Study Of Trap Levels Research Articles

Study of trap levels in β-Ga2O3 by thermoluminescence spectroscopy

Electronic defects with shallow and deep levels in β-Ga2O3 single crystals were investigated by thermoluminescence (TL) spectroscopy. Undoped, Fe-doped, Sn-doped, and Mg-doped β-Ga2O3 single crystals grown by different methods were studied, and thermal activation energies of defects were calculated using the initial rise method. Hall-effect measurements and optical absorption spectroscopy were performed to determine the electrical transport properties and optical bandgaps. It was found that the dopants do not have any effect on the bandgap energy, which is important for comparing the trap levels in the samples. Three deep trap levels were found in the undoped crystals; the activation energy, ED, and concentration of defect centers for all of them have slightly changed after doping with Fe and Mg. Fe doping induced an additional defect center with activation energy of 0.62 eV. The measurements revealed the absence of TL emission in Sn doped crystals indicating that Sn doping may quench luminescence centers or modified some original electronic defects to inactive electron traps. The second interpretation “decrease of traps” may align with the successful incorporation of Sn as a donor and the high conductivity of Sn doped crystals revealed from Hall-effect measurements. This work also illustrates that the semi-insulating characteristics of Fe and Mg doped Ga2O3 are associated with the increase of the concentration of original traps in the crystal as well as the formation of new electron traps acting as deep acceptors. Recombination centers in all crystals are assumed to be associated with iron impurities.

Influence of photoconductivity on the study of trap levels in polyimide films by photo-stimulated discharge

In this paper, the distribution of the charge trap levels in polyimide (PI) films was investigated by using photo-stimulated discharge (PSD) technique, which was to explore the effect of photoconductivity on photo-stimulated discharge current. The PSD spectra show that the photo-stimulated discharge current of the PI films is mainly distributed in the range of 649–320 nm, but there are two significant current peaks when the wavelength is 300 nm and 244 nm, respectively. By studying the reason of generating two current peaks, it is concluded that the two current peaks are not generated by trapped charge de-trapping but generated by photoconductivity of charge-transfer complex in the PI films. According to the research, it is concluded that the trap levels in PI films are mainly distributed in the range of 1.92 eV–3.88 eV.

Thermally stimulated current measurements in undoped Ga 3InSe 4 single crystals

The trap levels in nominally undoped Ga 3InSe 4 crystals were investigated in the temperature range of 10–300 K using the thermally stimulated currents technique. The study of trap levels was accomplished by the measurements of current flowing along the c-axis of the crystal. During the experiments we utilized a constant heating rate of 0.8 K/s. Experimental evidence is found for one hole trapping center in the crystal with activation energy of 62 meV. The analysis of the experimental TSC curve gave reasonable results under the model that assumes slow retrapping. The capture cross-section of the trap was determined as 1.0×10 −25 cm 2 with concentration of 1.4×10 17 cm −3.

Study of trapping levels in α-HgI 2 crystals by UV and isothermal current measurements

UV spectra and isothermal current ( I–t curves) measurements have been performed in order to determine the trapping levels in α-HgI 2 crystal grown by a static sublimation method. Four absorption bands, with different absorption intensity, were found at 1572.5, 1729.2, 2117.5 and 2305.8 nm in the UV spectra. According to a simple energy level model, the first two, corresponding to 0.79 0.01 and 0.72 eV, respectively, were confirmed to be the absorption of trapping levels from the I–t data, whereas the last two were not assigned due to insufficient data from the I– t measurements. Our discussions on the characterization of the energy levels suggest that the four absorption bands in the UV spectra may be derived from structural defects in the HgI 2 crystal.

Study of trap levels in Alq3 layers by photodipolar absorption

In this paper we develop arguments about the part of traps involved in the electronic conductivity of the 8-tris-hydroxyquinoline aluminium (Alq3) studied in the conventional electronic structure ITO/Alq3/Al. After the presentation of general models and some topical discussions about the expression of the mobility in organic materials, we present results obtained by photodipolar absorption, which is a thermo-photo-dielectric effect, and by impedance spectroscopy measurements. This last method permits to define the equivalent circuit that can be designed as a single capacitor Cp and parallel resistor Rp network with a series resistance 50 located on the anode side; the log – log plot Rp as a function of the dc bias voltage gives a linear law that can be seen in a first time as a consequence of a Trapped Charge Limited current (TCL); this TCL law could be improved with the introduction of a field dependent mobility. Indeed, the photodipolar absorption leads to more convincing arguments because this method acts as a probe to highlight the traps: in particular, we show that the optical pumping of electrons on trap levels gives a clear increase in the dielectric absorption generated by the reorientation of dipoles associated with trapped charges; the trap depth is located around Et = 0.19 eV, which is a value in good agreement with theoretical calculations or thermoluminescence measurements.

Requirements for synthetic diamond devices for radiotherapy dosimetry applications

CVD diamond is a remarkable material for the fabrication of radiation detectors. Radiation hardness, chemical resistance and high-temperature operation capabilities of diamond motivate its use for fabrication of devices operating in hostile environments such as that encountered in nuclear industry and high energy physics. Its potentialities for such applications have been well documented and recent studies have led to the developments of a few applications that are addressing specific industrial needs. One particular interest of diamond stands in the fact that its atomic number is close to that of human tissues. This implies that the response of a diamond device to radiation is close to that received by the human body. Its thus enables the straightforward measurement of the dose for radiotherapy applications. However, this requires high reproducibility and linearity. It is widely observed that radiation exposure is modifying the initial performances of diamond detectors and priming devices is therefore required to obtain the required linearity. However, the nature of defects in the material strongly influences the type of priming required. This paper will address this problem from the study of trapping levels and their influence on the device response. We present here the current status of the development of polycrystalline diamond for this type of application, and propose new techniques of improving the material characteristics toward the optimisation of ionisation chamber performances as well as that of thermoluminescent dosimeters for the particular field of radiotherapy applications.

Study of trap levels by electrical techniques in p-type CuInSe2 thin films prepared using chemical bath deposition

CuInSe2 thin films, prepared using the Chemical Bath Deposition (CBD) technique, were analysed using Thermally Stimulated Current (TSC) measurements in order to get a clear picture of the different trap levels present in it. As-prepared samples showed two trap levels: the prominent one was due to the presence of a Se vacancy, while the weak one was due to the presence of a Cu vacancy. After annealing in air, the Se vacancy disappeared and a new level appeared which is suspected to be due to adsorbed oxygen. But annealing in air does not affect the Cu vacancy. On the other hand, annealing in vacuum does not affect Se vacancy, but the presence of an Fe impurity was detected in this case. A possible explanation for this phenomenon is also discussed. The dark conductivity measurements were also conducted on as-prepared as well as annealed CuInSe2 samples. These results are found to be in good agreement with the results obtained from TSC measurements.

Study of trapping levels in doped HgI 2 radiation detectors

The transient charge technique, TCT, was used to measure the trapping levels of pure and doped HgI 2 detectors over the temperature range of 170–300 K. The dopants were excess of Hg and I 2, naphthalene, butane, heavy paraffins, polyethylene and polyethylene glycol. The charge carriers were induced by α particles as well as by a UV nitrogen (337 nm) pulsed laser beam. The ICT determined trapping levels are compared with levels reported in literature from other solid state measurements.

A study of trapping levels in some red mercuric iodide single crystals for nuclear radiation detection

Photon-stimulated currents (PSC) and thermally stimulated currents (TSC) have been measured in red mercuric iodide ( alpha -Hgl2) single crystals grown in our laboratory from tetrahydrofurane- alpha -Hgl2 saturated solution, dimethyl sulphoxide-methanol- alpha -Hgl2 saturated solution and from a polymer-controlled vapour phase. PSC measurements helped in determining uniquely the activation energies and nature (electron or hole) of different trapping levels in these crystals. Subsequently, by a comparative study of TSC and PSC measurements, the capture cross sections have been determined uniquely. Finally, after estimating the trap densities, an attempt has been made to predict the influence of different trapping levels on the performance of the detectors fabricated out of the three types of crystal.

The study of trapping levels in anodic A12O3films using thermally stimulated currents

Trapping levels in anodic AI2O3 films grown in an aqueous solution of diammonium tartrate hove been studied by measuring thermally stimulated currents (TSC) in these films, Three discrete levels at 0˙26, 0˙39 and 0˙49 eV are obtained in the as-grown oxide. Energies of the trapping centres have been determined by using the heating rate variation method. The pH value, the: collecting bias, the concentration of the solution and a variation of the growth temperature in the range 20°C— 50°C do not affect the position of peaks while in general there is a small shift in the TSC peaks if the films are kept under growth voltages in the electrolyte, for prolonged period. These trapping levels may be due to the amorphous nature of the oxide and the impurities incorporated into the oxide during the process of its growth.