Detecting buried silicon interlayers in GaN/diamond bonded structures

Abstract

We present a new approach for detecting interlayers in gallium-nitride (GaN) semiconductor structures bonded on single or polycrystalline diamond. GaN-on-diamond is advantageous because it integrates and effective heat spreader into GaN devices, which is important for high power density operation. However, analyzing GaN/diamond interlayers can be difficult because of nonuniformity as well as atomic-scale roughness across the wafer. In this work, we studied GaN/diamond samples using Raman spectroscopy and employed adaptive principal component analysis (PCA) to explore silicon interlayer properties. For each GaN sample bonded to diamond, the presence of a silicon interlayer was confirmed using high resolution scanning transmission electron microscope (HR-STEM) and electron energy loss spectroscopy (EELS). For comparison, we collected Raman spectroscopic data at 25 °C (5 different locations across the wafer, 10 microns apart in each direction) using 10 Raman spectrum acquisitions at each location in the 300-800 /cm range. Raman spectra only show three distinct vibrational modes at ~482 /cm, ~568 /cm and ~735 /cm, associated with the external lamp, GaN E2 (high) and A1 (LO) phonon modes. When spectra were analyzed using adaptive PCA, results reveal buried information in the baseline pertinent to the interlayer, including the ~520 /cm (silicon) phonon mode as well as ~360 /cm, and ~760 /cm modes, owing to nanoscale nonuniformities. Improved analysis of ultra-thin silicon interlayers in GaN/diamond opens up new opportunities to examine the impact of growth/post-growth steps, carrier density, and structure for modeling thermal boundary conductance.