Low Thermal Boundary Resistance in Direct Wafer Bonded GaN|Si Hetereojunction Interfaces

In this study, thermal and structural characteristics of direct wafer bonded (0001) GaN on (001) Si were examined as a continuation of a previous effort 1 . EVG ® ComBond ® equipment was used for bonding under high vacuum (~10 -8 mtorr) at room temperature by bombarding the GaN and Si surfaces with an Ar ion beam to remove unwanted native surface oxides. 1,2 The samples are placed face-to-face and pressure is applied to initiate the bond. The [1010] GaN edge was aligned parallel to the Si [110] edge. An X-ray diffraction reciprocal space map of the (004) Si and (0004) GaN revealed that there is a ~0.2° tilt between the GaN and Si layers. Bombardment of the bonded surface causes an amorphous region at the interface that has been seen in many other bonded systems. 3-5 High resolution transmission electron microscopy revealed a ~2 nm amorphous region at the bonded interface, which resides mostly in the Si as confirmed by energy dispersive x-ray spectroscopy. This is consistent with SRIM 6 simulations that predict a shallower damage profile in GaN as compared to Si. The thermal boundary resistance of the GaN|Si interface was measured to be 3.9 m 2 K/GW, 1 an interfacial thermal resistance lower than any of the current state-of-the-art GaN-based heterojunctions, including GaN|Si, 3 GaN|SiC, 4 and GaN|diamond. 5 Subsequent annealing is expected to alter the thermal properties as the bonded interface is allowed to recrystallize 10 . The intermediate steps of the recrystallization at the bonded interface were examined using TEM to give insight on the interface recovery and reconfiguration mechanism of this ion bombarded GaN|Si interface. Dragoi, et al., ECS Trans., 86(5), 23 (2018) Flötgen, et al., ECS Trans., 64(5), 103 (2014) E. Liao, et al., ECS Trans., 86(5), 55 (2018) Xu, et al., Ceramics International, 45, 6552 (2019) Mu, et al., Appl. Surf. Sci., 416, 1007 (2017) F. Ziegler, et al., The Stopping and Range of Ions in Solids vol 1 (Oxford, Pergamon), (1985) Yates, et al., ASME InterPACK (2015) Cho, et al., Phys. Rev. B, 89, 115301 (2014) Sun, et al., APL, 106(11), 111906 (2015) Mu, F. et al., (2019). ACS applied materials & interfaces , 11 (36), 33428-33434. Figure 1