Concentration Of Trapping Levels Research Articles

Reliability study of nano ribbon FET with temperature variation including interface trap charges

The nano ribbon FET (NR-FET) is an emerging device as multigate structure can be designed on a single substrate, which leads to improvement in device performance. However, the presence of multiple gate oxide and semiconductor interface creates a number of interface trap charges (ITCs), which leads to variation in device performance. In this paper, the assessment of reliability for NR-FET is performed under the impact of ITCs for different polarity. We have incorporated the ITCs along with wide variations in temperature from 200 to 500 K to study the DC, RF/analog, and linearity performance of NR-FET. It is seen that the increase in amount of positive ITCs (PITCs) leads to improvement in ON state current and less gate voltage is required to turn on the device. Also, the cut-off frequency and speed of the device can be improved through increasing the PITCs in NR-FET. The degradation in OFF state current and device efficiency (gm/ID) is observed with increased in temperature from 200 to 500 K. However, the linearity characteristics is improved at high temperature for different polarity in ITCs. This device provides ION = 9.77 × 10−4 A, IOFF = 6.23 × 10−13 A, maximum transconductance of 1.4 mS, maximum transconductance generation factor of 36.56 V−1, maximum cut-off frequency of 4.36 × 1012 Hz, delay of 39.6 ps, threshold voltage of 0.4301 V at trap level concentration of 1012 Ccm−2. It is also seen that NR-FET outperforms in terms of DC and RF/analog characteristics with the variation in temperature from 200 to 500 K. The temperature sensitivity is 150 (80) under PITC (NITC) for this NRFET. Due to its improved behaviour in wide range of temperature 200–500 K, this NR-FET can be applicable for defense and space applications.

Investigations of defect levels in different sized HgTe nanocrystals based photovoltaic devices using thermal admittance spectroscopy

HgTe nanocrystals (NCs) have unique properties that make them suitable for optoelectronic devices in the mid-wave infrared (MWIR) and short-wave infrared regions. However, electrically active defects can trap charge carriers, reducing their mobility and diffusion length, which degrades the NCs’ optical and electrical properties. In this study, we used the thermal admittance spectroscopic (TAS) method to analyze defects in HgTe NC-based photovoltaic devices. The ITO/HgTe/Al device structure was used to study the defect levels in HgTe nanocrystals and the effect of these traps on transport properties. Using low-temperature I–V measurements, we calculated the trap activation energy as 0.14 eV, and the transport was found to occur mainly through these trap states. From the TAS measurements, the trap activation energy obtained was 0.14 eV, and the concentration of trap level was 3.16×1016cm−3eV−1. We have also fabricated ITO/TiO2/HgTe/Au and fluorine doped tin oxide/TiO2/HgTe/MoO3/Au devices and did TAS measurements to understand the effect of adding electron and hole extraction layer on the formation of defect levels. Intriguingly, a distinct reversal in the capacitance–frequency (C–F) behavior is observed at different temperatures, leading to positive slopes in the Arrhenius plot. This peculiar phenomenon is attributed to the size-dependent doping effects within the HgTe nanocrystals. The outcomes of this study shed light on the significance of understanding and quantifying electrically active defects in HgTe nanocrystals for the advancement of NC-based optoelectronic devices.

Single thermal scan digital system for deep level transient spectroscopy.

We have developed a micro-controller based Deep Level Transient Spectroscopy (DLTS) system to identify the deep-level defects in semiconductors. It consists of Arduino-Due, a capacitance meter, and interface circuits. In addition, we have also developed the algorithms needed for the entire signal processing. It is not limited to Arduino-Due but can be implemented using other micro-controllers also. We have used Arduino-Due to generate the filling pulse and monitor the capacitance, temperature, data acquisition, timing control, and signal processing. The sequence of generating the filling pulse, reading the data, and signal processing is controlled digitally rather than by analog sampling circuits and timers. The minimum pulse width generated using Arduino-Due is 50ns; the pulse width generation depends on various hardware and software parameters and their integration. The resolution in reading the data is 0.8 mV/unit. The time delays in reading the data are appropriately taken care of in the system. The whole experiment can be completed in a single temperature cycle within 2-3h. The system is simple, inexpensive, in an easy-to-use platform, and less time-consuming; minimizes possible errors; and improves accuracy. The measurements using the "micro-controller based DLTS system" are verified by fabricating (Au) gold-doped silicon (Si) p-n junction samples (Au is a well-understood defect in Si). Using the Arduino-Due based DLTS system, we calculated the energy, the capture cross section, and the concentration of trap levels. The results are in good agreement with the literature, indicating the versatility of the system.

Particle size effect on TL/OSL response of NaMgF3:Tb phosphor

NaMgF3 is a nearly tissue equivalent material with low Zeff = 10.4 and a well-known phosphor for its high sensitivity concerning luminescence. The type of preparation route followed greatly affects the luminescence efficiency of a material. Grinding of NaMgF3:Tb phosphor for a long time induces several lattice defects in the phosphor. In this work, effect of particle size on TL/OSL response of NaMgF3:Tb irradiated by 60Co source of gamma radiations with a dose of 15 Gy has been investigated. NaMgF3:Tb samples has been synthesized by solid state reaction method using different grinding times i.e. 1 h and 5 h. XRD technique confirms its formation and crystallite size is calculated. TL studies show that sample synthesized by 5 h grinding is almost 2 times more intense than the sample obtained by 1 h grinding. Also, a clear enhancement is seen in the shoulder peak of sample grinded for 5 h. This could be due to increase in occupancy of trapped charge carriers in the trap levels. However, the position of main TL glow peak remains same in both the samples. Associated TL kinetic parameters such as order of kinetics, activation energy, frequency factor and trap density have been calculated by deconvoluting the TL glow peaks to understand the TL phenomenon. Continuous-wave optically stimulated luminescence (CW-OSL) decay curves have been obtained under blue LED stimulation for 40 s. Analyzing the CW-OSL decay curves reveal that grinding time significantly affects the OSL intensity of the phosphor as well. The decay constant and photoionization cross-section is determined for the faster and slower components of the total OSL intensity. It could be concluded that the time of grinding taken during preparation of the material has a major role in affecting the concentration of trap levels formed inside the forbidden gap of the phosphor.

Electrical conductivity of Cu/ZnO/Si heterostructures

The electrical conductivity studies of the Cu/ZnO/Si thin film heterostructures were carried out by the current-voltage (I-V) characteristics. It was found that the I-V characteristics were asymmetric and showed weak rectifying properties. The most probable mechanism of electrical conductivity was determined. The concentration of trapping levels and the carrier mobility were calculated.

Structure and luminescent properties of luminous polypropylene fiber based on Sr2MgSi2O7:Eu2+, Dy3+

The luminous polypropylene fiber based on long afterglow luminescent material Sr2MgSi2O7:Eu2+, Dy3+ was prepared by melt-spinning process. Micro-morphology, phase composition, crystal structure, spectral features and afterglow properties of the luminescent fiber were tested and analyzed. The results indicated that the fiber had independent superposition phase features of both Sr2MgSi2O7:Eu2+, Dy3+ and polypropylene. The range of its excitation wavelength was located between 250–450 nm; therefore, the luminescent fiber could be excited by ultraviolet or visible light. It could emit blue light of 460 nm wavelength after excitation, which was caused by the 5d-4f transition of Eu2+ ions within the host lattice. The initial luminescent intensity was more than 0.8 cd/m2, and afterglow life lasted 7 h. The afterglow decay was composed of rapid-decaying and slow-decaying processes, and the decay characteristics depended on the depth and concentration of trap level in the Sr2MgSi2O7:Eu2+, Dy3+.

Effect of swift heavy ion irradiation on deep levels in Au∕n-Si (100) Schottky diode studied by deep level transient spectroscopy

In situ deep level transient spectroscopy has been applied to investigate the influence of 100MeV Si7+ ion irradiation on the deep levels present in Au∕n-Si (100) Schottky structure in a wide fluence range from 5×109to1×1012ionscm−2. The swift heavy ion irradiation introduces a deep level at Ec−0.32eV. It is found that initially, trap level concentration of the energy level at Ec−0.40eV increases with irradiation up to a fluence value of 1×1010cm−2 while the deep level concentration decreases as irradiation fluence increases beyond the fluence value of 5×1010cm−2. These results are discussed, taking into account the role of energy transfer mechanism of high energy ions in material.

Current and optical noise of GaN∕AlGaN light emitting diodes

Low frequency noise of current and light intensity of ultraviolet light emitting diodes (LED) with wavelength from 265to340nm are the superposition of the 1∕f and generation-recombination noise. The dependence of generation-recombination noise on the LED current has a maximum caused by a relatively shallow trap level in the quantum well. The upper bound of this trap level concentration is estimated to be Nt=7×1015cm−3. The relative spectral noise density of the light intensity fluctuations decreased with an increase of the LED forward current. At high currents, the difference in the noise level for LEDs with different wavelength is small and is of the same order of magnitude or even smaller than for visible LEDs.

The Influence of Stressing at Different Biases on the Electrical and Optical Properties of CdS/CdTe Solar Cells

ABSTRACTCadmium Sulfide/Cadmium Telluride (CdS/CdTe) devices are subject to stress under various biases. Striking differences are observed with the Current-Voltage, and Capacitance- Voltage measurements for cells degraded at 100°C in dark under forward (FB), open circuit (OC), and reverse (RB) biases. RB stress provides the greatest degradation, and the apparent doping density profile shows anomalous behavior at the zero bias depletion width. Thin films of CdS, both doped and undoped, with Cu are characterized with photoluminescence (PL). The PL spectra from the CdS films are correlated with the CdS spectra from stressed devices, revealing that Cu signatures in the CdS layer of stressed devices are a function of stress biasing. Device modeling using AMPS-1D produces IV curves similar to that in RB degraded devices, by only varying the trap level concentration in the CdS layer.

Currents in narrow-gap photodiodes

Dark carrier transport mechanisms in Hg1-xCdxTe (x = 0.19-0.265) photodiodes in the temperature range 70-150 K and PbTe1-ySy/Pb1-xSnxTe (x = 0.2, y = 0.03) heterojunctions at T = 80 K are discussed. Two major current mechanisms were included into balance equations for the p-n junction: trap-assisted tunnelling (TAT) and Shockley-Reed-Hall generation-recombination processes for a defect trap level in the gap. Other current mechanisms (band-to-band tunnelling, bulk diffusion, etc) were taken into account as additive contributions. For TAT Anderson's matrix element of the impurity ionization was used and the tunnelling rate characteristics were calculated in the k-p approximation with constant barrier field. Using donor and acceptor concentrations in n- and p-type regions of the diode, trap level concentration, trap level energy and the in-junction trap level lifetimes as fitting parameters, a relatively good agreement with the experimental data for HgCdTe and PbSnTe diodes with large zero-resistance-area products R0A (e.g. for the 10 µm spectral region R0A>10 cm2) was obtained, which allows one to deduce the parameters of mercury-cadmium telluride and lead-tin telluride photodiodes from the parameters of the materials used for the diode fabrication. For the diodes with poor R0A characteristics (R0A<1 cm2 for the 10 µm spectral region) the agreement with the experimental data is not so good, which is apparently caused by the presence of several types of traps with different energy positions inside the gap and with different properties.

The effect of a strong electric field on the conductivity of a MnGaInS4: Eu single crystal

This paper presents the results of a study of the effect of a strong electric field on the electrical properties of MnGaInS4: Eu single crystals. The compound was obtained by the Bridgman method and consists of plane-parallel layered plates. The following parameters are determined on the basis of these studies: concentration of trap levels 1013–1014 cm−3 and activation energy 0.70–0.50 eV. It is established that the conductivity of MnGaInS4: Eu increases in strong electric fields mainly because the current-carrier concentration increases with electric field.

On the introduction of a measurement standard for high-purity germanium crystals to be used in radiation detectors

The IEEE and ANSI have recently approved "Standard Test Procedures for High-Purity Germanium Crystals for Radiation Detectors" proposed by the IEEE/NPSS/Nuclear Instruments and Detectors Committee. The standard addresses three aspects of the characterisation of high-purity germanium: (i) the determination by the van der Pauw method of the net carrier concentration and type; (ii) the measurement by capacitance transient techniques of the concentration of trapping levels; (iii) the description of the crystallographic properties revealed by preferential etching. In addition to describing the contents of this standard, the purpose of this work is also to place the issues faced in the context of professional consensus: points of agreement, points of disagreement, and subjects poorly understood.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Transient space charge limited current spectroscopy method of measuring the position and concentration of trap levels in semi-insulating materials

A new method is reported to measure the position and concentration of trap levels in semi-insulating materials where the regular deep level transient spectroscopy method is not applicable. In the proposed method, a transient space charge limited current (TSCLC) associated with the trap levels is measured using a capacitance balanced square wave voltage source, a voltage limiter-amplifier and a double box car averager. The TSCLC method is demonstrated on a p-type Y2.01Ca0.99Ge0.91Fe4.09O12 magnetic garnet sample ρ300=107 Ω cm. The trap level is located at 0.36 eV above the valence band edge and the concentration of the trapped holes is found to be 1013–1015 cm−3.

DLTS Study of Heat Treatments on n-CdTe Crystals

DLTS measurements were carried out on Schottky barriers formed on the surfaces of n-CdTe:In crystals heated in argon gas. Four electron trap levels were detected. The carrier concentration near the surface decreased to less than a tenth as a result of heat treatments at 350 or 400°C for 1 hour. A sample heated at 400°C showed a steep decrease in the carrier concentration near the surface. The concentration of an electron trap level (EC-ET=0.34 eV) was reduced by heat treatments. Heat treatments at temperatures higher than 350°C for 1 hour seemed to induce some defects related to cadmium vacancies or tellurium interstitials, which compensate donors and reduce the concentration of the trap level near the surfaces of CdTe.

Investigation of Trapping in Iodine Single Crystals by Repeating Carrier Injection

Free holes generated on the illuminated surface of an iodine crystal are injected into its bulk by applied voltage pulses. The space-charge-limited currents obtained with sequential pulses at various voltages and with different time intervals between the pulses allow one to calculate the density of trapped charge and the characteristic time constants of trapping and release. It is also possible to estimate the concentration of trapping levels, their capture cross section, and their energy position in the forbidden gap, in good agreement with previous results.

Space-charge-limited currents and electron traps in cds crystals

Thermally stimulated currents have been measured after the electrical injection of electrons in thin insulating crystals of cadmium sulphide which can support large space-charge-limited currents. Two trapping levels which lie 0.41 ev and 0.61 ev below the conduction band are filled with electrons when currents in the vicinity of the traps-filled limit are passed. When currents which lie within the region of Child's Law for solids are allowed to flow the concentration of trapping levels at 0.61 ev decreases while the number of levels at 0.41 ev increases. Measurements of the dark current in the ohmic region suggest that the 0.41 ev trapping complex is stable at temperatures below 0°C and is converted to a complex with a level at 0.61 ev at higher temperatures.