Simultaneous biaxial stress and composition measurements made on [Al.sub.x][Ga.sub.l-x] As thin films. .

Raman and photoluminescence peak shift measurements have been made on [Al.sub.x][Ga.sub.l-x] As thin films to determine simultaneously both biaxial stress and Al composition (x). [Al.sub.x][Ga.sub.l-x] As forms a family of materials used in multilayer thin film structures for photodiode sources and detectors. Residual stresses in the devices affect operating wavelength, electron-hole recombination rate, and mechanical reliability. Although shifts in the Raman peak position previously have been used to determine stress in Si-based devices, that approach could not be used in [Al.sub.x][Ga.sub.l-x] As because both stress and composition change shift the Raman peak position in this compound system. Until the Raman peak positions were calibrated for both x and stress, it was not clear whether contributions from the two effects could be separated.

NIST scientists used a set of films to demonstrate that combining Raman and photoluminescence measurements permits separation of composition-induced peak shifts from stress-induced peak shifts, allowing simultaneous evaluation of stress and composition. This approach is not expected to be limited to the [Al.sub.x][Ga.sub.l-x] As family, but is thought to be applicable to a wide range of compound semiconductor materials.

CONTACT: Grady White, [phone]; grady. [e-mail] or Albert Paul, [phone]; [e-mail].