Enhanced thermoelectric performance in single-crystal-like semiconducting flexible GaAs films

With the advancement of nano-technology and push toward flexible electronics, the opportunity to generate electricity using solid-state devices has ushered tremendous research interest in improving the thermoelectric (TE) properties of flexible semiconducting materials. The majority of research done so far was focused on finding suitable doping schemes for all-organic flexible substrates or mixing organic and inorganic components to obtain flexible substrates with an optimized thermoelectric performance. Unfortunately, their performance is limited by their low power factor (PF) values and often suffers from degradation issues due to the organic component that limits them to low temperature applications. Here, through coupled microstructural and thermoelectric analysis, we show how to overcome these limitations by introducing a new inorganic GaAs flexible substrate with enhanced TE performance. We show that these flexible thin films are single-crystal-like biaxially textured with low angle grain boundary misalignment; and charge transport is dominated by multi- valley electron conduction. This results in a PF ∼1300 µW/mK2, the highest value for non-toxic inorganic flexible thin films and an estimated 3-fold enhancement in the figure of merit compared with bulk GaAs. We present the temperature-dependent experimental PF, mobility, and carrier concentration data coupled with the theoretical models to elucidate the charge transport characteristics of this new class of films. Moreover, these unique charge transport characteristics are material growth dependent, and thus, such novel thermoelectric properties are expected in different material systems.