Thermal transport and structural improvements due to annealing of wafer bonded β-Ga2O3|4H-SiC

The impact of postbond annealing on the structural and thermal characteristics of 130 nm thick exfoliated ((2) under bar 01) beta-Ga2O3 (via H+ ion implantation) wafer bonded to (0001) 4H-SiC was studied. Thirty nanometer amorphous-Al2O3 was grown on the beta-Ga2O3 substrates prior to bonding as an interlayer between beta-Ga2O3 and 4H-SiC. The surface activated bonding technique was utilized for bonding, which induces a thin nanometer amorphous interfacial region at the bonded interface (Al2O3 vertical bar 4H-SiC). We demonstrate annealing the bonded structure at 800 degrees C up to 1 h is beneficial: (1) the removal of residual strain in the exfoliated beta-Ga2O3 layer that was due to the exfoliation implant, (2) reduction of lattice mosaicity in the beta-Ga2O3 layer, (3) nearly complete recrystallization of the amorphous bonded interfacial region, and (4) partial recrystallization of the initially amorphous-Al2O3 interlayer. The thermal characteristics correspondingly improve with the improvement in structural characteristics. The thermal conductivity of the as-bonded beta-Ga2O3 layer was 2.9 W/m K, and the thermal boundary conductance of the bonded interface was 66 MW/m(2) K. After annealing at 800 degrees C for 1 h, triple-axis x-ray diffraction omega:2 theta measurements showed a reduction in strain for the beta-Ga2O3 layer and the symmetric ((2) under bar 01) rocking curve widths. We simultaneously observe a doubling of the beta-Ga2O3 thermal conductivity to 6.0 W/m K and a 20% increase in the thermal boundary conductance. However, upon further annealing up to 10 h and fully recrystallizing both the Al2O3 interlayer and bonded interface, the thermal boundary conductance dropped by similar to 30%. This preliminary result suggests that crystalline heterointerfaces may not necessarily be the most optimal interfacial structure for thermal transport.

Automated summary

The impact of postbond annealing on the structural and thermal characteristics of 130 nm thick exfoliated β-Ga2O3 wafer bonded to 4H-SiC was studied. Annealing at 800 degrees C for 1 hour resulted in the removal of residual strain, reduction of lattice mosaicity, and recrystallization of the interfacial region, leading to improved thermal conductivity and thermal boundary conductance. However, further annealing up to 10 hours caused a decrease in thermal boundary conductance.