The Preparation Of β-FeSi₂ Semiconductor Films And The Study Of Its Properties

Because of its direct band gap value～0.85 eV (at room temperature) and high absorption coefficient>105 cm’1 (at 1300nm), semiconducting iron disilicide (β-FeSi2) can achieve full absorption of sunlight with a thinner film. Moreover β-FeSi2 meets the basic requirements of the electrical properties of the solar cell materials via doping to control the conductive type of semiconducting. Additionally, its ability to be chemically stable at temperatures of up to 937 ℃, abundance in nature and non-toxicity, make it a promising semiconductor material for PV application. As a consequence, β-FeSi2 is called "Kankyo (ecologically-friendly) semiconductor".In this work, a novel method was used to prepare the transparent conductive oxide films:High Target Utilisation Sputtering (HiTUS), of which the advantages are rapidly sputtering deposition, dense and uniform of the film, and good reproducibility. The P-FeSi2 films have been fabricated by HiTUS system, followed by a rapid thermal annealing process. Fe-Si mixed targets were installed with Fe purity of 99.99%(4N) and Si purity of 99.999%(5N). The conclusions are following:1, The preparation of β-FeSi2 films(1)、It has been proved that controlling the the Fe/Si ratio is an effective way to change the composition of the thin films. When Fe/Si ratio equals 1:4 and 1:5, single-phase and polycrystalline β-FeSi2 films have been obtained after rapid thermal annealing.(2)、The annealing temperature had a great effect on the phase structure of P-FeSi2 films. When the samples annealed at temperatures≤500℃, amorphous β-FeSi2 films were obtained according to the XRD spectra. When the samples annealed at temperatures≥600℃, polycrystalline β-FeSi2 films were obtained.(3)、The field emission scanning electron microscope (FESEM) was used to observe the surface morphology of films. The films prepared by HiTUS system were uniform, continuous, and no obvious defects.(4)、The mechanical properties of the β-FeSi2 films were superior, which can effectively improve the wear resistance and extend the life of the semiconductor material.2、The electrical properties and optical properties of P-FeSi2 films(1)、It has been proved that the resistivity of β-FeSi2 film samples were temperature dependent. When the samples annealed at temperatures≥600℃, the resistivity of P-FeSi2 films increased with the annealing temperature increasing. This can be attributed to the change of the crystal structure of β-FeSi2 films.(2)、The residual carrier concentration and Hall mobility of the β-FeSi2 films were temperature dependent. When the samples annealed at temperatures≤500℃, the residual carrier concentration of amorphous P-FeSi2 films were higher relatively, but the Hall mobility were very low. When the samples annealed at temperatures≥ 600℃, the residual carrier concentration of polycrystalline P-FeSi2 decreased and the Hall mobility increased respectively. The best β-FeSi2 films on Si(111) substrate behaved electron concentration 4.05 X 1017 cm-3 and mobility 21.01 cm2/V·s.(3)、The direct band gap values of β-FeSi2 films prepared by different conditions changed from 0.72 eV to 0.85 eV. This can be attributed to the differences of the carrier concentration and the optical crystallinity of β-FeSi2 films. When Fe/Si ratio equaled 1:5 and annealing temperature was 800℃, the best semiconductor material of the thin solar cells was obtained and its band gap value was 0.85 eV.In a word, the P-FeSi2 films with high quality and low defects were synthesized by HiTUS. When Fe/Si ratio equaled 1:5 and annealing temperature was 800℃, the best n-β-FeSi2 films on Si(111) substrate behaved electron concentration 4.05 ×1017 cm-3, mobility 21.01 cm2/V·s and band gap 0.85 eV.