, boules.
Already widely used in other materials, the slicing of such boules into thin discs could be an economical method of GaN substrate manufacture.
Aixtron s collaborators grew vertical-HVPE boules of 140 ?m depth at a speed of 400 µm/h, however cracks formed in the crystal due to build-up of strain.
Better morphology was found for a growth rate of 250 µm/h, with Aixtron detailing the production of a 2mm deep crack-free boule with an etch-pit density of 5 x 105 cm-2
The Aachen-based company presented results in conjunction with academic collaborators at the University of Linköping in Sweden, and Ferdinand-Braun Institut fuer Höchstfrequenztechnik (FBH) Berlin, who performed and measured the growth experiments.
Aside from its academic collaborators, Aixtron has supplied this apparatus to one, unspecified, commercial customer.
In the vertical HVPE system the boule is grown from a seed crystal which is hung from above the gas injector, the quality of which impacts on the quality of the final bulk material.
As the seed is retracted, GaN is deposited on the bottom of the growing crystal.
According to Schineller, in the new apparatus, for thick layers, the material quality improves as the crystal grows, meaning wafers cut from the bottom of the boule have fewer defects than those cut from the top.
Talking to compoundsemiconductor.net, Schineller predicted that the new reactors would be able to reduce the defect density of GaN wafers to 104 cm-2 by iteratively using the bottom of one boule to seed the growth of another.
