Electron Recombination Time Research Articles

High power non-linear magnetophotoconductivity in n-GaAs using the UCSB free electron laser

The kinetics of electrons bound to shallow donor impurities in n-GaAs was investigated by saturation spectroscopy using the University of California at Santa Barbara free electron laser. The resonant photothermal conductivity from 1s–2p+ transitions was measured at intensities greatly exceeding previous studies. Saturation of bound-to-free photoionization transitions was measured from 0 to 4 Tesla. The 1s–2p+ resonant photoconductive signal shows a distinct intensity dependence caused by the competing bound-to-free transitions which saturate differently. Evaluation of the electron recombination kinetics allows us to calculate the transition time of electrons from the 2p+ level to the ground state, the recombination time of free electrons, and the thermal ionization probability of the 2p+ state.

Transient photocurrent induced by nanosecond light pulses in BSO and BGO

We investigate photoconductive decay following a fast 3-ns light pulse excitation in bismuth silicium oxyde (Bi 12SiO 20) and bismuth germanium oxyde (Bi 12GeO 20) single crystals of different origins. According to the different studied samples, photoconductive decay times of 50 ns and even smaller than 3 ns are observed. These decay times are due to electron recombination time from the conduction band. If we try to obtain the electron mobility in the conduction band, which seems several orders of magnitude greater than usual mobility values, it appears necessary to determine a precise diffusion length value.

Photo conductivity of condensed electrons in the dilute metal N-type Hg 0.8Cd 0.2Te

We have measured time resolved photo conductivity in n-type Hg 0.8Cd 0.2Te above the magnetic quantum limit. In this dilute metal the low temperature magneto-transport is governed by a thermally activated mobility of the electrons, behaving like a viscous liquid of molecules or atoms. Photo conductivity proved to represent a valuable method to obtain information on electron correlation time, on the carrier density and on the recombination time of dondensed electrons.

Optical measurement of the photorefractive parameters of Bi12SiO20

We employ an optical technique requiring no electrodes to measure three parameters characterizing photorefractive traps in nominally undoped n-type bismuth silicate at 515- and 488-nm wavelengths. These parameters are (1) an effective density of active electron trap sites (∼1016 cm−3), (2) the contribution αpcm−1 of the photorefractive excitations to the total absorption coefficient (∼3.8 cm−1 or 54% at 488 nm and 1.4 cm−1 or 86% at 515 nm), and (3) the average distance over which an optically excited electron moves in the absence of electric fields before being retrapped (∼4 μm). With these parameters (and the crystal properties) standard models give predictions for all photorefractive effects, with or without applied electric fields and crystal motion, provided that there is negligible change in the density of occupied traps during an electron recombination time (∼microseconds). Our technique employs measurement of the light-induced exponential decays of spatial ‘‘gratings’’ of trapped charges as a function of the grating period. The expected three-parameter function is observed from which we determine the above three parameters.

Microwave Cavity Q Sampler for Plasma Diagnostics

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