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HgCdTe electron avalanche photodiodes (e-APDs) have been widely used for low-flux and high-speed application. To better understand the dark current transport and electron-avalanche mechanism of the devices and optimize the structures, we performed accurate numerical simulations of the current–voltage characteristics and multiplication factor in planar homojunction (p-i-n) HgCdTe APDs. Based on the Okuto–Crowell avalanche model, an efficient physical model has been obtained by concerning the major generation-recombination processes, such as trap-assisted tunneling and band-to-band tunneling (BBT) recombination. Simulated current–voltage characteristics were in good agreement with available data in the literature, which demonstrates the validity of the proposed model. The origins of dark current in high reverse voltages are jointly dominated by BBT and the avalanche mechanism. It is proved to be effective for reducing BBT by improving the uniformity of the electric field distribution across the junction. The electric performance of p-i-n e-APD can be improved by optimizing the APD structure, such as eliminating the sharp corners of junctions, light doping, and the appropriate thickness in multiplication region. Our works provide a good deal of insight into the fundamental carrier transport processes involved in HgCdTe e-APDs.

Investigations in the combination of graphene with noble-metal nanostructures mostly focus on the fabrication of stacked hybrid films or nanoparticle (Au or Ag NPs) decorated graphene sheets, while few are carried out in graphene built-in monodispersed microspheres. Herein, we propose a novel hierarchical composite with a silver-shelled Fe3O4 microsphere as the initial core and graphene oxide (GO) as the multifunctional inserted layer. The flexible GO provides abundant nucleation sites for further in situ growth of Au nanoparticles. Moreover, it introduces considerable chemical enhancement and enhances surface adsorption toward aromatic molecules. Considering the synergistic properties of versatile GO with noble-metal nanostructures, the synthesized Fe3O4@Ag-rGO-Au microspheres were expected to have excellent surface-enhanced Raman scattering (SERS) activity, which was verified by the detection of the sulfhydryl-contained PATP and aromatic DTTC, with respective detection limits of 10−11 M and 10−10 M. The enhancement factor (EF) was calculated to be 2.83 × 106 for totally symmetric (a1) vibrations located at 1077 cm−1 of PATP. Additionally, its fast magnetic response enables rapid separation from solution, which is a key factor for many practical applications. Therefore, the well-dispersed hybrid microspheres have enormous potential in sensing applications as well as in effective immobilization and enrichment of biomolecules and aromatic pollution.

International audience; Employing a pump-probe polarization-based two-frame shadowgraphy setup, the formation of filamentary damage induced in bulk fused silica by a nanosecond pulse at 1064 nm is investigated with a picosecond probe. Three different phases are exhibited in the damage experiments. The first phase is the formation of a micrometric plasma channel along the laser direction during the beginning of the pulse likely caused by multi-photon ionization. This channel exhibits growth during similar to 400 ps, and the newly grown plasma is discrete. Then, during the end of the pulse, this channel evolves into a tadpole-like morphology showing an elliptical head upstream the laser flux followed by a thin tail. This observed asymmetry is attributed to shielding effects caused by both the plasma and hot modified silica. Once the damage shows its almost final morphology, a last phase consists in the launch of a pressure wave enlarging it after the laser pulse. The physical mechanisms that might be involved in the formation of plasma channels are discussed. The experimental data are first confronted to the moving breakdown model which overestimates the filamentary damage length. Finally, taking into account the temporal shape of the laser pulses, the coupling between Kerr-induced self-focusing and stimulated Brillouin scattering is discussed to interpret the observations. (C) 2015 AIP Publishing LLC.

This paper reports on the disappearance of photosensitive area extension effect and the novel temperature dependence of junction performance for mid-wavelength HgCdTe detectors. The performances of junction under different temperatures are characterized by laser beam induced current (LBIC) microscope. The physical mechanism of temperature dependence on junction transformation is elaborated and demonstrated using numerical simulations. It is found that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation depended on temperature, and wider band gap compared with the long-wavelength HgCdTe photodiode may correlate with the disappearance of photosensitive area extension effect.

In this paper, we report on the disappearance of the photosensitive area extension effect and the unusual temperature dependence of junction transformation for mid-wavelength, n-on-p HgCdTe photovoltaic infrared detector arrays. The n-type region is formed by B+ ion implantation on Hg-vacancy-doped p-type HgCdTe. Junction transformations under different temperatures are visually captured by a laser beam induced current microscope. A physical model of temperature dependence on junction transformation is proposed and demonstrated by using numerical simulations. It is shown that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation dependence on temperature, and the weaker mixed conduction compared with long-wavelength HgCdTe photodiode contributes to the disappearance of the photosensitive area extension effect in mid-wavelength HgCdTe infrared detector arrays.