High-throughput, Non-Destructive, Three-Dimensional Imaging of GaN Threading Dislocations with in-Plane Burgers Vector Component via Phase-Contrast Microscopy

TL;DR

This paper presents a nondestructive, high-throughput phase-contrast microscopy method for three-dimensional imaging of threading dislocations in GaN, capable of resolving dislocations as close as 1.3 μm apart.

Contribution

The study introduces a novel application of phase-contrast microscopy for 3D, nondestructive imaging of dislocations in GaN, including in-plane Burgers vector detection.

Findings

PCM images correlate with multiphoton excitation photoluminescence contrasts.

Dislocations with in-plane Burgers vectors can be identified.

Dislocations spaced as close as 1.3 μm are resolvable.

Abstract

We demonstrate a nondestructive, high-throughput method for observing dislocations in GaN (0001) using phase-contrast microscopy (PCM). The PCM images (359x300 $\mu$m$^2$) analyzed in this study were acquired with an exposure time of 3 ms per image. The one-to-one correspondence between threading dislocation (TD) contrasts in PCM images and the corresponding contrasts in multiphoton excitation photoluminescence (MPPL) images provides clear evidence that PCM can detect TDs with in-plane Burgers vector components. The contrast shape in PCM reflects the inclination of dislocations with respect to the surface normal: dot contrasts correspond to vertical dislocations, whereas line contrasts correspond to inclined dislocations. By shifting the focal plane from the top surface to the back surface, the three-dimensional propagation paths of dislocations can be visualized. The PCM image obtained represents a projection of threading dislocations within a thickness of approximately 43 $\mu$m. Dislocations spaced as close as 1.3 $\mu$m can be individually resolved. In addition, the capability of PCM to detect scratches, subsurface scratches, facet boundaries, and voids was demonstrated. This study establishes PCM as a versatile and laboratory-accessible technique for three-dimensional, nondestructive characterization of dislocations and other defects in wide-bandgap semiconductors.