InGaN/GaN量子阱悬空微盘发光二极管

InGaN/GaN Quantum Well LED Based on Floating Microdisk Cavity

设计并制备了三种不同结构的电泵浦InGaN/GaN量子阱微盘发光器件,对其光增益和光损耗进行了分析和优化。以p型层的结构为分类标准,器件Ⅰ为圆柱形;器件Ⅱ为器件Ⅰ的悬空结构;器件Ⅲ是悬空的圆环形结构。实验和仿真结果表明,三种器件结构中,器件Ⅱ的结果最好。电极布局为内p外n型的圆柱形器件表面电流分布能够保证发光区和微腔高增益区重合,悬空结构能够降低微盘在垂直方向上的光损耗,有利于更好的光学增益。考虑到共振模式,器件Ⅱ在注入电流大于0.7 mA时,器件Ⅱ实现了峰值波长为408.2 nm、半峰宽为2.62 nm的振荡模式输出。这种电泵浦InGaN/GaN量子阱悬浮微盘二极管器件的设计思路对电泵浦微盘或微环激光器的研制具有重要参考意义。

Although microcavity lasers with different structures have been proposed,the on-chip laser is still a critical bottleneck restricting the development of integrated optoelectronic systems.Ⅲ-Ⅴsemiconductors Light Emitting Diodes(LEDs)and Laser Diodes(LDs)on Si substrates,featured with suitable for large-scale and large-wafer-size manufacturing,are a convenient option for on-chip light sources.With the development of material fabrication,the quality of GaN wafers is high enough,optically pumped lasing has been realized in Si-based GaN microcavity,and more effort has been put into studying electrically pumped lasers.The reported electrically pumped lasing devices could be classified as Vertical-Cavity Surface-Emitting Lasers(VCSELs)and waveguide lasers according to the type of structures.Until now,the electrically pumped GaN lasing has also been realized in the Fabry-Perot(F-P)cavity and Whispering Gallery Modes(WGM)cavity.Many issues,such as the optical loss between the gain materials and the substrate,the improvement of the cavity quality,and the photon-electron coupling in the cavity region,can highly influence the optical performance of the device.In general,the floating process of the device will reduce the optical loss significantly,and improving the cavity quality is a critical issue in realizing high-quality lasing.Hence,the structure design will be essential in achieving a high-quality GaN laser.In this paper,we designed and fabricated three types of electrically pumped InGaN/GaN Quantum Well(QW)microdisk devices to analyze and optimize their optical gain and loss and balance the coupling of the gain region and optical resonant region.The samples are fabricated using a standard microfabrication process,including photolithography,ICP etching,and wet etching based on 1nGaN/GaN epitaxial wafer on Si substrate.All the devices show well-circular structures.The deviceⅠ,with a planar structure,was designed with a cylindrical p-type GaN region on the inner side of the microdisk.The inner and outer radius is 95μm and 200μm for DeviceⅠ.DeviceⅡis a floating device with the same planar structure as that of deviceⅠ.DeviceⅢwas designed with a ring-shaped p-GaN region on the outside of the microdisk,and it is also designed as a floating structure.DeviceⅢhas an inner and out radius of 65μm and 95μm.We define a gap between the n-GaN and p-GaN area to avoid device short circuits.For DevicesⅡandⅢ,through the isotropic wet etching of Si substrate,the whole LED is suspended for several micrometers.This strategy can ensure the reduction of optical loss of the cavity.TheⅣcurves,EL spectra,and luminous images are recorded during the experiment.Ⅳcurves indicate that the turn-on voltage of deviceⅠis about 18 V,and the wetting etching process will increase the turn-on voltage of the device;the turn-on voltage of deviceⅢis over 21 V.Driven current-dependent EL spectra of different devices indicates that peak wavelength are located at about 408.5 nm,408.2 nm,and 406.3 nm for deviceⅠ,ⅡandⅢ,respectively.The EL intensity of the microdisk device gradually increases with the increase of injection currents.FWHM of deviceⅠ,and deviceⅢis in the region of 12~14 nm.What struck us was that the EL spectra are also related to the electrode region.CCD images of samples under fixed driven current indicate that the light emission mainly occurs near the electrode,but the light will be transmitted in the microcavity.Compared with others,deviceⅡcan ensure that the luminous and resonance microcavity regions overlap owing to the better surface current distribution.In addition,the floating structure of the microdisk reduces the optical loss of the microdisk laser in the vertical direction and favors better light confinement.Finally,deviceⅡrealizes EL emission with resonant mode under an injection current of about 0.7 mA.Considering the resonant spectra,the spectra show resonant mode at a peak wavelength of 408.2 nm and a Full Width at Half Maximum(FWHM)of 2.62 nm.The novel design of floating electrically pumped InGaN/GaN QW microdisk is significant for electrically pumped microdisk or microring laser.