THE EFFECTS OF YTTERBIUM DOPING UPON THE STRUCTURAL AND ELECTRICAL TRANSPORT PROPERTIES OF LEAD CHALCOGENIDE ALLOY THIN FILMS FOR THERMOELECTRIC APPLICATIONS

 

ABSTRACT

 

 

 

Motivated by the numerous energy applications of thermoelectric (TE), such as power generation, this study aims to develop novel TE materials with high TE power factor. First, the binary and ternary Pb1-xYbxTe, Pb1-xYbxSe (0.0  x  0.105), PbSe1-xTex (0.0  x  0.10) and the quaternary Pb1-xYbxSe0.2Te0.8 (0.0  x  0.105) lead chalcogenide semiconductor ingots with different Yb-mole fractions were synthesized via solid state microwave standard technique. Second, the aforementioned sets of lead chalcogenide TE thin films were grown via the thermal evaporation technique on glass substrates. The structural properties of the binary, ternary and quaternary lead chalcogenide semiconductors were characterized using several noncontact and nondestructive tools, including scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), atomic force microscopy (AFM), and high-resolution X-ray diffraction (HR-XRD). The tools used for electrical characterization included measurements for electrical conductivity, Hall effect, and Seebeck coefficient for calculating TE power factor, and I–V characterizations of TE generators. The influences of Yb doped, x, on the surface morphology, surface roughness, lattice constant (a), strain of the lattice, and crystalline quality of Pb1-xYbxTe and Pb1-xYbxSe lead chalcogenide semiconductors were evaluated. In addition, the alloying effects on the fundamental electrical properties, such as thermal activation energies ∆E, carrier concentration, carrier mobility, Seebeck coefficient, and TE power factor, were investigated thoroughly. The results showed that the best Pb1-xYbxTe samples were those with the optimal TE power factor at x=0.06 and 0.075, which were 24117.94 μW/mK2 and 28459.78 μW/mK2 at 523 K, respectively, compared with other samples of different Yb-doped. Lead-ytterbium-telluride (x=0.075) thin film-based microgenerators composed of 10-pair and 20-pair were fabricated on glass substrates. High output voltages of 742.7 mV and 467.9 mV and an estimated output power of 0.657 μW and 0.346 μW were obtained for 20-pair and 10-pair, at a temperature difference of ∆T=162 K, respectively. The structural and electrical transport properties of ternary PbSe1-xTex lead chalcogenide semiconductors with different doping Te composition were investigated. The structural parameters indicated that the thin films were grown without any phase separation but with a high quality rock salt (NaCl) structure. The electrical transport properties of the ternary semiconductors indicated enhanced electrical conductivity, carrier concentration, carrier mobility, Seebeck coefficient, and TE power factor with increasing Te content. Finally, the structural and electrical transport properties of quaternary Pb1-xYbxSe0.2Te0.8 lead chalcogenide semiconductors with different Yb-doped were analyzed. The XRD analysis confirmed that the Pb1-xYbxSe0.2Te0.8 thin films have a rock salt (NaCl) structure without any phase separation. SEM and EDX observations verified the quality of the films. The electrical transport properties exhibited an enhancement of the electrical conductivity, carrier concentration, carrier mobility, Seebeck coefficient, and TE power factor at Yb-doped, x=0.075. Lead-ytterbium-selenide-telluride (x=0.075) thin film-based microgenerators composed of 10-pair and 20-pair were successfully fabricated on glass substrates. High output voltages of 275.3 and 109.4 mV and estimated output power of 54.37 and 16.68 nW for 20-pairs and 10-pairs, respectively, were obtained at ∆T=162 K.

 

 

 

KESAN PENDOPAN YTERBIUM KE ATAS SIFAT STRUKTUR DAN ANGKUTAN ELEKTRIK FILEM NIPIS ALOI KALKOGEN PLUMBUM BAGI PENGGUNAAN THERMOELEKTRIK

 

ABSTRAK

 

Terdorong dengan kepelbagaian penggunaan tenaga termoelektrik (TE), seperti penjanaan kuasa, kajian ini bertujuan membangunkan bahan TE baru dengan faktor kuasa TE yang tinggi. Pertama, jongkong binari dan ternari Pb1-xYbxTe, Pb1-xYbxSe (0.0  x  0.105), PbSe1-xTex (0.0  x  0.10) dan kuaternari Pb1-xYbxSe0.2Te0.8 (0.0  x  0.105) semikonduktor kalkogen plumbum dengan pecahan mol Yb yang tinggi disintesis melalui teknik berdiri gelombang mikro keadaan pepejal. Kedua, filem nipis TE kalkogen plumbum bagi set bahan di atas dihasilkan melalui teknik penyejatan terma ke atas substrat kaca. Sifat struktur semikonduktor kalkogen plumbum binari, ternari dan kuaternari dikaji menggunakan beberapa peralatan tak sentuhan dan tak membinasakan, merangkumi mikroskop imbasan elektron (SEM), analisa sebaran tenaga sinar-X (EDX), mikroskop daya atom (AFM) dan pembelauan sinar-X (XRD) resolusi tinggi. Peralatan yang digunakan bagi mengkaji sifat elektrik merangkumi pengukuran kekonduksi elektrik, kesan Hall, pekali Seebeck bagi mengira faktor kuasa TE dan pencirian I-V bagi penjana TE. Pengaruh pendopan Yb, x, ke atas morfologi permukaan, kekasaran permukaan, pemalar kekisi (a), keterikan kekisi, kualiti berhablur Pb1-xYbxTe dan Pb1-xYbxSe semikonduktor kalkogen plumbum telah dinilai. Sebagai tambahan, kesan pengaloian ke atas sifat elektrik asas seperti tenaga pengaktifan terma ΔE, kepekatan pembawa, kelincahan pembawa, pekali Seebeck dan faktor kuasa TE juga telah dikaji dengan mendalam. Keputusan menunjukkan bahawa sampel Pb1-xYbxTe yang terbaik dengan faktor kuasa yang optimum adalah bagi x=0.06 dan 0.075 iaitu masing-masing dengan nilai 24117.94 µW/mK2 dan 28459.78 µW/mK2 pada 523 K dibandingkan dengan sampel terdop Yb yang lain. Penjana mikro berasaskan filem nipis plumbum-yterbium- telurida (x=0.075) yang terdiri daripada 10-pasangan dan 20-pasangan telah dibina di atas substrat kaca. Voltan keluaran yang tinggi bernilai 742.7 mV dan 467.9 mV serta anggaran kuasa keluaran 0.657 µW dan 0.346 µW masing-masing diperolehi daripada 20-pasangan dan 10-pasangan pada perbezaan suhu ∆T=162 K. Sifat struktur dan angkutan elektrik semikonduktor kalkogen plumbum ternari PbSe1-xTex dengan komposisi pendopan Te yang berbeza telah dikaji. Parameter struktur mendapati filem nipis ditumbuh tanpa sebarang pemisahan fasa tetapi dengan struktur garam batu (NaCl) berhablur tinggi. Sifat angkutan elektrik semikonduktor ternari menunjukkan peningkatan kekonduksian elektrik, kepekatan pembawa, pekali Seebeck dan faktor kuasa dengan peningkatan kandungan Te. Akhir sekali, sifat struktur dan angkutan elektrik semikonduktor kalkogen plumbum kuaternari Pb1-xYbxSe0.2Te0.8 dengan pendopan Yb yang berbeza telah dianalisa. Analisa XRD mengesahkan filem nipis Pb1-xYbxSe0.2Te0.8 mengandungi struktur garam batu (NaCl) tanpa sebarang pemisahan fasa. Pemerhatian daripada SEM dan EDX mengesahkan kualiti filem. Sifat angkutan elektrik mempamerkan peningkatan dalam kekonduksian elektrik, kepekatan pembawa, kelincahan pembawa, pekali Seebeck dan faktor kuasa TE pada pendopan Yb, x=0.075. Penjana mikro berasaskan filem nipis plumbum-yterbium-selenida-telurida (x=0.075) yang terdiri daripada 10-pasangan dan 20-pasangan telah dibina di atas substrat kaca. Voltan keluaran yang tinggi bernilai 275.3 dan 109.4 mV serta anggaran kuasa keluaran 54.37 dan 16.68 nW masing-masing diperolehi daripada 20-pasangan dan 10-pasangan di ∆T=162 K.