Electron Beam Induced Current Analysis Research Articles

Experimental and theoretical EBIC analysis for grain boundary and CdS/Cu (In, Ga)Se2 heterointerface in Cu (In, Ga)Se2 solar cells

AbstractThe behavior of carriers for an electron‐beam‐induced current (EBIC) evaluation is experimentally and theoretically analyzed for the polycrystalline Cu (In, Ga)Se2 (CIGS) thin‐film solar cells. The experimental EBIC signal in‐depth profiles of the CIGS layers show four features: peaks at grain boundaries (GBs), narrowed peaks near the surface, shifted peaks near the surface, and double peaks at the GBs and surface. Operating principles for CIGS solar cell devices under electron–hole pair excitation are systematically revealed utilizing a two‐dimensional theoretical EBIC simulation: (i) The EBIC peaks at the GBs are caused by a high hole barrier, including a valence band offset (ΔEV) and a band bending at the GBs; (ii) narrowing of EBIC peaks near the surface is caused by high defect densities at the GBs, grading of a conduction band minimum, and grading of acceptor concentration (Na) along with the CIGS depth direction; (iii) a shift in EBIC peaks near the surface is caused by high donor‐like defect densities at the surface; (iv) double peaks at the GBs and surface are caused by a thick surface layer (SL) with the ΔEV and the hole barrier at GBs. These findings of the EBIC analysis will help to comprehensively understand the complex polycrystalline CIGS carrier transport mechanism in realizing the highest‐efficiency CIGS solar cells.

Toward High-Efficiency Scalable GaAs and GaAsxP1-X Photoelectrodes Grown Via Vapor Transport from a Solid Source

GaAs and related III-V semiconductors are attractive materials for high-efficiency water-splitting photoelectrodes, but their implementation is limited in part by the high cost of metal-organic chemical vapor deposition, which employs toxic and pyrophoric gas-phase precursors. We report the study of GaAs and GaAsxP1-x grown by close-space vapor transport (CSVT), which uses solid GaAs as a source and water vapor as a transport agent as an alternative low-cost technique for depositing GaAs films and microstructures. The free carrier type and density (1016 – 1019 cm-3) in the films was adjusted by addition of Te or Zn powder to the GaAs source powder. The electronic properties of films grown under a variety of conditions are evaluated and correlated with the film structure and impurity content. We show using photoelectrochemical and electron beam-induced current analyses that the minority carrier diffusion lengths of the n- and p-GaAs epitaxial films reached 2-3 µm and 5-7 µm, respectively. Hall mobilities approach those achieved for GaAs grown by metal organic chemical vapor deposition, 500 - 4,000 cm2 V-1 s-1 for n-GaAs and 50-240 cm2 V-1 s-1 for p-GaAs depending on carrier concentration. Related efforts to control carrier collection through surface texture as well as the growth of GaAs on Si as an inexpensive high-efficiency tandem photoelectrode will also be discussed. Ritenour, A. J.; Boucher, J. W.; DeLancey, R.; Greenaway, A. L.; Aloni, S.; Boettcher, S. W. Doping and Electronic Properties of GaAs Grown by Close-Spaced Vapor Transport from Powder Sources for Scalable III-V Photovoltaics. Energy Environ. Sci. Accepted, 2014. Ritenour, A. J.; Levinrad, S.; Bradley, C.; Cramer, R. C.; Boettcher, S. W. Electrochemical Nanostructuring of n-GaAs Photoanodes. ACS Nano, 2013, 7 (8), 6840–6849. Ritenour, A. J.; Cramer, R. C.; Levinrad, S.; Boettcher, S. W. Efficient n-GaAs Photoelectrodes Grown by Close-Spaced Vapor Transport from a Solid Source. ACS Appl. Mater. Interfaces 2012, 4, 69-73.

Quantitative determination of electric field strengths within dynamically operated devices using EBIC analysis in the SEM

Although electron beam-induced current (EBIC) technique was invented in the seventies, it is still a powerful technique for failure analysis and reliability investigations of modern materials and devices. Time-resolved and stroboscopic microanalyses using sampling Fourier components decomposed by modulated charge carrier excitation are introduced. Quantitative determination of electric field strengths within dynamically operated devices in the scanning electron microscope (SEM) will be demonstrated. This technique allows investigations of diffusion and drift processes and of variations of electric field distributions inside active devices.

Long-term reliability of silicon bipolar transistors subjected to low constraints

We present in this study the effect of electrical ageing on silicon (Si) NPN bipolar transistors. This study is based on a sample of half-hundred components, which have been fabricated in the early 1980s, which represents an exceptional experience feedback. By means of static and low frequency noise measurements, which are used as diagnostic tools for reliability assessment, we have noticed a good accordance with a physical model based on an oxide charge modulation. We have also used emission microscopy and electron beam-induced current analysis in order to visualize and to localize the defects in the structure. These have been located in the spacer oxide at the periphery of the base-emitter junction.

Electrical Characterization of Ion-Implanted n<sup>+</sup>/p 6H-SiC Diodes

In this work the electrical characterisation of ion implanted n + /p planar SiC diodes is presented. When a silicon dioxide film passivated the surface, the presence of electrically conductive paths among the cathodes of the diodes were detected. Surface morphology investigations and Electron Beam Induced Current (EBIC) analyses allowed us to correlate the conductive paths with grooves induced on the SiC surface by the post implantation annealing. After removing the surface silicon oxide film, the diodes were electrically isolated and their currentvoltage (I-V) and capacitance voltage (C-V) characteristics were evaluated. At 10 V the best diodes had a leakage current density value lower than 5x10 -11 A/cm 2 while some other diodes showed a value higher than 1x10 -7 A/cm 2 . EBIC analyses pointed out a similar defect situation in the base region independently of the leakage current value. So no evidence of a correlation between the presence of electrically active defects and the leakage current behavior was found. The maximum measured value of the breakdown voltage (VB) was of about 280 V. For the best diodes, the ideality factor was 2.1 at low voltages and then reached 1.4 increasing the forward bias, but never got 1 before the series resistance dominated the characteristic. Base and emitter doping concentrations calculated using C-V measurements were in agreement with the expected values.

EBIC and XTEM Analysis of High Voltage SMOS Reliability Failures

AbstractMicroscopists are faced with many challenges in locating and examining failure sites in the ever-shrinking semiconductor device. The site must be located using electrical characterization techniques like electron beam induced current (EBIC), photo emission microscopy (PEM) or liquid crystal (LC) and then cross-sectioned with a focused ion beam (FIB). Both PEM and LC require the semiconductor circuit to be running near operating conditions which has been observed to locally melt the area of interest, frequently destroying evidence of the failure mechanism. In contrast, EBIC typically can be accomplished at low or no applied voltage eliminating further damage to the circuit. EBIC has been applied to locate leakage sites in high voltage metal oxide semiconductor (MOS) electro static discharge (ESD) reliability failures. In addition to a brief revisit of the basic principles of EBIC and describing a technique to successfully cross section ‘hot spots’ for transmission electron microscopy (TEM) observation, focus will be placed on a case study of the reliability testing failure analysis of ESD power transistors using EBIC, SEM, focused ion beam (FIB), and XTEM.

Carrier Trapping and Recombination at Point Defects and Dislocations in MOCVD n-GaN

We present the results of an approach that allows the analysis of grown-in defects in n-GaN grown by metal organic vapor phase epitaxy by relating the presence of various structural defects to the concentration and properties of distinct deep levels. Transmission electron microscopy and electron beam induced current (EBIC) microscopy together with post-growth hydrogenation are used to determine the threading dislocation density (TDD) and observe their local electrical activity. In conjunction, deep level optical and transient spectroscopies (DLOS and DLTS, respectively) are used to detect deep levels, determine their concentration and analyze their carrier trapping kinetics for these films. The comparison of EBIC analysis with trap spectra prior and after hydrogenation establishes a strong correlation between two specific levels, at Ec — Et = 0.58 and 1.35 eV, and recombination centers distributed in the field of the GaN films. Further, EBIC analysis shows that, independent of hydrogenation, TDs behave as strong recombination centers, and indicates that there must be a deep level associated with these regions. A level observed at Ec — 2.64/Ev + 0.87 eV is a good candidate to account for the electrical activity of the TDs because it captures both electrons and holes, which is characteristic of recombination centers. This is supported by DLTS analysis of the trapping kinetics for this level that reveals a behavior characteristic of a linear arrangement of point defects likely found along the TDs.

Spatial distribution of deep level traps in GaNAs crystals

GaNAs crystals grown by the metalorganic vapor-phase epitaxy (MOVPE) method are characterized by plane-view electron beam induced current (EBIC) and deep-level transient spectroscopy (DLTS). Localized deep-level traps with a diameter of 3–5 μm are clearly observed from EBIC analysis. The DLTS analysis shows that the dominant deep-level traps have energy levels of E v+0.58 eV and E c−0.72 eV. Such deep level traps are eliminated by annealing at 700°C. From our analysis, the change in the spatial distribution of deep-level traps due to annealing correlates strongly with the change in the PL intensity, indicating that observed deep-level traps are one of the major factors which degrade the optical properties of the GaNAs crystals. In addition to these localized traps, the inhomogeneity of minority diffusion length is also detected by EBIC.

The remote electron beam-induced current analysis of grain boundaries in semiconducting and semi-insulating materials.

When no charge collecting p-n junction or Schottky barrier is present in the specimen, but two contacts are applied, conductive mode scanning electron microscope (SEM) observations known as remote electron beam-induced current (REBIC) can be made. It was described as "remote" EBIC because the contacts to the specimen can lie at macroscopic distances from the beam impact point. In recent years, REBIC has been found to be useful not only for studies of grain boundaries in semiconducting silicon and germanium, but also in semi-insulating materials such as the wider bandgap II-VI compounds and electroceramic materials like varistor ZnO and positive temperature coefficient resistor (PTCR) BaTiO3. The principles of this method are outlined. Accounts are given of the five forms of charge collection and resistive contrast that appear at grain boundaries (GBs) in REBIC micrographs. These are (1) terraced contrast due to high resistivity boundary layers, (2) peak and trough (PAT) contrast due to charge on the boundary, (3) reversible contrast seen only under external voltage bias due to the beta-conductive effect in a low conductivity boundary layer, (4) dark contrast due to enhanced recombination, and (5) bright contrast apparently due to reduced recombination. For comparison, the results of the extensive EBIC studies of GBs in Si and Ge are first outlined and then the results of recent REBIC grain boundary studies in both semiconducting and semi-insulating materials are reviewed.

Characterization of GaP pyramidal textured p– n junctions

GaP pyramidal textured p– n junction (PTJ) diodes prepared using liquid phase epitaxy growth were characterized using field-emission scanning electron microscopy (FE-SEM), electron beam induced current (EBIC), I– V and C– V measurements. FE-SEM images of cross-sectional surfaces of the PTJ diode showed sharp textured p– n junction interfaces and flat surfaces. EBIC analysis proved that the current collection follows the textured junction profiles. I– V characteristics of GaP PTJ and flat junction (FJ) diodes prepared under the same conditions both demonstrated very low leakage current, indicating that the formation of PTJ does not introduce extra structure-related defects. Analysis of C– V measurement indicated a 25% increase in junction interface area for the PTJ compared with the flat junction devices, in agreement with the estimated area increase of the textured surfaces. The α particle irradiation response of a PTJ device showed an 88% increase in short circuit current as compared with that of a FJ counterpart.

The effect of beamwidth on the analysis of electron-beam-induced current line scans

A real electron beam has finite width, which has been almost universally ignored in electron-beam-induced current (EBIC) theories. Obvious examples are point-source-based EBIC analyses, which neglect both the finite volume of electron–hole carriers generated by an energetic electron beam of negligible width and the beamwidth when it is no longer negligible. Gaussian source-based analyses are more realistic but the beamwidth has not been included, partly because the generation volume is much larger than the beamwidth, but this is not always the case. In this article Donolato’s Gaussian source-based EBIC equation is generalized to include the beamwidth of a Gaussian beam. This generalized equation is then used to study three problems: (1) the effect of beamwidth on EBIC line scans and on effective diffusion lengths and the results are applied to the analysis of the EBIC data of Dixon, Williams, Das, and Webb; (2) unresolved questions raised by others concerning the applicability of the Watanabe–Actor–Gatos method to real EBIC data to evaluate surface recombination velocity; (3) the effect of beamwidth on the methods proposed recently by the author to determine the surface recombination velocity and to discriminate between the Everhart–Hoff and Kanaya–Okayama ranges which is the correct one to use for analyzing EBIC line scans.

Electron-beam induced current determination of shallow junction depth

Electron-beam induced current (EBIC) was investigated as a possible method of determining shallow junction depth. Molecular-beam epitaxy Si n+/p junctions 200–1800 Å deep were explored with both cross-sectional and plan-view EBIC geometry. Cross-sectional EBIC analysis proves to be accurate and reproducible in determining the center of the depletion region for the deep junctions (1800 Å) when using a conventional scanning electron microscopy (SEM) with a LaB6 filament. Confidence in the location of shallow junctions decreases due to sample drift and the resolution limits of the SEM and EBIC techniques. In the plan-view geometry, in which the EBIC current is recorded as a function of electron beam energy, we can distinguish between shallow junctions with greater precision than deeper junctions. Collection efficiency versus electron-beam energy curves reveal junction depth through shifts in both peak position and height. The collection efficiency versus electron-beam energy curves were modeled assuming the n+ layer is equivalent to a Schottky barrier. The model agrees well with peak shifts, but carrier loss due to the n+ layer must be implemented to sufficiently describe the change in peak height.

Electron and ion beam induced current in MOS 1C analysis

The electron beam induced current (EBIC) mode of the scanning electron microscope as well as the ion beam induced current (IBIC) mode of nuclear microprobes have been used for metal oxide silicon (MOS) IC observation. Two types of specimens have been investigated: standard n-channel MOS ICs and CMOS ICs. The techniques give useful information about the doped regions (such as source and drain regions of MOS transistors), as well as about some important dimensions (such as the channel length of a MOS transistor). Additional information from IBIC images of individual MOS transistors, not obtainable in the EBIC analysis only, was detected. The information gathered in the EBIC and IBIC analysis was found to depend on the experimental conditions. The sensitivity of the specimen to ion beam damage was found to be less than expected; no significant change in image quality was discernable after an observation of over 1 h.

Digital electron beam induced current imaging: Apparatus and analysis

The electron beam induced current (EBIC) method is a well known technique for studying charge carrier recombination at extended defects in semiconductors. In this work a new electron beam induced current apparatus is described. It employs computer automated measurement and control equipment to acquire high resolution beam induced current images using a conventional secondary electron microscope. The electron beam induced current images typically contain a matrix of 512×512 digitally measured points. They can be displayed on a workstation monitor and imaging processing can be performed. The increased current resolution of the apparatus necessitated the modification of traditional quantitative EBIC analysis methods. The modified quantitative analysis method is presented and applied to the problem of precipitates contained in a Czochralski silicon solar cell. It results in a characterization of the amount of charge carrier recombination at the defects and a calculation of the depth of the defects below the sample surface.

Trends in diffusion-length measurements in the original and dielectrically isolated-tub pi -silicon as a function of processing

An EBIC (electron-beam-induced current) analysis of diffusion length and, hence, lifetime as a function of processing history of dielectrically isolated (DI) tubs and the original pi -silicon was performed with a two-dimensional computer simulation. The simulation accounts for a pear-shaped excitation volume for the surface recombination at two sidewalls and the top and bottom surfaces and for excess electron diffusion to a planar junction with a planar back contact. The different processing histories include those which have undergone minimal high-temperature heat treatment (prior to and after DI-tub formation), a phosphorus getter, and a denuded-zone treatment. It is found that the DI-tub formation process results in a slight improvement in the diffusion length, but that the denuded-zero treatment results in a significant (ten times the diffusion length in untreated material) improvement in both the original and DI-tub pi -silicon.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>