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Register a new userAnalysis of Trapping and Detrapping in Semi-Insulating GaAs Detectors
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To investigate the trapping and detrapping in SI-GaAs particle detectors we analyzed the signals caused by 5.48 MeV alpha particles with a charge sensitive preamplifier. From the bias and temperature dependence of these signals we determine the activation energies of two electron traps. Additional simulation and measurements of the lifetime as a function of resistivity have shown that the EL2+ is the dominant electron trap in semi-insulating GaAs.
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We use optical transient-grating spectroscopy to measure spin diffusion of optically oriented electrons in bulk, semi-insulating GaAs(100). Trapping and recombination do not quickly deplete the photoexcited population. The spin diffusion coefficient of 88 +/- 12 cm2/s is roughly constant at temperatures from 15 K to 150 K, and the spin diffusion length is at least 450 nm. We show that it is possible to use spin diffusion to estimate the electron diffusion coefficient. Due to electron-electron interactions, the electron diffusion is 1.4 times larger than the spin diffusion.
The charge dynamics of hydrogen-like centers formed by the implantation of energetic (4 MeV) muons in semi-insulating GaAs have been studied by muon spin resonance in electric fields. The results point to the significant role of deep hole traps in the compensation mechanism of GaAs. Electric-field-enhanced neutralization of deep electron and hole traps by muon-track-induced hot carriers results to an increase of the non-equilibrium carrier life-times. As a consequence, the muonium ($mu^+ + e^-$) center at the tetrahedral As site can capture the tracks holes and therefore behaves like a donor.
Studies of n-CdZnTe crystals (photoluminescence, extrinsic photoconductivity, Hall effect, time-of-flight technique) have shown that the excess concentration of vacancies of cadmium (Vcd) is the main reason of low, as a rule, values of product of mobility to life time of holes (mhth). The reduction of the concentration of cadmium vacancies (decreasing of the intensity of near 1eV photoluminescence band and an intensity of the (0.9-1.3) eV extrinsic photoconductivity band) by annealing of the crystals at 600 C results in increasing of value of mhth. Influence of Zn on formation of the basic photoelectric properties of CdZnTe crystals has been explained by self-control of a concentration of cadmium vacancies Vcd due to addition of Zn results in formation of divacancies of metal, which in part dissociate and provide a crystal with necessary quantity of monovacancies for processes of complex formation. That makes process of obtaining of semi-insulating CdZnTe crystals less dependent from pressure Pcd in comparison with CdTe. However with the purpose of obtaining CdZnTe crystals with high value of mhth (i.e. with small concentration of the free vacancies of cadmium) it is necessary to control Pcd above the crystal at stages of its growth and annealing.
Semi-insulating Gallium Arsenide (SI-GaAs) samples experimentally show, under high electric fields and even at room temperature, negative differential conductivity in N-shaped form (NNDC). Since the most consolidated model for n-GaAs, namely, the model, proposed by E. Scholl was not capable to generate the NNDC curve for SI-GaAs, in this work we proposed an alternative model. The model proposed, the two-valley model is based on the minimal set of generation recombination equations for two valleys inside of the conduction band, and an equation for the drift velocity as a function of the applied electric field, that covers the physical properties of the nonlinear electrical conduction of the SI-GaAs system. The two valley model was capable to generate theoretically the NNDC region for the first time, and with that, we were able to build a high resolution parameter-space of the periodicity (PSP) using a Periodicity-Detection (PD) routine. In the parameter space were observed self-organized periodic structures immersed in chaotic regions. The complex regions are presented in a shrimp shape rotated around a focal point, which forms in large-scale a snail shell shape, with intricate connections between different shrimps. The knowledge of detailed information on parameter spaces is crucial to localize wide regions of smooth and continuous chaos.
The choice of electrostatic gating over the conventional chemical doping for phase engineering of quantum materials is attributed to the fact that the former can reversibly tune the carrier density without affecting the systems level of disorder. However, this proposition seems to break down in field-effect transistors involving SrTiO$_3$ (STO) based two-dimensional electron gases. Such peculiar behavior is associated with the electron trapping under an external electric field. However, the microscopic nature of trapping centers remains an open question. In this paper, we investigate electric field-induced charge trapping/detrapping phenomena at the conducting interface between band insulators $gamma$-Al$_2$O$_3$ and STO. Our transport measurements reveal that the charge trapping under +ve back gate voltage ($V_g$) above the tetragonal to cubic structural transition temperature ($T_c$) of STO is contributed by the electric field-assisted thermal escape of electrons from the quantum well, and the clustering of oxygen vacancies (OVs) as well. We observe an additional source of trapping below the $T_c$, which arises from the trapping of free carriers at the ferroelastic twin walls of STO. Application of -ve $V_g$ results in a charge detrapping, which vanishes above $T_c$ also. This feature demonstrates the crucial role of structural domain walls in the electrical transport properties of STO based heterostructures. The number of trapped (detrapped) charges at (from) the twin wall is controlled by the net polarity of the wall and is completely reversible with the sweep of $V_g$.
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