Stress and Crystal Quality Analysis of GaN Layers on Cost-Effective Substrates for Vertical High- Power Applications
V. Leitgeb1, B. Kosednar-Legenstein1, L. Mitterhuber1, F. Brunner2, E. Bahat-Treidel2, E. Kraker1
Published in:
26th International Conference on Thermal, Mechanical and Multi-Physics Simulation and Experiments in Microelectronics and Microsystems (EuroSimE 2025), Utrecht, Netherlands, Apr. 6-9, ISBN 979-8-3503-9300-2 (2025).
Abstract:
For vertical transistor technology in the highpower regime, Gallium Nitride (GaN) layers grown on foreign substrates provide a cost-effective alternative to native GaN substrates but face challenges due to structural and thermomechanical mismatch. This study compares the structural properties of GaN grown on silicon (Si) and sapphire (Al₂O₃) substrates with those on a native GaN substrate. The analysis focuses on micrometer-thick n⁺-GaN (drain) and n-GaN (drift) layers, which are critical for vertical transistor functionality. The high crystal quality of these layers is essential, as GaN’s large piezoelectric constants make it highly sensitive to strain. Defects alter the electrical potential and field, increasing threshold voltage and leakage currents while reducing charge carrier mobility and thermal conductivity. Raman spectroscopy with sub-micrometer spatial resolution reveals substratedependent stress distributions: slight tensile stress (about 100 MPa) in GaN on the native substrate, compressive stress (~ - 790 MPa) on Al2O3, and minimal residual stress (~ 10 MPa) on Si. The reduced stress on the Si substrate is attributed to an advanced buffer structure incorporating superlattice layers. Crystal quality, assessed through the full width at half maximum (FWHM) of the Raman E2 (high) phonon mode, shows that n⁺-GaN on Al2O3 achieves a FWHM of 2.4 cm-1, comparable to 2.3 cm-1 on the native substrate, while Si has broader peaks of about 4.0 cm-1. This work demonstrates the viability of GaN on Si and Al2O3 as cost-effective platforms for vertical power transistors, supporting the development of scalable, high-performance GaN-based devices on foreign substrates at Si costs.
1 Materials Center Leoben Forschung GmbH (MCL), Leoben, Austria
2 Ferdinand-Braun-Institut (FBH), Berlin, Germany
Keywords:
Gallium nitride, vertical transistor, foreign substrate, Raman, crystal quality, stress analysis
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