Uncovering the properties of homo-epitaxial GaN devices through cross-sectional infrared nanoscopy

TL;DR

This paper demonstrates that scattering-type scanning near-field optical microscopy (s-SNOM) effectively characterizes homoepitaxial GaN devices, revealing detailed information on carrier density, defects, and material properties beyond traditional methods.

Contribution

The study introduces the use of combined mid-IR and THz s-SNOM to analyze GaN devices, showing superior sensitivity and resolution compared to conventional techniques.

Findings

s-SNOM can resolve carrier density changes of ~10^18 cm^-3

It detects sub-surface defects with high sensitivity

s-SNOM outperforms micro-Raman and KPFM in resolution

Abstract

Validating material performance in electrical devices is crucial to product development. For Gallium Nitride (GaN) devices, evaluating material factors such as defects, dopant concentration, and overall production quality is essential to ensure their performance in advanced electronic and optoelectronic applications. This work demonstrates that scattering-type scanning near-field optical microscopy (s-SNOM) can meet the demanding performance requirements for characterizing homoepitaxial GaN devices. Specifically, we show that combining s-SNOM results in the mid-IR and terahertz (THz) spectral ranges can disentangle carrier and lattice changes in a GaN p-i-n diode, which is not possible using one spectral range alone. We observe strong, resonant near-field signals near the LO phonon mode of GaN that correlate well with point-dipole models. This data shows great sensitivity to the local carrier density, with changes on the order of 1018 cm-3 easily resolved experimentally. Further, we demonstrate high sensitivity to sub-surface defects, which remain a significant challenge for other non-destructive techniques. To validate the power of s-SNOM imaging, our results are compared to traditional metrologies, including micro-Raman mapping and Kelvin Probe Force Microscopy (KPFM). Our results show that s-SNOM shows superior resolution and sensitivity to perturbations, highlighting the power of this technique in semiconductor device characterization.