近年來，深紫外（deep ultraviolet, DUV, 波長 ≤ 290 nm）LED 的外部量子效率很難突破20％，遠低於可見光 LED 的水準，主因在於：DUV LED 的 P 型磊晶層必須同時具備高穿透率、高導電性，這是傳統 DUV LED 的材料—氮化鋁鎵（AlGaN）所欠缺的優點。而氮化硼（BN）兼具高能帶、低電洞活化能的特性，能使 DUV 波段的光不被氮化硼吸收，亦能大幅提升電洞濃度，增加導電性，是 DUV LED 所需的理想 P 型材料。此外，氮化硼的能帶高達 6 eV，能夠有效阻擋電子離開量子井。氮化硼的電洞活化能僅 30 meV，能提供大量電洞進入量子井，提升電洞電子對在量子井的複合數量，增強 DUV LED 的發光效率，也能降低操作電壓，減少熱能生成，有助於提升元件的使用壽命。上述的優點，使氮化硼成為目前 DUV LED 非常熱門的 P 型材料。 為了成長高品質的氮化硼，本研究利用有機金屬化學氣相沉積法製備氮化硼，架構為在藍寶石基板磊晶一層 1.5 微米的氮化鋁，之後再成長氮化硼磊晶層，透過改變五三比、三族載氣流量提升氮化硼的磊晶品質，再對氮化硼進行摻雜形成 P 型氮化硼。初步成果顯示：P 型氮化硼的穿透率及導電性均遠優於 P 型Al0.3Ga0.7N，在 DUV LED 應用上有極大的潛力。 ;Despite years of research efforts, external quantum efficiencies of deep ultraviolet (DUV, wavelength ≤ 290 nm) LED remain below 20 %. This is because the P-type material of DUV LED requires high transmittance and high conductivity, which is not achievable with the commonly used material, i.e. AlGaN. Boron nitride (BN) has the characteristics of high energy bandgap (~ 6 eV) and low hole activation energy (~ 30 meV), preventing the absorption of DUV photons in the p-type contact layer, while providing sufficient free hole concentration for the operation of DUV LED. In addition, the high energy bandgap of BN effectively blocks the electron overflow from quantum wells. The abundant holes injected from BN increase the luminous efficiency of DUV LED and decrease the turn-on voltage, extending the life of device operation. All of these promising traits make BN an attractive p-type material for DUV LED. To achieve high-quality BN, we grew the binary compound by metal-organic chemical vapor deposition (MOCVD). A 1.5-μm-thick aluminum nitride was firstly grown on the sapphire substrate. BN epitaxial layer was then attained with varied VIII ratios and carrier gas flow rates, with the attempt to improve crystal qualities. Finally, BN was doped with Mg2+ to accomplish p-type conductivity. Preliminary results suggest that the transmission and conductivity of p-type BN are significantly superior to those of p-type Al0.3Ga0.7N, exhibiting great potential for DUV LED applications.
