Thermoelectric Inorganic SiGe Film Synthesized on Flexible Plastic Substrate

Abstract

For developing thermoelectric thin-film devices using reliable inorganic materials, we investigated the synthesis of SiGe directly onto insulating substrates. An Al-induced layer exchange technique was employed, which enabled us to form SiGe on glass substrates at a low temperature (≤400 °C) in the whole SiGe composition range. The SiGe layers were observed to contain Al atoms in concentrations corresponding to their solid solubility limits during growth, which resulted in the formation of self-organically highly p-doped layers without requiring hightemperature-activation annealing. Results indicated that a high power factor (430 μW/mK 2 ) and a low process temperature were simultaneously achieved for SiGe on glass. A SiGe layer fabricated on a plastic substrate exhibited a power factor of 190 μW/mK 2 , which is higher than most thermoelectric films directly grown onto a plastic substrate. These achievements will present practical applications for flexible thin-film thermoelectrics with a high reliability.

Flexible Thermoelectric Generator Based on Polycrystalline SiGe Thin Films

“…The grain sizes were slightly smaller than those synthesized on a quartz glass substrate [35,36]. This behavior is a common trend for LE using a plastic substrate [31,33,39], and is likely due to either the surface roughness of the substrate or warpage and shrinkage during heat treatment. Indeed, slight warping was observed for the plastic substrate samples, which increased the difficulty of obtaining accurate thermal conductivity values.…”

“…Through this reaction between the metal and semiconductor, LE enables low-temperature synthesis and high-concentration doping in polycrystalline SiGe thin films. LE has been used to produce thermoelectric SiGe films using Al [31,32] and Zn [33,34] for p-type, and Zn:As [34] and Ag:As [35] for n-type alloys. Thermoelectric power factors (PFs) for layers formed on a glass substrate at 400-500 • C have been measured as 850 µW m −1 K −2 for p-type Si 0.4 Ge 0.6 [36] and 1000 µW m −1 K −2 for n-type Si 0.85 Ge 0.15 [35].…”

Thermoelectric Materials for Textile Applications

“…Various materials have been explored for use as thin-film TE materials, including those based on Bi-Te [52,83,84,97,98], Zn [60,[99][100][101], Cu [102][103][104][105], and cobalt oxide [106][107][108][109] based thin films. Inorganic thin films are usually applied onto various flexible substrates using either physical vapor deposition methods such as reactive sputtering [58,104,110,111], thermal coevaporation [97,112,113] and magnetron sputtering [114][115][116], ALD [74], printing [100,117], spin coating [118], and chemical bath deposition methods [119][120][121][122]. For integration into textiles, such inorganic materials are usually deposited onto flexible, organic substrates to allow flexibility and wearability.…”

High photoresponsivity in a GaAs film synthesized on glass using a pseudo-single-crystal Ge seed layer

“…Metal-induced layer exchange is known as a method for forming a large-grained Ge thin film at low temperature on inexpensive substrates such as glass [26][27][28][29][30][31][32] and even plastic. [33][34][35] We achieved highly (111)-oriented Ge thin films with large grains (>100 lm) using Alinduced layer exchange (ALILE). 28,32 Because the light absorption thickness for GaAs is approximately 3.5 lm owing to its large absorption coefficient, GaAs grown epitaxially on the ALILE-Ge layer will behave as a pseudosingle crystal.…”

“…The resistivity of ALILE-Ge is low enough (<10 À3 X cm) to be used as a bottom electrode due to highly Al doping. 35 The bias voltages were applied to the ALILE-Ge layer with respect to the ITO electrode, prepared as shown in the scanning electron microscopy (SEM) image in Fig. 4(b).…”