利用鋁突起陣列結構產生表面電漿子耦合效果來提升氮化鋁鎵深紫外光量子井的發光效率

Abstract

本研究中，我們在氮化鋁鎵深紫外光量子井上面有123奈米的氮化鋁鎵覆蓋層上製作不同深度和夾有折射率較氮化鋁鎵低的介電質中間層之鋁突起陣列結構，將表面電漿子耦合效應應用在深紫外光量子井上，量測從低溫到室溫的垂直偏振和水平偏振方向的光激螢光頻譜，得出不同激發偏振方向的內部量子效率。因為重輕電洞能階和分裂價帶的能階差異很小，導致垂直偏振和水平偏振的內部量子效率增強比率並無顯著差異，相同的內部量子效率也可歸因於表面電漿子耦合效應會同時在不同偏振方向的躍遷中產生。本實驗中主要是利用高階共振模態的局域表面電漿子跟量子井來產生耦合效應。在量子井的發光波段的局域表面電漿子共振強度越高則會產生越強的激發光和更高的內部量子效率，同時隨著鋁突起結構尖端與量子井的距離增大會導致內部量子效率的增強效果逐漸減弱。我們利用鋁突起陣列結構產生的表面電漿子耦合效應可以有效提升氮化鋁鎵深紫外光量子井的內部量子效率，以改善深紫外光量子井發光特性。

The enhancement of internal quantum efficiency (IQE) of deep-ultraviolet (UV) AlxGa1-xN/AlyGa1-yN (x < y) quantum wells (QWs) by fabricating Al nano-protrusion arrays on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse-electric- (TE-) and transverse-magnetic- (TM-) polarized emissions are about the same. With SP coupling, the similar IQEs between different polarizations can also be attributed to the simultaneous SP couplings of the TE- and TM-polarized transitions. The SP resonance mode for coupling with the QWs is dominated by higher-order localized surface plasmon (LSP). The strong LSP resonance at the excitation laser wavelength may lead to stronger excitation and hence higher IQE levels of the QWs. The IQE enhancement decreases with the distance between Al-protrusion tip and the QWs.