Thermoelectric and photosensitive characteristics of Bridgman grown CuxSb1−xSe2 (x = 0.2, 0.4, 0.6, 0.8) crystals with different Cu/Sb ratios†

To achieve high-performance optoelectronic devices and thermoelectric behaviour, non-stoichiometric compositions have been utilised in ternary transition metal dichalcogenides. This study marks the first report on the growth of Cu_xSb_1−xSe₂ (x = 0.2, 0.4, 0.6, 0.8) crystals using the Bridgman technique. We investigated the impact on their structural, optical, thermal and electrical properties in comparison with pure CuSbSe₂. Powder X-ray diffraction confirmed the presence of the dominant orthorhombic CuSbSe₂ phase along with minor secondary phases and this result was well supported by Raman spectroscopy. The crystallite size increases from 12 nm to 27 nm while the lattice strain decreases from 0.0116 to 0.0054 with Cu content in the crystal. Elemental analysis carried out by EDAX has reflected the desired stoichiometry of each crystal. FESEM images have shown flat as well as layer growth on their surfaces, thereby giving an indication that the growth of crystals occurred by a layer-by-layer growth mechanism. Raman spectra indicated the red shift in the A_g vibrational mode of CuSbSe₂ with increasing Cu proportion. The direct bandgap of each crystal is reduced from 1.55 eV to 1.42 eV with higher Cu percentage which is determined from the Kubelka–Munk function using the recorded reflectance spectrum which shows that these crystals can be promising candidates for optoelectronic applications. The positive value of the Seebeck coefficient (S) demonstrates the p-type semiconducting nature of each crystal measured in the temperature range of 323 K to 593 K. Among the grown crystals, P3 (Cu_0.6Sb_0.4Se₂) exhibited the superior power factor and ZT values of 0.0182 μW cm⁻¹ K⁻² and 0.935 × 10⁻⁴ at 595 K, respectively. The TGA of each crystal demonstrated single step decomposition, showcasing a maximum weight loss of 18.07% for the P4 crystal, which is confirmed by DTG. To assess the photodetection properties of each crystal, I–V curves and pulse photoresponses are recorded in parallel to plane configuration. Among all grown crystals, the P3 (Cu_0.6Sb_0.4Se₂) crystal based photodetector exhibits superior responsivity and detectivity of 0.014 mA W⁻¹ and 5.656 × 10⁸ Jones, respectively. These findings show that these crystals can be considered as a choice for thermoelectric as well as photodetection applications.