Xiaoshuang Chen

Polarity inversion and coupling of laser beam induced current in As-doped long-wavelength HgCdTe infrared detector pixel arrays: Experiment and simulation

In this paper, experimental results of polarity inversion and coupling of laser beam induced current for As-doped long-wavelength HgCdTe pixel arrays grown on CdZnTe are reported. Models for the p-n junction transformation are proposed and demonstrated using numerical simulations. Simulation results are shown to be in agreement with the experimental results. It is found that the deep traps induced by ion implantation are very sensitive to temperature, resulting in a decrease of the quasi Fermi level in the implantation region in comparison to that in the Hg interstitials diffusion and As-doped regions. The Hg interstitial diffusion, As-doping amphoteric behavior, ion implantation damage traps, and the mixed conduction, are key factors for inducing the polarity reversion, coupling, and junction broadening at different temperatures. The results provide the near room-temperature HgCdTe photovoltaic detector with a reliable reference on the junction reversion and broadening around implanted regions, as well a...

Novel SnSxSe1−x nanocrystals with tunable band gap: experimental and first-principles calculations

In this paper, the structural and electronic properties of ternary SnSxSe1−x semiconductor nanocrystals were systematically investigated through both experimental and computational methods. It reveals that the Eg can be modulated from 0.92 to 1.24 eV in an intrinsic linear variation by controlling the ratio of S/(S + Se). The varying tendency of band gap was also verified via first-principles calculations and analyzed by the density of states (DOS) curves.

Simulation and design consideration of photoresponse for HgCdTe infrared photodiodes

We report on 2D numerical simulations of photo-response characteristic for long-wavelength HgCdTe infrared photodiodes. Effects of thickness of absorption layer on the photoresponse have been investigated. Optimal thickness of absorption layers at different absorption length and diffusion length are extracted numerically. An empirical formula is proposed to predict reasonable optimal thickness of absorption layer by theoretically analyzing its correlations with absorption length and diffusion length.

High performance colored selective absorbers for architecturally integrated solar applications

Architecturally integrated solar thermal technologies such as solar water heaters and solar thermoelectric generators (STEGs) rely on spectrally selective solar absorbers. These solar absorbers need to have simultaneous high solar absorptivity (α) and low thermal emissivity (e), which always makes them look dark blue or black and so blocks architectural integrated solar applications. A colorful appearance should be taken into account for integration into architectural applications. Herein, colored absorbers with a TiNxOy absorbing layer and a TiO2/Si3N4/SiO2 dielectric stack are elaborately designed and can be fabricated with only two targets, Ti and Si, by using reactive magnetron sputtering. Both the theoretical and experimental results show that the color can be tuned a huge amount, while keeping solar absorptivity higher than 95% and thermal emissivity lower than 5%. The highest absorptivity and energy efficiency (α/e) values are 97.6% and 27.2, respectively. These materials can also be fabricated onto thermoelectric generators to demonstrate the conversion of solar energy into electricity. The open circuit voltage dramatically increases from 171 mV to 523 mV (3.1 times) when using the absorbers. Additionally, the colored solar absorbers can be deposited onto most types of substrate, even flexible substrates. They can simultaneously satisfy the aesthetic requirements and excellent energy performance required for architecturally integrated solar thermal and thermoelectric applications, as well as applications in other fields.

Finite-difference time-domain simulations of exciton-polariton resonances in quantum-dot arrays

The optical properties of nanosize quantum-dot (QD) arrays are found to vary significantly around the exciton resonance frequency of the QDs. In order to simulate the interactions between electromagnetic waves and QD arrays, a general auxiliary-differential-equation, finite-difference time-domain approach is introduced and utilized in this article. Using this numerical method, the exciton-polariton resonances of single-layer and double-layer GaAs QD arrays are studied. The optical properties of a single-layer QD array are found to be characterized by the Mie resonance of its constituent QDs, while a double-layer QD array is characterized by the quasi-dipole formed by two QDs positioned in each of the two layers.

Colorful solar selective absorber integrated with different colored units.

Solar selective absorbers are the core part for solar thermal technologies such as solar water heaters, concentrated solar power, solar thermoelectric generators and solar thermophotovoltaics. Colorful solar selective absorber can provide new freedom and flexibility beyond energy performance, which will lead to wider utilization of solar technologies. In this work, we present a monolithic integration of colored solar absorber array with different colors on a single substrate based on a multilayered structure of Cu/TiN(x)O(y)/TiO(2)/Si(3)N(4)/SiO(2). A colored solar absorber array with 16 color units is demonstrated experimentally by using combinatorial deposition technique via changing the thickness of SiO(2) layer. The solar absorptivity and thermal emissivity of all the color units is higher than 92% and lower than 5.5%, respectively. The colored solar selective absorber array can have colorful appearance and designable patterns while keeping high energy performance at the same time. It is a new candidate for a number of solar applications, especially for architecture integration and military camouflage.

High efficiency and rapid response superconducting NbN nanowire single photon detector based on asymmetric split ring metamaterial

With asymmetric split ring metamaterial periodically placed on top of the niobium nitride (NbN) nanowire meander, we theoretically propose a kind of metal-insulator-metallic metamaterial nanocavity to enhance absorbing efficiency and shorten response time of the superconducting NbN nanowire single photon detector (SNSPD) operating at wavelength of 1550 nm. Up to 99.6% of the energy is absorbed and 96.5% dissipated in the nanowire. Meanwhile, taking advantage of this high efficiency absorbing cavity, we implement a more sparse arrangement of the NbN nanowire of the filling factor 0.2, which significantly lessens the nanowire and crucially boosts the response time to be only 40% of reset time in previous evenly spaced meander design. Together with trapped mode resonance, a standing wave oscillation mechanism is presented to explain the high efficiency and broad bandwidth properties. To further demonstrate the advantages of the nanocavity, a four-pixel SNSPD on 10 μm × 10 μm area is designed to further reduce 75% reset time while maintaining 70% absorbing efficiency. Utilizing the asymmetric split ring metamaterial, we show a higher efficiency and more rapid response SNSPD configuration to contribute to the development of single photon detectors.

Impact of resonator rotational symmetry on infrared metamaterial absorber

We investigate the impact of rotational symmetry of the metamaterial perfect absorber on its performance. The calculated results show that a absorption peak appears at the same wavelength in the absorption spectrum no matter the polarization of the incident light parallels to x axis or y axis when the absorber possesses four-fold rotational symmetry. However, in the case of two-fold rotational symmetry, the absorption peak splits into two peaks when the polarization of the incident light parallels to x axis. The results of the absorption peak properties with different rotational symmetry may be helpful to design novel polarization-insensitive absorbers.

A novel plasmonic nanofilter based on complementary H-fractal shape components

We propose a novel infrared nanofilter of localized enhanced field with multiband resonant frequencies. Compared to the resonant wavelength, the structure size is very subwavelength. We establish the effective medium theory to illustrate the light field distribution of the fractals. The loss factor is used to retrieve relative permittivity which is utilized to reproduce of reflection and transmission coefficients in the effective homogeneous plate. By bringing the inevitable metal loss to advantage, the enhanced factor of the field in the filter can reach a factor of 16 times amplification.

Simulation of superconducting single photon detector coupled with metal-insulator-metal circular grating

Metal-insulator-metal (MIM) circular grating structure has been introduced to couple with superconducting nanowire single-photon detector (SNSPD) to enhance its response. According to our numerical simulation results, the coupling efficiency at 1.55μm can be enhanced by MIM circular grating and improving the response of SNSPD obviously. About 19.5 times of enhancement in response can be obtained with proper structure parameters.