紫外光LED的短波長具備高能量，可淨化水和空氣，在醫療衛生的應用上極具價值。然而紫外光LED的發光效率低，尚未普及在市場上。造成發光效率低的其中一個原因為極性量子井，當量子井受到極化效應時，會產生內建電場，產生量子侷限史塔克效應 (Quantum Confined Stark Effect，QCSE)，使得電子和電洞分離，降低發光效率。為了解決這問題，我們以立方氮化硼(cubic boron nitride,c-BN)做為紫外光LED的磊晶材料，希望減輕量子井的QCSE，以提升紫外光LED的發光效率。 本研究利用金屬有機化學氣相沉積 ( Metal-organic Chemical Vapor Deposition，MOCVD) 成長紫外光LED磊晶層，並在AlGaN量子井 (multiple quantum well，MQWs) 下方插入一層c-BN，藉此評估這種磊晶結構的發光效率。完成元件製程後，我們利用電致發光光譜 (Electroluminescence spectra，EL spectra) 以及電壓-電流特性曲線分析元件特性。EL的量測結果含c-BN的LED無法發光。根據一維 drift-diffusion charge control solver (1D DDCC) 模擬的能帶圖，c-BN的能隙太大，阻擋來自n型AlGaN的電子流。為了改善電流注入量子井的效率，我們將c-BN移至n型AlGaN下方，並透過能帶圖確認MQWs/n-AlGaN/c-BN可以提升電子注入量子井的效率，也有機會減緩MQWs裡的QCSE。 ;Because of its short wavelength, ultraviolet(UV) LEDs have been applied in various fields including water and air purification, medical hygiene, and more. However, the low luminous efficiency of UV LEDs has hindered their penetration into the market. One of the reasons for the low luminous efficiency is the polarization of AlGaN quantum wells. When the quantum wells are subjected to polarization effects, the induced Quantum Confined Stark Effect (QCSE) creates an internal electric field, leading to the separation of electrons and holes, thus reducing the radiative recombination efficiency. To reduce the QCSE, we adopt cubic boron nitride (c-BN) in the growth of UV LEDs. The UV LED, with c-BN inserted under the AlGaN multiple quantum wells (MQWs), was grown by metal-organic chemical vapor deposition (MOCVD) on two-inch sapphire substrates. Characterization of electroluminescence (EL) spectra and current-voltage curves showed that the UV LED with c-BN did not emit light. According to the band diagram simulated by the one-dimensional drift-diffusion charge control solver (1D DDCC), election injection from the n-type AlGaN was blocked by the large bandgap (~6.2eV) of c-BN. In order to increase the injection efficiency, the c-BN layer was moved from MQWs/c-BN/n-AlGaN to MQWs/n-AlGaN/c-BN. In the simulated band diagram of MWQs/n-AlGaN/c-BN, the electron-blocking band offset at c-BN/n-AlGaN is removed, and the band tilting of MQW is also likely to be mitigated.
