提升發光二極體電洞注入效率技術與表面電漿子耦合之薄p-型層發光二極體的特性

A Technique for Hole Injection Efficiency Enhancement in a Light-emitting Diode and the Performances of Thin-p-type Light-emitting Diodes with Surface Plasmon Coupling

蘇佳瑩(Chia-Ying Su)

指導教授 ： 楊志忠

國立臺灣大學/電機資訊學院/光電工程學研究所/博士(2017年)

https://doi.org/10.6342/NTU201702043

摘要

於本論文中，首先我們提出藉由提高鎂摻雜濃度而增加電洞濃度於p-型氮化鋁鎵電子阻擋層，尤其是位於發光二極體的電子阻擋層與最上層量子屏障的界面上，可降低電子阻擋層的內部極化電場，進而降低電洞於價電帶上由p-型層進入量子井的位能障，增加電洞進入量子井的穿隧機率，由此提升整體發光二極體的發光效率。我們利用一個新穎的鎂摻雜技術可提高p-型層的鎂濃度；即於p-型氮化鋁鎵或p-型氮化鎵成長之前，於有機金屬氣相沉積系統的腔體中，先吹入鎂金屬源一段時間。相較於傳統成長方式，以此技術生長，於電子阻擋層與最上層量子屏障界面上的鎂濃度可提高約20倍，發光二極體的發光強度可提升約9.4倍。根據模擬結果，當提高電子阻擋層中的鎂摻雜濃度，此層內價電帶與電洞的準費米能階間的能量差值會減少，也就是降低電洞進入量子井的位障，因此增加量子井內的電洞密度，提升發光二極體的發光效率。

透過上述摻雜技術提高p-型氮化鋁鎵電子阻擋層的鎂摻雜濃度，提升發光二極體的電洞注入效率，我們成長p-型層厚度僅38奈米的薄p-型層發光二極體，能維持良好運作性能。我們探討表面銀奈米粒子產生表面電漿子耦合效應於不同厚度之p-型層發光二極體的作用，包含提升內部量子效率、增加發光強度、減少發光效率滑落現象、增加調變頻寬，我們發現上述優越的特性隨著p-型層厚度減少而更明顯。我們製作半徑為10微米的發光二極體圓形元件，其調變頻寬高達625.6 MHz，是目前文獻紀錄上c平面氮化鎵發光二極體最高的調變頻寬。

此外，我們在內部量子效率(> 80 %)的量子井結構上生長p-型層，提升發光二極體的電洞注入效率，我們生長不同厚度p-型層的發光二極體結構，在表面製作銀奈米粒子產生表面電漿子耦合效應。我們改善電洞注入效率後，發光強度可增加16 %。我們減少p-型層厚度以縮短量子井與表面銀奈米粒子間的距離後，雖然減少p-型層厚度會些微增加阻抗並降低發光強度，但結合表面電漿子耦合效應後，表面電漿子耦合變強，能改善發光二極體的整體表現。配合增加電洞注入效率與表面電漿子耦合效應，我們成長僅31奈米的薄p-型層發光二極體結構，表面銀奈米粒子與最上層量子井的距離僅66奈米，發光強度能增加24 %。

關鍵字

發光二極體 ； 電洞注入效率 ； 表面電漿子耦合效應

並列摘要

In this dissertation, we first demonstrate by increasing the Mg-doping level and hence the hole concentration in the p-AlGaN electron-blocking layer (EBL), particularly around the interface between the EBL and the top quantum barrier, of a light-emitting diode (LED), the polarization field in this layer can be screened for reducing the potential barrier of hole and hence enhancing the hole tunneling efficiency such that the overall LED emission efficiency is increased. The increase of Mg-doping level is implemented based on an Mg pre-flow growth technique, in which Mg source is supplied into the metalorganic chemical vapor deposition chamber for several minutes before the growth of p-AlGaN or p-GaN. It is found that by increasing the Mg doping level by ~20 times near the interface between the EBL and the top quantum barrier, LED emission intensity can be enhanced by ~9.4 times. Based on a simulation study, we observe that the energy difference between the valence band-edge and the quasi-Fermi level of hole in the EBL is reduced by increasing the Mg-doping level in this layer such that the total hole density in the quantum wells is increased for enhancing the LED emission efficiency.

By increasing the Mg doping concentration in the p-AlGaN EBL through an Mg pre-flow process, the hole injection efficiency can be significantly enhanced. Based on this technique, the high LED performance can be maintained with a thin p-type layer. The high performance of an LED with the total p-type thickness as small as 38 nm is demonstrated. Then, the surface plasmon (SP) coupling effects through the fabrication of surface Ag nanoparticles (NPs), including the enhancement of internal quantum efficiency (IQE), increase of output intensity, reduction of efficiency droop, and increase of modulation bandwidth, among the thin p-type LED samples of different p-type thicknesses are compared. These advantageous effects are stronger as the p-type layer becomes thinner. However, the dependencies of these effects on p-type layer thickness vary. With a circular mesa size of 10 um in radius, we achieve the record-high modulation bandwidth of 625.6 MHz among c-plane GaN-based LEDs.

Furthermore, the performance improvements of the LED samples of high IQEs (> 80 %) by increasing their hole injection efficiencies through an Mg pre-flow process before the growth of the p-AlGaN electron blocking layer and producing the SP coupling effect through the fabrication of surface Ag NPs are demonstrated. The increase of the hole injection efficiency can significantly increase the LED output intensity by 16 %. For increasing the SP coupling strength through the reduction of the distance between the quantum wells (QWs) and the surface Ag NPs, we reduce the p-type thicknesses of the LED samples. Although the reduction of the p-type thickness can lead to slight detrimental effects, the consequent enhancements of SP coupling effects can significantly improve the LED performances. Combining the two factors of hole injection improvement and SP coupling, the LED output intensity can be increased by 24 % when the p-type thickness is reduced such that the distance between the surface Ag NPs and the top QW is decreased to 66 nm.

並列關鍵字

Light-emitting Diode ； Hole Injection Efficiency ； Surface Plasmon Coupling

參考文獻

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