ASNOM mapping of SiC epi-layer doping profile and of surface phonon polariton waveguiding

TL;DR

This study uses apertureless SNOM to map doping profiles and surface phonon polariton waveguiding in SiC epitaxial layers, revealing how carrier concentration affects local polarizability and wave confinement at different frequencies.

Contribution

It demonstrates the capability of ASNOM to visualize doping profiles and surface phonon polariton waveguiding in SiC epitaxial layers with high spatial resolution.

Findings

Contrast between substrate and epitaxial layer varies with laser frequency.

Local polarizability changes are more pronounced at higher frequencies.

Waveguide-like confinement of surface phonon polaritons is observed.

Abstract

The apertureless SNOM mapping of the slightly-doped 4H-SiC epitaxial layer grown on a heavily-doped 4H-SiC substrate was performed with a cleaved edge geometry. ASNOM images taken at the light frequencies of a $C^{13}O_{2}^{16}$ laser show a clear contrast between the substrate and the epitaxial layer. The contrast vanishes at the laser frequency of $884cm^{-1}$, and gets clearer at higher frequencies $(923cm^{-1})$. This can be explained by changes in the local polarizability of SiC caused by the carrier concentration, which are more pronounced at higher frequencies. Since the light frequency is tuned up further ($935cm^{-1}$), a transversal mode structure appears in the ASNOM map, indicating a waveguide-like confinement of a surface phonon polariton wave inside the strip of an epi-layer outcrop.