Photoelectric Properties Of Pd Doped Amorphous Carbon/Silicon Dioxide/Silicon Heterojunctions Fabricated By Magnetron Sputtering

The Pd doped amorphous carbon (a-C:Pd) films were deposited on n-Si substrates using direct current magnetron sputtering, and their photovoltaic characteristics, photoconductivity and light-induced spatial sensitivity of the resistance were studied.The photovoltaic characteristics of the a-C:Pd/SiO₂/Si and a-C:Pd/Si junctions were studied. The a-C:Pd/Si junction prepared at room temperature, exhibits an eminent photovoltaic characteristics, with a VOC of 0.079 V and an energy conversion efficiency of 0.002% under the light illumination of 15 mW/cm2. The a-C:Pd/Si fabricated at 350°C exhibits a higher conversion efficiency of 0.91%, and the a-C:Pd/SiO₂/Si solar cell with a native SiO₂ layer shows the highest V_OC (0.33 V) and J_SC (3.5 mA/cm²) andη(4.7%), which is much better than the a-C/Si junctions reported before. The high conversion efficiency is ascribed to the Pd doping and the increase of sp²-bonded carbon clusters in the carbon film caused by the high temperature deposition. This study shows that the a-C:Pd/SiO₂/Si structure has great potential in photovoltaic solar cells for its high power conversion efficiency, low cost, and it is highly chemical and environmentally stable.The dark and photo current-voltage (I-V) characteristics of the a-C:Pd/SiO₂/Si were investigated. We can find that the photocurrent under white light illumination of 1 mW/cm² is about 100 times higher than dark current. Besides, the sample exhibits a good linear relationship between photocurrent and illumination power at a given forward voltage of 1 V. It is found that the a-C:Pd/SiO₂/Si fabricated at 350°C has a gigantic photoconductivity of about 2000 under light illumination of 20 mW/cm2 at RT, which is much better than the a-C based junctions reported before. The photoconductivity is attributed to the reverse I-V characteristics of the a-C:Pd/SiO₂/Si junction with eminent light sensitivity caused by the Pd doping. Besides, it is found that the Pd doping can greatly improve the photoconductivity of the a-C films. This study shows the a-C:Pd/SiO₂/Si structure has great potential application as photoelectric sensors for its gigantic photoconductivity, good linear relationship between photocurrent and illumination power.The light-induced spatial sensitivity of the resistance of the a-C:Pd/SiO₂/Si structure was investigated. The laser spot displacement on the sample surface can lead to an obvious resistance change. When the different position of the sample was illuminated by a laser, the sample has a huge the change ratio in resistance of about 15000%. The light-induced spatial sensitivity of the resistance of the a-C:Pd/SiO₂/Si structure is attributed to the eminent photosensitivity of a-C films caused by the Pd doping and the difference of carriers density between the illuminated and the unilluminated regions. This study shows that the a-C:Pd/SiO₂/Si structure has great potential application as photoelectric displacement sensors.