Chemical Vapor Deposition Of Graphene And Its Applications In Photonic Devices

Due to the special electronic and optical character, graphene has spread applications in photonics and microelectronics. Chemical vapor deposition, with the advantage like proper cost, good film quality forming, good graphene layers control and so on, have become the main method to producing graphene. Lots of scientists in the world have invested huge energy in the related technology of graphene. However, the applications of graphene in most areas are not maturity. There are many problems in graphene growth and applications in the devices.In this thesis, cold-wall vertical CVD method was used to produce graphene. Due to the rapid heat up and heat down speed and vertical gas flow, the growth time can be shorten sharply, meanwhile remaining the good film quality. However, some main problems in graphene applications were intractable, like insufficiency conductivity and stability, unavoidable pollution and crack by graphene transfer, poor ohmic contact with semiconductors. To solve them, some studies were carried out, like graphene growth on liquid copper, transfer-free directly growth on target substrate, improving the contact of graphene and p Ga N. Besides, some work about graphene applications in Ga N LED and Ga N UV detector was have done. In our work, high quality graphene was got and it is very significant for expand of graphene applications.The main work of this thesis was as follows.1) Single layer graphene growth on copper foil and platinum foil were studied. And the graphene growth on Pt foil was successfully transferred to Si O2/Si by improved bubbling method. Due to the flatness of copper film on Si O2/Si, it is easier to get high quality graphene on Cu/Si O2/Si. The graphene growth on the Cu/Si O2/Si was studied, and the high quality single layer graphene was got, whose Raman signal with no D peak and a 4.1 ratio of intensity of 2D/G. In order to transfer of graphene on Si O2/Si, a technology named self-detaching technology was studied, which make the transfer of the large area graphene on Si O2/Si very convenient. The solid copper foil has a big roughness, while the liquid copper surface is very flat and the grain boundary disappear which is beneficial to form large single crystal and good film quality. Through the liquid copper graphene growth, single layer graphene with a size large to hundred μm with a 3.1 ratio of intensity of 2D/G was got.2) The transfer of graphene growth by CVD with metal foil as catalysis,in the application of graphene in Ga N LED, is a big problem. To solve this question, we used transfer-free direct growth to deposition graphene on Ga N. And to make a good contact between graphene and p-Ga N, 3-5nm Ni was fabricated on Ga N. We found that graphene can be growth on Ga N epitaxy at 800 °C after 3-5nm Ni was fabricated which avoids the damage to the Ga N surface caused by high temperature and makes good contact between graphene and p-Ga N. And then we used up Cu to do the re-catalysis. It was found that the sputtered Cu can make the as-grown graphene quality become better.3) In order to make the graphene-Ga N LED more practical, improvement of ohmic contact between graphene and p Ga N and graphene-Ga N LED stability were studied. ITO nanolayer as an interlayer can improve the contact between graphene and p-Ga N, while the transparency is almost unchanged. Some reports have report the problem about the failure of graphene-Ga N LED. However, little literature has explained the problem clearly. The failure mechanism was studied in this thesis through the graphene thermal stability. A graphene-Ga N LED with long life span was fabricated.4) Surface micro-structure is an effective way to improve the LED light extraction efficiency. Hence application of graphene in nanorods Ga N LED was studied. The graphene as transparency conductive layer can simplify the processing of nanorods Ga N LED. What’s more the suspended graphene on nanorods have a high conductivity which can improve the current spreading. The graphene-nanorods Ga N LED was successfully fabricated which improved the output power 32%. Application of graphene in photo crystal Ga N LED was studied, too. And graphene-photo crystal Ga N LED with uniform luminance was fabricated.5) In traditional Ga N Schottky UV detector, the anode is semitransparency metal layer with low transmittance which has a big influence on light absorption. The transmittance of graphene is very high in UV region and its work function is tunable. Graphene-(n-Ga N) Schottky ultraviolet detector was studied. And a device was fabricated whose leakage current density is 1e-8 A/cm2 with several ms response time. The performance was improved by Au Cl3 doping. The Schottky barrier change by Au Cl3 doping was calculated through hot carrier emit theory. To improve the performance of this kind device, nanorods and surface etching two methods were employed which got large responsivity were 1.98 A/W and 357 A/W at-6V. And the reason for the large responsivity was analyzed. Finally, graphene-based photo detector was realized by half chemical doping and half field effect tuned. A photo response was observed in this device.