深紫外發光二極體(deep ultraviolet light-emitting diodes, DUV LEDs, 波長 ≤ 290 nm)需要高穿透、高導電的P型半導體，才能發出更多的DUV光子。目前，大多數的研究團隊都以氮化鎵(GaN)作為DUV LEDs的P型電極接觸層，但P型氮化鎵的能隙(3.4 eV)太小，會吸收深紫外光，導致LED的外部量子效率(external quantum efficiency, EQE)很難超過10%。為了解決這個問題，我們嘗試以氮化硼(boron nitride, BN)來取代氮化鎵。氮化硼具備高能隙(~ 5.9 eV)與低電洞活化能(30-300 meV)，有潛力展現高穿透、高導電的光電特性，值得應用在DUV LED。 本研究中，我們在BN磊晶層的表面，以不同的製程條件形成含鋁(Al)的金屬電極，希望能取代傳統常用的鎳/金(Ni/Au)電極，希望能降低BN表面的接觸電阻、並提升金屬/BN介面的反射率。若能達到高導電、高反射的金屬/BN介面，就能將之應用在覆晶型(flip-chip) 的DUV LED。我們發現，以Pt/Al/Ti/Au製作BN表面的電極，並以700 °C氮氣退火1分鐘，能將280 nm波段的反射率由25% (Ni/Au電極)，提升至44%，並維持相同的接觸電阻。 ;Deep ultraviolet light-emitting diodes (DUV LEDs, λ ≤ 290 nm) require high-transparent and high-conductive p-type semiconductor to produce sufficient photons. GaN is currently the most used p-type material for DUV LEDs because of its mature growth/fabrication process. However, since the band gap of GaN is only 3.4 eV, the severe light absorption in the p-type region usually leads to the external quantum efficiencies (EQEs) below 10 % of the device. To address the issue, we adopt boron nitride (BN) as the alternative. The large band gap (~ 5.9 eV) and small hole activation energy (30-300 meV) of BN make it a promising candidate for high transparent and high conductive p-type material in DUV LEDs. In this study, we propose an Al-based metal contact on BN, aiming to replace the conventional Ni/Au contact. The Al layer is employed to increase the reflectance at the metal/BN interface, which is suitable for flip-chip devices. It is found that Pt/Al/Ti/Au, annealed at 700 °C in N2 for 1 min, can increase the reflectance at 280 nm from 25 % (by Ni/Au) to 44 %, without sacrificing the contact resistance.
