Electrical and Thermal Properties of BeO Gate Dielectrics for β-Ga₂O₃ Power Devices

Monoclinic gallium oxide (β-Ga₂O₃) is a promising wide-bandgap semiconductor for power device application. β-Ga₂O₃demonstrates superior material performance, including an ultra-wide bandgap of 4.8-4.9 eV, a high breakdown field of approximately 8 MV/cm, and a remarkable bulk electron mobility of ~300 cm²V^-1s^-1, showing a Baliga’s Figure of Merit (BFOM) of up to 3444. Despites these properties, the primary drawback of β-Ga₂O₃ lies in its heat management capabilities. It exhibits a low thermal conductivity of 10-30 Wm^-1K^-1, which is significantly lower compared to other power semiconductors such as GaN (220 Wm^-1K^-1) and SiC (280-342 Wm^-1K^-1), which potentially makes β-Ga₂O₃ susceptible to malfunctions under high-temperature operation.<br/>The use of conventional gate dielectrics for β-Ga₂O₃ power devices might worsen the thermal dissipation issue. Oxides typically possess low thermal conductivity. For instance, SiO₂ exhibits approximately 1.4 Wm^-1K^-1, and HfO₂ exhibits approximately 1.2 Wm^-1K^-1 of thermal conductivity. To address these challenges, we propose beryllium oxide (BeO) gate dielectrics for β-Ga₂O₃ power devices. BeO possesses unique properties, including a bandgap energy of 10.6 eV, a high dielectric constant of 6.8, and most importantly, an extraordinarily high thermal conductivity of approximately 330 Wm^-1K^-1 coupled with high thermal stability. Its thermal conductivity is the highest among oxides, surpassing that of most metals except for copper and silver. Consequently, BeO holds significant potential in improving the heat dissipation capabilities of β-Ga₂O₃ power devices. However, its application to nanoscale front-end devices has been constrained by the absence of well-established thin film deposition techniques.<br/>In this work, we developed the atomic layer deposition (ALD) of BeO. This technique enables the precise and high-quality deposition of thin film on the substrates. ALD BeO gate dielectrics were successfully grown on β-Ga₂O₃ substrates. We comprehensively analyzed the physical and electrical properties of ALD BeO deposited on β-Ga₂O₃. A BeO on β-Ga₂O₃ was confirmed via a survey scan of X-ray Photoelectron Spectroscopy (XPS). The cross-section TEM image revealed a uniform thickness and a sharp interface between BeO and β-Ga₂O₃. The crystalline growth of BeO in the (102) diffraction on the β-Ga₂O₃ substrate was confirmed using Grazing Incidence X-ray Diffraction (GI-XRD). In addition, we analyzed the electrical properties of BeO gate dielectrics on β-Ga₂O₃ power devices. We determined the conduction band offset (3.4 eV) between the BeO film and β-Ga₂O₃ substrate using Kraut’s method, which involved the determination of the valence band offset (0.5 eV) using the XPS core level and valence band maximum energies of the BeO film and β-Ga₂O₃ substrate. The bandgap energies of BeO (8.6 eV) and β-Ga₂O₃ (4.7 eV) were determined using reflection electron energy loss spectroscopy (REELS). The large conduction band offset of ALD BeO on the β-Ga₂O₃ substantially lowered the gate leakage current of β-Ga₂O₃ MOS capacitors. The forward leakage current was 2.21×10^-9 A/cm² at 1 MV/cm for 100 nm Mo electrodes/24 nm BeO dielectrics/β-Ga₂O₃ substrates, demonstrating the potential of ALD BeO as gate dielectrics for high-performance β-Ga₂O₃ power devices.