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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]

Investigates the defective states induced in floating zone silicon by the heavy diffusion of dopants by means of the electron beam-induced current (EBIC) method. Evolution of the electrical and morphological properties of the induced defects; Role of aluminum in the electrical activity of bulk defective states; Sample mounting geometries utilized for EBIC analyses.

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.

Abstract: Electron beam induced current (EBIC) and optical beam induced current (OBIC) methods of scanning microscopy are here described in view of their applications in the analysis of recombination and generation of carriers in devices and materials. These analyses allow to evidence peculiarities in the charge carriers transport and/or failure in devices charge collection, measuring electrical parameters in the micrometer range, such as potential distribution within the sample, diffusion length and surface recombination velocity. This review will illustrate some case studies relevant to devices and material investigations in the two geometrical configurations: normal and planar. Literature results are reviewed in order to show capabilities and effectiveness of these methods in the investigation of the defect electrical activity and resulting localized minority carrier recombination and generation in devices under operating conditions, as well as in native semiconductor materials such as silicon, gallium arsenide and gallium nitride. [Copyright &y& Elsevier]

Presently, there is a high interest in silicon-based optical devices that would render possible the development of fully silicon-based optoelectronics. Being an indirect-gap semiconductor, silicon is poorly efficient as a light emitter since radiative emission is limited by carrier recombination at non-radiative centers. One of the possible approaches to enhance the radiative emission from Si is the controlled introduction of micro-(dislocations) or nano-(nanocrystals) structures, which, providing quantum confinement of free carriers, prevent their diffusion towards non-radiative channels. Dislocations introduced in silicon by plastic deformation and Si nanocrystals embedded in the amorphous silicon matrix have been investigated by junction spectroscopy and scanning probe microscopy methods. [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 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]

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]

Abstract: Monolayer thin films with ethylene-glycol function onto gold surfaces by using thiols have been extensively investigated. They have been proposed as precursors for applications to bio-detection, where their hydrophilic character improves both specificity and sensitivity. The aim of this letter is to characterize ethylene-glycol monolayer precursors formed onto silicon chips by using silanes. The importance of the ethylene-glycol function is demonstrated by comparing with the well known 3-Aminopropyltriethoxysilane. The different nano-scale structures of the two precursor monolayers are investigated by using atomic force microscopy (AFM). Longer, wider, and deeper grooves were measured in the images acquired on 3-Aminopropyltriethoxysilane. Fluorescence investigation demonstrates that the presence of ethylene-glycol function improves target hybridization onto silicon chips, assuring highly-specific detection of DNA. [ABSTRACT FROM AUTHOR]

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]

The interaction between dislocations and impurities in silicon has been the subject of many studies over several years; nevertheless, many questions mainly relevant to the electronic states of complex defects containing impurities and dislocations are still unclear. In oxygen precipitated and plastically deformed p-type silicon deep levels were detected by deep level transient spectroscopy (DLTS). The comparison between differently treated samples allowed us to clarify the influence of oxygen on the defective states. One of the most prominent DLTS peaks usually observed in plastically deformed silicon was found to change substantially as a function of O precipitation. In particular, O precipitation increased the thermal stability of the peak, and also changed the capture and emission processes at the deep level. [ABSTRACT FROM AUTHOR]

Surface photovoltage (SPV) method for the characterization of multicrystalline silicon material for photovoltaic applications has been investigated, in view of its application as in-line characterization tool in photovoltaic industry. Minority carrier diffusion lengths have been measured by SPV on as-grown multicrystalline Si wafers as well as on emitter diffused multicrystalline Si wafers, showing the capability and the flexibility of the method. The usual assumptions for SPV data analyses have been critically discussed. The SPV values of diffusion length have been related with material characteristics and process control. [Copyright &y& Elsevier]

The performance of photovoltaic devices is greatly influenced by the surface characteristics such as surface roughness and presence of organic contaminants; therefore, their measurement is of great importance for photovoltaic industry. Moreover, these parameters should be measured by non-contact, fast methods capable of application as in-line techniques in photovoltaic industry. Surface roughness measurements and detection of organic contaminants by work-function measurements are the subject of this contribution. Monocrystalline and multicrystalline silicon wafers have been analyzed by Scanning Kelvin Probe (SKP ) in order to obtain work-function maps. These presented regions of higher work-function values correspond to organic contaminants, which are deliberately deposited on the wafer surface. In this way we have demonstrated the capability of work-function measurements for the detection of the contaminants. Moreover, unintentional organic contamination has been detected on multicrystalline Si wafers by SKP analyses. At the same time, the surface roughness has been obtained from surface topography maps. [Copyright &y& Elsevier]

Abstract. Reliable minority carrier diffusion length and surface recombination velocity values have been obtained from stationary photocurrent measurements. A modified surface photovoltage method has been used to determine diffusion lengths longer than the wafer thickness in high-purity Si, whereas the spectral variation of the photocurrent has been employed to measure the surface recombination velocity. The novelty presented in this paper is that a Schottky diode has been employed in both the methods to collect generated charged carriers. Moreover the same Schottky diode has been employed in both the methods in order to avoid any a priori assumptions on the material transport parameters. This combined application of the two methods at the same device enables the determination of highly reliable results. [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]

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]

A careful analysis of the features of the spectroscopic properties of Er-doped and undoped epitaxial silicon films grown by liquid-phase epitaxy at 950 °C in silicon-saturated indium melts shows that threading dislocations work as effective gettering sites for erbium and oxygen. The last impurity is incorporated in the epitaxial film by back diffusion from the Czochralski substrate during the growth. The photoluminescence emitted by these films appears to be related to the dislocation and is enforced by the presence of erbium-oxygen complexes. [ABSTRACT FROM AUTHOR]

In spite of the high potentiality of silicon carbide (SiC), its technology shows at the moment some limitations, due to the defects present in the crystalline structure. We have focused our analysis on commercial 4H–SiC epitaxial layers. A preliminary investigation has been performed by Optical and Scanning Electron microscopies with the aim to evidence the defect morphology on a large scale. An insight on the defect structure has been obtained by Atomic Force Microscopy, profilometer technique, Micro-Raman and Micro-Photoluminescence spectroscopies. Different types of defects such as comets, super dislocations, etch pits and so on, have been characterized finding interesting peculiarities such as different polytypes inclusions. Moreover, the influence of such defects on the SiC electrical performance has been deeply analyzed through the realization of Schottky barriers onto SiC regions including specific kinds of defects, then performing electrical characterization such as current–voltage (I–V) analysis. Deep Level Transient Spectroscopy (DLTS) yielded the energy position in the SiC gap, the concentration and the capture cross section of two center of recombination. [Copyright &y& Elsevier]

We investigate the fabrication of nanometric patterns on silicon surfaces by using the parallel-local anodic oxidation technique with soft stamps. This method yields silicon oxide nanostructures 15 nm high, namely at least five times higher than the nanostructures made with local anodic oxidation using atomic force microscopy, and thanks to the size of the stamp enables one to pattern the surface across a centimetre length scale. To implement this technique, we built a machine to bring the metallized polydimethylsiloxane stamp in contact with the silicon surface, subsequently inserted in a sealed chamber with controlled relative humidity. The oxide nanostructures are fabricated when a bias voltage of 36 V is applied between the stamp and the silicon for 2 min, with a relative humidity of 90%. The flexibility of the stamp enables a homogeneous conformal contact with the silicon surface, resulting in an excellent reproducibility of the process. Moreover, by means of two subsequent oxidations with the same stamp and just rotating the sample, we are able to fabricate complex nanostructures. Finally, a detailed study of the oxidation mechanism, also using a finite element analysis, has been performed to understand the underlying mechanism. [ABSTRACT FROM AUTHOR]