Composition variation in Al-based dilute nitride alloys using apertureless scanning near-field optical microscopy

作者：Kolhatkar G; Boucherif A; Dab C; Fafard S; Aimez V; Ares R; Ruediger A^*

来源：Physical Chemistry Chemical Physics, 2016, 18(44): 30546-30553.

DOI：10.1039/c6cp05063h

We use apertureless scanning near-field optical microscopy to study the phase separation in chemical beam epitaxy grown Al0.1Ga0.9NxAs1-x alloys. Pits attributed to nitrogen-clustering observed on the Al0.1Ga0.9NxAs1-x surface grown at 420 degrees C become larger at higher growth temperatures, and 3D islands appear on the surface at 565 similar to C. Atomic force microscopy phase measurements reveal a composition difference between the islands and the pits, whereas the sample grown at 420 degrees C appears to be homogeneous. Confocal Raman spectra show that all the N atoms are bonded to Al instead of Ga. Using apertureless scanning near-field optical microscopy, the luminescence of a gold tip is mapped over the surface of the sample grown at 565 degrees C. We extract the shift of the tip's surface plasmon resonance and determine the variation in the refractive index between the islands and the pits to be close to 0.2. Numerical simulations of the tip luminescence while in contact with the sample predict a similar variation of similar to 0.3 in the refractive indices between AlGaAs islands and AlN pits, a substantially smaller value than the difference in the bulk refractive indices of the two media (similar to 1.8), which we attribute to a convolution of material distribution in an uneven topography. The excellent agreement between simulation and experiments supports the hypothesis of nitrogen-clustering in the pits.

• 出版日期2016