Market Outlook and Product Performance Requirements for Nitride-Based LEDs

W. Brock Alexander
UNIROYAL Optoelectronics

Increased availability and product performance of nitride-based LEDs has led to exciting application developments in the consumer, automotive, and medical industries, among others. The large full color displays seen in Time Square and many sport stadiums may be the most recognized application for high brightness LEDs, which employ red (626nm), green (525nm) and blue (470nm) LEDs. These displays use from 2M to more than 16M LEDs, and produce one billion colors for 10-bit systems. Below we discuss expected growth in the LED industry and also what performance criteria, such as optical power and color, are required to meet demand and fuel development of future applications.

Briefly, LED products can be categorized as epitaxial wafers, package ready die (PRD), lamps, and applications. Taiwan, China and other Far East countries have many years of experience fabricating LEDs, but have not yet acquired the capacity to grow a sufficient number of GaN epitaxial wafers, thus a market exists for these wafers. Further, since a large fabrication and packaging capacity is available and the technological resources are relatively easily adaptable from the older GaP-based LED to GaN-based LEDs, the Far East continues to absorb much of this product. In fact, the market for GaN grown on SiC has been fueled partly on the ability for these package houses to mount these devices using the same approach, i.e., only one contact to the top of the device. Two contacts to the top surface are currently used for nitride-based LEDs on sapphire.

The worldwide LED industry is expected to grow by approximately 17% each year, and reach nearly $4B in 2003 (RER), with the blue and green LEDs contributing nearly $620M. These estimates include a variety of LED products, both older technology and high-Brightness LEDs (HBLED). It is difficult to find market analyses that separates the nitride-based LED products from the other LED products, including those of low brightness. However, it is estimated that the blue and green LED market will be ~$380M in 2000, and may reach $620M by 2003.

The major consumers of LEDs by region are both North America and Japan, accounting for approximately $1.3B and $1.2B, respectively by 2003, with the blue and green making up nearly 15% of those dollars ($172M and $215M respectively).

The current life time requirements for HBLEDs is 100,000 hours. It is expected that the brightness of the devices may be degrade by 20-50% over this period. Improved thermal management at the lamp level, or even on large applications, minimizes brightness degradation.

The forward voltage, brightness/optical power, and color, measured at typically 20mA, and the reverse leakage, measured at typically -4uA, are still the baseline for reporting LED packaged product performance. For brevity, we will limit our discussion to optical power and color.

Probably the most impressive attribute of an LED is the optical power, and as the output of the semiconductor material increases and the optical package is optimized, we expect this to continue to improve. The optical power can be reported in both radiometric and photometric quantities. This in combination with the strong influence of the packaging on the optical output of the device, and measuring techniques, results in lack of agreement between different suppliers and customers. A common method for measuring optical power is to use an integrating sphere, and by exchanging LED standards with suppliers/customers, more alignment can be achieved. PRD from GaN on sapphire can routinely be fabricated which produce optical powers at 1.5 mW, and better than 2mW can be achieved. After packaging, the power may increase 2 to 4 fold. Continued efforts involving leaders from LED research and industry backgrounds to facilitate agreement on measurement and test methods may prove strongly beneficial.

Color or dominant wavelength is the other exciting attribute of an LED. The specification is strongly dependent on the application. Monochromatic applications (back lighting, etc) typically have a loose requirement, i.e., the dominant wavelength requirement may be +/- 10 nm for customers using a 470nm blue LED. It should be noted that this variation is similar to that observed across a typical 2-inch wafer. This implies that whole wafers may be sold as one product, and then lamp packagers may sort at the lamp level.

Color blending applications do not necessarily require a tight control of wavelength (+/- 3nm) to produce white radiation from yellow and blue LEDs and true color and RGB displays, although helpful, the blending is achieved through electrical power control to the different elements of the pixel. Further, narrow FWHM (<30nm) and high purity (>95%) is also desirable.

In short, each wafer has multiple products, and PRD suppliers must be able to test and sort their product to meet customer requirements and ensure appropriate market value is assigned. Color is the artistic attribute of the LED, and allows us to create applications where visual appearance is king, and unlike optical power, is relatively routine to measure accurately.

The nitride-based LED market will continue its strong growth, although the revenue per LED will decrease similar to other semiconductor products. Areas for improvement include both reliability and optical power. Of course, improved lifetimes increases the value of the product, and higher optical powers will be the catalyst for future applications.

Acknowledgements

Special appreciation to Bill Kennedy and Ed Walker at UNIROYAL Optoelectronics for providing market and financial information.