MOCVD GaN on silicon deposition services
Technical details are as below.
Specifications of GaN layers grown on Si(111) substrates:
|Wafer φ||Gallium nitride layer thickness||Typical GaN XRC data||Types of layer structures|
|150 mm||3.0 – 4.0 µm||
FWHM of (0002): ~450-500 arcsecs
|200 mm||3.0 – 4.0 µm||
FWHM of (0002): ~500-550 arcsecs
Photos of MOCVD GaN epitaxial-grown φ6″ and φ8″ Si(111) wafers
Introduction to GaN on Silicon deposition
Nowadays there very much research and development effort ongoing in the quest of finding energy-efficient solutions in several markets. In the lighting market, conventional technologies used such as CFLs and filament light bulbs consume a large amount of power so alternatives as III-nitride devices that offer low power consumption while maintaining high device performance are being explored and, to some extent, already used in the market.
InGaN/GaN blue light-emitting diodes (LEDs), among others, have already been a commercial success.
However, despite of the energy savings that GaN-based LEDs offer, they cannot fully replace the conventional technologies in the market because of cost.
In order for LEDs to get larger market penetration, the cost needs to be reduced by a factor of ten at least, on a kilolumen basis and in order to do this, the industry must address several issues that prevent substantial savings, such as the adoption of new materials and larger wafer sizes.
Recent advances in GaN-based technology include the development of GaN on Silicon deposition method wherein the GaN layer is grown on a silicon substrate.
Since silicon wafers cost only about an eighth of the price of sapphire substrates, GaN on Silicon offers a more cost effective way of growing GaN on a substrate. Moreover, silicon wafers also come in larger diameters (e.g. 8″, 12″, 150mm or larger), and are compatible with the existing machines used in wafer fabrication.
One major concern in growing GaN on a silicon substrate is wafer cracking due to mismatched lattice constant and thermal expansion of gallium nitride and silicon. To create a crack-free GaN-on-Si wafer, a number of solutions has been developed: one of them is using AlN or AlGaN as an intermediate layer between GaN and silicon.
This technique neutralizes the thermal expansion stress on GaN and silicon substrate by compressing the GaN during deposition and reduces the thermal expansion gap between the film and the substrate.
Widely studied materials to be used as intermediate layer are AlN and AlGaN. The lower thermal expansion of AlN complels the GaN to be deposited in compression, therefore balancing the thermal tensile stress of the silicon surface. Using this process, it is also possible to reduce dislocations.