2. Experimental
N-type Bi-Te films were fabricated from high-purity (5 N) Bi and Te targets (2 in. in diameter) in a radio frequency (RF) magnetron co-sputtering system
(ATC ORION Sputtering System, AJA).
Prior to the Bi-Te film deposition at room temperature (RT), an Sio2 layer with 300 nm thickness was thermally grown on the Si substrate.
The RF power was set to 24 W for Bi and 55 W for Te, and the working pressure was maintained at 3 mTorr while the substrate holder was rotated at the speed of 50 rpm for uniform film deposition.
The thickness of deposited films was maintained around 300 nm. Subsequently, the samples were post-annealed for 8 h at different temperatures (100, 150 and 200°C) under N2 ambient.
The film composition was checked using energy dispersive X- ray spectroscopy (EDS) and found around 61 at. Te. In addition, we did not observe any composition change after annealing. The surface morphology of Bi-Te films was investigated using field emission scanning electron microscopy (FE-SEM) (S4800, HITACHI) operating at 10kV.
The microstructure of Bi-Te films was characterized using X-ray diffraction (XRD) (RINT 2000, RIKAGU) The in-plane electron mobility and resistivity of the films were mea- sured with a Hall effect measurement system (HMS-5000, EcoPIA). and the Seebeck coefficient was measured in a thermoelectric measurement setup (Fraunhofer IPM).