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Valence and conduction band offsets of atomic layer deposition (ALD) Al2O3 deposited on bulk AlN crystals were determined using x-ray photoelectron spectroscopy to be ΔEV = 0.75 eV and ΔEC = −1.45 eV, with a measured energy gap of the Al2O3 film of 6.9 eV. In addition, crystalline AlN deposited by atomic layer epitaxy on sapphire was evaluated, resulting in a valence band offset of ΔEV = −0.75 eV and a conduction band offset of ΔEC = 3.25 eV due to the wider bandgap of the crystalline Al2O3 substrate compared to amorphous ALD Al2O3. Both heterojunctions exhibited type-II behavior and similar valence band offsets. [ABSTRACT FROM AUTHOR]

Gallium oxide (Ga2O3) has attracted great attention for electronic device applications due to its ultra-wide bandgap, high breakdown electric field, and large-area affordable substrates grown from the melt. However, its thermal conductivity is significantly lower than that of other wide bandgap semiconductors such as SiC, AlN, and GaN, which will impact its ability to be used in high power density applications. Thermal management in Ga2O3 electronics will be the key for device reliability, especially for high power and high frequency devices. Similar to the method of cooling GaN-based high electron mobility transistors by integrating it with high thermal conductivity diamond substrates, this work studies the possibility of heterogeneous integration of Ga2O3 with diamond for the thermal management of Ga2O3 devices. In this work, Ga2O3 was deposited onto single crystal diamond substrates by atomic layer deposition (ALD), and the thermal properties of ALD-Ga2O3 thin films and Ga2O3–diamond interfaces with different interface pretreatments were measured by Time-domain Thermoreflectance. We observed a very low thermal conductivity of these Ga2O3 thin films (about 1.5 W/m K) due to the extensive phonon grain boundary scattering resulting from the nanocrystalline nature of the Ga2O3 film. However, the measured thermal boundary conductance (TBC) of the Ga2O3–diamond interfaces is about ten times larger than that of the van der Waals bonded Ga2O3–diamond interfaces, which indicates the significant impact of interface bonding on TBC. Furthermore, the TBC of the Ga-rich and O-rich Ga2O3–diamond interfaces is about 20% smaller than that of the clean interface, indicating that interface chemistry affects the interfacial thermal transport. Overall, this study shows that a high TBC can be obtained from strong interfacial bonds across Ga2O3–diamond interfaces, providing a promising route to improving the heat dissipation from Ga2O3 devices with lateral architectures. [ABSTRACT FROM AUTHOR]

The electrical quality of HfO2 dielectrics grown by thermal atomic layer deposition at 175 °C on n-type (201) β-Ga2O3 has been studied through capacitance- and current-voltage measurements on metal-oxide-semiconductor capacitors. These capacitors exhibited excellent electrical characteristics, including dual-sweep capacitance-voltage curves with low hysteresis and stretch-out and a frequency-stable dielectric constant of k ~14 when measured between 10 kHz and 1MHz. The C-V curves exhibited a uniform and repeatable +1.05V shift relative to the ideal case when swept from 3.5 to ~5V, yielding positively measured flatband (+2.15 V) and threshold (+1.05 V) voltages that may be useful for normally off n-channel Ga2O3 devices. Using the Terman method, an average interface trap density of 1.3 x 1011 cm-2eV-1 was obtained between 0.2 and 0.6 eV below the conduction band edge. The forward bias current-voltage characteristic was successfully fitted to the Fowler-Nordheim tunneling model at a field strength of 5MV/cm, allowing an extraction of a 1.3 eV conduction band offset between HfO2 and Ga2O3, which matches the value previously determined from x-ray photoelectron spectroscopy. However, a temperature dependence in the leakage current was observed. These results suggest that HfO2 is an appealing dielectric for Ga2O3 device applications. [ABSTRACT FROM AUTHOR]

The electrical quality of HfO2 dielectrics grown by thermal atomic layer deposition at 175 °C on n-type (201) β-Ga2O3 has been studied through capacitance- and current-voltage measurements on metal-oxide-semiconductor capacitors. These capacitors exhibited excellent electrical characteristics, including dual-sweep capacitance-voltage curves with low hysteresis and stretch-out and a frequency-stable dielectric constant of k ~14 when measured between 10 kHz and 1MHz. The C-V curves exhibited a uniform and repeatable +1.05V shift relative to the ideal case when swept from 3.5 to ~5V, yielding positively measured flatband (+2.15 V) and threshold (+1.05 V) voltages that may be useful for normally off n-channel Ga2O3 devices. Using the Terman method, an average interface trap density of 1.3 x 1011 cm-2eV-1 was obtained between 0.2 and 0.6 eV below the conduction band edge. The forward bias current-voltage characteristic was successfully fitted to the Fowler-Nordheim tunneling model at a field strength of 5MV/cm, allowing an extraction of a 1.3 eV conduction band offset between HfO2 and Ga2O3, which matches the value previously determined from x-ray photoelectron spectroscopy. However, a temperature dependence in the leakage current was observed. These results suggest that HfO2 is an appealing dielectric for Ga2O3 device applications. [ABSTRACT FROM AUTHOR]