目前生長紫外光發光二極體的磊晶結構時，通常會以藍寶石(c-plane)為基板，並利用氮化鋁(AlN)作為緩衝層來生長氮化鋁鎵(AlGaN)多層量子井(multiple quantum wells, MQWs)。這樣的磊晶結構會產生很強的偏極電場，使得電子、電洞分別集中量子井的上下側，造成發光效率低落。雖然有研究人員使用非極性的氮化物基板、生長非極性量子井，但這樣的非極性基板非常昂貴且面積小，難以量產。為了解決這問題，本研究利用立方氮化硼(cubic boron nitride, cBN)成長非極性AlGaN MQWs，以提高量子井的發光效率。 利用一維 drift-diffusion charge control solver (1D DDCC) 軟體，我們模擬AlGaN MQWs/cBN與AlGaN MQWs/AlN的能帶結構，顯示AlGaN MQWs/AlN的偏極電場會產生傾斜的量子井能帶，降低MQW的發光效率。為了降低AlGaN MQWs裡的偏極電場，我們在AlGaN MQWs與藍寶石基板之間插入一層cBN，並以脈衝噴氣(pulsed flow)的方式生長cBN，最後以光致發光(photoluminescence spectra, PL)光譜確認cBN表面能成長均勻發光的AlGaN MQWs結構。與AlGaN MQWs/AlN相較，AlGaN MQWs/cBN的PL強度較低，這是由於cBN表面的AlGaN MQWs磊晶品質較低的關係。我們將持續優化cBN的磊晶參數，以提升cBN表面的AlGaN MQWs磊晶品質。 ;In the epitaxial growth of ultraviolet light-emitting diodes (UV LEDs), AlN is often used as the buffer layer for AlGaN multiple quantum wells (MQWs) on c-plane sapphire substrates. The strong polarization-induced electrical field in the c-plane epilayers severely reduce the radiative recombination efficiency in MQWs. Although the internal electrical field can be avoided by growing the MQWs on nonpolar AlN substrates, the nonpolar substrates are very expensive and limited in size. To address the issue, we adopted cubic boron nitride (cBN) as the template for the growth of AlGaN MQWs. Using drift-diffusion charge control solver (1D DDCC), we compare the band tilting of AlGaN MQWs/cBN and AlGaN MQWs/AlN, showing that the electrons and holes are concentrated on the opposite sides of QW, which decreases the radiative recombination efficiency. To reduce the internal electrical field in MQWs, a thin cBN epilayer was inserted between MQWs and sapphire. For the growth of cBN, a pulse-flow technique was used to improve the surface flatness. The uniform radiation of MQWs on cBN was confirmed by photoluminescence (PL) spectra. The PL intensity of AlGaN MQWs on cBN was slightly lower than that on AlN, which is due to the deteriorated crystal quality of MQWs on cBN.
