GaN-on-Si advances from Translucent and Bridgelux

August 15, 2011 — Gallium nitride is typically grown on sapphire substrates, as the coeffecient of thermal expansion (CTE) between gallium nitride and silicon can lead to cracks and bowed wafers. Two companies are now announcing advances with gallium nitride grown on silicon (GaN-on-Si), opening up the fabless/foundry economies of scale and production expertise/capital equipment infrastructure of the silicon fab industry to LEDs. Translucent launched its Si wafer templates commerically for GaN growth, and Bridgelux set a new Lumens/W record for Gan-on-Si LEDs.

Translucent Inc., rare-earth-oxide (REO) engineered silicon substrates maker, launched its vGaN (virtual gallium nitride) family of silicon-based wafer templates commercially, offering lower-cost epitaxial surfaces for gallium nitride (GaN) device growth. The main target applications include light-emitting diodes (LED) and field-effect transistors (FET).

The III-N semiconductors family uses scalable GaN-on-Si wafers: crystalline REO layers provide stress relief and wafer flatness is acheived through customized lattice engineering. The REO layer’s wide bandgap of the REO layer could create higher breakdown-voltage characteristics for FETs grown on vGaN.

vGaN provides a semiconductor growth surface that has the physical properties of GaN, but utilizes a silicon substrate upon which is grown an epilayer of REO material that accommodates a top epilayer of Group III nitrides such as GaN. The vGaN substrate enables industry-standard metal-organic chemical vapor deposition (MOCVD) growth processes.

GaN is typically grown on sapphire substrates, which are significantly more expensive at large diameters, especially 200 mm and larger. Additionally, a major challenge facing device manufacturers today is the handling of the large, heavy, and expensive sapphire wafers. Such handling may require the purchase of special handling equipment for the fabrication plants. Conversely, the widely-used infrastructure of fabrication plants that are ready to run silicon wafers up to 200 mm already exists. This makes large-diameter silicon an ideal choice to bring economies of scale into the lighting (LED) and power electronics (FET) industries.

Translucent’s vGaN wafers are available at 100mm diameters; 150 and 200mm will be available during the next year.
 
Translucent, Inc., a subsidiary of Australian listed company Silex Systems Limited. (SLX: ASX), is a materials-based company focuses on using rare-earth oxides to provide low-cost, silicon-based templates for epitaxial growth of semiconductors. More information is available at www.translucentinc.com and www.silex.com.au.


LED lighting developer Bridgelux Inc. set a new company record for Lumen per Watt values for GaN-on-Si. Dr. Steve Lester, Bridgelux chief technology officer, claims LED performance comprable to sapphire-based LEDs, fabbed using Bridgelux’s proprietary buffer layer technology. Lester credits a focus on epitaxial process technology for the new Lumens/W numbers. Crack-free GaN layers were demonstrated on 8" silicon wafers, without bowing at room temperature.

Bridgelux suggests that GaN-on-Si LEDs could offer a 75% cost reduction from conventional LEDs made using sapphire or silicon carbide substrates.

Bridgelux’s first commercially available GaN-on-Si products are on schedule for delivery to the market within the next two years, the company says.

GaN-on-Si Lumens/W results: Cool white GaN-on-Si LEDs showed efficiencies as high as 160Lm/W at a CCT of 4350K. Warm white LEDs delivered 125 Lm/W at 2940K color temperature and CRI of 80. Encapsulated 1.5mm blue LEDs emit 591mW with wall plug efficiencies as high as 59% at 350mA. The LEDs have very low forward voltages, 2.85V at 350mA, making them ideal for use at high current densities. At a drive current of 1 amp the LEDs emitted 1.52 Watts of blue power at a forward voltage of 3.21V, resulting in a wall plug efficiency of 47%. Wavelength uniformity of sigma 6.8nm has been demonstrated for 8" LED wafers with median wavelength of 455nm.

Bridgelux develops and manufactures technologies and solutions for the global lighting industry, using solid-state lighting (SSL). For more information about the company, please visit www.bridgelux.com.

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