Single crystals of Ag3In5Te9 were investigated by optical absorption spectroscopy, current–voltage measurements, Hall-effect analysis, thermoelectric-power measurements, and prototype thermoelectric-device testing over a broad temperature range. Optical absorption analysis indicates that Ag3In5Te9 is a direct-band-gap semiconductor, with band-gap energies of Eg = 1.05–1.06 eV at 300 K and Eg = 1.08–1.09 eV at 100 K. The corresponding temperature coefficient of the optical band gap is dEg/dT ≈ − 1.5 × 10−4 eV K−1. Urbach-tail analysis yielded EU = 0.035–0.040 eV at 300 K and EU = 0.025–0.030 eV at 100 K, indicating reduced band-tail disorder upon cooling. Weak sub-band-gap absorption below 0.8 eV is attributed to defect-related localized states rather than to fundamental interband transitions. Space-charge-limited-current analysis at 77 K revealed trap-controlled transport with a trap-filled-limit voltage of UTFL ≈ 25 V. Using a discrete-trap SCLC model, an effective trap-filling factor of θ ≈ 1.6 × 10−5, a trap depth of Et ≈ 0.13 eV, and a localized trap density of Nt ≈ 4.2 × 1013 cm−3 were obtained. Temperature-dependent Hall-effect measurements revealed a mixed-conduction anomaly near 230–240 K. Analysis based on a two-band transport model yielded an electron-to-hole mobility ratio of μn/μp ≈ 5 and a carrier concentration ratio of c = n/p ≈ 0.04 near the Hall anomaly, indicating partial compensation between electron and hole contributions. Thermoelectric-power measurements showed a positive low-temperature plateau below approximately 215 K, which may be associated with a phonon-drag contribution; however, further magnetic-field-dependent thermoelectric-power measurements are required for direct confirmation. Nondegenerate Pisarenko analysis gave a hole effective mass of mp* = (0.12 ± 0.001) m0. A prototype Ag3In5Te9-based thermopile integrated with a Bi2Te3-based Peltier element was also evaluated under ΔT = 1 K. Near 510 K, the effective voltage sensitivity increased from 0.70 to 1.42 mV K−1, the effective device-level thermoelectric parameter Zeff increased from 0.21 × 10−3 to 1.10 × 10−3 K−1, and the output voltage increased from 157 to 272 mV. These device-related results should be regarded as preliminary prototype-level observations rather than evidence of an abrupt intrinsic change in the bulk semiconductor. Overall, the results clarify the relationship between defect states, mixed charge transport, and thermoelectric response in Ag₃In₅Te₉, supporting its further investigation for thermoelectric sensing, signal-conditioning, and near-infrared optoelectronic applications.

Optical absorption, defect-assisted transport, and prototype thermoelectric response in Ag₃In₅Te₉ single crystals

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发表日期：

2026年7月9日

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Huseyn Mammadov,
Suleyman Sarmasov,
Rahim Rahimov

摘要

Single crystals of Ag₃In₅Te₉ were investigated by optical absorption spectroscopy, current–voltage measurements, Hall-effect analysis, thermoelectric-power measurements, and prototype thermoelectric-device testing over a broad temperature range. Optical absorption analysis indicates that Ag₃In₅Te₉ is a direct-band-gap semiconductor, with band-gap energies of E_g = 1.05–1.06 eV at 300 K and E_g = 1.08–1.09 eV at 100 K. The corresponding temperature coefficient of the optical band gap is dE_g/dT ≈ − 1.5 × 10⁻⁴ eV K⁻¹. Urbach-tail analysis yielded E_U = 0.035–0.040 eV at 300 K and E_U = 0.025–0.030 eV at 100 K, indicating reduced band-tail disorder upon cooling. Weak sub-band-gap absorption below 0.8 eV is attributed to defect-related localized states rather than to fundamental interband transitions. Space-charge-limited-current analysis at 77 K revealed trap-controlled transport with a trap-filled-limit voltage of U_TFL ≈ 25 V. Using a discrete-trap SCLC model, an effective trap-filling factor of θ ≈ 1.6 × 10⁻⁵, a trap depth of E_t ≈ 0.13 eV, and a localized trap density of N_t ≈ 4.2 × 10¹³ cm⁻³ were obtained. Temperature-dependent Hall-effect measurements revealed a mixed-conduction anomaly near 230–240 K. Analysis based on a two-band transport model yielded an electron-to-hole mobility ratio of μ_n/μ_p ≈ 5 and a carrier concentration ratio of c = n/p ≈ 0.04 near the Hall anomaly, indicating partial compensation between electron and hole contributions. Thermoelectric-power measurements showed a positive low-temperature plateau below approximately 215 K, which may be associated with a phonon-drag contribution; however, further magnetic-field-dependent thermoelectric-power measurements are required for direct confirmation. Nondegenerate Pisarenko analysis gave a hole effective mass of m_p^* = (0.12 ± 0.001) m₀. A prototype Ag₃In₅Te₉-based thermopile integrated with a Bi₂Te₃-based Peltier element was also evaluated under ΔT = 1 K. Near 510 K, the effective voltage sensitivity increased from 0.70 to 1.42 mV K⁻¹, the effective device-level thermoelectric parameter Z_eff increased from 0.21 × 10⁻³ to 1.10 × 10⁻³ K⁻¹, and the output voltage increased from 157 to 272 mV. These device-related results should be regarded as preliminary prototype-level observations rather than evidence of an abrupt intrinsic change in the bulk semiconductor. Overall, the results clarify the relationship between defect states, mixed charge transport, and thermoelectric response in Ag₃In₅Te₉, supporting its further investigation for thermoelectric sensing, signal-conditioning, and near-infrared optoelectronic applications.

Optical absorption, defect-assisted transport, and prototype thermoelectric response in Ag3In5Te9 single crystals

摘要

Optical absorption, defect-assisted transport, and prototype thermoelectric response in Ag₃In₅Te₉ single crystals