| 摘要: | 近年來，深紫外（deep ultraviolet, DUV, 波長 ? 290 nm）發光二極體 (light-emitting diodes,
LEDs) 的外部量子效率很難突破 20％，遠低於可見光 LED 的水準，主要原因在於：深紫外
LED 的 P 型磊晶層必須同時具備高穿透率、高導電性，而這是一般 DUV LED 常用材料—氮
化鋁鎵（AlGaN）所不具備的特性。然而 hBN (hexagonal Boron Nitride)是近年來熱門的三五
族氮化物材料，其兼具高能帶、低電洞活化能的特性，能使深紫外光波段的光不被吸收，
亦能大幅提升電洞濃度，增加導電性，是深紫外 LED 所需的理想 P 型材料。此外，氮化硼
的能帶高達 6 eV，接近氮化鋁 (AlN) 的 6.1 eV，能阻擋電子離開量子井，增加 DUV LED 的
內部量子效率。文獻顯示，氮化硼的電洞活化能最低可達 30 meV，遠低於 AlN 的 510 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;Despite years of research efforts, the external quantum efficiency of deep ultraviolet (DUV,
wavelength ? 290 nm) LEDs rarely exceed 20%, far below the level of visible LEDs. The main
reason is that the p-type contact layer of DUV LEDs must simultaneously fulfill the requirement of
high transparent and high conductive, which is extremely difficult to achieve with the commonly
used material, AlGaN. To address the issue, hexagonal boron nitride (hBN) is recently regarded as a
potential alternative to AlGaN. hBN has the characteristics of high energy band and low hole
activation energy, which can prevent light absorption and provide sufficient free hole concentration
in the p-type layer. Because of the two merits, hBN is an ideal p-type material for DUV LEDs. In
addition, the wide bandgap (6 eV) of hBN can form a large band offset with AlGaN, effectively
blocking the electron spill from quantum wells. The hole activation energy of boron nitride is
reported to be as low as 30 meV, which is much lower than the ~510 meV of AlN. With such small
activation energy, hBN can provide a large number of holes to enter the quantum well, enhancing
the quantum efficiency of DUV LEDs. The low hole activation energy can also lower the operating
voltage, reduce heat generation, and thus improve device lifetime. The above-mentioned advantages
make boron nitride a promising p-type material for DUV LEDs. |
