News Article

AlGaAs Standard To Make Industry 'more Efficient'

The National Institute of Standards and Technology has issued its first reference compound semiconductor alloy - a small square of AlGaAs.

Compound semiconductor manufacturers will now be able to measure the composition of AlGaAs films more accurately than ever before, thanks to a new material standard issued by the National Institute of Standards and Technology (NIST).

The Boulder, CO, authority says that the 1 cm2 AlGaAs/GaAs pieces (denoted SRM 2841) will increase the accuracy of characterization of AlGaAs films by ten times compared with current analytical methods.

AlGaAs layers are used widely in both microelectronic and optoelectronic device applications, in particular for the red lasers that are deployed in optical disc drives.

Kris Bertness, the NIST scientist who has led the development, told compoundsemiconductor.net: "There really have not been any absolute standards in the past."

"People are much more used to thinking in terms of how reproducible their measurements are, but that does not address the absolute accuracy of the measurement."

As a result, Bertness says, the III-V industry has been operating largely on knowing how the material they grow one day compares with what they grew the month before.

"Most laboratories had an internal reference system that worked as a bootstrap standard," she added. "The X-ray diffraction rocking curve or the photoluminescence peak energy was used to determine the approximate composition of an epitaxial layer using literature values."

Comparisons between the way that different laboratories measure AlGaAs compositions have shown that not only is there a variation in the calibration equations used, but also a tendency by experimentalists to ignore absolute calibration of their own measurement equipment.

In response to an initial request from members of the Optoelectronics Industry Development Association (OIDA), and with NIST funding, Bertness and colleagues set about developing the standard back in 1998.

"The main challenges have been achieving absolute accuracy," said Bertness. The new standard is certified with reflection high-energy electron diffraction (RHEED) growth rate measurements and photoluminescence (PL).

The PL measurement is calibrated against both RHEED and two direct chemical analyses "“ one made using an electron microprobe, and another based on inductively-coupled plasma optical emission spectroscopy.

Bertness believes that the SRM 2841 standard will reduce wasteful duplication of reference wafers and increase the free exchange of thin-film materials between vendors and their customers. "We hope to make the industry more efficient," she concluded.

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