Improving Thermoelectric Properties of Bi2Te3 Thin Films By Manganese Co-Sputtering

Summary

A radiofrequency co-sputtering protocol was developed to fabricate manganese-doped Bi₂Te₃ thin films and evaluate how manganese input influences structural and thermoelectric transport properties. Moderate manganese incorporation improved film uniformity and power-factor-related transport behavior, while higher manganese input increased structural disorder and resistivity.

Abstract

Bi₂Te₃ remains a benchmark n-type thermoelectric (TE) material for low-temperature energy conversion, but its small band gap can reduce efficiency because of thermally generated parasitic carriers. Elemental doping has been explored to improve TE performance, although systematic studies on manganese (Mn)-doped Bi₂Te₃ thin films remain limited. In this study, a radiofrequency magnetron co-sputtering workflow was used to fabricate Mn-doped Bi₂Te₃ thin films by varying Mn target power while maintaining constant Bi₂Te₃ deposition conditions. Structural, microstructural, compositional, and TE transport properties were evaluated using X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and temperature-dependent transport measurements. X-ray diffraction confirmed retention of the rhombohedral Bi₂Te₃ phase with a preferred (015) orientation, while peak shifts toward higher 2θ values were consistent with Mn-related lattice contraction. All films exhibited negative Seebeck coefficients, confirming n-type conduction. Increasing Mn doping enhanced the magnitude of the Seebeck coefficient but also increased electrical resistivity, demonstrating a transport tradeoff. The film deposited at 5 W Mn power achieved the highest power factor of 529.33 µW m⁻¹ K⁻² at 523 K because of its low resistivity combined with adequate thermopower. These results demonstrate that moderate Mn incorporation can improve the power-factor-related performance of Bi₂Te₃ thin films within the measured temperature range.

Introduction

Thermoelectric (TE) materials play a crucial role in the sustainable conversion of heat into electrical energy, primarily through the Seebeck and Peltier effects. The performance of TE materials is typically evaluated using the power factor (PF = S²/ρ), where S is the Seebeck coefficient and ρ is the electrical resistivity^1,2. A high S coupled with low ρ indicates efficient carrier transport, which is essential for applications such as waste-heat recovery, micro-power generation, and solid-state cooling in industrial systems and microele....

Protocol

No human participants, animal subjects, or biological tissues were used in this study; therefore, institutional ethics approval was not required.

Overview
Mn-doped Bi₂Te₃ thin films were deposited on soda-lime glass (SLG) substrates by RF magnetron co-sputtering. Depositions were performed without intentional substrate heating, and the chamber/substrate temperature during sputtering was maintained at 298 K ± 1 K. The target-to-substrate distance was fixed at 55 mm for both sputter guns. The Bi₂Te₃ target was operated at a fixed RF power of 100 W, while the Mn target RF power w....

Results

Representative outcomes are presented for the Mn power series (0, 5, 10, 15 W), using the undoped film (0 W) as the control condition for structural and transport comparisons.

Crystal structure (XRD)
XRD patterns confirm that all samples retained the rhombohedral Bi₂Te₃ phase (JCPDS No. 15-0863) across the Mn power series, as shown in Figure 4. The dominant reflections, including a strong (015) preferred orientation, indi.......

Discussion

This study demonstrated an RF co-sputtering workflow for tailoring the TE behavior of Bi₂Te₃ thin films by controlling Mn RF input while maintaining a constant Bi₂Te₃ target power. XRD confirmed the presence of the rhombohedral Bi₂Te₃ phase (JCPDS No. 15-0863) with a preferred (015) orientation across all samples. The systematic shift of the (015) reflection toward higher 2θ values is consistent with Mn-related lattice contraction and possible Mn inco.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone (≥99.5%)	Merck	100012	Substrate cleaning solvent
Aluminum foil	Pospaperroll	86871915	Chamber lining and substrate-holder covering
Argon gas (Ar)	Gaslink Industrial Gases Sdn. Bhd.	N/A (supplied by distributor)	Sputtering working gas; 4 sccm flow; grade 5.0 (99.999%)
Bismuth telluride sputtering target, 50.8 mm diameter, 4.25 mm thickness, 99.999%	Changsha Xinkang Advanced Materials Co., Ltd.	xk-Bi2Te3	Bi2Te3 target; fixed RF power = 100 W
Deionized water	In-house	N/A	Substrate rinsing and ultrasonic cleaning
Energy-dispersive X-ray spectroscopy detector	Integrated with FESEM system	N/A	Thin-film compositional analysis
Field-emission scanning electron microscope	Carl Zeiss	SUPRA 55VP	Surface microstructure imaging
Glass substrates, soda-lime glass, 1.1 mm thickness	Mevid	B105-2002	Substrate for thin-film deposition
Hot plate	IKA	C-MAG HS 7	Substrate drying at 393 K
Isopropyl alcohol (≥99.8%)	Merck	109634	Substrate cleaning solvent
Laboratory detergent	Merck	107553	Initial substrate cleaning
Coolant circulation unit	Fisher Scientific	250LCU	Cooling circulation for sputter guns
Methanol (≥99.9%)	Merck	106009	Substrate cleaning solvent
Manganese sputtering target, 50.8 mm diameter, 5.08 mm thickness, 99.999%	Hunan Boyu Technology Co., Ltd.	N/A	Mn target; RF power varied from 0 to 15 W
Multimeter	RS PRO	EN61010-1 CATIII	Electrical isolation verification
Nitrogen gas (N2)	Gaslink Industrial Gases Sdn. Bhd.	N/A (supplied by distributor)	Substrate drying after cleaning; grade 4.0 (99.99%)
Petri dish lid	Merck	41121812	Chamber viewing-window protection; approximately 94 mm diameter × 16 mm height
RF magnetron sputtering system	Custom-built	N/A	Co-sputtering of Bi2Te3 and Mn thin films
Seebeck/resistivity measurement system with platinum adapter	Linseis	LSR-3 (LSR L31)	Seebeck coefficient and electrical resistivity measurements
Tweezers	Fisher Scientific	10-316B	Handling cleaned substrates
Ultrasonic bath	Elma	ElmaSonic S30H	Solvent cleaning for methanol, acetone, isopropyl alcohol, and DI water
UV–ozone cleaner	Novascan Technologies	PSDP-UV4	Substrate surface treatment
Vacuum storage container	AS ONE Corporation	VM	Sample storage after deposition
Stylus profilometer	Bruker	DektakXT	Thin-film thickness measurement
X-ray diffractometer	Bruker	D8 ADVANCE	θ–2θ XRD scans using Cu Kα radiation
DIFFRAC.EVA	Bruker	DIFFRAC.EVA version 8	Peak fitting, diffraction analysis, and graph plotting
Origin	OriginLab	OriginPro (64-bit)	Peak fitting and graph plotting