[20a-234B-1~10] 22.1 Joint Session M "Phonon Engineering"

▼ [20a-234B-7] Cross-plane thermal conductivity of InGaO₃(ZnO)_m (m=integer) single crystalline thin films

〇(M1)Yuzhang Wu¹, HaiJun Cho^1,2, Bin Feng³, Masashi Mikami⁴, Woo Seok Shin⁴, Yuichi Ikuhara³, Hiromichi Ohta^1,2 (1.IST-Hokkaido Univ., 2.RIES-Hokkaido Univ., 3.Univ. Tokyo, 4.AIST)

Keywords:thermal conductivity, Kapitza resistance, superlattice

The efficiency of thermoelectric power generation depends on the figure of merit ZT (=S²・σ・T・κ^-1, where S is thermopower, σ is electrical conductivity, T is temperature, and κ is thermal conductivity). In several studies, reducing κ values by utilizing impurities and grain boundaries was proven to be very effective for achieving very high ZT > 2. Thus, understanding the effect of grain boundaries on heat transportation, which is measured by Kapitza resistance, is of significant interest for developing better thermoelectric materials. However, since crystalline defects are often challenging to control, it is difficult to evaluate the effect of boundaries on in the heat transportation in thermoelectric materials.
InGaO₃(ZnO)_m (m=integer) has a natural superlattice structure with adjustable periods. Therefore, it is an ideal material to evaluate the effect of boundaries on κ. We fabricated single crystalline InGaO₃(ZnO)_m thin films on (111) YSZ substrates with different m values, which have periodic structures with the periods varying from 1.4 nm to 9.1 nm.
The κ of the resultant InGaO₃(ZnO)_m films was measured by the TDTR method at RT. As the interface density increased, κ of InGaO₃(ZnO)_m decreased, which is similar to the observation of In₂O₃(ZnO)_m ceramics. In this research, we quantify the Kapitza resistance at interfaces in InGaO₃(ZnO)_m superlattice to determine the role of boundaries in the transportation of heat in layer stacking direction of InGaO₃(ZnO)_m.