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107 defects. This technique would add an extra step to the manufacturing process for LEDs, but it would result in higher quality, more efficient LEDs.”
More details of this research are described in the paper “Embedded voids approach for low defect density in epitaxial GaN films,” by P. Frajtag, N. A. El-Masry, N. Nepal and S. M. Bedair in Applied Physics Letters, 98, 023115 (2011); doi:10.1063/1.3540680)(published online 17 Jan 2011)
Entegris Wafer
The new technique reduces the number of defects in those films by two to three orders of magnitude, increasing the output of light by a factor of two for a given amount of power. (Image courtesy of Lukasz Tylec)
The researchers started with a GaN film that was two microns thick and embedded half of that thickness with large voids (empty spaces that were one to two microns long and 0.25 microns in diameter).
Using transmission electron and atomic force microscopy, the scientists found that defects in the film were drawn to the voids and became trapped leaving the portions of the film above the voids with far fewer defects.
Defects are slight dislocations in the crystalline structure of the GaN films. These dislocations run through the material until they reach the surface. By placing voids in the film, the researchers effectively placed a “surface” in the middle of the material, preventing the defects from travelling through the rest of the film.
The voids were embedded near the sapphire substrate, where high densities of dislocations are present.
The network of voids acts as dislocation sink or termination site for the dislocations generated at the GaN/sapphire interface.
“Without voids, the GaN films have approximately 1010 defects per square centimetre,” says Bedair, one of the researchers. “With the voids, they have
Shipper Enhances LED Manufacturing
The Ultrapak100 is designed to reduce damage and contamination to protect thin substrates used in LED manufacturing and other applications.
Entegris has introduced a wafer shipper that specifically meets the critical handling needs of compound semiconductor and thin silicon wafers.
The Ultrapak 100 mm thin wafer shipper is designed to reduce damage and contamination in order to better protect thin substrates used in LED manufacturing and other applications.
Currently, the LED industry predominantly uses shippers designed for silicon semiconductor applications. These wafer shippers are not designed for compound semiconductor or thin silicon shipment and can cause wafer damage or breakage, cross-slotting and particle generation via rotation if used in these sensitive applications.
Entegris’ latest thin wafer shipper offers several design features that help silicon and compound semiconductor manufacturers reduce these risks, including cradle strap support (upper and lower cushions) of the wafer that limits wafer rotation. This ensures reduced particle contamination, and secures the wafers in the cassette to safeguard against breakage.
The tool also has enhanced perimeter support of the substrate to reduce stress levels during impact events during transport. The ultrapure polypropylene provides a clean shipping
January / February 2011
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