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AlGaN/GaN high electron mobility transistors (HEMTs) showed its promising features in high power and high frequency applications such as inverter units in hybrid electric vehicles, advanced radar systems, and satellite-based communication networks with its high density of sheet carrier concentration, high electron mobility, and radiation hardness. In order to lower the cost of HEMTs, larger diameters substrates are needed. Currently, the HEMT structures are grown on non-native sapphire, SiC and Si substrates or on native substrate of vapor phase epitaxy (VPE) GaN wafers. HEMTs grown on sapphire substrate suffer from poor heat dissipation and higher defect density due to the relative larger lattice mismatch to GaN. SiC has a very good thermal conductivity and is less lattice mismatch to GaN, but high quality semi-insulating SiC substrates are quite expensive. Although, Si substrates are fair low cost and available for larger diameter substrates, due to larger lattice mismatch to GaN, it requires to grow thick complex AlGaN buffers prior to the growth of GaN layer to reduce the threading dislocation density. These thick AlGaN layers are very defective and thermal resistive, which will hinder device heat dissipation. VPE grown GaN wafers are limited to 2-3” diameter and very expensive. Recently, it was reported that high quality GaN layers were grown by RF plasma-assisted molecular beam epitaxy (PA-MBE) or metal organic chemical vapor deposition (MOCVD) on high-quality, single crystal ZrTi refractory metal alloys deposited by plasma sputtering on c-plane sapphire and Si substrates. These ZrTi refractory metal alloys are not only lattice match to GaN, but have a similar coefficient of thermal expansion (CTE) as the CTE of GaN [1]. By employing these ZrTi alloys, there is no need to grow thick AlGaN buffer, both photonic and electronic GaN based device structure can be grown on large area Si substrates to achieve low cost GaN based device fabrication. In this work, we have demonstrated AlGaN/GaN HEMTs grown on ZrTi refractory metal alloys, which were deposited on both Si and sapphire substrates. HEMTs with a gate dimension of 1 µm × 100 um were fabricated and characterized. Both dc and rf performance of AlGaN/GaN HEMTs fabricated on the ZrTi metal alloys will be presented. 1. “Epitaxial Growth of High Quality GaN Films on Lattice Matched Metallic Layers”, A.M. Dabiran, F. Machuca, I. De, and R. Weiss, ECS Trans. 66, 113-117 (2015). |
