Probing photoelectric characteristics of graphene

• Main Authors: Chen, Chau-Bi, 陳喬弼
• Other Authors: Jian, Wen-Bin
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/15755436008357435322

碩士 === 國立交通大學 === 電子物理系所 === 102 === In this experiment, we probe into photocurrent of graphene devices and graphene/PbS thin film devices. Graphene flakes were made by mechanical exfoliation and PbS thin films were deposited by thermal evaporation. Due to its feature of a gapless semiconductor, graphene does not exhibit considerable photocurrent effects. The photocurrent of graphene flakes is about 36 nA and the enhancement ratio due to blue light excitation is 1.88 % at 80 K. In contrast, the PbS deposited graphene flakes may show higher photocurrent. It is argued that, after light illumination, the graphene is p-type doped. It implies that only holes transport to graphene after the generation of electron-hole pairs in PbS by light illumination. Therefore, the photocurrent is strongly dependent on the gating field. Though it does not show visible photoresponsivity at 300 K, the photoresponsivity increases largely at 80 K. When the gate biases are applied at -35 V and 35 V, the enhancement ratios raise up to 15.77 % and -10.66 %, respectively. The photocurrent of PbS is strongly dependent on temperature, and enhancement ratio is inversely proportional to the temperature. On the other hand, the graphene/Pbs heterostructures do not exhibit appreciable gating effects. It is argued that the holes and electrons will recombine and the holes transporting to graphene will be reduced much more. From the photocurrent measurements, we observed that the recombination rate of PbS is proportional to temperature and we proposed the photocurrent transmission mechanism of graphene/PbS heterostructure devices.