Investigation of Energy Levels of Small Vacancy Clusters in Proton Irradiated Silicon by Laplace Photoinduced Transient Spectroscopy

Abstract

Laplace photoinduced transient spectroscopy has been applied to determine the electronic properties and concentrations of deep traps in high purity n-type silicon irradiated with high fluences of 23-MeV protons. From the temperature dependence of thermal emission rates of excess charge carriers obtained by the analysis of the photocurrent relaxation waveforms measured at temperatures of 30–320 K, eight deep traps with activation energies ranging from 255 to 559 meV have been resolved. The dependence of these trap’s concentrations on the proton fluence are demonstrated for the fluence values ranging from 1 × 1014 to 5 × 1015 neq/cm2. In comparison to the previously reported results of theoretical and experimental studies on the electronic properties of small vacancy clusters in irradiated silicon, we tentatively attribute four detected traps with activation energies of 255, 367, 405, and 512 meV to the energy levels related to the 2−/− charge state changes of divacancy (V2), trivacancy (V3), tetravacancy (V4), and pentavacancy (V5), respectively. Simultaneously, we propose the attribution of four deep traps with higher activation energies of 415, 456, 526, and 559 meV to the energy levels related to the −/0 charge state changes of these small vacancy clusters, respectively.

Formation of Grown-In Nitrogen Vacancies and Interstitials in Highly Mg-Doped Ammonothermal GaN

“…In other words, the temperature increase in the μτ is stronger for sample #2 than for sample #1. Since the μτ product determines the quality of semiconductor material in terms of its application for the fabrication of various kinds of sensors, used as photodetectors, X-ray detectors, and radiation detectors, the results shown in Figure 2 b are of practical importance [ 31 , 35 ]. They demonstrate that by increasing the doping level in SI AT-GaN:Mg crystals, it is possible to obtain the material suitable for making unique detectors operating at 600 K. In view of the fact that above 300 K the mobility of charge carriers decreases with temperature due to the lattice scattering, the observed in Figure 2 b rise in the μτ values as a function of temperature can only result from the strong increase in the excess charge carriers lifetime [ 35 ].…”

“…In the LPITS method, the occupation of defect levels is changed by the capture of excess charge carriers excited by optical pulses and after the excitation is switched off, the photocurrent relaxation waveforms (PRWs) induced by the thermal emission of excess electrons or holes from the defect levels are produced [ 31 ]. At a given temperature, the PRW is observed as a bottom part of the photocurrent decay, occurring in the photocurrent transient when the optical excitation is switched off.…”

“…The faster decay rate, which is observed for the shorter times, is related to the excess charge carrier recombination. Thus, the PRWs are the distinctive parts of the photocurrent transients and their analysis as a function of temperature enables the properties and concentrations of charge carrier traps to be determined [ 31 ]. Most frequently, a PRW observed in the photocurrent transient recorded at a given temperature is composed of a few exponential signals related to the thermal emission of charge carriers, and an advanced numerical procedure is used to extract the time constant of each exponential signal [ 31 ].…”

“…Thus, the PRWs are the distinctive parts of the photocurrent transients and their analysis as a function of temperature enables the properties and concentrations of charge carrier traps to be determined [ 31 ]. Most frequently, a PRW observed in the photocurrent transient recorded at a given temperature is composed of a few exponential signals related to the thermal emission of charge carriers, and an advanced numerical procedure is used to extract the time constant of each exponential signal [ 31 ]. This procedure, based on the inverse Laplace transformation algorithm (ILT), uses the CONTIN code [ 38 ] adapted to the commercially available MATLAB computational environment.…”

“…The temperature dependences of dark current (TDCC) were carried out at a voltage of 20 V and from the slope of linear parts of the dark current characteristics plotted as log( T 3/2 / I ) versus 1000/ T , where T and I denote the absolute temperature and electrical current, respectively, the activation energy of dark conductivity ( E ADC ) was determined. The temperature dependences of the μτ product for both kinds of samples were determined using the transient photocurrent method (TPM), based on the assumption that μτ value at a given temperature is proportional to the amplitude of the photocurrent pulse when the optical pulse generating the excess charge carriers is terminated [ 30 , 31 ]. The μτ measurements were carried out at a low flux of 3.31 eV photons incident on the sample, being ~9.7 × 10 14 s −1 cm −2 .…”