Photon Management Employing Photonic Crystal in InGaN Quantum Well Based Devices

本論文探討以光子晶體提昇氮化銦鎵多重量子井 (multiple quantum well) 為主動層之太陽能電池及發光二極體元件效率。在太陽能電池效率提昇方面，利用自我組裝之聚苯乙烯奈米球微影術 (PS nanosphere lithography) 及活性離子蝕刻 (reactive ion etching) 於元件表面製作週期性二氧化矽蜂窩陣列 (SiO2 nano-honeycomb arrays) ，結果顯示二氧化矽蜂窩狀光子晶體能夠在可見光波段有效的抑制反射率，並在模擬太陽光源(air mass 1.5G, AM1.5G)照射下提升34%之光電轉換效率。本實驗亦配合有限時域差分法 (finite-difference time-domain, FDTD) 作光場模擬，以進一步了解結構與光特性之影響。另外，聚苯乙烯奈米球亦可直接堆疊於元件上以提升光電轉換效率，利用數值模擬設計奈米球之最佳化層數，並配合實作堆疊三層奈米球，使光電轉換效率提昇30%。 氮化銦鎵量子井之發光二極體目前已廣泛的被研究，然而最大的瓶頸之一在於因空氣與氮化鎵之折射率差異極大，易在介面處形成全反射在元件內形成橫向傳播之導波模態。二氧化矽蜂窩狀光子晶體可以提供額外的晶體動量，有效的將原本在元件內傳播的模態以不同角度繞射至空氣中，在各方向都能大幅的提升出光效率，其中在400mA之電流注入之下，能夠使垂直方向之出光效率提昇78%。In this study, the schemes of enhancing the performances of indium gallium nitride (InGaN) based multiple quantum well (MQW) solar cells and light-emitting diodes (LEDs) are investigated. For the enhancement of conversion efficiencies of solar cells, SiO2 nano-honeycomb photonic crystals are fabricated on the devices. The nano-honeycombs are found to be effective in suppressing the undesired surface reflections over visible wavelengths. Under the illumination of air mass 1.5G solar simulator, conversion efficiency of the solar cell is enhanced by 34 %. To investigate light propagation behaviors across the interfaces, simulations based on finite-difference time-domain (FDTD) method are also carried out. In addition, 3 layer of PS nanospheres can be coated on the device based on the optimization design by simulations, contributing to the 30% enhancement of conversion efficiency. One of the major bottlenecks restricts light extraction efficiency of LEDs is the limited photon escape cone for light emission. SiO2 nano-honeycombs diffract the waveguide mode out of the device by providing an additional wave vector. At the current injection of 400mA, the optical power of the device is enhanced by 78 %