1. AlN/Si interface engineering to mitigate RF losses in MOCVD grown GaN-on-Si substrates
- Author
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Cardinael, Pieter, Yadav, Sachin, Hahn, Herwig, Zhao, Ming, Banerjee, Sourish, Esfeh, Babak Kazemi, Mauder, Christof, Sullivan, Barry O, Peralagu, Uthayasankaran, Vohra, Anurag, Langer, Robert, Collaert, Nadine, Parvais, Bertrand, and Raskin, Jean-Pierre
- Subjects
Physics - Applied Physics - Abstract
Fabrication of low-RF loss GaN-on-Si HEMT stacks is critical to enable competitive front-end-modules for 5G and 6G applications. The main contribution to RF losses is the interface between the III-N layer and the HR Si wafer, more specifically the AlN/Si interface. At this interface, a parasitic surface conduction layer exists in Si, which decreases the substrate effective resistivity sensed by overlying circuitry below the nominal Si resistivity. However, a clear understanding of this interface with control of the parasitic channel is lacking. In this letter, a detailed physical and electrical description of MOCVD-grown AlN/Si structures is presented. The presence of a $\text{SiC}_\text{x}\text{N}_\text{y}$ interfacial layer is revealed and its importance for RF losses is shown. Through C-V and I-V characterisation, an increase in the C concentration of this interfacial layer is linked to the formation of negative charge at the AlN/Si interface, which counteracts the positive charge present in the 0-predose limit. The variation of TMAl predose is shown to allow precise tuning of the C composition and, consequently, the resulting interface charge. Notably, a linear relationship between predose and net interface charge is observed and confirmed by the fabrication of an AlN/Si sample with close to zero net charge. In addition, a higher $D_{it}$ ($\sim 2\times 10^{12}$ cm$^\text{-2}$) for such compensated samples is observed and can contribute to low RF loss. An exceptionally high effective resistivity of above 8 k$\Omega\cdot$cm is achieved, corresponding to an RF loss below 0.3 dB/mm at 10 GHz., Comment: The following article has been accepted for publication in Applied Physics Letters. After it is published, it will be found at https://pubs.aip.org/aip/apl
- Published
- 2024