Photoluminescence mapping and time-domain thermo-photoluminescence for rapid imaging and measurement of thermal conductivity of boron arsenide

Cubic boron arsenide (BAs) is attracting greater attention owing to the recent experimental demonstration of ultrahigh thermal conductivity k higher than 1000 W/m.K. However, its bandgap has not been settled and a simple yet effective method to probe its crystal quality is missing. Furthermore, traditional kappa measurement methods are destructive and time consuming, thus they cannot meet the urgent demand for fast screening of high kappa materials. After we experimentally established 1.82 eV as the indirect bandgap of BAs and observed room-temperature band-edge photoluminescence, we developed two new optical techniques that can provide rapid and non-destructive characterization of kappa with little sample preparation: photoluminescence mapping (PL-mapping) and time-domain thermo-photoluminescence (TDTP). PL-mapping provides nearly real-time image of crystal quality and kappa over mm-sized crystal surfaces; while TDTP allows us to pick up any spot on the sample surface and measure its kappa using nanosecond laser pulses. These new techniques reveal that the apparent single crystals are not only non-uniform in kappa but also are made of domains of very distinct kappa. Because PL-mapping and TDTP are based on the band-edge PL and its dependence on temperature, they can be applied to other semiconductors, thus paving the way for rapid identification and development of high-kappa semiconducting materials. (C) 2020 Elsevier Ltd. All rights reserved.