Effect Of Recombination Processes Research Articles

Effect of recombination process in femtosecond laser-induced modification on Ge crystal* *Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 11804227).

The dynamics of produced excited carriers under the irradiation of Ge crystal is investigated theoretically by using femtosecond laser pulse. A two-temperature model combined with the Drude model is also used to study the nonequilibrium carrier density, carrier and lattice temperatures, and optical properties of the crystal. The properties of the surface plasmon wave when excited are also studied. The influences of non-radiation and radiative recombination process on the photoexcitation of the semiconductor during pulse and the relaxation after the pulse are described in detail. The results show that the effects of Auger recombination on the nonequilibrium carrier density and optical properties of the crystal and the properties of the surface plasmon polariton are great, whereas the effect of radiative recombination is extremely small.

Degradation Under Influence of Radiation Defects of Detector Properties of CdTe and Cd0.9Zn0.1Te Irradiated by Neutrons

This work is devoted to the study by computer simulation of the mechanisms of the influence of radiation defects, arising under the influence of neutron irradiation, on the changes in electrical properties: resistivity ρ, electron mobility μn, lifetime of nonequilibrium electrons τn and holes τp in Cd0.9Zn0.1Te and charge collection efficiency η of uncooled ionizing radiation detectors based on this material. Radiation defects, which are corresponded by deep energy levels in the band gap, act as trapping centers of nonequilibrium charge carriers, noticeably affect the degree of compensation by changing ρ of the detector material, the recombination processes, decreasing τn and τp, and also the scattering of conduction electrons, decreasing μn, that ultimately can cause degradation of the charges collection efficiency η. The specific reasons for the deterioration of the electrophysical and detector properties of this semiconductor under the influence of neutron irradiation were identified, and the main factors affecting the increase in the resistivity of Cd0.9Zn0.1Te during its bombardment by low-energy and high-energy neutrons, leading to complete degradation of the recording ability of detectors based on this materials, were found. The recombination of nonequilibrium charge carriers is noticeably stronger than the decrease in μn affects the degradation of detector properties, therefore, the effect of recombination processes at deep levels of radiation defects on the degradation of τn, τp, and η of detectors based on Cd0.9Zn0.1Te was studied. A comparative analysis of the properties of Cd0.9Zn0.1Te with the previously studied CdTe:Cl was made. An attempt was made to explain the higher radiation resistance of Cd0.9Zn0.1Te compared to CdTe:Cl under neutron irradiation by the influence of the radiation self-compensation mechanism with participation of deep donor energy levels: interstitial tellurium and tellurium at the site of cadmium. In addition, the rate of recombination at defect levels in Cd0.9Zn0.1Te is, ceteris paribus, lower than in CdTe:Cl due to the smaller difference between the Fermi level and the levels of radiation defects in cadmium telluride. The relationship between the band gaps of Cd0.9Zn0.1Te and CdTe:Cl, the concentration of radiation defects, the Fermi level drift during irradiation, and the radiation resistance of the detectors were also noted. The important role of purity and dopant shallow donor concentration in initial state of the detector material is indicated.

Silicon Photodiode for Visible Spectral Region

Photodiodes with high sensitivity in the short-wavelength portion of the visible region of the spectrum, fabricated based on high-ohmic silicon, are widely used in scintillation devices for visualization of gamma radiation and x-radiation in nuclear physics and medicine [1]. The following have been used to improve collection of minority charge carriers generated by short-wavelength photons in the immediate vicinity of the silicon surface: a shallow p-n junction with a vertical [2] or a horizontal [3, 4] structure, a graded p-n junction formed by diffusion of boron through the lattice of a thin layer of silicon oxide on the substrate surface [5], and an inversion layer photodiode [6]. The use of an inversion layer photodiode is limited by the narrow range of linearity typical of the spectral responsivity. A general disadvantage of photodiodes formed by boron diffusion into n-type silicon is the presence in the near-surface layer of silicon of a barrier layer under the oxide, preventing electrons generated by light in the p-region of the silicon from crossing into the p-n junction [7]. Photodiodes based on n-p junctions formed by diffusion of phosphorus or arsenic are more stable in the short-wavelength portion of the visible region of the spectrum [8, 9]. Their sensitivity at O 1 [12]. This allows us to ensure the minimum depth for the non-photoactive zone on the silicon surface. Arsenic is selected because of the following considerations. Its low diffusion coeffi cient makes it possible to form shallow junctions. The depth of the arsenic-doped n-region in our case is 0.2 om. Due to the relatively low atomic weight and the similar size of the ionic radii for silicon and arsenic, mechanical strains arising when doping with arsenic are relatively small, which lets us decrease the number of defects in the n-region and reduce the effect of recombination processes compared with the phosphorus-doped n + -regions [13]. The ohmic contact to the n-region is formed on the periphery of the arsenic-doped n-region. A guard ring reduces the surface component of the dark current. It is designed to be combined with the ohmic contact to the substrate. The dimensions of the photosensitive region of the photodiode are 5 × 5 mm. A two-layer SiO2/Si3N4 antirefl ective coating is formed on the photosensitive surface of the n-i-p junction.

Simulation study of the effect of recombination processes in an expanding plasma

Using particle-in-cell computer simulation, the processes occurring in a plasma formed by isothermal evaporation of ions and electrons off a planar wall are studied. A simple model to implement three-body recombination is introduced into this scheme: it fulfills momentum and energy conservation and obeys the well-known dependences of the recombination rate on density and temperature. Ion acceleration processes are investigated, during booth the particle emission phase and afterwards, during expansion into vacuum. Recombination strongly enhances ion acceleration, since due to the recombination-heated electron subsystem the expansion-front space-charge field is increased. Spatial segregation of the neutral gas cloud and the plasma cloud is demonstrated.

Separation of non-radiative and below-gap emission lifetimes in a heavily Si-doped GaAs/AlGaAs quantum well

The excitation density dependence of the time-resolved photoluminescence in a heavily Si-doped GaAs/AlGaAs multiple quantum well structure was investigated. By examining the trap-filling effect of the dominant non-radiative recombination process, we have measured separately the non-radiative recombination lifetime and the below-gap emission lifetime which can be used to analyze the physical mechanism of these recombination processes. The effect of these recombination processes on the band-to-band emission in the quantum well and its structural dependence became clear quantitatively.

Effect of recombination processes and nonisothermality of the ionospheric plasma on the thermal parametric instability

Effect of recombination processes and nonisothermality of the ionospheric plasma on the thermal parametric instability