A GeTe-based thermoelectric thin film material with excess Ge, its preparation method and application
By using Ge overdoping and magnetron sputtering, a Ge1+xTe thermoelectric thin film without Ge nanocrystal precipitation was prepared, which solved the problem of high carrier concentration in GeTe thermoelectric materials and achieved a combination of high Seebeck coefficient and low resistivity, thus improving the thermoelectric performance of the thin film.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN INSTITUTE OF CHEMICAL PHYSICS CHINESE ACADEMY OF SCIENCES
- Filing Date
- 2022-08-10
- Publication Date
- 2026-06-30
AI Technical Summary
Existing GeTe thermoelectric materials have too many Ge vacancies, resulting in high carrier concentration, which limits the improvement of their thermoelectric performance. Furthermore, poor thin film orientation affects conductivity and power factor.
Ge1+xTe thermoelectric thin films were prepared by magnetron sputtering using the method of Ge overdoping. The Ge/Te ratio was controlled to ensure that the film exhibited a (003) preferred orientation and to avoid the precipitation of Ge nanocrystals. The composition of the film was adjusted by using a radio frequency power supply, and the preparation conditions were optimized to obtain high-performance thin films.
The prepared Ge1+xTe thermoelectric thin film exhibits low resistivity, high Seebeck coefficient, and significantly improved power factor at room temperature, reaching 2500-2800 μW/mK2 at room temperature and exceeding 5200 μW/mK2 after 600 K, making it suitable for high-efficiency thermoelectric devices.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of thermoelectrics, specifically a GeTe-based thermoelectric thin film material with excess Ge, its preparation method, and its applications. Background Technology
[0002] Thermoelectric technology enables the conversion between thermal and electrical energy. In today's rapidly developing 5G era, it can meet the mobile energy needs of various sensors and alleviate energy and environmental problems to some extent, thus possessing broad application prospects. The performance of thermoelectric materials can be expressed using the dimensionless thermoelectric figure of merit. To measure, Calculated by the following formula ,in It is the Seebeck coefficient. It is electrical conductivity. It's temperature. It refers to thermal conductivity. In thin-film thermoelectric materials, the power factor is commonly used. Thermoelectric performance is measured using GeTe. GeTe exhibits excellent thermoelectric properties and has been applied in fields such as aerospace exploration. However, GeTe readily forms a large number of Ge vacancies, leading to excessively high carrier concentrations within the system, which limits further improvements in GeTe performance. Reducing Ge holes and lowering carrier concentration are effective means to enhance the thermoelectric performance of GeTe. In 2020, Li Jingfeng's research group prepared GeTe with high power factor (PF) through excessive Ge self-doping, but the highest doping ratio (Ge / Te) only reached 1.04:1; adding more Ge resulted in significant Ge precipitation. These Ge nanoprecipitates limit the effective doping amount of Ge and also affect carrier transport performance, further reducing the system's conductivity. Meanwhile, to open up new possibilities for self-powered IoT devices and applications, researchers need to develop GeTe thin films with higher thermoelectric performance to utilize the high-density heat generated during the operation of electronic devices and systems. Especially for localized cooling using thin-film thermoelectric devices, the power factor (PF) of the thermoelectric thin film material becomes a key factor limiting cooling performance. Therefore, controlling the orientation of thin films and adjusting their thermoelectric properties to obtain GeTe thin films with high power density (PF) is of great significance for applications. Summary of the Invention
[0003] This invention addresses the following technical problem: overcoming the shortcomings of existing methods, it prepares a Ge-excess GeTe thermoelectric thin film material with no obvious Ge precipitation. The film exhibits a preferred orientation of (003) and a resistivity of less than [value missing] at room temperature. The resistivity is still less than 600 K. It also has a Seebeck coefficient higher than that of intrinsic GeTe, resulting in a very high power factor exceeding 2800 at room temperature. After heating to 600 K, it can exceed 5200 K. It exhibits excellent thermoelectric properties.
[0004] This invention provides a GeTe thermoelectric thin film material with excess Ge and its preparation method. The general chemical formula of the GeTe thermoelectric thin film material with excess Ge is GeTe. 1+x Te, where x is the mole fraction of excess Ge. Within this range, no obvious Ge nanocrystals precipitate in the material, and it exhibits a preferred orientation of (003). After further performance optimization, the range of x is... .
[0005] The preparation steps of the material using magnetron sputtering are as follows:
[0006] (1) Evacuate the sputtering chamber to eliminate interference from impurities such as moisture and oxygen;
[0007] (2) The sputtering chamber is filled with inert gas, which facilitates subsequent ignition without introducing active impurities;
[0008] (3) Heat the substrate before sputtering begins and keep the substrate temperature constant during sputtering;
[0009] (4) Select a suitable power supply and power, and perform co-sputtering of GeTe and Te targets to deposit thin films.
[0010] In step (1), the sputtering chamber is evacuated, i.e., the background vacuum should be... The optimized background vacuum can reduce the impact of moisture and oxygen in the sputtering chamber on the preparation of GeTe thin films.
[0011] In step (2), the gas introduced is Ar, and the gas flow rate is 10-100 sccm, preferably 30 sccm. The preferred gas flow rate can ensure subsequent ignition and a suitable sputtering rate.
[0012] In step (3), the substrate temperature is 473 K-623 K, preferably 573 K-593 K. The preferred temperature can ensure good crystallinity of the film.
[0013] In step (3), the selected substrate can be any, but sapphire is preferred. The preferred substrate can make the prepared film exhibit good preferred orientation, thereby further improving the conductivity of the film.
[0014] In step (4), the GeTe target is sputtered by DC power supply with a sputtering power of 10 W-50 W, preferably 35 W. The preferred sputtering power can achieve a suitable sputtering rate and effectively utilize the target.
[0015] In step (4), the Te target is sputtered by radio frequency power supply with a sputtering power of 0 W-50 W, preferably 10-30 W. The preferred power can prepare the preferred Ge / Te GeTe film and make the film exhibit the preferred orientation of (003) to obtain higher thermoelectric performance.
[0016] The obtained Ge 1+x Te thermoelectric thin film materials have a rhombohedral crystal structure, exhibiting excellent thermoelectric properties and requiring no additional annealing.
[0017] The obtained Ge 1+x There was no obvious Ge precipitation in the Te thermoelectric thin film material, no Ge elemental peaks were observed in the XRD observation of the sample, and no Ge aggregates were observed in SEM-EDS and TEM.
[0018] The obtained Ge 1+x Te thermoelectric thin film material exhibits (003) preferred orientation. XRD observation of the sample shows obvious (003) preferred orientation peaks, and SEM observation shows that the sample morphology is a stack of corresponding plate-like crystals.
[0019] Beneficial effects
[0020] The advantages of this invention compared to the prior art are:
[0021] (1) This invention prepares Ge-rich Ge by excessive Ge self-doping. 1+x Te thermoelectric thin films avoid the precipitation of Ge nanocrystals within the system, effectively achieving Ge self-doping. This level of Ge doping is difficult to achieve in bulk phase, thus significantly reducing the Ge hole concentration within the GeTe thin film system, and lowering the carrier concentration from the intrinsic GeTe... cm -3 Reduce to cm -3 Simultaneously, by adjusting the preferred orientation of the thin film, Ge... 1+x Te thermoelectric thin film materials maintain low resistivity while possessing a higher Seebeck coefficient than the bulk intrinsic GeTe, thus exhibiting a high power factor of 2500-2800 μW / mK at room temperature. 2 It can exceed 5200 μW / mK after 600K. 2 The highest value was achieved in GeTe thin films.
[0022] (2) This invention controls the thin film composition through co-sputtering of GeTe and Te targets. Existing methods sputter GeTe alloy targets using DC power, but due to the preferential sputtering of Ge, the thin film composition deviates from the alloy target composition. By introducing a Te target and supplementing it with radio frequency power, a wider range of thin film composition can be adjusted. At the same time, using radio frequency power to sputter the Te target with higher resistivity not only facilitates discharge at lower gas pressure and operating voltage, but also improves the quality of the film layer.
[0023] (3) The preparation method used in this invention is simple to operate and can easily achieve the preparation of large-area uniform thin films, which is beneficial to the practical application of thermoelectric thin film devices.
[0024] (4) The thin-film thermoelectric device provided by the present invention, by using the above-mentioned high-performance Ge 1+x Te thermoelectric thin film materials can establish a large temperature difference, achieving ~mW / cm 2 The order-of-magnitude high output power density further validates Ge 1+x The potential value of Te thermoelectric thin film materials in thin film thermoelectric devices. Attached Figure Description
[0025] Figure 1 The resistivity of Embodiment 1 of the present invention The resistivity at room temperature is less than [value missing]. The resistivity is still less than 600 K. ;
[0026] Figure 2 The Seebeck coefficient of Embodiment 1 of the present invention Curve showing the change with temperature;
[0027] Figure 3 The power factor of Embodiment 1 of the present invention PF Curve showing the change with temperature;
[0028] Figure 4 This is the powder X-ray diffraction (XRD) pattern at room temperature in Example 1 of the present invention;
[0029] Figure 5 The images shown are scanning electron microscope (SEM) images and corresponding energy dispersive spectroscopy (EDS) results from Embodiment 1 of the present invention.
[0030] Figure 6 This is a schematic diagram of the thin-film device according to Embodiment 1 of the present invention;
[0031] Figure 7 The output power of the thin-film device in Embodiment 1 of the present invention at different temperature differences;
[0032] Figure 8 The output power density of the thin-film device in Embodiment 1 of the present invention at different temperature differences;
[0033] Figure 9 The images shown are scanning electron microscope (SEM) images and corresponding energy dispersive spectroscopy (EDS) results for Comparative Example 1 of this invention.
[0034] Figure 10 This is a scanning electron microscope (SEM) image of Comparative Example 2 of the present invention;
[0035] Figure 11 The resistivity of Comparative Example 2 of this invention Graph showing the change with temperature;
[0036] Figure 12 Seebeck coefficients for Comparative Example 2 of this invention Curve showing the change with temperature;
[0037] Figure 13 The power factor of Comparative Example 2 of this invention PF Curve showing the change with temperature;
[0038] Figure 14 The resistivity of Comparative Example 3 of this invention Graph showing the change with temperature;
[0039] Figure 15 Seebeck coefficients for Comparative Example 3 of this invention Curve showing the change with temperature;
[0040] Figure 16 The power factor of Comparative Example 3 of this invention PF Curve showing the change with temperature. Detailed Implementation
[0041] The following are specific embodiments of the present invention, but the invention is by no means limited to these embodiments.
[0042] In the following examples and comparative examples, the GeTe target material is the same, and the atomic ratio of Ge to Te is 1:1.
[0043] Example 1
[0044] In this embodiment, an alumina single-crystal substrate is used, with a length of 10 mm, a width of 2-3 mm, and a thickness of 0.5 mm. After cleaning, the substrate is placed in a magnetron sputtering system, and a vacuum is evacuated until the background vacuum is less than [value missing]. Pa. The substrate was heated to 583 K and maintained at this temperature, with argon gas introduced at a volumetric flow rate of 30 sccm. GeTe and Te targets with a purity of 99.99 wt% were co-sputtered. A DC power supply of 35 W was applied to the GeTe target, and an RF power supply of 15 W was applied to the Te target. Both targets were sputtered simultaneously for 2700 s. After sputtering, the sample was removed after cooling to room temperature, yielding high-performance GeTe. 1+x Te thermoelectric thin film material. Electron probe microanalysis (EPMA) confirmed that x=0.19 in this embodiment.
[0045] The prepared material was characterized by XRD, SEM, and EDS, and the results are as follows: Figure 4 and Figure 5 As shown, no Ge precipitation was observed in the system, and the thin film exhibited a (003) preferred orientation and a morphology of stacked plate-like crystals.
[0046] The prepared material was characterized by PPMS, and the carrier concentration in the thin film at room temperature was measured to be [value missing]. cm -3 The migration rate was 53.5%. This explains why the thin film has a low resistivity.
[0047] This invention also provides Ge with such high thermoelectric properties 1+x Methods for fabricating thin-film thermoelectric devices using Te thin films:
[0048] On an alumina substrate with a diameter of 4 inches and a thickness of 0.5 mm, using a stainless steel mask, eight 10 mm diameter hairs were first deposited under the sputtering conditions described above. 3 mm Ge 1.19 A Te thin film serves as the P-type thermoelectric arm, which is then connected with a metal Au to form a closed circuit. A schematic diagram of this thin-film thermoelectric device is shown below. Figure 6 A temperature difference can be established across the two ends of a thin-film device. The output power at different temperature differences and the corresponding output power density are shown in [link to documentation]. Figure 7 and Figure 8 .
[0049] This embodiment illustrates the Ge prepared by the method of this patent. 1+x Te thermoelectric thin films with excess Ge but no significant Ge precipitation effectively suppress excessively high carrier concentration caused by excessively high Ge hole concentration. The films exhibit a (003) preferred orientation, which is beneficial for reducing resistivity and thus improving thermoelectric performance. A high film power factor (2500-2800 μW / mK at room temperature) is achieved. 2 It can exceed 5200 μW / mK after 600K. 2) and device output power density (~mW / cm) 2 (magnitude).
[0050] Comparative Example 1
[0051] In this comparative example, the same x=0.19 Ge material as in Example 1 was prepared using the conventional bulk thermoelectric material preparation method—spark plasma sintering (SPS). 1.19 Te. First, according to Ge 1.19 To determine the chemical ratio of Te, the required elemental Ge and Te powders were weighed and placed in a ball mill jar filled with inert gas to prevent oxidation during milling. Milling was performed at 450 rpm for 12 hours to ensure thorough mixing. The milled powder was then removed, and a layer of carbon paper was placed inside a graphite mold to protect it. The powder was then placed in a graphite mold with an inner diameter of 12.7 mm and placed in an SPS apparatus. Pressure of 50 MPa was applied to both ends of the mold, followed by evacuation to 5 Pa. Heating was then initiated at 20 K / min to 823 K, held for 10 min, and then cooled while maintaining a pressure of 50 MPa. The current was gradually reduced to lower the temperature to room temperature before removal. The prepared material was characterized by SEM and EDS, and the results are as follows: Figure 9 As shown.
[0052] Compared with Example 1, this comparative example shows that obvious Ge aggregates are visible in the system, indicating that traditional bulk material preparation methods cannot achieve such a high Ge doping level.
[0053] Comparative Example 2
[0054] In this comparative example, a quartz substrate was used, with a length of 10 mm, a width of 2-3 mm, and a thickness of 0.5 mm. After cleaning, the substrate was placed in a magnetron sputtering system, and a vacuum was evacuated until the background vacuum was less than [value missing]. Pa. The substrate was heated to 593 K and maintained at that temperature. Argon gas was introduced at a volumetric flow rate of 30 sccm. A GeTe target with a purity of 99.99 wt% was sputtered using a DC power supply at 35 W for 1800 s. After sputtering, the sample was removed after the temperature cooled to room temperature. Electron probe microanalysis (EPMA) confirmed that x=0.50 in this example.
[0055] See Figure 10 Compared with Example 1, this embodiment has a higher Ge / Te ratio in the thin film and the thin film exhibits columnar crystals without obvious preferred orientation, which indicates that the thin film prepared under the optimized conditions used in Example 1 has better thermoelectric properties.
[0056] Compared with Example 1, the comparative example showed that the carrier concentration in the thin film measured at room temperature was [value missing]. cm -3 However, the migration rate actually decreased to 33.5%. Therefore, in this embodiment, the thin film has a high resistivity, leading to the final PF Lower.
[0057] Comparative Example 3
[0058] In this embodiment, a sapphire substrate is used, with a length of 10 mm, a width of 2-3 mm, and a thickness of 0.5 mm. After cleaning, the substrate is placed in a magnetron sputtering system, and a vacuum is evacuated until the base vacuum is less than [value missing]. Pa. The substrate was not heated. Argon gas was introduced at a volumetric flow rate of 30 sccm. GeTe and Te targets with a purity of 99.99 wt% were co-sputtered. A DC power supply of 35 W was applied to the GeTe target, and an RF power supply of 25 W was applied to the Te target. The sputtering time was 1800 s. After sputtering, the temperature was raised to 583 K and held for half an hour. The sample was then removed after cooling to room temperature.
[0059] Compared with Example 1, this comparative example uses room temperature sputtering followed by annealing to prepare the thin film, achieving the transformation of the GeTe thin film from the amorphous state to the rhombohedral phase through annealing. PF The level is low, only 200 μW / mK at room temperature. 2 .
[0060] Comparative Example 4
[0061] In this comparative example, a sapphire substrate was used, with a length of 10 mm, a width of 2-3 mm, and a thickness of 0.5 mm. After cleaning, the substrate was placed in a magnetron sputtering system, and a vacuum was evacuated until the base vacuum was less than [value missing]. Pa. The substrate was heated to 423 K and maintained at this temperature, with argon gas introduced at a volumetric flow rate of 30 sccm. GeTe and Te targets with a purity of 99.99 wt% were co-sputtered. A DC power supply of 35 W was applied to the GeTe target, and an RF power supply of 15 W was applied to the Te target. Both targets were sputtered simultaneously for 2700 s. After sputtering, the sample was removed after the temperature cooled to room temperature.
[0062] The difference between this comparative example and Example 1 is that the substrate temperature is 423 K. At this temperature, the GeTe thin film is still not amorphous, and the band gap is very large. It can be regarded as an insulator with very poor electrical properties.
[0063] Comparative Example 5
[0064] In this comparative example, a sapphire substrate was used, with a length of 10 mm, a width of 2-3 mm, and a thickness of 0.5 mm. After cleaning, the substrate was placed in a magnetron sputtering system, and a vacuum was evacuated until the base vacuum was less than [value missing]. Pa. The substrate was heated to 633 K and maintained at this temperature, with argon gas introduced at a volumetric flow rate of 30 sccm. GeTe and Te targets with a purity of 99.99 wt% were co-sputtered. A DC power supply of 35 W was applied to the GeTe target, and an RF power supply of 15 W was applied to the Te target. Both targets were sputtered simultaneously for 2700 s. After sputtering, the sample was removed after the temperature cooled to room temperature.
[0065] The difference between this comparative example and Example 1 is that the substrate temperature is 633 K. At this temperature, the re-evaporation phenomenon on the substrate surface is intensified, and GeTe thin films can no longer be deposited.
[0066] Comparative Examples 4 and 5 illustrate that the temperature range is an important window condition for preparing high-performance GeTe thin films using magnetron co-sputtering.
[0067] The above embodiments are provided merely for the purpose of describing the present invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. Various equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.
Claims
1. A GeTe-based thermoelectric thin film material with excess Ge, characterized in that: The general chemical formula of the GeTe-based thermoelectric thin film material is Ge. 1+x Te, where x is the mole fraction of excess Ge, 0.04≤x≤0.25, and there is no obvious precipitation of Ge nanocrystals inside the material; GeTe-based thermoelectric thin film materials with excess Ge have a rhombohedral crystal structure and exhibit a preferred orientation of (003); The thin film material has a power factor exceeding 2800 μW / mK at room temperature. 2 When heated to 600 K, the temperature exceeds 5200 μW / mK. 2 ; The preparation method of the GeTe-based thermoelectric thin film material with excess Ge comprises the following steps: (1) Remove impurities from the sputtering chamber; (2) The sputtering chamber is filled with inert gas, which facilitates subsequent ignition without introducing active impurities; (3) Heat the substrate before sputtering begins and keep the substrate temperature constant during sputtering; (4) Select a suitable power supply and power, and co-sputter GeTe and Te targets to deposit thin films; No additional annealing operation is required in the preparation method described above; In step (1), the method is as follows: the sputtering chamber is evacuated to eliminate interference from moisture and oxygen impurities, and the background vacuum should be <1×10 -4 Pa; In step (2), the gas introduced is Ar, and the gas flow rate is 30 sccm; In step (3), the substrate temperature is 583 K; The selected substrate is a sapphire single crystal; In step (4), the sputtering of the GeTe target is performed by DC power supply sputtering with a sputtering power of 35W; In step (4), the sputtering of the Te target is done by radio frequency power supply sputtering, and Te is sputtered in a supplementary manner to adjust the thin film orientation. The sputtering power is 10-30 W.
2. The thermoelectric thin film material of claim 1 is applied in the field of thin film thermoelectric devices or phase change storage.