Wavelength-Tunable Waveguide Emissions from Electrically Driven Single ZnO/ZnO:Ga Superlattice Microwires

Because of the superlattice structures comprising periodic and alternating crystalline layers, one-dimensional photon crystals can be employed to expand immense versatility and practicality of modulating the electronic and photonic propagation behaviors, as well as optical properties. In this work, individual superlattice microwires (MWs) comprising ZnO and Ga-doped ZnO (ZnO/ZnO:Ga) layers were successfully synthesized. Wavelength-tunable multipeak emissions can be realized from electrically driven single superlattice MW-based emission devices, with the dominant wavelengths tuned from ultraviolet to visible spectral regions. To illustrate the multipeak character, single superlattice MWs were selected to construct fluorescent emitters, and the emission wavelength could be tuned from 518 to 562 nm, which is dominated by Ga incorporation. Especially, by introducing Au quasiparticle film decoration, emission characteristics can further be modulated, such as the red shift of the emission wavelengths, and the multipeaks were strongly modified and split into more and narrower subbands. In particular, electrically pumped exciton-polariton emission was realized from heterojunction diodes composed of single ZnO/ZnO:Ga superlattice MWs and p-GaN layers in the blue-ultraviolet spectral regions. With the aid of localized surface plasmons from Au nanoparticles, which deposited on the superlattice MW, significant improvement of emission characteristics, such as enhancement of output efficiencies, blue shift of the dominant emission wavelengths, and narrowing of the spectral linewidth, can be achieved. The multipeak emission characteristics would be originated from the typical optical cavity modes, but not the Fabry-Perot mode optical cavity formed by the bilateral sides of the wire. The resonant modes are likely attributed to the coupled optical microcavities, which formed along the axial direction of the wire; thus, the emitted photons can be propagated and selected longitudinally. Therefore, the novel ZnO/ZnO:Ga superlattice MWs with a quadrilateral cross section can provide a potential platform to construct multicolor emitters and low-threshold exciton-polariton diodes and lasers.

由于包含周期性交替晶体层的超晶格结构，一维光子晶体可用于极大地拓展调制电子和光子传播行为以及光学性质的通用性和实用性。在这项工作中，成功合成了包含氧化锌（ZnO）和镓掺杂氧化锌（ZnO/ZnO:Ga）层的单个超晶格微丝（MWs）。从电驱动的基于单个超晶格微丝的发射器件中可实现波长可调的多峰发射，其主波长可从紫外光谱区域调谐至可见光谱区域。为了说明多峰特性，选取单个超晶格微丝构建荧光发射器，发射波长可从518纳米调谐至562纳米，这主要由镓的掺入所主导。特别是，通过引入金准粒子薄膜修饰，发射特性可进一步被调制，例如发射波长红移，多峰被强烈改变并分裂成更多更窄的子带。尤其在蓝 - 紫外光谱区域，从由单个ZnO/ZnO:Ga超晶格微丝和p - GaN层构成的异质结二极管中实现了电泵浦激子 - 极化激元发射。借助沉积在超晶格微丝上的金纳米粒子的局域表面等离子体，可实现发射特性的显著改善，例如输出效率提高、主发射波长蓝移以及光谱线宽变窄。多峰发射特性源于典型的光学腔模式，而非由微丝两侧形成的法布里 - 珀罗模式光学腔。共振模式可能归因于沿微丝轴向形成的耦合光学微腔；因此，发射的光子可纵向传播和被选择。因此，具有四边形横截面的新型ZnO/ZnO:Ga超晶格微丝可为构建多色发射器以及低阈值激子 - 极化激元二极管和激光器提供一个潜在的平台。