直接生長大面積石墨烯作為深紫外光發光二極體之透明電流擴散層

Abstract

石墨烯(graphene)由碳原子與相鄰碳原子以共價鍵sp2軌域混成，排列呈六角形蜂巢結構之二維材料，其具有高載子遷移率、高光穿透率、低電阻率與高熱導性等優點，而最為顯著之優勢為於紫外光波段具有高穿透度，故本研究發展石墨烯應用於發深紫外光之發光二極體(UVCLED)作為透明電流擴散層(TCE)。然而發展石墨烯作為透明電流擴散層其關鍵需克服與深紫外光發光二極體表層材料之接觸問題。 本論文提出藉由原子層化學氣相沈積(ALD)進行沉積氧化鎳作為緩衝層以降低蕭特基能障，並改善接觸電阻不佳問題。而在本論文中致力於發展直接生長之大面積石墨烯，研究使用電漿輔助式化學氣相沉積(PECVD)，藉由鎳薄膜作為金屬催化劑直接成長石墨烯於目標基板，省去傳統石墨烯應用之轉印步驟，以利量產之可行性，同時也使得製程溫度降低以符合深紫外光發光二極體晶片之熱積存(thermal budget)。最後於深紫外光發光二極體之p型氮化鎵上完成氧化鎳緩衝層之沉積與約為四層直接生長之石墨烯，並測得其接觸電阻值ρc = (2.29 ± 0.73) × 10-1 Ω-cm2，且石墨烯/氧化鎳於280 nm深紫外光穿透度仍具有62.1%，得此為一具潛力以取代銦錫氧化物(ITO)作為深紫外光發光二極體之電流擴散層材料。Graphene is arranged from the carbon atoms and the adjacent carbon atom with a covalent bond, forming sp2 hybridization. It is a two-dimensional material which arranges in a hexagonal honeycomb structure. Graphene has advantages such as high carrier mobility, high transmittance, low resistivity and good thermal properties, among those advantages the high transmittance in UV region is the most significant characteristic, so we applied the graphene on UVCLED as transparent conductivity electrode. However, the key of applying the graphene on UVCLED is the contact problem between the graphene and the surface material of UVCLED. In the thesis, we proposed using atomic layer chemical vapor deposition to deposit nickel oxide as the buffer layer decreasing the Schottky barrier height, which also improved the poor contact. We also dedicated to directly growing large-scale graphene by plasma-enhanced chemical vapor deposition(PECVD). Using nickel film as a metal catalyst, we directly grew graphene on the substrate. Obviously, we could apply the graphene without transferring process. It makes large area production of graphene be feasible, at the same time it decreases the process temperature to confirm the thermal budget. Finally, we deposited nickel oxide and directly grew about four layers of graphene on the p-GaN, then measuring the contact resistance is (2.29 ± 0.73) × 10-1Ω-cm2. The transmittance of graphene with nickel oxide is 62.1%. It shows graphene is the potential material to replace indium tin oxide as a transparent conductive electrode of UVCLED.