Interface Characterization of Cobalt Contacts on Bismuth Selenium Telluride for Thermoelectric Devices

Gupta, Rahul; Iyore, O. D.; Xiong, Ka; White, John B.; Cho, Kyeongjae; Alshareef, Husam N.; Gnade, Bruce E.

doi:10.1149/1.3196237

Cited by 32 publications

(30 citation statements)

References 13 publications

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“…Gupta et al noted that annealing sputter-cleaned contacts after metallization, even at temperatures as low as 100 C, has potential to cause undesirable interdiffusion between the semiconductor and contact metal. 5 That interdiffusion is deleterious because permanently diminishes TE device performance. As Liao and colleagues showed, the diffusion-governed formation of undesired intermetallic compounds at the interface with thermoelectric materials can irreversibly degrade R c .…”

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confidence: 99%

“…The reason is that the ion implantation dose was somewhat large and that caused the surface temperature of the samples to rise between 100 and 200 C for a time equivalent to, or longer than, an annealing step. 5 R c values from the full range of concentric-circle spacings were obtained from samples of (Bi,Sb) 2 (Se,Te) 3 that received the ion-implantation process, as well as otherwise identical sections of the same samples that were not ion implanted; i.e., in the set of bulk samples, some were implanted, and otherwise identical samples were not and for the set of thin-film epitaxial samples, each was cleaved into two parts: one part was ion-implanted and the other was not.…”

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confidence: 99%

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Controlled improvement in specific contact resistivity for thermoelectric materials by ion implantation

Taylor¹,

Maddux²,

Meissner³

et al. 2013

Applied Physics Letters

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To obtain reduced specific contact resistivity, iodine donors and silver acceptors were ion-implanted into n-type and p-type (Bi,Sb)2(Se,Te)3 materials, respectively, to achieve >10 times higher doping at the surface. Implantation into n-type materials caused the specific contact resistivity to decrease from 1.7 × 10−6 Ω cm2 to 4.5 × 10−7 Ω cm2. Implantation into p-type materials caused specific contact resistivity to decrease from 7.7 × 10−7 Ω cm2 to 2.7 × 10−7 Ω cm2. For implanted thin-film superlattices, the non-implanted values of 1.4 × 10−7 Ω cm2 and 5.3 × 10−8 Ω cm2 precipitously dropped below the detection limit after implantation, ≤10−8 Ω cm2. These reductions in specific contact resistivity are consistent with an increase in tunneling across the contact.

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mentioning

confidence: 99%

mentioning

confidence: 99%

Controlled improvement in specific contact resistivity for thermoelectric materials by ion implantation

Taylor¹,

Maddux²,

Meissner³

et al. 2013

Applied Physics Letters

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“…The reductions in the contact resistivity at annealing temperatures as low as 100°C are attributed to the electrically favorable interfacial phase formation for both Ni and Co. Previous work on interfacial reactions 21 has shown the formation of NiTe and CoTe 2 as the preferred phases formed at temperature as low as 100°C for Ni and Co.…”

Section: H668mentioning

confidence: 83%

Low Resistance Ohmic Contacts to Bi[sub 2]Te[sub 3] Using Ni and Co Metallization

Gupta

Xiong

White

et al. 2010

J. Electrochem. Soc.

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A detailed study of the impact of surface preparation and postdeposition annealing on contact resistivity for sputtered Ni and Co contacts to thin-film Bi 2 Te 3 is presented. The specific contact resistivity is obtained using the transfer length method. It is observed that in situ sputter cleaning using Ar bombardment before metal deposition gives a surface free of oxides and other contaminants. This surface treatment reduces the contact resistivity by more than 10 times for both Ni and Co contacts. Postdeposition annealing at 100°C on samples that were sputter-cleaned further reduces the contact resistivity to Ͻ10 Thermoelectric ͑TE͒ coolers have been extensively used in the optoelectronic, automotive, space, and semiconductor industries where low device operational temperature is key to device performance in terms of speed and reliability.1-3 However, despite these advantages the use of TE devices has been limited for high watt density applications. 4 To allow TE coolers to reach the next level in terms of performance and power density, the thickness of the device needs to be scaled down.5 Contact resistance becomes a serious limitation to the efficiency of TE material based solid-state coolers with thermoelement leg lengths Ͻ100 m, as can be seen in Fig. 1, where the ratio of device figure-of-merit ͑Z d ͒ and material figureof-merit ͑Z m ͒ is plotted vs the thermoelement leg length ͑L͒ as a function of contact resistance. 6 The relationship between Z d and Z m is given by Eq. 1where L is the thermoelement leg length, r c is the contact resistance, and is the bulk conductivity.As can been seen in Fig. 1a, for a device leg length of 100 m, Z d /Z m drops from 0.9 to 0.5 as the contact resistivity increases from 5 ϫ 10 −7 to 5 ϫ 10 −6 ⍀ cm 2 . The resulting drop in the device dimensionless figure-of-merit Z d T impacts the coefficient of performance ͑COP͒ of the device as shown in Fig. 1b, which can be expressed aswhere T c and T h represent the temperature of the cold side and the hot side, respectively. Therefore, from a device point of view, although a high Z material can be achieved, the device COP can still be low due to the degradation of Z due to the contact resistivity. For thin TE materials, the losses become even more extreme and low electrical contact resistivity of Ͻ10 −7 ⍀ cm 2 is needed to minimize the impact of contact resistance on COP. High contact resistance at the electrode/TE material interface remains a challenge that is limiting widespread adoption of TE technology in many applications.For industry standard TE devices, electroless plated Ni is used as a diffusion barrier to Cu and solder components such as Sn. However, electroless Ni gives a relatively high contact resistivity ͑Ͼ5 ϫ 10 −6 ⍀ cm 2 ͒. 9 Bi 2 Te 3 is a small bandgap semiconductor with a bandgap of 0.16 eV. Therefore it is theoretically possible to obtain a very low contact resistance, Ͻ10 −7 ⍀ cm 2 , for an ideal metalsemiconductor contact; however, real metal-semiconductor interfaces are far more complex.10 Extrinsic factors ...

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“…It was found that NiTe formed at the interface between sputtered Ni films and Bi 2 (Te,Se) 3 . 13 Table 3 presents the EPMA results for the atomic composition of the IMCs at the Ni/Bi 0.5 Sb 1.5 Te 3 interfaces after Sn-3Ag-0.5Cu was reflowed at 250°C for 30min. It indicates that the major elements in this layer are nickel and tellurium with a small amount of dissolved bismuth and antimony.…”

Section: Resultsmentioning

confidence: 99%

Evaluation of Diffusion Barrier Between Lead-Free Solder Systems and Thermoelectric Materials

Lin

Liao

2011

Journal of Elec Materi

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The intermetallic compound SnTe rapidly formed at interfaces between p-type bismuth telluride (Bi 0.5 Sb 1.5 Te 3 ) thermoelectric materials and lead-free solders. The intermetallic compound influences the mechanical properties of the joints and the reliability of the thermoelectric modules. Various lead-free solder alloys, Sn-3.5Ag, Sn-3Ag-0.5Cu, Sn-0.7Cu, and Sn-2.5Ag-2Ni, were used to investigate the interfacial reactions. The results thus obtained show that Ag and Cu preferentially diffused into the Te-rich phase in Bi 0.5 Sb 1.5 Te 3 , so layers of Ag-Te and Cu-Te compounds could not form an effective diffusion barrier. Electroless nickel-phosphorus was plated at the interfaces to serve as a diffusion barrier, and the (Cu,Ni) 6 Sn 5 compound formed instead of SnTe. Furthermore, the intermetallic compound NiTe formed between nickelphosphorus and Bi 0.5 Sb 1.5 Te 3 and also served as a diffusion barrier. A plot of thickness as a function of annealing time yielded the growth kinetics of the intermetallic compounds in the thermoelectric material systems. The activation energy for the growth of the NiTe intermetallic compound is 111 kJ/mol.

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Interface Characterization of Cobalt Contacts on Bismuth Selenium Telluride for Thermoelectric Devices

Cited by 32 publications

References 13 publications

Controlled improvement in specific contact resistivity for thermoelectric materials by ion implantation

Controlled improvement in specific contact resistivity for thermoelectric materials by ion implantation

Low Resistance Ohmic Contacts to Bi[sub 2]Te[sub 3] Using Ni and Co Metallization

Evaluation of Diffusion Barrier Between Lead-Free Solder Systems and Thermoelectric Materials

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