Effect of Buffer Charge Redistribution on RF Losses and Harmonic Distortion in GaN-on-Si Substrates
Understanding and mitigation of substrate RF losses and signal distortion are critical to enable high-performance GaN-on-Si front-end-modules. While the origin of RF losses and consequently a decreased effective substrate resistivity <inline-formula> <tex-math notation="LaTeX">...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IEEE
2024-01-01
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| Series: | IEEE Journal of the Electron Devices Society |
| Subjects: | |
| Online Access: | https://ieeexplore.ieee.org/document/10495002/ |
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| Summary: | Understanding and mitigation of substrate RF losses and signal distortion are critical to enable high-performance GaN-on-Si front-end-modules. While the origin of RF losses and consequently a decreased effective substrate resistivity <inline-formula> <tex-math notation="LaTeX">$({\rho }_{eff})$ </tex-math></inline-formula> in GaN-on-Si substrates is now understood to be diffusion of Al and Ga atoms into the silicon substrate during III-N growth, the effect of upper III-N buffer layers on the <inline-formula> <tex-math notation="LaTeX">${\rho }_{eff}$ </tex-math></inline-formula> degradation under stressed conditions remains unclear. In this paper, we show that up to 50% variation in <inline-formula> <tex-math notation="LaTeX">${\rho }_{eff}$ </tex-math></inline-formula> at 2 GHz can take place over more than 1,000 s when the substrate is stressed at 50 V. Additionally, Coplanar Wave Guide (CPW) large-signal measurements under the same experimental conditions show a variation of <inline-formula> <tex-math notation="LaTeX">$2^{\mathrm{ nd}}$ </tex-math></inline-formula> harmonic power of up to 5dB. A thermally activated stress and relaxation behavior shows the signature of traps which are present in the C-doped layers. With the help of a simplified TCAD model of the GaN-on-Si stack, we link this behavior to slow charge redistribution in the C-doped buffer continuously modifying the flat-band voltage (<inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {FB}}$ </tex-math></inline-formula>) of the Metal-Insulator-Semiconductor (MIS) structure. Free carrier transport across the buffer is shown to have the greatest contribution on the large time constants, highlighting the importance of vertical transport paths in GaN-on-Si stacks. |
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| ISSN: | 2168-6734 |