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

Area of Science:

• Materials Science
• Semiconductor Physics
• Nanotechnology

Background:

• Alloy semiconductors are crucial for optoelectronic devices.
• Understanding phase separation in AlxGayN(1-x) alloys is vital for controlling material properties.
• Nitrogen incorporation in III-V materials presents unique challenges.

Purpose of the Study:

• To investigate phase separation in Al0.1Ga0.9NxAs1-x alloys grown by chemical beam epitaxy.
• To characterize the morphology and composition of surface features at different growth temperatures.
• To elucidate the role of nitrogen clustering in the observed phase separation.

Main Methods:

• Apertureless scanning near-field optical microscopy (aSNOM) for high-resolution surface imaging.
• Atomic Force Microscopy (AFM) for topographical and phase measurements.
• Confocal Raman Spectroscopy for chemical bonding analysis.
• Numerical simulations to model tip-sample interactions and refractive index variations.

Main Results:

• Nitrogen clustering was observed, forming distinct AlN-rich islands and pits on the Al0.1Ga0.9NxAs1-x surface.
• Surface features evolved with growth temperature, with larger pits at higher temperatures and 3D islands appearing at 565 °C.
• Raman spectroscopy confirmed nitrogen bonded to Aluminum (AlN), not Gallium (Ga).
• aSNOM measurements revealed a refractive index difference of ~0.2 between islands and pits, consistent with simulations (~0.3).

Conclusions:

• Nitrogen clustering is the primary mechanism driving phase separation in these alloys.
• The observed refractive index variations are significantly smaller than bulk differences due to topographical convolution.
• The findings provide critical insights into controlling alloy composition and morphology for device applications.