High-speed photoluminescence mapping of III-V epitaxial layers for light emitting diodes

Photoluminescence (PL) mapping has been developed at the Hewlett-Packard Optoelectronics Division as a non-destructive characterization tool for the evaluation of III-V semiconductor epitaxial layer uniformity in light emitting diode (LED) devices. It has been used as an aid in the development of new epitaxial growth processes and as a quality screening method for cost reduction in a high volume manufacturing line. The design and characterization of a high-speed full wafer PL mapping system based on an optical multichannel analyzer is discussed. This system allows simultaneous mapping of peak wavelength, PL power and power uniformity at several hundred points per wafer in under 10 minutes. Three examples are given of the application of this tool in a combined development/manufacturing environment. In the development of a new MOCVD AlInGaP epitaxial growth process it is being used to evaluate epi reactor designs, gas flow dynamics and the effect of substrate rotation on uniformity. In a well-established production VPE GaAsP epi process PL mapping is routinely used to get rapid feedback on the effect of minor process variations made to improve uniformity. Finally, as a manufacturing tool in high volume production lines, PL mapping can be used to reduce product costs by screening epi into LED product lines with different uniformity requirements.