Electron Beam Induced Current Images Research Articles

Defect accumulation and strength reduction in single crystalline silicon induced by cyclic compressive stress

Internal defect accumulation process in single crystalline silicon induced by cyclic compressive stress was investigated by applying a semiconductor defect analysis technique, i.e., electron beam induced current (EBIC). A specimen with an oval trench, which was made of a p-type wafer, was designed for compressive stress concentration over 2GPa applicable without any possibility of fracture. A p–n junction and ohmic contacts were made on the specimen for the EBIC observation of the defects inside silicon. Fatigue tests with compressive stress were performed at a frequency of 20Hz ranging from 1×106 to 1×107cycles under a controlled atmosphere of 80°C and 80% relative humidity. EBIC images were successfully obtained with a scanning electron microscope showing accumulation of recombination defects which reduces the current level generated by electron beam. After the compression fatigue test, static tensile test was carried to confirm fracture strength reduction due to the damage accumulation. This is quite likely a mechanism leading to fatigue failure of silicon.

Electron beam induced current imaging of dislocations in Cd0.9Zn0.1Te crystal

Electron beam induced current (EBIC) imaging of semi-insulating nuclear radiation detector grade cadmium zinc telluride (CZT) crystal is reported in this paper. The correlation of the EBIC results with the results of defect delineating chemical etching suggests that the irregular shaped pattern in the EBIC image is due to agglomerates of dislocations in CZT crystal.

Microanalysis of post-deposition annealing of Cu(In,Ga)Se2 solar cells

The influence of selenium background pressure during post-deposition annealing of Cu(In,Ga)Se2 (CIGS) is investigated. Solar cells made from samples post-annealed with selenium showed the same solar cell parameters as references without any annealing treatment. Dark JV measurements of microscopic devices with sizes of 10μm×10μm from the sample annealed with selenium showed good agreement with the corresponding macroscopic solar cells. Samples annealed without selenium showed degradation in terms of open circuit voltage and fill factor. Electron beam induced current (EBIC) imaging for these degraded solar cells revealed patches of reduced current. Microscopic JV measurements showed that the deterioration is not limited to these patches. Cross-sectional transmission electron microscopy analysis showed phase decomposition of the CIGS absorber in areas of the patches toward the back contact. We conclude that in addition to the local phase decomposition of the CIGS leading to patches in the EBIC image the anneal in vacuum without selenium background pressure also leads to other modifications of the CIGS layer influencing the interface region on a macroscopic scale.

Fabrication and Characterization of ${\rm Cd}_{0.9}{\rm Zn}_{0.1}{\rm Te}$ Schottky Diodes for High Resolution Nuclear Radiation Detectors

Cadmium zinc telluride (CZT) Schottky diodes with very low reverse leakage current have been fabricated and characterized for high resolution gamma ray detectors. The diodes were made using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Cd}_{0.9}{\rm Zn}_{0.1}{\rm Te}$</tex></formula> detector grade crystals grown from zone refined Cd, Zn, and Te (7N) precursor materials using low temperature tellurium solvent method. Various crystallographic defects including Te-inclusions/precipitates were identified and characterized using electron beam induced current (EBIC) measurement and thermally stimulated current (TSC) spectroscopy. The EBIC images were correlated with transmission infrared (TIR) images of CZT crystals and the EBIC contrast was attributed to the nonuniformities in spatial distribution of Te inclusions. Characterization by TSC revealed shallow and deep level centers with activation energies 0.25–0.4 eV and 0.65–0.8 eV respectively, which were attributed to intrinsic defects associated with Te inclusions. Pulse height measurements were carried out using <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$^{137}{\rm Cs}$</tex></formula> (662 keV) radiation source and energy resolution of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\sim 1.51}\%$</tex></formula> full width at half maximum (FWHM) was obtained from the as-grown boule.

Competitive Role of Impurities on the Electrical Activity of as-grown Σ=13, Σ=25 and Deformed Σ=9 Grain boundaries in p-type Silicon Bi-crystals

ABSTRACTElectrical properties of grain boundaries grown by Czochralski process were studied by microwave phase shift (μW-PS) and electron beam induced current (EBIC), before and after gold diffusion at 700°C. As-grown samples had similar doping levels determined by four-point probe measurements but somewhat different oxygen concentrations, obtained by Fourier transform infrared spectroscopy (FTIR). It is shown that the increase of the grain boundary activity due to Au gathering at this planar defect can be hindered by native impurities (likely oxygen). EBIC and μW-PS techniques gave respectively electron diffusion lengths and lifetime values, both in good agreement. EBIC images on deformed Σ =9 showed that extrinsic dislocations do not activate the grain boundary at 300K.

A simultaneous observation of dislocations in 4H-SiC epilayer and n+-substrate by using electron beam induced current

With a new structure of Ni/n-SiC/n+-SiC/Al, we have achieved a simultaneous observation of the dislocations in n-SiC epilayer and n+-SiC substrate by electron beam induced current (EBIC). The EBIC images were compared to the results of a depth-controlled wet etching in KOH+Na2O2. It has been found that each type of dislocations has its own signature in EBIC images in terms of the darkness, shape and orientation of the dark contrast. By changing the accelerating voltage of the electron beam, we can also observe the depth dependent presence of each type of dislocations and where and how the dislocation conversion happens.

Dislocation Analysis in Highly Doped n-Type 4&lt;i&gt;H&lt;/i&gt;-SiC by Using Electron Beam Induced Current and KOH+Na&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt; Etching

Dislocations in highly doped n-type 4H-SiC (n+-SiC, n&gt;1019 cm-3) substrate have been studied by means of electron beam induced current (EBIC). Ni/n-SiC/n+-SiC/Al structure was fabricated in order to simultaneously observe the dislocations in n-SiC epilayer and n+-SiC substrate. We have found that dark dots in the EBIC image correspond to threading screw dislocations (TSDs) and threading edge dislocations (TEDs) with the former being relatively darker. Short dark lines along off-cut are attributed to basal plane dislocations (BPDs) in the epilayer; and the randomly oriented long dark lines are caused by the BPDs in the substrate. The classification of the dislocations by EBIC has been examined by wet etching in KOH+Na2O2.

Comparison of dislocation behavior in Si‐ and C‐face 4H‐SiC

AbstractThe dislocation behavior in C‐face 4H‐SiC homoepitaxial films was studied by using electron‐beam‐induced current (EBIC) technique and is compared with that in Si‐face ones. For the basal plane dislocations (BPDs) with the same line shape appearing in the EBIC images, the mobile partial dislocations (PDs) originated from the dissociation of such BPDs move in two opposite directions, while they move in one direction in the Si‐face samples. The difference of the PD movement between two faces is discussed (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Quantitative imaging of electronic nonuniformities in Cu(In,Ga)Se2 solar cells

Equations describing the effect of electronic nonuniformities on electroluminescence (EL) and electron beam induced current (EBIC) images are derived and tested on Cu(In,Ga)Se2 solar cells. EL images are sensitive to fluctuations in band gap and carrier collection across a cell. EBIC images are only sensitive to variations in carrier collection allowing the two nonuniformities to be separated. Equations are derived connecting the distribution of EL intensities to the open circuit voltage loss from band gap fluctuations. Experimentally, the samples studied show the largest variation in carrier collection function on a length scale of over 100 μm while the band gap varied almost linearly across the cell. The influence of shunt, series, and stack resistances on EL images is also discussed.

Grain Boundary Evaluation of Cu(In1-xGax)Se2 Solar Cells

The grain boundary (GB) properties of polycrystalline Cu(In1-x,Gax)Se2 (CIGS) have been characterized using electron beam-induced current (EBIC) measurements, electron backscatter diffraction (EBSD) patterns, and scanning spreading resistance microscopy (SSRM) measurements. The polished cross section of CIGS solar cells was evaluated by these three methods, and the surface EBIC image was obtained by scanning electron microscopy (SEM). A combination of the EBIC and EBSD techniques makes it possible to investigate the effect of the GBs on the minority carrier collection. Furthermore, the SSRM mapping enables the analysis of grain-by-grain carrier profiling by measuring the spreading resistance of CIGS solar cells. It was found from these results that the twin boundaries of CIGS grains do not contribute to carrier recombination. Furthermore, the brighter EBIC signals were observed at the GBs of CIGS, which showed that the produced electron–hole pairs easily separate from each other and that the minority carriers are repelled from the GBs. This remarkable property of the GBs is suitable for application of CIGS to solar cells.

Electrical and Optical Properties of Stacking Faults in 4H-SiC Devices

By using electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques, we characterized the electrical and optical properties of stacking faults (SFs) in 4H-SiC p + /� n junctions and compared with those in Schottky diodes. In the EBIC images, SFs penetrating the p + /� n junction

Electrical properties of pinholes in GaN:Mn epitaxial films characterized by conductive AFM

Mn doped GaN films have been studied by conductive Atomic Force Microscopy (AFM), Cathodoluminescence (CL) and Electron Beam Induced Current (EBIC). AFM measurements revealed the presence of pinholes with diameters between 130 and 380 nm. The distribution, density and size of the pinholes depend on the Mn doping concentration. AFM Leakage Current images (LC) show a defined contrast at the pinhole planes { 101 1 ̄ } in the sample with Mn concentration of 6.2×10 20 cm −3. For the sample with an Mn concentration of 1.1×10 20 cm −3, LC contrast appears around the pinholes, while no LC contrast was observed for sample with lower Mn concentration. CL measurements indicate that the samples exhibit strain related to Mn incorporation. In correlation with LC measurements, EBIC images show that pinholes are recombination sites. The combination of these techniques enabled us to analyze the Frenkel–Poole conduction in the samples and its relationship with the residual strain and the doping concentration in the films, which would exclude the mechanism of conduction through dislocations.

Electrical activities of stacking faults and partial dislocations in 4H-SiC homoepitaxial films

The electrical activities of stacking faults (SFs) and partial dislocations in 4H-SiC homoepitaxial films were investigated by using the electron-beam-induced current (EBIC) technique. The basal plane dislocation was dissociated into Si ( g) 30 ∘ and C ( g) 30 ∘ partials under electron-beam irradiation, with a SF formed in between. The SF shows bright contrast at RT and dark contrast at 50 K in EBIC images. The reasons were discussed according to the quantum-well state of SF. C ( g) 30 ∘ partial is always more electrically active than Si ( g) 30 ∘ partial at each specific accelerating voltage. The EBIC contrasts of those two partials were discussed with the number of recombination centers.

Electron-beam-induced current study of stacking faults and partial dislocations in 4H-SiC Schottky diode

Electrical properties of stacking faults and bounding partial dislocations in 4H-SiC Schottky diode were investigated by using electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques. EBIC images show that basal plane dislocation is easily dissociated into two partial dislocations [Si(g) 30° and C(g) 30° partials], with a stacking fault between them. The EBIC contrast of C(g) 30° partial is always several percent higher than that of Si(g) 30° partial. The stacking fault is brighter than the background, having the negative EBIC contrast. CL spectrum shows that a new peak (417nm) appears at stacking fault position. The origin of bright stacking fault in EBIC image is discussed according to its quantum-well state.

EBIC imaging using scanning transmission electron microscopy: experiment and analysis

The electron-beam-induced-current (EBIC) technique using scanning transmission electron microscopy (STEM) has been applied to the observation of grain boundaries in polycrystalline Si. It was shown that defects in thin regions can disappear or give bright contrast in EBIC images, but are distinct in STEM images. For the sample with a high carrier concentration, the surface effect was shown to dominate the EBIC current for a thin region. The bright contrast of the defects observed for the sample with a low carrier concentration can be attributed to the combination of the diffraction effect and the built-in electric field induced by the depletion of the entire thickness.

Electron-beam-induced current study of electrical activity of dislocations in 4H–SiC homoeptaxial film

The types of dislocations and their electrical activity in 4H–SiC homoepitaxial film were characterized by molten KOH etching and electron-beam-induced current (EBIC) method. Chemical etching has revealed that there exists four kinds of dislocations, namely basal plane, screw, edge-I and edge-II dislocations. EBIC image has indicated that they are electrically active at room temperature, and the EBIC contrasts of such dislocations are stronger in the order of basal > screw > edge-I > edge-II. Their EBIC contrasts gradually decrease by cooling, which is different from those of clean dislocations in Si, suggesting that the dislocations are accompanied with deep levels. Secondary electron images of etch pits show that the sizes for screw and edge dislocations have the sequence of screw > edge-I > edge-II, suggesting their Burgers vectors decrease in this order. The EBIC contrasts of these dislocations are discussed in relation to their Burgers vectors.

Mapping of extended defects in B-doped (001) homoepitaxial diamond films by electron-beam-induced current (EBIC) and cathodoluminescence (CL) combination technique

We have studied on a spatial distribution of extended defects with shell-shape pits in B-doped (001) homoepitaxial diamond films using electron-beam-induced current (EBIC) and cathodoluminescence (CL) combination technique. The EBIC image corresponded to the comprehensive one of band-A emission (430 nm) in CL measurements. In addition, both EBIC and CL images also corresponded to optical microscope image (Nomarski) with shell-shape pits. These experimental results indicate that the shell-shape pits are accompanied with localized electrically-active-defects originating from extended defects such as dislocation with band-A CL emission. It is suggested that extended defects such as dislocations result in the formation of shell-shape pits.

Displacement Damage Evolution in GaAs Following Electron, Proton and Silicon Ion Irradiation

We characterize radiation induced defects in n-type GaAs following electron, proton, and silicon ion irradiations using deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC) measurements. EBIC micrographs show the existence of radiation induced recombination centers following high energy proton (E MeV) or 22 MeV silicon ion irradiations, which were not observed following 1 MeV electron or 2 MeV proton irradiations. The evolution of the U-band defect as determined by DLTS seems to occur when active recombination centers are observed in the EBIC images and therefore, appears to be produced by high energy recoils probably creating defect clusters.

High-resolution scanning near-field EBIC microscopy: Application to the characterisation of a shallow ion implanted p +–n silicon junction

High-resolution electron beam induced current (EBIC) analyses were carried out on a shallow ion implanted p +–n silicon junction in a scanning electron microscope (SEM) and a scanning probe microscope (SPM) hybrid system. With this scanning near-field EBIC microscope, a sample can be conventionally imaged by SEM, its local topography investigated by SPM and high-resolution EBIC image simultaneously obtained. It is shown that the EBIC imaging capabilities of this combined instrument allows the study of p–n junctions with a resolution of about 20 nm.

Properties of Thermally Etched 4H-SiC by Chlorine-Oxygen System

By the use of Cl2-O2 thermal etching method, the etching rates of 4H-SiC were reached to about 1μm/h for Si and 40μm/h for C face at 950oC. Etch pits only appeared over 0.25-μm-etched depth on the 4H-SiC (0001) Si face. The shapes and density of etch pits are similar tendencies in the case of molten KOH etched surface. To study the relationship between thermally etched surface features and crystal defects, the planar mapping electron-beam-induced current (EBIC) technique was carried out. Almost dark areas in the EBIC image correspond to the etch pits. From the EBIC image, a shell-like pit formed by the Cl2-O2 etching on the (0001) Si face is a basal plane dislocation.