Studies On Thermoelectric Properties Of MnSi_1.73 Film

P-and n-type higher manganese silicide (MnSi_1.7) films are characterized by Auger electron spectroscopy (AES). The relationship between Auger chemical shift and electrical property of the film has been established. Compared with pure Mn, the peak positions of Mn [MVV] Auger spectra in p- and n-type MnSi_1.7 films move to higher energy regions with +2.0 and +7.0 eV, respectively. Compared with pure Mn [LMM] Auger peaks at 545, 592, and 638 eV, the peak at 545 eV remains unchanged while the one at 592 eV moves to a lower energy region with -0.5 eV for both p- and n-type MnSi_1.7 films. The peak at 638 eV moves to a higher energy region with +0.5 eV for p-type MnSi_1.7 film and remains unchanged for n-type MnSi_1.7 film, respectively. New peaks around 50 eV in the Mn [MVV] Auger spectra, and 600, 654, and 705 eV in the Mn [LMM] Auger spectra appear in MnSi_1.7 films prepared by magnetron sputtering. The new peaks have much stronger intensities for the n-type MnSi_1.7 film. These new peaks are considered to arise from iron impurities. Compared with the pure Si, the peak position of Si [LVV] Auger spectra move to higher energy regions with + 1.0 eV for both p- and n-type MnSi_1.7 films.N-type MnSi_1.7 films with addition of carbon are prepared by magnetron sputtering. With addition of carbon, the film is still n-type. With addition of carbon, the Seebeck coefficient increases a little while the resistivity decreases. As a result, the thermoelectric power factor increases. When the thickness of the carbon layer is 2 nm, the power factor reaches to 1048μW/m-K² at 683 K. This value is close to that of p-type bulk material.Nanoscale MnSi_1.7 films with thicknesses between 14 and 27 nm are prepared by electron beam evaporation. Contrary to the p-type conductivity for MnSi_1.7 bulk materials and thin films reported in the open literature, the carriers of these nanoscale films are p-type around room temperature and transform to n-type at high temperatures. With addition of iron, the film becomes n-type. When the thickness of the FeSi₂ layer is 11 nm, the electrical resistivity of the nanoscale film decreases and the Seebeck coefficient increases. As a result, the thermoelectric power factor increases greatly. The Seebeck coefficient can reach to -662μV/K at 483 K, while the power factor can reach to 5133μW/m-K² at 533 K. When the thickness of the nanoscale film is 14 nm, a n-type film is prepared. The thermoelectric power reaches to - 967μV/K at 483 K. The large thermoelectric power may be due to the increase in the electronic density of states in low-dimensional semiconductors.