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A crystalline silicon (Si) surface was modified using nanosecond laser pulses in an argon atmosphere. The laser-modified Si (M-Si) samples have a higher performance and thermostable absorption in the broadband range (400–2400 nm) than conventional Si. The concentration of carrier electrons in the M-Si layer is at least five orders of magnitude greater than the carrier concentration of the Si substrate. Using the N+–N− junction formed between the M-Si layer and the Si substrate, visible and near-infrared (VIS-NIR) M-Si photodetectors are made. The N+–N− photodiode has good rectification characteristics and a high photoresponse to the subbandgap NIR light at 1310 nm. At the same time, the M-Si photodetector at a low reverse bias shows a large gain to the VIS-NIR light above the bandgap. By comparing the response time of the M-Si photodetector to the light of 900 and 1310 nm, the response speed of the device to the photon above-bandgap energy is faster.

Micro-ripple and micro-bead structures are formed on a silicon (Si) surface after irradiation with femtosecond laser pulses in nitrogen (N2) atmosphere. Simultaneously, supersaturated nitrogen (N) atoms, with a concentration above 1020 cm−3, are doped into the textured black Si layer via laser ablation. The N-doped Si exhibits strong below-bandgap infrared absorption from 1.1 to $2.5~\mu \text{m}$ , which remains nearly unchanged after annealing for 30 min at 873 K. The mechanism of this thermally stable infrared absorption is analyzed by first-principles calculations. According to the transmission electron microscopy results, multiple phases (including single crystalline, nanocrystalline, and amorphous phases) are observed in the laser-irradiated layer. Hall Effect measurements prove that N-dopants induce a low background free-carrier concentration ( $\sim 1.67\times 10^{16}\,\,\text {cm}^{-3}$ ). Finally, a Schottky-based bulk structure photodiode is made. This broadband photodiode exhibits good thermal stability and a photo-responsivity of 5.3 mA/W for $1.31~\mu \text{m}$ at a reverse bias of 10 V.

Ge–Sb–Te superlattice (GST-SL) is a newly emerging electronic material for nonvolatile phase-change memory with ultralow energy cost. However, its switching mechanism is still unclear with intensive debates. In this work, by first-principles calculations and an electron counting model study, we study the possible mechanism of phase change and the accompanying property transition of GST-SL. GST-SL are separated into individual layers by van der Waals gaps. We demonstrate that both the global chemical stoichiometry of the material and the local chemical stoichiometry of individual layer block are required to have an insulating band gap according to an electron counting model analysis. The electrical property can be adjusted by changing the local stoichiometry, such as producing defects around van der Waals gaps. Inspired by a previous experiment, we propose that a stacking-fault motion can spontaneously alter the band gap and results in a metal–insulator transition. This transition may provide a significant change of carrier concentration and indicate an ultralow energy-consumption process with a low energy barrier. The present investigations reveal a picture of electrical transition in GST-SL and may guide us to improve its device performances.

We study the eigenmodes of optical Tamm states (OTSs) at metal-distributed Bragg reflector interface. A peculiar type of non-propagating OTSs, named as evanescent OTSs, is found with mode propagation constant exhibiting the imaginary part to be much larger than the real part. The existence of such evanescent OTSs is attributed to the extension of Bragg forbidden band under complex propagation constants. An analytical solution of the evanescent OTSs is derived. Compared with propagating OTSs, transverse magnetic-polarized evanescent OTSs are found to exhibit more strongly localized field distributions associated with enhanced surface field intensity, which may be beneficial for surface-related applications such as sensing. Potential application as modulators is also demonstrated by using the nearly vertical dispersion characteristics around the transition wavelength between propagating OTSs and evanescent OTSs.

In this paper, we derive a theory for the modeling of 3-D cylindrical cloak based on 2-D finite-difference time-domain method, which is less time consuming and memory saving. By using the method, we develop the concept of invisibility angle and investigate the invisibility performance of the 3-D cylindrical cloak with 2-D constitutive parameters under off-plane incident waves. The bistatic radar cross sections as well as the scattered fields are calculated to evaluate the scatterings, from which the invisibility performance is observed to get worse with the increase in the incident angle, while the defined invisibility angle diminishes with the decrease in the cloak thickness and wavelength. The deterioration of the invisibility performance is mainly caused by the scatterings of TM wave defined in the study. The present results point out a possible way to evaluate the 2-D cloak on 3-D applications.

Presents corrections to the paper, “Metal–insulator transition ofGe–Sb–Te superlattice: An electron counting model study,” (Chen, N.-K.), IEEE Trans. Nanotechnol., vol. 17, no. 1, pp. 140–146, Jan. 2018.

Supersaturated S-doped black silicon (Si) samples are produced by femtosecond laser fabrication in mixed atmosphere of sulfur hexafluoride and oxygen (SF6/O2). The surface morphology with cone-microstructures has been observed in black Si samples fabricated in mixed atmosphere. After thermal annealing, the absorption below bandgap of black Si is obviously reduced. Moreover, the contents of sulfur in black Si samples obtained in mixture are also decreased by the lead in of oxygen. In contrast, an obvious increase of valent state ratio of Si4+ (SiO2) to Si0 (Si) is observed after the implantation of oxygen due to the formation of SiO2 in S-doped Si. Based on the passivation effect of SiO2, we have produced near-infrared black Si photodiode devices and showed photo-response properties of the devices. A notable photo-response of 11 mA/W at −3 V (26.6 mA/W at −5 V) for near-infrared 1.31- $\mu \text{m}$ detection light is obtained for the photodiode fabricated in mixture, which outweigh the performance of photodiode fabricated in pure SF6 atmosphere.