Quasi-Physical Equivalent Circuit Model of RF Leakage Current in Substrate Including Temperature Dependence for GaN-HEMT on Si

Abstract

This article proposes a quasi-physical equivalent circuit model of RF leakage current in the substrate including temperature dependence for GaN-high-electron-mobility transistor (HEMT) on Si. In the proposed model, the effects of electrons and holes near the interface between the buffer layer and the Si substrate are considered to model the RF leakage current. Furthermore, the physical mechanism of the RF leakage current is analyzed using technology computer aided design (TCAD) simulation. Through the analysis, it was found that the RF leakage current increased at a high drain voltage and high temperature; this is because electrons were generated in the inversion layer at the interface between the buffer layer and the Si substrate with a low acceptor concentration. To model the RF leakage current, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> circuit corresponding to the physical structure of GaN-on-Si between the drain and the source terminal was added to Angelov-GaN large-signal model. Moreover, the resistance and capacitance in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R$</tex-math> </inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C$</tex-math> </inline-formula> circuit were derived from the physical equation of the electron and hole densities in the Si substrate to consider the temperature and bias dependence of the RF leakage current. Upon the verification of the proposed model, it was proven to accurately reproduce the measurement of the temperature characteristics of the power sweep. The large-signal model with the proposed quasi-physical model of RF leakage current can simulate the degradation of the RF performance due to the extrinsic RF leakage current generated by the electrons and holes in the Si substrate. Moreover, the model also agreed with the measured dependence of large-signal characteristics on the drain electrode width. The proposed model was confirmed to be useful for the design of the transistor and amplifier.