Zizheng Li

Roughness reduction of large-area high-quality thick Al films for echelle gratings by multi-step deposition method.

Generally, echelle grating ruling is performed on a thick Al film. Consequently, high-quality large-area thick Al films preparation becomes one of the most important factors to realize a high-performance large-size echelle grating. In this paper, we propose a novel multi-step deposition process to improve thick Al films quality. Compared with the traditional single-step deposition process, it is found that the multi-step deposition process can effectively suppress large-size grains growth resulting in a low surface roughness and high internal compactness of thick Al films. The differences between single- and multi-step deposition processes are discussed in detail. By using multi-step deposition process, we prepared high-quality large-area Al films with a thickness more than 10 μm on a 520 mm × 420 mm neoceramic glass substrate.

Radial-quality uniformity investigations of large-area thick Al films

Abstract. The fabrication of high-quality large-area thick Al films with a thickness around 10  μm or even more is one of the most important factors to realize high-performance large-size echelle gratings. During the deposition process of large-area Al films, Al film quality generally exhibits a different behavior along the radius (R) direction, which seriously affects the performance of echelle gratings. In this study, for the first time, we investigate the radial-quality uniformity of large-area (R=400  mm) thick (>10  μm) Al films in detail. We not only analyze the radial-quality difference of Al films prepared by the traditional electron-beam evaporation process, but also significantly improve the radial-quality uniformity of large-area thick Al films by using a coevaporation process. By comparing two kinds of film coating processes, we clarify the origin of the radial-quality difference of Al films, and prepare large-area thick Al films with excellent radial-quality uniformity.

Novel aluminum plasmonic absorber enhanced by extraordinary optical transmission.

We report a theoretical and experimental study on a novel type of aluminum super absorber which exhibits a near perfect absorption based on the surface plasmon resonance in the visible and near-infrared spectrum. The absorber consists of Ag/SiO2/Al triple layers in which the top Al layer is patterned by a periodic nano hole array. The absorption spectrum can be easily controlled by adjusting the structure parameters including the radius of the nano hole and the maximal absorption can reach 99.0% in theory. We completely analyze the SPP and LSP modes supported by the metal-dielectric-metal structure and their contribution to the ultrahigh absorption. On this basis, we find a novel method to enhance the absorption via the simultaneous excitation of SPP at different interfaces theoretically and experimentally. Moreover, for the first time we clarify the EOT caused by the nano hole array can enhance the absorption by experiment, which is not reported in previous works. This kind of absorber can be fabricated by low-cost colloidal sphere lithography and the use of stable Al overcomes the disadvantages brought by the noble metal, which make it a more appropriate candidate for photovoltaics, spectroscopy, photodetectors, sensing, and surface enhanced Raman scattering.

Effects of hetero-related bulk-traps on photoresponse for long-wavelength HgCdTe infrared photodiode

Effects of hetero-related bulk traps on photoresponse for long-wavelength Hg1−xCdxTe infrared photodiodes have been numerically studied. The model involves a generalized approach, taking into account absorption coefficient, trap-assisted and band-to-band tunneling recombination mechanism, and bulk traps distributions associated with misfit dislocations present in the GaAs-substrate/Hg1−xCdxTe hetero-structure. The characteristic x-dependent material parameters, used in the simulations, such as donor concentration, trap density and level, and minority lifetime, are extracted by the simultaneous-mode nonlinear fitting procedure.

Microcavity electrodynamics of hybrid surface plasmon polariton modes in high-quality multilayer trench gratings

In common plasmonic structures, absorption and radiation losses are often mutually restricted and can seriously influence the device performance. The current study presents a compound structure composed of multilayer grating stripes and multilayer shallow trenches. A small depth was adopted for the trench configuration to exclude the extra bend loss. These two sections supported Fabry–Perot resonance and cavity modes, respectively, with hybrid modes formed through intercoupling. In addition, the total loss for the entire framework was clearly reduced due to the introduction of the trench geometry, indicating that both absorption and radiation losses were successfully taken into consideration in the compound structure. Significantly, such a low loss realized by the hybridization of surface plasmon polariton modes has rarely been seen before. Moreover, the debatable relationship between the total and partial quality factors was described for the first time based on a hybrid mode analysis to establish a new approach to investigate the different resonance modes. In the detailed calculation process, the relative electric field intensity was first adopted to stipulate the effective areas for the various modes, which is more reasonable than using the common definition that is based on a unit structure. The multilayer trench grating exhibited a relatively low loss without weakening energy localization, which is significant in the design of plasmonic devices.Plasmonic gratings: finding quality in the trenchesLosses associated with confining surface waves inside metal–insulator–metal waveguides can be minimized by optimizing trench structures in microscale gratings. Jinsong Gao from the Chinese Academy of Sciences and colleagues used direct laser patterning to create 450-nanometer deep periodic patterns in silicon wafers, then coated the waveguide with five alternate aluminum and silicon layers. In the higher, stripe-shaped portions of the device, multiple modes of trapped surface plasmon polaritons appeared, following a pattern known as Fabry-Pérot resonance. Trenches, however, had surface waves generated by the microcavity shape. By customizing the grating dimensions, the team merged the two types of resonances into new modes with exceptionally low levels of radiation and absorption loss. Analytical treatments revealed quality factors of the hybrid modes were better predicted using relative electric field intensities than periodic cell lengths.

Simulation of laser beam induced current for HgCdTe photodiodes with leakage current

We report on 2D numerical simulations of laser beam induced current (LBIC) for HgCdTe photovoltaic detector. The effect of junction leakage current on the LBIC signal is investigated, and different leakage paths caused by different reasons in HgCdTe photodiode arrays are taken into account in the simulation. The simulation results are in good agreement with the experiment data. Simulation results suggest that the LBIC can be used to determine the existence of the junction leakage current and investigate the original of the junction leakage current.

Raman study of InAs quantum dots on GaAs/InP grown by low pressure metal-organic chemical vapor deposition

Raman spectra of InAs quantum dots (QDs) on InP substrate were investigated. Both longitudinal-optic (LO) and transverse-optic (TO) frequency of InAs QDs showed a large blue-shift comparing to its bulk due to the compressive strain in InAs QDs. Raman scattering of InAs QDs with a thin GaAs interlayer was studied. We obtained that the peak position of LO and TO mode of InAs QDs became larger blue-shifted when we inserted the GaAs layer. At the same time, we found a red-shift of the frequency of GaAs LO mode because of tensile strain. Theoretical calculation was performed and its prediction coincided with our experiment results well. They both showed that strain played an important role in formation of InAs QDs.