Simultaneous Multiple Peak Analysis Research Articles

Determination of Defect Levels in Melt-Grown All-Inorganic Perovskite CsPbBr3 Crystals by Thermally Stimulated Current Spectra

Further improvement of optoelectronic performance is a target for all-inorganic lead halide perovskite material CsPbBr3; however, it is greatly limited by the quality of the material which is dominated to some extent by defects, especially intrinsic point defects. In this study, the intrinsic point defects in melt-grown CsPbBr3 crystals were studied by thermally stimulated current technology and the simultaneous multiple peak analysis (SIMPA) method. The defect formation mechanism was analyzed systematically by combining the SIMPA fitting results with defect-related parameters, material properties, and external conditions. The main analytical defects, VCs and VBr vacancies, Csi and Pbi interstitials, and PbBr antisites, matched up with theoretical prediction well. Such systematic studies of defect types and concentration give us more insights into the carrier transport mechanism of CsPbBr3 and will help us find ways to improve the crystal quality by controlling the types and concentration of point defects.

The effects of deep-level defects on the electrical properties of Cd0.9Zn0.1Te crystals**Project supported by the National Natural Science Foundation of China (No. 51502234) and the Scientific Research Plan Projects of Shaanxi Provincial Department of Education of China (No. 15JS040).

The deep-level defects of CdZnTe (CZT) crystals grown by the modified vertical Bridgman (MVB) method act as trapping centers or recombination centers in the band gap, which have significant effects on its electrical properties. The resistivity and electron mobility–lifetime product of high resistivity Cd0.9Zn0.1Te wafer marked CZT1 and low resistivity Cd0.9Zn0.1Te wafer marked CZT2 were tested respectively. Their deep-level defects were identified by thermally stimulated current (TSC) spectroscopy and thermoelectric effect spectroscopy (TEES) respectively. Then the trap-related parameters were characterized by the simultaneous multiple peak analysis (SIMPA) method. The deep donor level ( dominating dark current was calculated by the relationship between dark current and temperature. The Fermi-level was characterized by current–voltage measurements of temperature dependence. The width of the band gap was characterized by ultraviolet-visible-infrared transmittance spectroscopy. The results show the traps concentration and capture cross section of CZT1 are lower than CZT2, so its electron mobility–lifetime product is greater than CZT2. The Fermi-level of CZT1 is closer to the middle gap than CZT2. The degree of Fermi-level pinned by of CZT1 is larger than CZT2. It can be concluded that the resistivity of CZT crystals increases as the degree of Fermi-level pinned near the middle gap by the deep donor level enlarges.

The relationship between deep-level defects and high resistivity characteristic in CdZnTe crystals

The internal defects of CdZnTe crystals grown by the modified vertical Bridgman (MVB) method act as trapping centers or recombination centers in the band gap, which have effects on its resistivity. The relationship between deep-level defects and high resistivity characteristic in Cd0.9Zn0.1Te:In single crystal was studied. The deep-level defects were identified by thermally stimulated current (TSC) spectroscopy and thermoelectric effect spectroscopy (TEES) in the temperature range of 18–315 K. The trap-related parameters, e.g., activation energy, capture cross section, trap density were characterized by the simultaneous multiple peak analysis (SIMPA) method and Arrhenius fitting. The deep donor level (\({{E}_{\text{DD}}}\)) dominating dark current was about 0.664 eV near the middle gap by fitting the plots of the natural logarithm of dark current intensity ln(IDC) versus 1/(kT). The doubly ionized Te antisite (\(\text{Te}_{\text{Cd}}^{\text{2+}}\)) below the conduction band acting as a deep donor level was mainly the origin of \({{E}_{\text{DD}}}\) level. The energy value of Fermi-level was about 0.671 eV characterized by current–voltage (I–V) measurements of temperature dependence in the temperature range from 275 K to 315 K. The resistivity was about 8.17 × 109 Ω·cm measured by I–V measurement at room temperature. The high resistivity performance of Cd0.9Zn0.1Te:In crystal is mainly due to the Fermi-level pinned near the middle gap by the \({{E}_{\text{DD}}}\) level.

Correlated analysis of 2 MeV proton-induced radiation damage in CdZnTe crystals using photoluminescence and thermally stimulated current techniques

Radiation damage induced by 2MeV protons in CdZnTe crystals has been studied by means of photoluminescence (PL) and thermally stimulated current (TSC) techniques. A notable quenching of PL intensity is observed in the regions irradiated with a fluence of 6×1013p/cm2, suggesting the increase of non-radiative recombination centers. Moreover, the intensity of emission peak Dcomplex centered at 1.48eV dominates in the PL spectrum obtained from irradiated regions, ascribed to the increase of interstitial dislocation loops and A centers. The intensity of TSC spectra in irradiated regions decreases compared to the virgin regions, resulting from the charge collection inefficiency caused by proton-induced recombination centers. By comparing the intensity of identified traps obtained from numerical fitting using simultaneous multiple peak analysis (SIMPA) method, it suggests that proton irradiation under such dose can introduce high density of dislocation and A-centers in CdZnTe crystals, consistent with PL results.

Thermally stimulated current spectroscopy applied on defect characterization in semi-insulating Cd0.9Zn0.1Te

Defects exhibiting trapping behaviors in semi-insulating (SI) materials were investigated by thermally stimulated current (TSC) spectroscopy. The variation of measurement conditions during the initial photoexcitation and thermal emission, such as the heating rate, bias voltage, illumination time and delay time, may bring some significant effects on TSC spectra, leading to incomplete characterization of trap levels. In this work, defects with deep levels in the band gap of SI-Cd0.9Zn0.1Te crystal, grown by the modified vertical Bridgman (MVB) method, were studied via TSC measurements. TSC measurement of the SI-CZT sample was performed with the optimized measurement conditions. Ten different traps and a deep donor (EDD) level were characterized from the as-obtained spectrum in the temperature range from 25 to 310K with the aid of simultaneous multiple peak analysis (SIMPA). The origins of these traps were identified in detail as well.

Irradiation-Induced Defects in Cd0.9Zn0.1Te:Al

The effects of gamma-irradiation, produced by a 60Co source with a dose of 2.7 kGy, on defect levels in a Cd0.9Zn0.1Te:Al (CZT:Al) crystal were investigated by thermally stimulated current spectroscopy. Nine observed defect levels were identified, and the irradiation-induced variations of trap signatures for these levels, i.e., the thermal activation energy, concentration, and capture cross-section, have been evaluated using simultaneous multiple peak analysis. In addition, the dark-current spectra dominated by the deep donor (EDD) level have been certified. By fitting plots of the logarithm of dark current ln(IDC) versus 1/kT, the EDD level is determined to be 0.554 ± 0.001 eV and 0.792 ± 0.004 eV before and after gamma-irradiation, respectively. One month after irradiation, the EDD level moved slightly to 0.782 ± 0.003 eV. This result indicates that the EDD level is closer to the middle of the bandgap of CZT:Al after irradiation, which should be responsible for Fermi-level pinning near the middle of the bandgap, leading to high resistivity. This is consistent with the resistivity variation of CZT:Al at room temperature from the original value of 7.5 × 109 Ω cm before irradiation to the irradiated value of 5.6 × 1010 Ω cm as determined by current–voltage measurements.

Investigation on defect levels in CdZnTe : Al using thermally stimulated current spectroscopy

Defect levels present in as-grown semi-insulating CdZnTe : Al samples, taken from the top, middle and tail of the same ingot, have been investigated by thermally stimulated current (TSC) spectroscopy. Their trap signatures, particularly the thermal activation energy, capture cross section and concentration, were characterized and discussed, respectively, by fitting the measured TSC spectra with the simultaneous multiple peak analysis method. Furthermore, the deep donor levels EDD from the top, middle and tail were found to be positioned at 0.692 eV, 0.659 eV and 0.618 eV below the conduction band, respectively, by fitting the ln(I) versus 1/kT plots above room temperature. The Fermi level was positioned at 0.716 ± 0.05 eV by fitting the linear plots of the temperature dependence of resistivity, which was pinned by the EDD level near the middle of the band gap, which in turn caused the observed high resistivity in the as-grown CdZnTe : Al ingot.

Identification of deep trap levels from thermally stimulated current spectra of semi-insulating CdZnTe detector material

Deep trap levels in the semi-insulating (SI) CdZnTe detector material were characterized by simultaneous multiple peak analysis based on thermally stimulated current (TSC) measurements. In our TSCs that have been published previously electron hole pairs were created through the use of proton beam irradiation. Charge carriers were captured in deep traps and afterward released by thermal emission, which was recorded in the 90–300 K range. We showed that the obtained TSC spectra could be well fitted with a unique set of 14 different deep traps, which were all simultaneously and completely characterized. The obtained trap data are in good accordance with earlier deep trap characterizations of the other authors obtained on similar SI CdZnTe materials using different methods.

Thermoelectric effect spectroscopy measurements on semi-insulating GaN

A simplified setup for thermoelectric effect spectroscopy (TEES) was introduced. This was applied for measurements on semi-insulating GaN, grown on a sapphire substrate in order to investigate deep level traps. TEES currents were found to be negative at lower temperatures and positive at higher temperatures, indicating that shallower levels belong to electron traps, and deeper levels to hole traps. Traps were fully characterized by using the thermally stimulated current measurements and the simultaneous multiple peak analysis method. The shallowest observed electron and hole traps have activation energies E C −0.09 eV and E V +0.167 eV, respectively. The possible microscopic origin of analyzed defects was discussed.

Thermoelectric effect spectroscopy of deep levels in semi-insulating GaN

The report of thermoelectric effect spectroscopy (TEES) applied on semi-insulating GaN was presented. The type of TEES setup, especially suitable for film-on-substrate samples, was devised. TEES enabled determination of sign of observed deep traps. Using TEES and thermally stimulated current spectroscopy measurements in combination with the simultaneous multiple peak analysis formalism all important trap parameters were determined. The shallowest identified electron and hole traps had activation energies Ec−0.09 eV and Ev+0.167 eV, respectively. Results indicate that both these traps, oppositely charged are present in the studied material in relatively high concentrations causing the electrical compensation and high resistivity.

Complete set of deep traps in semi-insulating GaAs

Reevaluation and recalculation of thermally stimulated current (TSC) data from semi-insulating (SI) GaAs, published by many different authors over a period of three decades were done by means of the new analytical method, simultaneous multiple peak analysis (SIMPA). The SIMPA procedure clearly resolved contributions from various overlapping TSC peaks and enabled the precise determination of signatures (activation energy, Ea and capture cross section, σ) of all observed deep traps. The analyzed TSC spectra refer to SI GaAs samples that have been grown/treated in quite different ways (various growth techniques, growth under As or Ga rich conditions, different annealing procedures, irradiation with neutrons, γ rays, etc.). Although the SIMPA procedure was applied to apparently quite different TSC spectra, in all cases excellent fits were achieved, with the unique set (or subset from it) of eleven different deep traps, the only difference being in relative and absolute concentrations of traps. Despite a broad variety of samples analyzed in this article, the set of deep traps obtained is the same as the one being previously seen in the narrow range of SI GaAs samples. This finding suggests that this set of traps is a finite and complete set of all defects with deep levels in SI GaAs. It was also concluded that these defects are primarily complexes containing simple native defects.

Precise determination of deep trap signatures and their relative and absolute concentrations in semi-insulating GaAs

The new analytical method, simultaneous multiple peak analysis (SIMPA) which comprises simultaneous fitting of whole measured thermally stimulated current (TSC) spectra is presented. The procedure clearly resolves contributions from various overlapping TSC peaks, which results in precise determination of trap parameters (signature) for each trap. In combination with photocurrent temperature dependent measurements, IPC(T), which reflects free carrier lifetime temperature dependence, the estimates of relative and absolute trap concentrations were made as well. The advantage of the SIMPA method in comparison with the single peak approach was demonstrated and analyzed. The SIMPA method was applied to different semi-insulating (SI) GaAs samples, particularly to samples having very high and others having very low deep trap concentrations; and for both extremes excellent fits were achieved. The method also seems very promising for characterization of deep levels and other similar SI materials, like SI InP or SI CdTe.