Improvements From SiC Substrate Thinning in AlGaN/GaN HEMTs: Disparate Effects on Contacts, Access and Channel Regions

Abstract

We report the positive effects of SiC substrate thinning on the DC and RF performance of AlGaN/GaN high electron mobility transistors (HEMTs). The substrate is thinned down from 500 to ~ 100 μm. This leads to a strain redistribution at the AlGaN/GaN interface confirmed through X-ray diffraction measurements. The contact resistance decreases significantly. The two-dimensional electron gas (2DEG) density decreases, and mobility increases in the source/drain access regions from reduced polarization. The decrease in 2DEG dominates, leading to an increase in the sheet resistance. An opposite trend is manifested in the channel region below the gate contact. The increase in mobility and saturation velocity dominates the decrease in the 2DEG density, which is minimal. The channel resistance decreases. The combined effects of contact, access, and channel regions are further investigated and verified in high-performance AlGaN/GaN HEMTs. The ON-resistance decreases, and saturation drain current increases substantially. The RF performance in critical parameters, including unity-current gain frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ), gain, and output power density, increases significantly. The disparate effects of the contact, access, and channel regions are used in a calibrated TCAD simulator, which shows consistent HEMT performance improvements as observed experimentally.