The Impact of Substrates on the Performance of Top-Gate p-Ga203 Field-Effect Transistors: Record High Drain Current of 980 mA/mm on Diamond

For high power devices, monolithic $\beta$ -Ga203 has been identified as an emerging ultra-wide bandgap semiconductor material because it has a large bandgap of 4.8 eV and a high breakdown electric field of 8 MV/cm [1]. $\beta$ -Ga203 has also the potential to realize low-cost large-size native bulk substrates by melt-grown methods [2], [3]. However, the output power density and the maximum drain current density of $\beta$ -Ga203 devices can be seriously limited due to its low thermal conductivity $(\kappa$ of 10–25 W/m·K and self-heating effect (SHE) [4], [5]. If the heat from the channel cannot be well dissipated through the substrate, SHE can lead to significant channel temperature increase, thus degrade the device performance and the long-term reliability [6]. In order to overcome this material constraint, we explored nano-membrane transferring technique and studied $\beta$ -Ga203 nano-membrane field-effect transistors (FETs) on different foreign substrates such as sapphire $(\kappa=40\ \mathrm{W}/\mathrm{m}\cdot \mathrm{K})$ and Si0 2 /Si $(\kappa=1.5\ \mathrm{W}/\mathrm{m}\cdot \text{K for}\ 270\ \text{nm SiO}_{2})$ and compared the impact of these substrates on the device performance [7]–[9]. In this work, furthermore, we demonstrate the first B-Ga203 Fet on a diamond substrate with an extremely high thermal conductivity of $1,000\sim 2,200\ \mathrm{W}/\mathrm{m}\cdot \mathrm{K}$ [10] and compare with devices on a sapphire or Si0 2 /Si substrate.