Activation Capture Cross Section Research Articles

DLTS study of deep level defects in Li-ion irradiated bipolar junction transistor

Commercial npn transistor (2N 2219A) irradiated with 50MeV Li3+-ions with fluences ranging from 3.1×1013ionscm−2 to 12.5×1013ionscm−2, is studied for radiation induced gain degradation and minority carrier trap levels or recombination centers. The properties such as activation energy, trap concentration and capture cross section of induced deep levels are studied by deep level transient spectroscopy (DLTS) technique. Minority carrier trap levels with energies ranging from 0.237eV to 0.591eV were observed in the base–collector junction of the transistor. In situ I–V measurements were made to study the gain degradation as a function of ion fluence. Ion induced energy levels result in increase in the base current through Shockley Read Hall (SRH) or multi-phonon recombination and subsequent transistor gain degradation.

Luminescence properties of hole traps in homojunction gallium nitride diodes grown by metal organic vapour phase epitaxy

A detailed investigation on p–n junction diodes of GaN using deep level transient Fourier spectroscopy (DLTFS) has been carried out. The typical deep level spectra on the various diodes on the same wafer demonstrate three electron levels labelled as E1, E2 and E3 and a hole trap H1 together with a broad band constituting three new hole levels H2, H3 and H4 therein. The electrical parameters like activation energy, trap concentration and capture cross section due to the observed levels have been measured for the comparison with the literature. The hole levels H1–H4 are found to be potentially involved in the radiative recombination and thereby, the luminescence role of the levels in the device is discussed.

Capture barrier for DX centers in gallium doped Cd1−xMnxTe

We report on the capture barrier for the gallium related DX center in Cd0.99Mn0.01Te. In order to determine the barrier height, two methods were applied: an analysis of the persistent photoconductivity decay and the optical deep level transient spectroscopy technique. Over a range of temperatures varying from 77to105K, the capture barrier height, deduced from the decay time constants of photoconductivity, has been found to be equal to 0.22eV. An apparent hole trap, observed with the optical deep level transient spectroscopy, was attributed to the thermally activated capture cross section of a DX center with a 0.23eV capture barrier. The obtained data are close to 0.21eV, the value of the capture barrier which we determined earlier with the help of the deep level transient spectroscopy method.

Deep electron states in indium‐doped Cd0.93Mn0.07Te DLTS study

AbstractElectron traps in indium doped Cd0.93Mn0.07Te were studied with Deep Level Transient Spectroscopy. Five electron traps were found (labeled as E1 ‐ E5). Energy levels ET of related defects are equal to E T 1 = 0.09 eV, E T 2 = 0.12 eV, E T 3 = 0.18 eV, E T 4 = 0.56 eV and E T 5 = 0.65 eV. Three of them (E1, E2, E3 ) are related to the defects with thermally activated capture cross section. Electric field enhanced electron emission from the trap E4 was observed and described in the terms of the Poole‐Frenkel ‐ mechanism. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Defect states investigation in poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)

In this study, application of the charge based Deep Level Transient Spectroscopy (Q-DLTS) has been extended to poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) single layer diodes, whose cathode consisted of aluminium and anode of indium tin oxide (ITO). The results reveal a broad Q-DLTS spectrum, with at least two maxima, consistent with a complex distribution of trap states. Only the Q-DLTS maximum with the shortest relaxation time could be fully resolved over the temperature range used here (100–300 K), yielding activation energies and capture cross sections in the ranges 0.3–0.4 eV and 10 − 20–10 − 18 cm 2, respectively. It will be shown that this energy level is likely related to a majority-carrier (hole) trap, consistent with a Poole–Frenkel injection mechanism and p-type doping of the MEH-PPV film. The origin of the second (non-resolved) Q-DLTS peak will also be discussed.

Deep level defects in Si-doped AlxGa1−xN films grown by molecular-beam epitaxy

The deep trap levels of AlxGa1−xN films with x in the range from 0 to 0.15 grown on c-plane sapphire substrates using rf-plasma-assisted molecular-beam epitaxy have been investigated by deep level transient spectroscopy measurements. Two distinct defect levels (denoted as Ei and Di) were observed. The origins of the Ei and the Di are associated with point defects such as the N vacancies and extended defects, such as the threading dislocations, respectively. According to Al content (x), the activation energy and capture cross section for the Di defect ranged from 0.19to0.41eV and 1.1–6.6×10−15cm2, respectively. The trap energy levels of Di defects in AlxGa1−xN were calculated and the values were nonlinear with Al content. The bowing parameter of AlxGa1−xN films was determined to be b=1.22.

Deep hole traps in Be-doped Al0.2Ga0.8As layers grown by molecular beam epitaxy

Deep hole traps in Be doped p-type Al0.2Ga0.8As grown by molecular beam epitaxy have been studied by the deep-level transient-spectroscopy method applied to samples with a Schottky diode configuration. Six hole traps, labeled as H1–H6, were found. Activation energies and capture cross sections have been determined for all the traps. Hole emission from the traps H1 and H2 was electric field dependent obeying the Poole–Frenkel effect relation. Their thermal activation energies when extrapolated to zero electric field were ET1,0=0.31 and ET2,0=0.36. For the traps H3–H6 the activation energies for emission were equal to: ET3=0.30eV, ET4=0.46eV, ET5=0.55eV and ET6=0.59eV. Comparison with the data for LPE material indicates that the levels H5 and H6 can be Cu and Fe related, respectively.

Deep level transient spectroscopic studies of high-energy nitrogen-irradiated Au/n-GaAs Schottky barrier diodes

Au/n-GaAs Schottky barrier diodes have been irradiated by high-energy (70 MeV) nitrogen ions of various fluences: 1 × 1011, 1 × 1012 and 1 × 1013 cm−2. Deep level transient spectroscopic studies of control and irradiated diodes have been carried out and analysed. For the diodes subjected to the fluence of 1 × 1012 cm−2, five distinctive electron trap levels (labelled E1–E5) are observed. The activation energies and capture cross sections of the levels have been calculated. The level E4 (0.552 eV) is due to NGa anti-site defects created by the irradiation. Trap level concentrations of all the energy levels are found to decrease up to the fluence of 1 × 1012 cm−2 and to increase for the fluence of 1 × 1013 cm−2. The shallow level concentrations of the diodes are determined using capacitance–voltage measurements.

Behavior of CdTe and CdZnTe detectors following electron irradiation

When exposed to an intense radiation field, the spectroscopic capabilities of room-temperature CdTe and CdZnTe detectors can be strongly altered by the remarkable injection of energy in the material structure due to the absorption of ionizing particles. In this paper, we report on the effects of electron irradiation on both CdTe and CdZnTe detectors. We have studied the detector response to electron irradiation through dark current measurements and by spectroscopic analyses at low and medium energies. The deep traps present in the material have been characterized by means of photo-induced current transient spectroscopy analyses, which allow for the determination of the trap apparent activation energy and capture cross section. The evolution of the trap parameters with increasing irradiation doses has been monitored and compared with the results already obtained by using other radiation sources.

Electrical characterization of vapor-phase-grown single-crystal ZnO

Gold Schottky-barrier diodes (SBDs) were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal ZnO reported up to now.

Metastable defect characterization in Cd 0.9Mn 0.1Te : In

In indium doped Cd 0.9Mn 0.1Te, the presence of metastable defects has been detected by observation of persistent photoeffects. By DLTS measurements several deep levels have been found and one of them exhibited thermally activated capture cross section, indicating on its metastable character. Photocapacitance measurements performed at liquid nitrogen temperature yield optical threshold energy for the deep-shallow transition equal to around 0.75 eV. This value is 0.63 eV higher than the thermal activation energy. The large difference between these two energies has confirmed strong interaction of related defect with surrounding lattice.

Semiconductor impurity parameter determination from Schottky junction thermal admittance spectroscopy

The problem of interpretation of thermal admittance spectroscopy data for semiconductor impurity parameter extraction is considered. Traditional analysis predicts that the Arrhenius plot for conductance peak temperatures is a straight line with the slope proportional to impurity activation energy and the intercept determining its capture cross section. Using a general model of the Schottky junction admittance we show that conductance peak positions strongly depend on the impurity bulk occupation number and potential distribution in the space-charge region, and, as a result, the Arrhenius plot is nonlinear for some semiconductor parameters and experimental conditions, in particular for relatively shallow impurities. In this case, the traditional linear approximation of the Arrhenius plot yields inaccurate values of activation energy and capture cross section. We propose a more accurate procedure for admittance spectroscopy data analysis involving least-squares fitting using the general and the small-signal models of the junction admittance. Although much more computationally intensive, the general model is shown to provide a better fit to the data at low temperatures, where the small-signal approximation is invalid. This approach is applied for an example admittance data and yields a better fit of the theoretical curve to the data and an improved value of activation energy for the nitrogen donor in 6H-SiC.

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.

Effect of thermal annealing on hole trap levels in Mg-doped GaN grown by metalorganic vapor phase epitaxy

Deep trap levels in a Mg-doped GaN grown by metalorganic vapor phase epitaxy are studied with deep level transient spectroscopy (DLTS). The Mg concentration of the sample was 4.8×1019 cm−3, but the hole concentration was as low as 1.3×1017 cm−3 at room temperature. The DLTS spectrum has a dominant peak D1 with an activation energy of 0.41±0.05 eV, accompanied by two additional peaks with activation energies of 0.49±0.09 eV (D2) and 0.59±0.05 eV (D3). It was found that the dominant peak D1 consists of five peaks, each of which has different activation energy and capture cross section. In order to investigate these deep levels further, we performed heat treatment on the same samples to observe the variations of activation energy, capture cross section, and amplitude of DLTS signals. It was found that the longer the heat treatment duration is, the lower the amplitude of DLTS peaks become. This suggests that the decrease of the DLTS signal originates from hydrogen atom outgoing from the film during the annealing process. The possible originality of multiple trap levels was discussed in terms of the Mg–N–H complex.

Characterisation of deep level trap centres in 6H-SiC p-n junction diodes

Deep level transient spectroscopy (DLTS) measurements were performed on silicon carbide (6H-SiC) n +p −p + junction diodes in order to compare the electrical properties and quality of epitaxial layers in the implanted and the epitaxial emitter diodes, where the p −p + layers are the same. Four hole trap centres were detected on the implanted emitter diodes. Their thermal activation energy’s are 0.49, 0.6, 0.7 and 0.87 eV, respectively, referred to the valence band. The last three trap centres are also observed on the epitaxial emitter diodes. The origin of deep levels, with E a=0.7 and 0.87 eV, is still under investigation. The thermal activation energy and capture cross section (0.6 eV, 4.3×10 −15 cm 2) is in good agreement with values reported for the boron-related D-centre. The trap centre with E a=0.49 eV is associated to the ion-implantation process of the n + layer. Double deep level transient spectroscopy measurements (DDLTS) have been performed to accurately profile this last defect through the depletion region. Its trap concentration N T( x) as a function of the depletion region width indicates that this defect is located near the n +/p − junction.

Persistent photoconductivity and DLTS in indium-doped Cd0.9Mn0.1Te

The properties of an indium-related DX center were determined in indium-doped Cd0.9Mn0.1Te by deep-level transient spectroscopy (DLTS). These studies, carried out within a 77–360K temperature range, revealed the presence of five electron traps. It was possible to determine the activation energy for four of them. Their values were equal to 0.22–0.30, 0.43, 0.51 and 0.63 eV, respectively. For the first energy level, the concentration of the associated traps was higher than 10% of the concentration of the shallow levels and the capture cross section was thermally activated, with an energy barrier for capture equal to 0.1 eV. The concentration of the other three traps was lower than 1014cm−3. Persistent photoconductivity was also observed at low temperatures. At 77 K, the photoconductivity continued for a very long time after the light was extinguished, and was present until the temperature of the sample increased to 170 K. The very high concentration and thermally activated capture cross section for the first trap suggest its DX center nature.

A deep semiconductor defect with continuously variable activation energy and capture cross section

A deep level with a continuously varying activation energy and capture cross section has been observed in CdS/CdTe thin-film solar cells. Given that the activation energy and capture cross section of a level are usually considered to be a unique identifier or signature for a particular deep level, this has important implications for the application of deep-level transient spectroscopy and related techniques for the characterization of deep levels in this and similar systems. We believe this phenomenon explains the well-known but poorly understood efficacy of CdCl2 treatment for CdS/CdTe thin solar cells.

Deep Levels in Hg0.766Cd0.234Te Grown by Metal-Organic Chemical Vapor Deposition

The deep levels in Hg0.766Cd0.234Te grown on Si substrates by metal-organic chemical vapor deposition (MOCVD) have been studied. Spectral analysis of deep level transient spectroscopy (SADLTS) was used to evaluate the deep levels for this device. Three levels (LM1, LM2 and LM3) were confirmed in this device. The values of activation energy and capture cross section for these levels were as follows: LM1 (21 meV, 6.1×10-18 cm-2), LM2 (21 meV, 1.3×10-18 cm-2) and LM3 (35 meV, 9.8×10-18 cm-2). The midgap level in p-HgCdTe reported by several authors could not be confirmed in this work.

Nondestructive SAW technique of acoustic transient spectroscopy to study deep centers in semiconductor heterostructures

A new technique of acoustic deep level transient spectroscopy (A-DLTS) using a high-frequency transverse acoustoelectric signal produced by a surface acoustic wave (SAW) electric field was used to study deep centers in semiconductor heterostructures. The basic idea of the presented A-DLTS technique is connected with the fact that the time development of the acoustoelectric response signal arising from the interaction between the SAW electric field and free carriers at heterostructure interface after an injection bias voltage pulse has been applied reflects relaxation processes associated with the thermal recombination of excited carriers moving toward their equilibrium state. The technique of computer evaluation of isothermal acoustoelectric transients applying the date compression algorithms [P. Bury and I. Jamnický, Acta Phys. Slovaca 46, 693–700 (1996)] was used to calculate deep center parameters as activation energies and capture cross sections. The technique has been applied for both Si MIS and GaAs/AlGaAs heterostructures. [Work supported by Grant of Slovak Ministry of Education No. 1/4261/97.]

A comparison of the trap properties and locations within GaAs field effect transistors measured under different bias conditions

The activation energy and capture cross section of traps found in GaAs field effect transistors (GaAs FETs) have been measured with both ohmic channel and current saturation bias using a variety of transient, frequency dispersion, and noise spectroscopy techniques. With current saturation bias these effects have been seen in both the transconductance and the output conductance. The results for all methods and bias conditions are compared with those found by others. The relative sensitivity of the techniques and the location of the traps are discussed.