To realize the near-infrared detection of silicon-based detectors and avoid the incompatibility between III-V photodetectors and silicon-based integrated circuits, the development of Ge/Si detectors has become a research hotspot, with the breakthrough of preparation technology of Ge / Si heterojunction materials. In this paper, the research progress of Ge / Si heterojunction photodetectors in the wavelength range of 1.1μm to 1.6μm is summarized from the aspects of the device structure, working principle, the current situation at home and abroad, the advantages and disadvantages, and so on.
A series of two-dimensional TiX2 (X=Cl, Br, I) monolayers and their corresponding van der Waals heterostructures were predicted by the first-principle calculations. The dynamic and thermodynamic stability of TiX2 (X=Cl, Br, I) monolayers are confirmed by the phonon spectra and molecular dynamics simulations, respectively. The Heyd-Scuseria-Ernzerhof-based band values are 0.311-0.989 eV, showing the tunable transition probability between valence and conduction band. Additionally, the significant visible-light absorption coefficient (~ 105 cm-1) and high power conversion efficiency (~12%) of TiBr2/TiCl2 heterojunctions provide promising potentials for solar cells.
The self propagating welding of Kovar and sapphire was carried out with NiAl nano multilayers. The samples were tested by X-ray machine, scanning acoustic microscope, scanning electron microscope and bonding tester. The results show that sapphire and Kovar can be well self propagating welded using multilayer NiAl nano multilayers as heat source and solder to form uniform weld joint. The void ratio of the weld joint is 1.1%, and the welding strength is ~ 3.38 MPa. This study lends credible the welding of sapphire and similar metal materials.
The dynamic population processes of infrared radiation in dysprosium-doped different host materials (LaF3, Y2O3, YAlO3 and silicate glass) are theoretically investigated. The radiation and non-radiation transition rates of each energy level are calculated using Judd-Ofelt (J-O) theory and according to “energy-gap law”. It is demonstrated that the non-radiative transition rate increases significantly as the phonon energy increases, indicating that the choice of host materials has a great influence on the infrared transition processes. By solving the rate equations we establish, it is found that the population profiles of the same energy levels are almost the same, but the time to reach equilibrium population varies greatly among different materials. The population probability of 6H9/2 and 6H11/2 energy levels increases first and then decreases, whereas that of 6H13/2 and 6H15/2 monotonically increases or decreases with time. The excited state 6H13/2 has a quite long decay lifetime of 38.97 ms in dysprosium-doped LaF3, which is a good metastable state for mid-infrared emission.. These results are helpful to the material selection and application of infrared lasers.
Transmission properties of transverse magnetic light through periodic sub-wavelength slit apertures on a metallic film, behind which is another planar metallic film, are studied by finite-difference-time-domain method with constant periodicity and slit width. The result shows that the transmitted energy is strongly correlated to both the thickness of the metallic grating and the distance between such two films at a specific wavelength. The thickness of the grating acts as a filter that allows specific wavelengths to go through the slits, while the distance of dual metallic film dominantly determines a constructive or destructive interference between the transmitted light through the slits and the reflected wave from the back film. Besides, a strong vibration in the transmission spectrum as a function of the grating thickness is interestingly observed, which can be interpreted by the resonance of the surface plasmons of the front and the back metallic films.
Impact ionization in charge layer and multiplication layer of InAlAs/InGaAs avalanche photodiodes (APDs) with separated absorption, grading, charge and multiplication structures has been studied by two-dimensional simulations using Silvaco TCAD. Special attention has been paid to the charge layer and multiplication layer with different thicknesses and doping concentrations in order to optimize the structure for low band discontinuities and an appropriate electric field distribution. Band-edge profile calculations as well as current–voltage characteristic and electric field results of the APDs will be discussed in this article.