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An experiment on degradation mechanisms of InGaN light-emitting diode (LED) test structure which do not fulfill the requirements of longlife products is described and a combined capacitance-voltage (C-V), deep level transient spectroscopy (DLTS), electro-luminescence (EL), and cathodoluminescence (CL) study of short-term instabilities of InGaN/GaN LEDs submitted to low current aging test at room temperature is presented. The main cause of the degradation is the generation of nonradiative paths, due to the generation/propogation of defects activated by carrier transport.

The effects on 4H-silicon epilayers of irradiation with protons and electrons having particle energies, respectively, of 6.5 and 8.2 MeV are studied and critically compared. The findings reveal that a set of deep levels is same in both cases of proton and electron irradiations.

The irradiation effects on the charge balance off donorlike and acceptorlike defects in semi-insulating GaAs Schottky diodes are analyzed. The Fermi-level shift affects the charge collection efficiency of GaAs-based detectors by lowering the electric-field strength, even though the field-enhanced neutralization of the EL6 family defectsr accounts for the larger active layer.

Deep levels in liquid crystal phase epitaxy-grown Er-doped Si and those associated with luminescence activity are analyzed using deep level transient spectroscopy (DLTS), optical DLTS and capacitance-voltage measurements. The optical features of the material are investigated by photoluminescence, cathodoluminescence analyses. Two emission lines, A and B, are discovered, line A appeared at 0.806 eV. The results show that a real interaction happens between dislocations and Er-related emitting centers.

Electron beam induced current (EBIC) method is employed to analyze gettered Czochralski silicon. The effect of three different sequences of thermal treatments applied in ultralarge scale integration device manufacturing, both on the denuded zone (DZ) and intrinsic site formation, is assessed. EBIC method offers essential and direct data on DZ thickness and thorough homogeneity as well as on minority carrier diffusion length degradation in silicon substrates. The results are discussed.

Deep energy levels in semiconducting undoped CdTe and semi-insulating Cd0.8Zn0.2Te were characterized and identified using cathodoluminescence, photo-induced current transient spectroscopy, deep level transient spectroscopy (DLTS) and photo-DLTS. Twelve different traps were identified. Results obtained from the various materials were compared and the status of defect models was reviewed.

Electrical properties and distribution of defects in liquid-encapsulated Czochralski GaAs:Te wafers correspond to formation of Te concentration related deep electronic levels. Deep levels related to dislocations regulate diffusion length of minority carriers. Te concentration affects impurity segregation at complex defects.

The effect of material impurities on defective states brought about by heavy dopant diffusion was investigated using the electron beam-induced current technique. The results showed that in samples where Al had been codiffused, there was a significant improvement in the diffusion length. This behavior indicated that Al played a role in the electrical activity of the bulk defective states.

Electron beam induced current profiles were used to investigate diffusion length and surface recombination velocity in semiconductor devices containing a barrier perpendicular to the scanned surface. The results showed that noise on the profile tail significantly affected the determination of the diffusion length and the surface recombination velocity. Diffusion length and surface recombination velocity were determined by analyzing the steepness dependence.

The effects of gamma irradiation on CdTe:C1 were studied using photoinduced current transient spectroscopy analyses.

Optically induced electronic transitions in nitride based polar heterostructures have been investigated by absorption and emission spectroscopy. Surface photovoltage (SPV), photocurrent (PC), and photo luminescence spectroscopy have been applied to high quality InAlN/AlN/GaN structures to study the optical properties of two dimensional electron gas. Energy levels within the two dimensional electron gas (2DEG) well at the interface between the GaN and AlN have been directly observed by SPV and PC. Moreover, a strong enhancement of the photoluminescence intensity due to holes recombining with electrons at the Fermi Energy, known as fermi energy singularity, has been observed. These analyses have been carried out on InAlN/AlN/GaN heterojunctions with the InAlN barrier layer having different In content, a parameter which affects the energy levels within the 2DEG well as well as the optical signal intensity. The measured energy values are in a very good agreement with the ones obtained by Schrödinger-Poisson simulations. [ABSTRACT FROM AUTHOR]

High resistivity CdTe can be achieved by introducing impurities that create deep levels which, in turn, control the electronic transport properties of the material via a compensation process. We have characterized the effects of thermal annealing of high resistivity CdTe:Ge under either Te- or Cd-rich atmosphere to understand how modifications in the structure of Ge-related defective states and their electrical activity affect the material transport properties. We have investigated the transport properties with current-voltage analyses, the electrically active deep traps by photo-induced current transient spectroscopy and the local environment of Ge atoms by x-ray absorption spectroscopy. By correlating the modifications observed, we determined the occurrence of Ge clustering effects and associated them to the formation of electrically active deep donor traps, one located at EC-0.31 eV and the other one at midgap, with an activation energy of 0.82 eV. [ABSTRACT FROM AUTHOR]

Hydrogenated nanocrystalline silicon (nc-Si:H) is a multiphase, heterogeneous material, composed of Si nanocrystals embedded in an amorphous matrix. It has been intensively studied recently due to very promising photovoltaic and optoelectronics applications. The present paper aims to study electronic transitions in nc-Si:H grown by Low Energy Plasma Enhanced Chemical Vapor Deposition by Surface Photovoltage Spectroscopy. The study of several thin films grown at different conditions and the comparison with recently published computational studies allowed us to advance a hypothesis on the defect structure responsible for electronic transitions in nc-Si:H. [ABSTRACT FROM AUTHOR]

The electrical properties of high-purity 4H–SiC epitaxial layers are investigated. The current density versus applied voltage curves shows that some specimens have space charge limited transport behavior. Lampert–Mark model for trap-controlled electron transport in semi-insulating materials demonstrated the presence of an intragap state at 0.26 eV below the conduction band. Photodeep level transient spectroscopy has confirmed the presence of a deep level at about 0.3 eV below the conduction band only in samples with non-Ohmic behavior. Cathodoluminescence imaging has revealed the presence of high luminescent areas related to stacking faults (SFs) under the devices showing non-Ohmic behavior. The presence of single-layer SFs was detected by cathodoluminescence spectroscopy due to the typical emission at 2.95 eV. Thus, we demonstrated that the SFs modified the charge transport from Ohmic conduction to space charge limited conduction of the affected samples. [ABSTRACT FROM AUTHOR]

CdZnTe-based detectors possess unique properties as room-temperature x- and gamma-ray detectors. We report on the effects of x-ray irradiation on CdZnTe and CdTe:Cl detectors with increasing x-ray doses. We correlate the “macroscopic” performance of the detectors, investigated by gamma-ray spectroscopy to the “microscopic” effects induced by the impinging radiation, i.e., the defective states introduced in the crystal lattice. The electrical activity of the defects and their activation energy have been investigated by photo induced current transient spectroscopy and by space charge limited current analyses. We identify the x-ray dose that induces a significant degradation in the detector performance, and by cross-correlating the results obtained, we achieve a reliable estimate of the actual concentration of electrically active deep states and assess the potentiality of these experimental methods as tools for quantitative analyses of high resistivity materials. [ABSTRACT FROM AUTHOR]

The electrical compensation processes of high resistivity CdTe is controlled by deep levels. We have characterized the electrical activity of deep traps by means of three different and complementary spectroscopic methods: photoinduced current transient spectroscopy, surface photovoltage spectroscopy, and space charge limited current analyses. The aim is twofold: to achieve a thorough characterization of the deep trap properties and to assess the potentiality and limitations of the three experimental techniques by a cross correlation of the results obtained with each one of them. We have obtained a direct quantitative estimate of the major deep trap concentration, and we have assessed the sensitivity limit in deep-level detection for surface photovoltage spectroscopy. [ABSTRACT FROM AUTHOR]

This paper analyzes the thermal degradation of GaN-based light emitting diodes with hydrogen-rich passivation layer by combined capacitance and current measurements. The decrease of optical power arising during thermal treatment at T=250 °C is well related to a decrease in the high-frequency capacitance and to the generation of a further peak in the conductance/frequency curves. Deep level transient spectroscopy measurements excluded the role of further deep levels introduced/generated in the p-n junction region. Transmission line method analysis showed that stress induces nonlinearity of the characteristics of the contacts, related to the increase of Ohmic contact resistivity. All these modifications are explained using a small-signal model in which a parasitic impedance arises as a consequence of stress in the portion of metal/(p-GaN) interface exposed to diffusion of hydrogen from the passivation layer. Therefore, degradation is shown to be related to the worsening of the properties of the metal/semiconductor interface at the p side of the diode, due to the interaction between the hydrogen-rich passivation layer and the acceptor dopant. This interaction is well confined to the immediate proximity of the interface, leaving the activated acceptor concentration in the bulk almost unaffected. [ABSTRACT FROM AUTHOR]

Cd1-xZnxTe alloys have been studied by surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS). The analyses of surface photovoltage spectra have been perfomed at near and above band gap energies. Surface recombination effects on the surface photovoltage have been investigated. SPS analyses of Cd1-xZnxTe alloys with different surface conditions have shown that the surface recombination velocity significantly affects the SPS determination of the material band gap. Accounting for this and preparing the surfaces accordingly, SPS spectra of Cd1-xZnxTe samples have allowed an accurate determination of the optical band gap as a function of the Zn concentration, determined via EDS analyses. The local increases in the density of states associated with band structure features in Cd1-xZnxTe alloys have been investigated by SPS spectra in the above band gap energy range. [ABSTRACT FROM AUTHOR]

Defects in freestanding gallium nitride were examined in this work. Electron beam induced current mapping evidence a low density of dislocations in the first microns from the upper Ga-terminated surface; correspondingly, deep levels detected by junction spectroscopy exhibit point-like characteristics. Spectral photoconductivity measurements in the poorly dislocated region show the characteristic red, yellow, green, and blue bands, which shift toward higher energies with decreasing temperatures according to Varshni’s law. Spectral photoconductivity measurements carried out in depth evidenced, instead, the quenching of the defect-related yellow band and the prevalence of the green band when temperature increases. This behavior suggests a dislocation-assisted connection between the yellow and green bands, in agreement with theoretical models on their common origin involving complexes VGa-ON. [ABSTRACT FROM AUTHOR]

We studied a GaN epitaxial wafer grown by metal organic chemical vapor deposition, in which a lateral variation in the density of dislocations and associated defects was induced by a special preparation of the GaN buffer layer. Electron beam induced current and photocurrent measurements reveal lateral variations in the electrical properties of the GaN epilayer corresponding to the gradient in the defect density. The photocurrent spectra show four well distinct peaks separating the well known defect related yellow band in a blue, a green, a yellow, and a red component. In particular, we observe a strong dependence of the green component on the density of the a-type threading dislocations. There is evidence that the green and the yellow components are also significantly influenced by point defects. [ABSTRACT FROM AUTHOR]

The effects of low-temperature annealing in 8.2 MeV electron-irradiated 4H-SiC Schottky diodes were investigated. Deep-level transient spectroscopy and minority-carrier diffusion length (Ld) measurements were carried out on not-irradiated samples and on irradiated samples before and after thermal treatments up to T=450 °C. We found that several deep levels in the upper half band gap (S1 with enthalpy ET=0.27 eV, S2 with ET=0.35 eV, S4 with ET=0.71 eV, and S5 with ET=0.96 eV) anneal out or modify at temperature values lower or equal to T=450 °C, whereby their progressive annealing out is accompanied by a net increase of Ld, up to 50% of the value in the as-irradiated sample. We drew some conclusions regarding the microscopic nature of the defects related to the deep levels, according to their annealing behavior. [ABSTRACT FROM AUTHOR]

The electronic recombination properties of Mg-doped GaN have been investigated by steady state and time-resolved cathodoluminescence (TRCL) in the scanning electron microscope, photocurrent (PC) spectroscopy, and optical beam induced current (OBIC). CL and OBIC maps reveal an inhomogeneous recombination activity in the investigated material. Deep levels giving rise to level-to-band transitions were detected by PC spectroscopy. A large PC quenching observed upon illumination with light of (2.65–2.85) eV is tentatively attributed to metastable traps within the band gap. CL spectra reveal the existence of emission bands centered at 85 K at 3.29, 3.20, 3.15, and 3.01 eV, respectively. Both time-resolved and steady-state CL measurements carried out under different excitation conditions indicate that the 3.15 and 3.01 eV emissions are likely related to donor-acceptor pair transitions. TRCL measurements also reveal different recombination kinetics for these bands and suggest that deep donors are involved in the mechanism responsible for the 3.01 eV emission. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The features of current deep level transient spectroscopy (I-DLTS) spectra are investigated in AlGaAs/GaAs heterostructure field-effect transistors both through experiments and two-dimensional numerical device simulations. Differently from electron traps located in the n-type semiconductor bulk, which can only be detected in emission-mode by I-DLTS, deep levels located at the ungated device surface are shown to be revealed both in emission and capture transients by I-DLTS. Experimental and simulation results indicate that this behavior originates from inherent physical properties of surface deep levels interacting with holes attracted at the ungated surface by the negative charge associated with ionized traps. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present a study of the effects of high and low energy neutron irradiation on CdTe and CdZnTe high resistivity detector grade material. The evolution of the defect states under increasing irradiation fluence has been monitored by means of photoinduced current transient spectroscopy analyses. Particular attention is placed on the comparison and correlation between the results from the two materials under the two different neutron irradiation energies. The behavior of the observed deep traps associated with defect states allowed us to attribute an origin to most of them and to understand the role they play in the charge carrier collection process and in the degradation of material spectroscopic capabilities. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Time-resolved cathodoluminescence (TRCL) and photocurrent (PC) spectroscopies have been applied to the study of the yellow band of Si-doped GaN. Measurements carried out combining both techniques unambiguously reveal the complex nature of this broad emission and confirm that different deep defect levels are involved in the observed luminescence. Five emission bands centered at 1.89, 2.03, 2.16, 2.29, and 2.38 eV were found by steady state and time-resolved CL investigations, while PC spectra showed four transitions at about 2.01, 2.14, 2.28, and 2.43 eV. The behavior of the deep-level emissions intensity as a function of the excitation pulse width as well as their decay times were investigated by TRCL. A decay time of 245 μs was measured for the 2.29 eV emission band, while longer decay times of 315 and 340 μs were found, respectively, for the 2.16 and 2.38 eV bands, in agreement with TRCL spectra. The appearance of the 2.03, 2.16, 2.29 eV and 2.38-2.43 eV peaks both in PC and CL spectra suggests that these bands are related to deep acceptor to band transitions, as supported by the single exponential character of the corresponding decay transients. [ABSTRACT FROM AUTHOR]

Photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements were used to study the origin of optical emissions in the 0.8-1.0 eV region of selected oxygen precipitated and dislocated silicon samples. It was shown that the D1 band, present in both types of samples, is the convolution of different sub-bands, narrowly spaced between 0.802 and 0.820 eV. The emission at 0.807 eV, assigned in the literature to dislocations, was found only in samples where dislocations were intentionally generated by plastic deformation or induced by the clustering of self-interstitials generated during the growth of oxide precipitates. A comparison of the results of PL, DLTS, and optical DLTS measurements allows the assignment of levels involved in the radiative recombination processes. [ABSTRACT FROM AUTHOR]

This article concerns the existence of a double-junction effect in proton-irradiated silicon p[sup +] υ-n[sup +] (pin) diodes demonstrated by surface potential and optical-beam-induced current (OBIC) investigations. By increasing the diode biasing, the junctions existing at both ends in the irradiated devices move towards each other up to join, hence, causing a full depletion of the diodes. Due to the inhomogeneity of the electric field, however, the charge-carrier collection is strongly dependent on the position. The extent of the diode depletion layers at both ends and the shape of the electric field within the p[sup +]-υ-n[sup +] diodes are determined as a function of the bias applied. Three-dimensional photocurrent maps obtained by OBIC profiles allow for imaging the double junction. The deep level analysis evidences the presence of irradiation-induced defects, which are responsible for the double-junction effect. [ABSTRACT FROM AUTHOR]

A combination of surface photovoltage spectroscopy (SPS) and energy dispersive spectroscopy (EDS) were utilized to study the [Cd.sub.1-x][Zn.sub.x]Te alloys. The results showed that the electron-hole recombination at the surface have a strong effect on the determination of band gap energy through surface photovoltage signal (SPV) spectra.

A GaN epitaxial wafer grown is studied by metal organic chemical vapor deposition, in which a lateral variation in the density of dislocations and associated defects is induced by a special preparation of the GaN buffer layer. Electron beam induced current and photocurrent measurements reveal lateral variations in the electrical properties of the GaN epilayer corresponding to the gradient in the defect density.

Presents information on the study which investigated the electrical and optical characteristics of Erbium-doped silicon by liquid phase epitaxy. Experimental details; Results and discussion; Conclusions.

The yellow band of Si-doped GaN is studied by applying time-resolved cathodoluminescence (TRCL) and photocurrent (PC) spectroscopies. Studies confirm that different deep defect levels are involved in the observed luminescence.

Presents a study which obtained the diffusion length of minority in n-type floating-zone silicon samples with the electron-beam-induced current technique in planar configuration. Background on the moment method; Experimental procedures; Results of the study.