Search

Bowing parameter and intra gap states have been measured on good quality undoped and n-type Si doped InGaN layers, by surface photovoltage spectroscopy (SPS). Bowing parameter calculations have been done with consideration of strain and relaxed nature of InGaN layers. Si donor levels have been measured by SPS on layers with different indium content. Free carrier concentration and Si donor level variations as a function of In content have been analysed. It has been found that the interaction between In and Si plays a fundamental role in Si doping process in InGaN. [ABSTRACT FROM AUTHOR]

Silk is a natural biocompatible material that can be integrated in a variety of photonic systems and optoelectronic devices. The silk replication of patterned substrates with features down to tens of nanometers is exploited to realize highly transparent, mechanically stable, and free-standing structures with optical wavelength size. We demonstrate organic lasing from a blue-emitting stilbene-doped silk film spin-coated onto a one-dimensional distributed feedback grating (DFB). The lasing threshold is lower than that of organic DFB lasers based on the same active dye. These findings pave the way to the development of an optically active biocompatible technological platform based on silk. [ABSTRACT FROM AUTHOR]

Deep level transient spectroscopy was performed on InGaN/GaN multiple quantum well light emitting diodes (LEDs) in order to determine the effect of the dislocation density on the deep intragap electronic levels. The LEDs were grown by metalorganic vapor phase epitaxy on GaN templates with a high dislocation density of 8 × 109 cm-2 and a low dislocation density of 3 × 108 cm-2. Three trapping levels for electrons were revealed, named A, A1, and B, with energies EA≅0.04 eV, EA1≅0.13 eV, and EB≅0.54 eV, respectively. The trapping level A has a much higher concentration in the LEDs grown on the template with a high density of dislocations. The logarithmic dependence of the peak amplitude on the bias pulse width for traps A and A1 identifies the defects responsible for these traps as associated with linearly arranged defects. We conclude that traps A and A1 are dislocation-related intragap energy levels. [ABSTRACT FROM AUTHOR]

We report on the current transport properties of AlInN/AlN/GaN high electron mobility transitors with different AlN interlayer thickness. We determined the two-dimensional electron gas (2DEG) properties directly from simple current-voltage measurements, carried out with two Schottky contacts in a planar back-to-back configuration. A model has been developed to straightforwardly extract the 2DEG electrical properties from room-temperature current-voltage curves, and we correlated them to the effects of varying AlN thickness. The 2DEG properties calculated from current-voltage analyses are in very good agreement with results obtained with standard Hall measurements. [ABSTRACT FROM AUTHOR]

GaN based heterostructures have recently gained increased interest due to their applications for high electron mobility transistors. In this letter AlInN/AlN/GaN heterojunctions grown by metal-organic chemical-vapor deposition with different AlN thicknesses have been investigated by surface photovoltage spectroscopy. The density of the two-dimensional electron gas (2DEG) forming at the interface has been measured by Hall effect. A band gap shift has been detected and its dependence on the 2DEG electron density at the AlN/GaN interface has been analyzed on the basis of the Moss-Burstein and renormalization effects. [ABSTRACT FROM AUTHOR]

AlInN/AlN/GaN heterostructures were characterized by atomic force microscopy. V-defects and channels were observed. In phase-contrast mode, these features were found related to inhomogeneities associated with In-segregation (and/or In-diffusion) and Al-rich surface reconstruction. The electrical characterization via conductive atomic force microscopy showed enhanced conductivity regions related to In-rich traces within channels and V-defects. [ABSTRACT FROM AUTHOR]

We report on Photocurrent (PC) and optical absorption spectroscopy analyses of the electronic density of states (DOS) distribution around the band-edge of pentacene films of different thickness (from 50 to 300 nm). Both experimental methods allowed us to independently monitor the increase with increasing film thickness of the Davydov splitting of the first absorption band, correlated with modifications in the film molecular structure and packing when passing from a dominant “thin film” to a dominant “bulk” phase. We show how PC spectroscopy has the remarkable ability to detect the modification of the DOS distribution in a noninvasive way, thus allowing the study of fully operational organic thin film transistors. [ABSTRACT FROM AUTHOR]

We report on UV responsivity of 4H-SiC photodiodes irradiated by 1 MeV neutrons. Current-voltage characteristics, photoresponse spectra, and responsivity were obtained with light wavelength from 200 to 450 nm. Photoresponse results slightly affected by irradiation up to the threshold fluence [uppercase_phi_synonym]critical=8×1014 cm-2. At fluences ≥[uppercase_phi_synonym]critical the rejection rate is in the order of 103 in the range of 200–320 nm while it is less than 102 at about 320 nm. The abrupt increase in midgap traps induced by irradiation at [uppercase_phi_synonym]critical, observed by photoinduced current transient spectroscopy, proves carrier generation/trapping to be the controlling mechanism for the responsivity. [ABSTRACT FROM AUTHOR]

Technological procedures able to produce high quality electrodes from magnetic oxides in vertical organic-inorganic hybrid devices is a challenging task in the field of organic spintronics. Thin films of magnetite (Fe3O4) have been successfully grown directly on top of organic semiconductor layers, tris(8-hydroxyquinoline)aluminium(III) (Alq3), by pulsed-electron ablation technique. The films show ferromagnetic behavior and good structural quality, properties detected by magneto-optical Kerr effect, superconductor quantum interference device, micro-Raman spectroscopy, and Atomic Force Microscopy. The ferromagnetic behavior persists even for 10 nm thick films. Charge injection at magnetite-organic interface has been finally demonstrated by detecting electroluminescence from Alq3. [ABSTRACT FROM AUTHOR]

In this work the authors report on photocurrent spectroscopy analyses on pentacene thin film transistors that have been bias stressed and exposed to atmosphere over a long period of time (up to 80 days). They have studied the charge transport properties and the electronic excited state energy and distribution of these organic thin film devices. They also have identified the major excitonic and band gap transition energies and have investigated their quite different behavior following exposure to atmosphere or to bias stress. Different charge carrier distributions and trapping phenomena are proposed to describe the observed effects. [ABSTRACT FROM AUTHOR]

Defect-related bands and their properties are widely investigated in gallium nitride, especially by luminescence techniques, which evidenced a broad yellow band, and seldom, a green band. We present here a study of the visible portion of the photoconductivity spectra obtained in samples of different thicknesses and doping. The superior resolution of photoconductivity with respect to luminescence techniques allows for clearly distinguishing green and yellow bands, both showing a double peak structure. Moreover, while the yellow band shape results were unchanged with sample properties, the green band is sensitive to the growth conditions. Hence some hypotheses about their microscopic origin can be proposed. [ABSTRACT FROM AUTHOR]

Point and extended defects introduced in p-type Cz Si by oxygen precipitation and plastic deformation have been investigated with electrical and optical methods. Different materials (oxygen precipitated and/or deformed Cz Si and Fz Si) were examined in order to separate the role of oxygen precipitation, plastic deformation, and metallic contamination on the radiative and nonradiative electronic transitions at defect centers. A deep hole trap, named T1, has been associated with dislocation-related impurity centers; additional deep traps have been related to contamination by grown-in transition metals and to clusters involving oxygen atoms. [ABSTRACT FROM AUTHOR]

Low temperature annealing of electron irradiation-induced deep levels in 4H-SiC is reported. The major deep level transient spectroscopy peak S2 associated with the energy level at Ec-0.39 eV disappears in the temperature range 360–400 K, and some rearrangement of the peak S3, associated with the defect Z1/Z2 with energy level at Ec-0.5/Ec-0.65 eV occurs in the temperature interval 400–470 K. A net free charge carrier concentration increase goes along with the disappearance of peak S2 at Ec-0.39 eV, whereas the charge collection efficiency of the diode does not experience any significant change. An interpretation of the annealing of peak S2 on a microscopic scale is given. [ABSTRACT FROM AUTHOR]

Electrical properties of gallium nitride (GaN) epitaxially grown on sapphire show significant dependence on layer thickness. In this letter we show some of the main features observed by spectral photoconductivity (PC), electron beam induced current, and current–voltage characteristics. We focus our attention on the blueshift of the PC peak corresponding to the energy gap, which we associated to the strain acting in the GaN epilayers. The good energetic resolution of photoconductivity spectra allows for a direct study of the energy gap dependence on thickness. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate that the process of local oxidation of surfaces by atomic force microscopy (AFM) can be upscaled in a straightforward way by using a solid support with multiple protrusions as the cathode electrode. A metallized digital video disk DVD polymeric support has been used as a stamp to generate an array of features of variable length and 100 nm in width on a silicon surface covering a 5×6 mm[sup 2] region. The parallel patterning process involves the formation of as many liquid bridges as there are protrusions in the stamp. The growth rate of the parallel local oxides is slightly smaller than the one obtained by AFM experiments. Nonetheless, results from AFM local oxidation experiments can be readily extended to parallel oxidation which in turn opens the possibility of patterning centimeter-square regions with 10 nm motives. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The temporal behavior of deep-level luminescence emissions in undoped hydride-vapor-phase-epitaxy GaN layers of different thicknesses has been investigated by time-resolved cathodoluminescence (TRCL). The complex nature of the yellow luminescence is revealed in the TRCL spectra by the presence of two bands peaked at 2.22 and 2.03 eV. A red band with a decay time of 700 μs, centered at about 1.85 eV, dominates spectra recorded for long delay times. Exponential transients with associated decay times of hundreds of ms were measured at 87 K for all the deep-level emissions found in the layers. [ABSTRACT FROM AUTHOR]

The optical activity of Er-doped silicon is related to the presence of defects which enhance the typical radiative transition at 0.8 eV but whose nature and properties are still largely unknown. We have investigated the deep levels present in Er-doped liquid phase epitaxy silicon to identify the traps possibly related to the luminescence. Among the observed levels, two minority carrier traps labeled E2 (E[sub C]-0.20 eV) and E3 (E[sub C]-0.39 eV), and one majority carrier trap labeled H1 (E[sub v]+0.32 eV) are good candidates for the material optical activity. The onset of luminescence occurs after a thermal treatment and is accompanied by a high space charge density localization at the epilayer-substrate interface. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the electrical and optical properties of the deep levels responsible for the 1.4–1.5 eV luminescence band usually observed in II–VI compounds. We compared the energy levels found by cathodoluminescence and junction spectroscopy methods for semi-insulating (CdTe:Cl and Cd0.8Zn0.2Te) and semiconducting samples (undoped CdTe). The techniques utilized were deep level transient spectroscopy (DLTS) on semiconducting samples and photoinduced current transient spectroscopy and photo-DLTS on high resistivity materials. These last two techniques are complementary and allow the determination of the trap character (donor/acceptor). Three acceptor levels are seen in the electrical transient data at Ev+0.12, 0.14, and 0.16 eV with hole capture cross sections of 2×10-16, 1×10-16, and 4×10-17 cm2, respectively. The lowest level is seen only in Cl doped material corroborating the literature optical and electron spin resonance identification of a level at Ev+0.12 eV as being a VCd+ClTe donor–acceptor pair center. All three levels may be present in the 1.4 eV luminescence band. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A correction to the article "Role of surface trap states on two-dimensional electron gas density in InAIN/AINGaN heterostructures" that was published in the 2012 issue is presented.

In order to clarify the effect of charged dislocations and surface donor states on the transport mechanisms in polar AlInN/AlN/GaN heterostructures, we have studied the current-voltage characteristics of Schottky junctions fabricated on AlInN/AlN/GaN heterostructures. The reverse-bias leakage current behaviour has been interpreted with a Poole-Frenkel emission of electrons from trap states near the metal-semiconductor junction to dislocation induced states. The variation of the Schottky barrier height as a function of the AlN layer thickness has been measured and discussed, considering the role of the surface states in the formation of the two dimensional electron gas at AlN/GaN interface. [ABSTRACT FROM AUTHOR]

The behavior of detector-grade Cd[sub 0.9]Zn[sub 0.1]Te in a radiation-hostile environment has been investigated by studying the effects on the material defective states induced by γ irradiation. The detector performance is strongly affected by the presence of charge-trapping centers which may also intervene in the material compensation properties. We have investigated by photoinduced current transient spectroscopy analyses the evolution with increasing irradiation dose of the deep levels both present in the as-grown material and induced by the ionizing radiation. A significant correlation between the material resistivity and some deep levels behavior has been observed. We have compared this trend to the results obtained from γ-irradiated CdTe:Cl to better understand the role deep traps play in the compensation process of II-VI materials. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Charge collection analyses have been carried out on Er-doped silicon to investigate the excitation and de-excitation mechanisms of the Er[sup 3+] ion related to the λ=1.54 μm luminescence. Carrier recombination and trapping at the defective states induced in the material by the presence of Er play a significant role in the excitation of the Er[sup 3+] ion and in its nonradiative decay by the energy back-transfer process. We have obtained a two-dimensional map of the lattice sites where the back-transfer process occurs, and provided experimental proof of the cooperation of two different defects in the excitation and de-excitation processes. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]