| Graphene is an attractive material for both electronic and optoelectronic. Graphene is a gapless material, so it can absorb the light over a wide energy range of the spectrum, such as ultraviolet light, visible light, infrared light and even terahertz. In addition, graphene also exhibited extremely high carrier mobility, so it can be used in ultrafast optoelectronic devices. The existing graphene photodetectors mostly use mechanical stripping method to obtain graphene, so it is not conducive to mass productions and applications. Morever, the response is relatively low, so a focused laser beam is uesd to test. The graphene this paper used is a metal-catalyzed CVD grown, fabricated a graphene photodetectors using back-gate FET structure. We study the design, technology, testing method and explain the mechanism of response. The device has a high response, and a clear response is obtained in a non-focused infrared laser and visible light.The main contents of this paper are as follows:(1)The graphene used in the detector is growed by metal catalyzed CVD.As different metal catalyst used in the growth process, examined a number of aspects of the transfer process, such as coating, baking, etching and washing, avoided graphene damaged and pollution resulting in the Dirac point moves, mobility change and other issues. We fianlly found appropriate transfering graphene technology, tested graphene by FET method and Rama.(2)We designed graphene photodetector based on back gate field effect structure, determined the key parameters of the detector, such as the thickness of gate oxide layer, distance among the electrodes, the size of electrodes contacted with the graphene. Researched on the shape of graphene affecting the detection performance. Although a large aspect ratio of graphene devices have fast response time, the ratio of the photocurrent and the dark current is also large, but it is more difficult to get. After the experiment, the appropriate size was ultimately determined.(3)We researched the approach to improve the reliability of the device. Due to the electrode resulting in high level, which may cause breakage or damage and other problems of the graphene films. We made a proposed method of making planar electrode, effectively overcomed this problem.(4) We researched the device response. Selection of 790 nm infrared laser and white light source as testing and found that only applied to the bias between source and drain, have obvious photoresponse, the photocurrent is proportional to the bias. Through theoretical analysis and calculation, we believed the mechanism of photocurrent generated mainly by photoconductive effect and bolometric effects. The photocurrent is dependent with gate voltage, different gate voltage decided different leading role mechanism. When the positive gate voltage is 15 V or more, the photocurrent is positive, which the photoconductive plays a major role. When the gate voltage is below 15 V and in negative gate voltage, the photocurrent is negative, so that the bolometric effect plays a major role. At Dirac point resulting from a positive gate voltage, the maximum photocurrent signal is positive. We calculated response of the device is 104 m A/W,which was under 790 nm infrared laser with the power density was 500 m W/cm2. Besides, the distance between the laser and the device was 1cm, resulting in the maximum photocurrent 9.23?A. |
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