Electron Beam Induced Current Images Research Articles

Control of Ag acceptor concentration and pn-junction depth in single crystalline Mg2Si photodiodes

We have investigated the relationship between the Ag concentration and the pn-junction depth in the Mg2Si pn-junction photodiodes fabricated by thermal diffusion of the Ag acceptor. The Ag concentration profiles and pn-junction depths in the samples annealed between 400 and 550 °C were studied by secondary ion mass spectroscopy and electron beam-induced current (EBIC) images. We observed two kinds of lattice diffusions of substitutional and interstitial Ag atoms with two different diffusion coefficients, of which activation energies were ∼0.97 and 0.75 eV, respectively. The depth of pn-junction observed by EBIC images increased with annealing temperature and annealing time. On the other hand, the average Ag concentration did not depend on the annealing time but depended on the annealing temperature. These results indicate that the average Ag concentration and pn-junction depth in Mg2Si photodiodes can be controlled by annealing temperature and annealing time, respectively. This study would contribute to the development of Mg2Si pn-junction photodiodes.

EBIC Imaging of Conductive Paths Formed in Graphene Oxide as a Result of Resistive Switching

The electron-beam-induced current (EBIC) method is utilized in this work to visualize conductive channels formed in graphene oxide as a result of resistive switching. Using metal–insulator–semiconductor (MIS) structures, an increase in the electron beam induced current by a few orders of magnitude as compared with the EBIC signal in metal–insulator–metal (MIM) structures is achieved. The mechanism of the EBIC image formation related to the conductive channels is explained by the separation and collection of the e-beam generated excess carriers by rectifying barrier nanocontacts formed at the graphene oxide/Si interface during resistive switching. It is shown that the collection efficiency of the formed nanocontacts decreases with the beam energy, in agreement with the theoretical predictions for the Schottky-like nanocontacts. An important advantage of the EBIC method is demonstrated in its ability to monitor the generation and elimination of high density conductive channels even when the current–voltage measurements cannot detect and separate these processes. EBIC study of the dynamics of the conductive channel formation can help better understand the underlying physical mechanisms of their generation.

Understanding SiOx Layer Breakup in poly-Si/SiOx Passivating Contacts for Si Solar Cells Using Precisely Engineered Surface Textures

The contact resistivity of polycrystalline silicon on silicon oxide (poly-Si/SiOx) passivating contacts depends on the formation of pinholes in SiOx for thicknesses ≳1.7 nm. We fabricated these contacts on inverted pyramids and v-grooves in addition to the alkaline-textured random pyramids and planar surface morphologies. The thermal breakup of SiOx was achieved at peak annealing temperatures of 1050 and 1100 °C. SiOx breakup at 1050 °C resulted in pinholes created preferentially at vertices in the inverted pyramids, while at 1100 °C, their formation was random. The density of pinholes was greater in textured samples than in polished samples. Both chemical etching and electron beam-induced current (EBIC) were used to visualize the pinholes, the latter being sensitive only to transport pinholes in the p–n junction but not the n+-n junction. We ascribe this difference in EBIC images based on the contact polarity to differences in the collection probability of the minority carriers generated by the electron beam. Our work demonstrates that texture morphology can be exploited to enable the precise engineering of pinholes in poly-Si/SiOx passivating contacts.

Use of passive, quantitative EBIC to characterize device turn-on in 7 nm technology

A novel analysis routine is proposed that visualizes the opening of a transistor channel using Electron Beam Induced Current (EBIC) with a net zero-volt bias across a channel. nFET devices on a 7 nm technology node chip were examined in two different regions of the sample. With varying gate voltage, the device turn-on was clearly evident in the resulting EBIC image. Quantitative analysis of the resulting currents is demonstrated, and shows the channel opening up at voltages earlier than shown by I-V measurement. A mechanism for this difference is proposed. The analysis, also involving a 2-dimensional map of the space, provides opportunities for detecting regional variations in the electrical properties or performance at the high resolutions afforded with a scanning electron microscope (SEM).

Depth-dependent EBIC microscopy of radial-junction Si micropillar arrays

Recent advances in fabrication have enabled radial-junction architectures for cost-effective and high-performance optoelectronic devices. Unlike a planar PN junction, a radial-junction geometry maximizes the optical interaction in the three-dimensional (3D) structures, while effectively extracting the generated carriers via the conformal PN junction. In this paper, we report characterizations of radial PN junctions that consist of p-type Si micropillars created by deep reactive-ion etching (DRIE) and an n-type layer formed by phosphorus gas diffusion. We use electron-beam induced current (EBIC) microscopy to access the 3D junction profile from the sidewall of the pillars. Our EBIC images reveal uniform PN junctions conformally constructed on the 3D pillar array. Based on Monte-Carlo simulations and EBIC modeling, we estimate local carrier separation/collection efficiency that reflects the quality of the PN junction. We find the EBIC efficiency of the pillar array increases with the incident electron beam energy, consistent with the EBIC behaviors observed in a high-quality planar PN junction. The magnitude of the EBIC efficiency of our pillar array is about 70% at 10 kV, slightly lower than that of the planar device (≈ 81%). We suggest that this reduction could be attributed to the unpassivated pillar surface and the unintended recombination centers in the pillar cores introduced during the DRIE processes. Our results support that the depth-dependent EBIC approach is ideally suitable for evaluating PN junctions formed on micro/nanostructured semiconductors with various geometry.

STEM electron beam-induced current measurements of organic-inorganic perovskite solar cells

We describe a new approach for preparing organic-inorganic perovskite solar cells for electron beam-induced current (EBIC) measurements in plan-view geometry. This method substantially reduces sample preparation artefacts, provides good electrical contact and keeps the preparation steps as close as possible to those for real devices. Our EBIC images were acquired simultaneously with annular dark-field scanning transmission electron microscopy images using a home-made highly sensitive EBIC amplifier. High-angle annular dark-field images and energy dispersive X-ray maps were recorded from the same area immediately afterwards. This allowed the EBIC contrast to be correlated with regions containing N and a deficiency of O. The EBIC contrast was also found to be similar to secondary electron contrast recorded with a scanning electron microscope. By identifying the generation and absorption electron processes, we determine that EBIC cannot be separated from the secondary electron and absorbed currents. This means that careful analysis needs to be performed before conclusions can be made on the origin of the current measured across p-n or p-i-n junctions.

Three-Dimensional Imaging of Beam-Induced Biasing of InP/GaInP Tunnel Diodes.

Electron holographic tomography was used to obtain three-dimensional reconstructions of the morphology and electrostatic potential gradient of axial GaInP/InP nanowire tunnel diodes. Crystal growth was carried out in two opposite directions: GaInP-Zn/InP-S and InP-Sn/GaInP-Zn, using Zn as the p-type dopant in the GaInP but with changes to the n-type dopant (S or Sn) in the InP. Secondary electron and electron beam-induced current images obtained using scanning electron microscopy indicated the presence of p-n junctions in both cases and current-voltage characteristics measured via lithographic contacts showed the negative differential resistance, characteristic of band-to-band tunneling, for both diodes. Electron holographic tomography measurements confirmed a short depletion width in both cases (21 ± 3 nm) but different built-in potentials, Vbi, of 1.0 V for the p-type (Zn) to n-type (S) transition, and 0.4 V for both were lower than the expected 1.5 V for these junctions if degenerately doped. Charging induced by the electron beam was evident in phase images which showed nonlinearity in the surrounding vacuum, most severe in the case of the nanowire grounded at the p-type Au contact. We attribute their lower Vbi to asymmetric secondary electron emission, beam-induced current biasing, and poor grounding contacts.

Electronic imaging of subcritical defect accumulation in single crystal silicon under fatigue loading

High resolution electron beam induced current (EBIC) imaging technique successfully visualized defect accumulation process in single crystal silicon under compression fatigue loading at 50 °C with the relative humidity of 75%. Dark line-like defect contrast emanating from deep-etched stress concentration notch appeared in EBIC images in a scanning electron microscope, after a certain number of fatigue cycles, but they were mostly invisible with secondary electron. This line-like defect contrast eventually extended along the direction which was expected in correspondence to one of the crystal slip systems of silicon with the largest resolved shear stress. Hence it is strongly suggested that crystal slips take place in bulk silicon under repeated loading, which presumably leads to local stress concentration and further to fatigue fracture especially in case tensile stress is applied in fatigue cycles.

Study of Low Voltage Prebreakdown Sites in Multicrystalline Si Based Cells by the LBIC, EL, and EDS Methods

Breakdown sites in multicrystalline Si solar cells have been studied by reverse-bias electroluminescence, electron beam induced current (EBIC) and laser beam induced current (LBIC), and Energy Dispersive X-Ray Spectroscopy methods. In the breakdown sites revealed by EL at small reverse bias (~5 V), the enhanced aluminum and oxygen concentration is revealed. Such breakdowns can be located inside the depletion region because they are not revealed by the EBIC or LBIC methods. Breakdowns revealed by EL at larger bias correlate well with extended defects in the EBIC and LBIC images.

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Reprint of “Imaging of diamond defect sites by electron-beam-induced current”

The method of electron-beam-induced current (EBIC) was used to visualize the defect sites on a p-type (boron-doped) diamond (001) film. For this purpose, an Ag-Schottky layer (~2mm×~2mm×~50nm) was deposited on the oxygen-terminated p-type diamond (001) film and used as a source of EBIC signal. The signal current of EBIC image appeared to be as large as ~1200 times that of the incident electron-beam current and the difference range in image intensity was also large (1–1200). The observed EBIC images showed many kinds of signatures that are possible ‘killer’ defects for Schottky devices. In order to identify ‘killer’ defects in the EBIC image, an array of Ag-dots (~40×~50μm2) was deposited on an oxygen-terminated p-type diamond (001) film and I–V characteristics were measured on 53 Ag-dots. The resulting I–V characteristics showed that 21 Ag-dots reside on ‘killer’ defects. Comparison between the EBIC image and the positions of Ag-dots residing on ‘killer’ defects showed that large dark dots in EBIC image correspond to the position of ‘killer’ defects. The number density of the large dark dots (i.e., ‘killer’ defects) was ~104/cm2 in the present sample. It is suggested that a high yield Schottky-junction device may be fabricated by avoiding these ‘killer’ defects by the use of EBIC.

Imaging of diamond defect sites by electron-beam-induced current

The method of electron-beam-induced current (EBIC) was used to visualize the defect sites on a p-type (boron-doped) diamond (001) film. For this purpose, an Ag-Schottky layer (~2mm×~2mm×~50nm) was deposited on the oxygen-terminated p-type diamond (001) film and used as a source of EBIC signal. The signal current of EBIC image appeared to be as large as ~1200 times that of the incident electron-beam current and the difference range in image intensity was also large (1–1200). The observed EBIC images showed many kinds of signatures that are possible ‘killer’ defects for Schottky devices. In order to identify ‘killer’ defects in the EBIC image, an array of Ag-dots (~40×~50μm2) was deposited on an oxygen-terminated p-type diamond (001) film and I–V characteristics were measured on 53 Ag-dots. The resulting I–V characteristics showed that 21 Ag-dots reside on ‘killer’ defects. Comparison between the EBIC image and the positions of Ag-dots residing on ‘killer’ defects showed that large dark dots in EBIC image correspond to the position of ‘killer’ defects. The number density of the large dark dots (i.e., ‘killer’ defects) was ~104/cm2 in the present sample. It is suggested that a high yield Schottky-junction device may be fabricated by avoiding these ‘killer’ defects by the use of EBIC.

EBIC investigations of dislocations in ELOG GaN

AbstractDislocations in the ELOG n‐GaN films have been studied by the Electron Beam Induced Current (EBIC) method. The effect of dopant concentration and diffusion length values on the dislocation EBIC profile is revealed. It is shown that the width of dislocation image in the EBIC mode decreases with a diffusion length decrease and the dopant concentration increase. In the crystals with the submicron diffusion length the individual dislocations can be separated in the EBIC images up to the dislocation densities higher that 109cm‐2. The radius of dislocation related defect cylinder was found to increase with the dopant concentration decreasing that could be explained under an assumption that dislocations in GaN are charged. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cathodoluminescence Hyperspectral Imaging of Nitride Semiconductors: Introducing New Variables

Cathodoluminescence (CL) hyperspectral imaging—the acquisition of a full optical emission spectrum at each pixel of an image—has become firmly established as a measurement mode in scanning electron microscopy (SEM) [1]. CL is sensitive to the structural, compositional and electrical properties of a sample, and the inherent multimode nature of SEM makes it possible to combine CL with other techniques which are also sensitive to one or more of these properties. For example, combining CL hyperspectral imaging with simultaneous X-ray microanalysis has been used to probe composition variations within semiconductors [2] and minerals [3]. In this work we present recent results combining CL hyperspectral imaging with other SEM modes, and also demonstrate the benefits of introducing additional measurement parameters, such as sample applied bias and microscope chamber pressure. Structural defects are central in determining the performance of electrical and optical devices based on III-nitride semiconductors. To better understand the effect of threading dislocations on carrier recombination in such materials, we have carried out CL imaging together with electron channeling contrast imaging (ECCI), which is sensitive to the lattice distortions associated with such defects. Using this combination of techniques we have shown that both pure edge dislocations and mixed (combination of edge + screw) dislocations act as nonradiative recombination centers in GaN epilayers [4]. Since CL provides information only about radiative recombination, it needs to be coupled with other techniques to provide a fuller picture of the different carrier loss mechanisms which limit device performance, an objective we achieved by measuring CL together with electron beam induced current (EBIC). This signal originates within the junction of an electrically contacted device (measured via an external circuit) and is dependent on the total (i.e. radiative + nonradiative) recombination. By carrying out both techniques simultaneously on InxGa1-xN/GaN light-emitting diodes (LEDs), we have separated out nonradiative recombination from other loss mechanisms, such as light extraction or electrical contacting issues [5]. These CL/EBIC measurements on contacted LEDs have opened up the possibility of introducing an additional variable into CL imaging: applied bias voltage. Figure 1 shows an example of such measurements for an InGaN/GaN LED device. This capability allows the emission to be imaged under conditions closer to those of a device in normal operation. It also allows us—by imaging at several bias values—to differentiate between the drift and diffusion components of the current, and to probe the influence of the quantum-confined Stark effect in the active region of the LED. Furthermore, comparison with electroluminescence (EL) hyperspectral images yields additional information: for example, in some areas of the LED we see correlations between contrast features in EL and EBIC images which are not present in the CL, implying that they originate in the diode junction or contacts rather than in the active layer itself [5]. Finally, we have demonstrated CL hyperspectral imaging in an environmental SEM operating with a variable pressure of water vapor. This has allowed us to measure for the first time such insulating

Electrical activity of geometrically necessary dislocations in polycrystalline silicon thin films prepared by solid phase crystallization

We combine electron backscatter diffraction (EBSD) with the electron beam induced current (EBIC) technique, by carefully aligning the EBIC images with EBSD grain average misorientation (GAM) maps of selected polycrystalline thin-film regions to correlate intragrain misorientation with the film's electrical properties. Applying this method to large (>3 µm diameter) solid phase crystallization (SPC) poly-Si grains, we find that regions with low EBIC signals coincide with regions that have a high degree of misorientation. EBIC signals from the edge regions of these large grains are about 30% lower than those measured in their central regions. Combination of EBIC and GAM maps suggests that geometrically necessary dislocations (GNDs) are electrically active and present in the regions of the poly-Si grains with misorientations larger than 3° (whereby these regions are typically close to the grain boundaries). On the other hand, grains smaller than 3 µm show a homogenous spatial distribution of the electrical activity of defects. In addition, the electrical performance in the central regions of the large grains is better than that of the smaller grains. These observations suggest that the origins of the dominant recombination centres of the smaller grains are different from those of the larger grains.

A direct evidence of fatigue damage growth inside silicon MEMS structures obtained with EBIC technique

Electron beam induced current (EBIC) is a semiconductor analysis technique performed in a scanning electron microscope (SEM) or scanning transmission electron microscope (STEM). It is able to sense defects beneath the surface even invisible by SEM. This paper presents the results of a trial to observe the defect growth inside silicon MEMS structures under fatigue loading by applying EBIC technique. The tests were performed on two specimens fabricated from an n-type single crystal silicon wafer. While the test region of the specimens was repeatedly subjected to compressive stress, EBIC images were obtained to visualize damage evolution which presented by the growth of the dark region on EBIC images. It was proved that the damage is not due to the growth of oxidation layer on the surface of the specimens but due to the growth of intrinsic defects of silicon crystal. The results would be evidences to elucidate that the fatigue damages grow inside silicon MEMS structures but not in oxidation layer.

Investigations on residual strains and the cathodoluminescence and electron beam induced current signal of grain boundaries in silicon

Cathodoluminescence (CL) and electron beam induced current (EBIC) measurements were used to investigate the optical behavior and electrical activity of grain boundaries (GBs) in coarsely grained silicon. Electron backscatter diffraction (EBSD) was applied for a comprehensive characterization of the structural properties of the high angle and low angle GBs (HAGBs and LAGBs) in the sample. It was found that not only the EBIC but also the panchromatic (pan) CL contrast of Σ3 HAGBs strongly depends on the hkl-type of the boundary plane. At room temperature coherent Σ3 GBs exhibit no significant contrast in the CL or EBIC images, whereas at low temperatures the pan-CL contrast is strong. For incoherent Σ3 GBs, a strong pan-CL and EBIC contrast was observed in the entire temperature range. Only on a LAGB (misorientation angle 4.5°) CL investigations at low temperatures revealed a line with peak position at about (0.82 ± 0.01) eV, usually related to the dislocation associated D1 transition. Cross-correlation EBSD was applied to analyze the strain fields of Σ3 HAGBs as well as of the LAGB. All the components of the local strain tensors were quantitatively determined. The relationship between the extension of the strain field at the LAGB and the spatial D1 intensity distribution is discussed.

Evaluation of the performance correlated defects of metamorphic InGaAs photodetector structures through plane-view EBIC

To evaluate the performance correlated imperfection or defect features of metamorphic InGaAs photodetector structures, a scanning electron microscopy scheme including both plane-view electron beam induced current (EBIC) and secondary electron (SE) images have been used. The abilities, merits and limitations as well as some case-dependent properties of EBIC have been discussed in detail. The devices of similar structures grown on InP or GaAs substrates with quite different lattice mismatch show discriminated defect distribution patterns, prompting their distinct origins, which have been confirmed by cross-sectional transmission electron microscopy observation. Using self-developed image processing software the EBIC features of the samples are statistically analyzed, which validated the qualitative correlation between the EBIC data and device dark current. Fusing of EBIC and SE images has also been attempted to enhance the defect visibility. Results indicate that EBIC is feasible to investigate the effects of defects on the device performance not only in research work, but also for product quality monitor purposes.

J2240305 シリコン単結晶における疲労損傷の集積過程に及ぼす応力比の効果([J224-03]『マイクロ・ナノ機械の信頼性』のための材料創製・測定・解析技術 シリコンの破壊と疲労)

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 stress concentration over 2 GPa. A p-n junction and ohmic contacts were made on the specimen for the EBIC observation of the defects inside silicon. Fatigue tests were performed at a frequency of 5 Hz under a controlled atmosphere of 80 ℃ and 80 % relative humidity. There is no change on EBIC images obtained from stress ratio -∞ and stress ratio -1 fatigue test. In order to fully understand fatigue behavior of silicon, further detailed study would be essential to identify what the defects are and how they are structured with tensile stress component to grow into larger defects to determine the fatigue lifetime.