Gallium nitride (GaN) is the semiconductor material of choice for solid-state lighting. GaN is part gallium (not a plentiful mineral) and part nitrogen (plentiful, in the atmosphere). Even though gallium is not plentiful, if white LEDs achieve the efficiencies envisioned in the 2002 OIDA Roadmap (see here ), there is still enough gallium to light the world with LEDs. A rough estimate of the amount of gallium necessary to do so is 50 tons/year.

Gallium Nitride Bulk (Photo courtesy of TDI Inc. )

Worldwide gallium production capacity in the year 2003 was about 200 tons/year, with actual production about 100 tons/year (see 2003 USGS Minerals Yearbook -- Gallium). Hence, the additional use of gallium for white LED lighting could be easily accommodated by the current production capacity. In addition, gallium is available as a byproduct of bauxite refining, with known reserves of bauxite enabling the potential production of about 1.1 million tons of gallium (see 2003 USGS Gallium mineral commodity summary ). Thus, there is more than enough of this natural resource to accommodate the needs of GaN-based LEDs in lighting well into the foreseeable future.

The rough estimate of the need for 50 tons/year of gallium is based on the following assumptions and calculations:

• Lighting Needs: By 2012, we can project (roughly) that there will be about 40 Teralumens (1 Tlm = 1012 lumens) of installed lighting. If we assume that 20% of this is replaced every year, then about 8 Tlm of new lighting would need to be manufactured every year.

• Efficacy of LED Lighting: If we achieve LED lighting with luminous efficacies of 150 lumens/watt and input power densities to the LED chip of 500 Watts/cm2, we will need to produce 10,000 m2 of LED chips per year.

• Gallium Necessary to Produce LEDs: The actual volume of GaN will depend on whether the LED chips use GaN only to create thin layers grown on wafers made of other materials (e.g., sapphire, or Al2O3), or use GaN to create the wafers themselves. Creating wafers would use the most gallium. If these wafers are approximately 400 microns thick, then the volume of GaN necessary to produce those wafers in a given year would be approximately 4 million cm3, and the mass of gallium in that volume of GaN would be roughly 25 tons.

• Efficiency of Gallium Usage in LED Chips: Then, assuming the original gallium mined and produced is utilized in the GaN-based LED chips with an efficiency of 50%, the mass of gallium that would be needed would be double that, or 50 tons.

Source: Sandia National Laboratories

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