Electron Beam Induced Current Research Articles

Mapping Ferroelectric Fields Reveals the Origins of the Coercivity Distribution.

Better techniques for imaging ferroelectric polarization would aid the development of new ferroelectrics and the refinement of old ones. Here we show how scanning transmission electron microscope (STEM) electron beam-induced current (EBIC) imaging reveals ferroelectric polarization with obvious, simply interpretable contrast. Planar imaging of an entire ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2, HZO) capacitor shows an EBIC response that is linearly related to the polarization determined in situ with the positive-up, negative-down (PUND) method. The contrast is easily calibrated in MV/cm. The underlying mechanism is magnification-independent, operating equally well on micrometer-sized devices and individual nanoscale domains. Coercive-field mapping reveals that individual domains are biased "positive" and "negative", as opposed to being "easy" and "hard" to switch. The remanent background E-fields generating this bias can be isolated and mapped. Coupled with STEM's native capabilities for structural identification, STEM EBIC imaging provides a revolutionary tool for characterizing ferroelectric materials and devices.

Study on subgrain boundaries in cast monocrystalline silicon

Cast monocrystalline silicon (mono-Si), also known as quasi-mono-Si, has been recognized for its potential as a high-performance crystalline silicon material due to its low manufacturing costs and high crystal quality. This study investigated the occurrence of high-density dislocation loops in cast mono-Si, which exhibited grid-like propagation caused mostly by subgrain boundaries. The study looked at the fundamental properties of these subgrain boundaries as well as the mechanisms that allow them to propagate in a grid-like pattern within cast mono-Si. Observations revealed differences in the crystallographic misorientation of subgrain boundaries across the ingot, ranging from 1 to 3°. Electron Beam Induced Current (EBIC) tests revealed strong recombination activity at these boundaries under typical conditions. As the temperature gradually decreases from 300 K to 80 K during EBIC testing, subgrain boundaries with shallower energy states emerge, which become more apparent in photoluminescence (PL) tests conducted on Si wafers cut from different heights of the ingot.

One-Probe Nanoprobing of Power Devices and Electronic Packages

Results involving the use of a single nanoprobing contact are presented, on both a SiC planar MOSFET device, and a small system-in package. In both cases, mechanical polished samples were prepared, and then probed with a single contact. For the SiC MOSFET, the depletion zones were imaged while the samples were mounted on a 45 ° stub. Discussion of the different signals generated from Passive Voltage Contrast (PVC) and Electron Beam Induced Current (EBIC), as well as possible artifacts of sample grounding, are provided. For the package, Electron Beam Absorbed Current (EBAC) provided indication of connected features within the sample. The experiment showed the capability of measuring features across three orders of magnitude in size.

Enhancement and Broadening of the Internal Electric Field of Hole-Transport-Layer-Free Perovskite Solar Cells by Quantum Dot Interface Modification.

Hole-transport-layer-free perovskite solar cells have attracted strong interest due to their simple structure and low cost, but charge recombination is serious. Built-in electric field engineering is an intrinsic driver to facilitate charge separation transport and improve the efficiency of photovoltaic devices. However, the enhancement of the built-in electric field strength is often accompanied by the narrowing of the space charge region, which becomes a key constraint to the performance improvement of the device. Here, we propose an effective regulation method, the component engineering of quantum dots, to enhance the strength of the built-in electric field and broaden the range of space charge. By using all inorganic CsPbBrxI3-x (x = 0, 1, 2, 3) quantum dot interface modification to passivate the defects of MAPbI3 perovskite films, the regulation law of quantum dot components on the work function of perovskite films was revealed, and the mechanism of their influence on the internal electric field intensity and space charge region distribution was further clarified, thereby fundamentally solving the serious problem of charge recombination. As directly observed by electron-beam-induced current (EBIC), the introduction of CsPbBr2I quantum dots can effectively enhance the interfacial electric field intensity, widening the space charge region from 160 to 430 nm. Moreover, the efficiency of the hole-free transport layer perovskite solar cells modified by CsPbBr2I quantum dots was also significantly enhanced by 1.5 times. This is an important guideline for electric field modulation and efficiency improvement within photovoltaic devices with other simplified structures.

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.

Optoelectronic and structural characterization of trapezoidal defects in 4H-SiC epilayers and the effect on MOSFET reliability

To this day, trapezoidal defects are found in clusters and high counts in wafers representing the industry standard in terms of material quality being produced. This study sheds light on the nature, origin, behavior, and impact of this defect on device yield and reliability. Trapezoidal defects in 4H-SiC epitaxial layers were investigated by photoluminescence (PL) imaging, scanning electron microscopy (SEM), cathodoluminescence spectrum imaging (CLSI), SEM electron beam induced current (EBIC) imaging, and by transmission electron microscopy (TEM) observation. The bar-shaped stacking faults were identified by the PL and CL measurements with a peak emission wavelength of 420 and 450 nm. An optoelectronic behavioral study based on the recombination enhanced dislocation glide mechanism revealed how expanding dislocations and stacking faults interact with each other. Combining the luminescence and microscopy results, the nature of the stacking faults was identified as being a combination of Shockley-type and Frank-type stacking faults. The TEM analysis showed that these defects originate from the substrate and the stacking sequences of some of the faults were determined as (…2, 4, 2…) and (…2, 3, 2…) in the Zhdanov's notation by high-resolution TEM. The origin of this defect is speculated based on our results and previous reports. The EBIC imaging showed that the high density of SFs in these towers is a strong site of carrier recombination, which presumably has an impact on the transfer characteristics of SiC devices. Furthermore, these defects have shown to impact metal oxide semiconductor field effect transistors electrical performance via an increase in the on-state resistance depending on the coverage percentage of the tower of defects in the active area of the device.

Analysis of EBIC time-variation using 2D simulation including charge states in V Se–V Cu divacancy complex

Electron beam induced current (EBIC) measurements have been widely used to investigate charge carrier collection in Cu(In,Ga)Se2 solar cells. However, we found that this electron beam irradiation could significantly change the EBIC signal intensity during the measurement. In this study, the charge state variation of the V Se–V Cu divacancy proposed by Lany et al. was introduced into the device simulator to explain the phenomenon. In the simulation, the defects take on three different charged states, i.e. positive, neutral, and negative states, where their transitions are affected by the quasi-Fermi level position in the bandgap. The transient response of the EBIC signal was successfully explained by incorporating these complex state defects.

Electron beam-induced current imaging of ferroelectric domains and local polarization reversal in Hf0.5Zr0.5O2

Because of their full compatibility with CMOS technology, HfO2-based ferroelectrics, and especially Hf0.5Zr0.5O2 (HZO), attract a lot of attention. However, the overwhelming majority of measurement techniques provides only information about the cumulative electrical response of many domains of HZO, i.e., at the macroscopic level. So far, only piezoresponse force microscopy technique was applied to visualize distinct ferroelectric domains in HZO and to analyze the local switching behavior in the microscopic level. This work introduces the possibility of using electron beam-induced current (EBIC) technique in the scanning electron microscope to visualize the gradual polarization reversal of HZO and to obtain the local polarization dynamics. We show that although the local EBIC signal is affected by surrounding domains, studying the variations in the ferroelectric response of individual domains as well as the spread of the local stiffness and local imprint is possible by this method. Besides, we show the connection between the EBIC current and an electric field across passive non-ferroelectric layers at interfaces between HZO and metal electrodes, which opens up additional opportunities to use the EBIC technique for investigations of interface-dependent properties of HZO ferroelectrics in the future.

Mechanism for Long Photocurrent Time Constants in α-Ga2O3 UV Photodetectors

Deep centers and their influence on photocurrent spectra and transients were studied for interdigitated photoresistors on α-Ga2O3 undoped semi-insulating films grown by Halide Vapor Phase Epitaxy (HVPE) on sapphire. Characterization involving current-voltage measurements in the dark and with monochromatic illumination with photons with energies from 1.35 eV to 4.9 eV, Thermally Stimulated Current (TSC), Photoinduced Current Transients Spectroscopy (PICTS) showed the Fermi level in the dark was pinned at Ec−0.8 eV, with other prominent centers being deep acceptors with optical thresholds near 2.3 eV and 4.9 eV and deep traps with levels at Ec−0.5 eV, Ec−0.6 eV. Measurements of photocurrent transients produced by illumination with photon energies 2.3 eV and 4.9 eV and Electron Beam Induced Current (EBIC) imaging point to the high sensitivity and external quantum efficiency values being due to hole trapping enhancing the lifetime of electrons and inherently linked with the long photocurrent transients. The photocurrent transients are stretched exponents, indicating the strong contribution of the presence of centers with barriers for electron capture and/or of potential fluctuations.

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.

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.

The Physics of Twin Boundary Termination in Cu(In, Ga)Se2 Absorbers

The grain boundaries (GBs) in the absorber of a Cu(In,Ga)(S,Se)2 (CIGS) solar cell play a vital role in its efficiency and cells with polycrystalline absorbers exhibit high conversion efficiency (>23%). Previous investigations confirm that the traits of GBs in CIGS are directly connected to their composition. However, such a relationship cannot be established for twin boundaries (TBs). This is because although electron beam‐induced current (EBIC) highlights the existence of both electrically inactive and active TBs, atom probe tomography is not able to detect composition fluctuations in a very limited volume (one or two monolayers). Therefore, herein, high‐resolution scanning transmission electron microscopy at TBs to investigate their differences and correlate them with their traits is used. It is found that the electrically neutral TBs are cation–anion‐terminated boundaries, whereas the electrically beneficial TBs are cation–cation terminated. Density functional theory results show that the formation of point defects next to cation–cation TBs is more favorable compared to the case with cation–anion TBs. The presence of Cu vacancies can result in a passivated TB and a hole‐depletion region next to the cation–cation TBs, and consequently a better electron transport, as the bright contrast observed in the EBIC map suggests.

Two-dimensional hole gas formation at the κ-Ga2O3 /AlN heterojunction interface

Typically, semiconducting oxides and nitrides exhibit strong conductivity type asymmetries. In this work, we observed and interpreted the emergence of p-type conductivity at the κ-Ga2O3/AlN interface. Films of lightly Sn-doped -Ga2O3 were deposited by Halide Vapor Phase Epitaxy (HVPE) on AlN/Si templates. Capacitance-voltage (C-V), current-voltage (I-V) measurements on Ni Schottky diodes and Ti/Au Ohmic contacts deposited on the layer surface unexpectedly showed p-type-like behavior, while Electron Beam Induced Current (EBIC) images collected with different beam energies suggest that the EBIC collection occurs near the Ga2O3/AlN interface, which also implies the formation of a p-type layer at this interface. We modelled this effect, taking into account the difference in spontaneous electrical polarization of κ-Ga2O3 and AlN and this indicated a layer of two-dimensional holes can form at this interface. The possibility to detect this layer depends on the balance between the doping level and the thickness of the κ-Ga2O3.

Multiple Resistive Switching Mechanisms in Graphene Oxide-Based Resistive Memory Devices.

Among the different graphene derivatives, graphene oxide is the most intensively studied material as it exhibits reliable and repeatable resistive switching. The operative mechanisms that are responsible for resistive switching are being intensively investigated, and three models explaining the change in the resistive states have been developed. These models are grounded in the metallic-like filamentary conduction, contact resistance modification and the oxidation of/reduction in the graphene oxide bulk. In this work, using Al/GO/n-Si structures, we demonstrate that all three of these operative mechanisms can simultaneously participate in the resistive switching of graphene oxide. Multiple point-like conduction channels in the graphene oxide films were detected by the electron beam-induced current (EBIC) technique. At the same time, large areas with increased conductivity were also revealed by EBIC. An analysis of these areas by Raman spectroscopy indicates the change in the graphene oxide bulk’s resistive properties. The EBIC data along with the measurements of the capacitance–voltage characteristics provided strong evidence of the involvement of an aluminum/graphene oxide interface in the switching processes. In addition, by using Al/GO/n-Si structures, we were able to identify unique local properties of the formed conductive channels, namely the change of the charge state of a conductive channel due to the creation of negatively charged traps and/or an increase in the GO work function.

Efficient hole extraction with Eu3+-doped CsPbBr3 QD interface modification for HTL-free CH3NH3PbI3:Na perovskite solar cells

Hole transport layer free perovskite solar cells (HTL-Free PSCs) have attracted extensive attention due to their advantages of simple structure and low cost. However, due to the serious energy level mismatch caused by the direct contact between the perovskite layer and the opposite electrode, the space for improving the efficiency of HTL-Free PSCs is greatly limited. We use Eu3+ doped CsPbBr3 quantum dots (QD) to modify the interface between MAPbI3:Na layer and C electrode, and study its effect on the surface defect passivation, interface energy level arrangement and carrier transport behavior in the device. It was found that compared with the interfacial modification of CsPbBr3 QD alone, the interfacial modification of CsPbBr3:Eu QD could effectively solve the problem of energy level mismatch in HTL-Free PSCs, resulting in a remarkable improvement of conversion efficiency from 9.01 % to 12.95 %. Furthermore, electron beam induced current (EBIC) was used to prove that CsPbBr3:Eu QD interface modification significantly improved the hole collection ability. This provides an experimental basis and theoretical guidance for the optimization of the efficiency of other types of transport layer free photovoltaic devices.

An insight into optical beam induced current microscopy: Concepts and applications.

Laser scanning optical beam induced current (OBIC) microscopy has become a powerful and nondestructive alternative to other complicated methods like electron beam induced current (EBIC) microscopy, for high resolution defect analysis of electronic devices. OBIC is based on the generation of electron-hole pairs in the sample due to the raster scanning of a focused laser beam with energy equal or greater than the band gap energy and synchronized detection of resultant current profile with respect to the beam positions. OBIC is particularly suitable to localize defect sites caused by metal-semiconductor interdiffusion or electrostatic discharge (ESD). OBIC signals, thus, are capable of revealing the parameters/factors directly related to the reliability and efficiency of the electronic device under test (DUT). In this review, the basic principles of OBIC microscopy strategies and their notable applications in semiconductor device characterization are elucidated. An overview on the developments of OBIC microscopy is also presented. Specifically, the recent progresses on the following three OBIC measurement strategies have been reviewed, which include continuous laser based single photon OBIC, pulsed laser based single photon OBIC, and multiphoton OBIC microscopy for three-dimensional mapping of photocurrent response of electronic devices at high spatiotemporal resolution. Challenges and future prospects of OBIC in characterizing complex electronic devices are also discussed. HIGHLIGHTS: Characterization of electronic device quality is of paramount importance. Optical beam induced current (OBIC) microscopy offers spatially resolved mapping of local electronic properties. This review presents the principle and notable applications of OBIC microscopy.

The importance of nucleation layer for the GaN N-face purity on the annealed Al2O3 layers deposited by atomic layer deposition

This study presents the results of N-face GaN layers MOCVD grown on the 20 nm thick Al2O3 layer (ALD-AlO), as a composite of a waveguiding structure. The shortening of GaN nucleation time from 195 to 60 s revealed the appearance of Ga-face inclusions in the N-face GaN, which has improved the layers’ crystal quality. It also changed surfaces’ morphology and roughness which decreased from 17 ÷ 22 nm to 5 nm. To determine the GaN face, the samples were rinsed in a KOH solution. Time-dependent etching experiment and scanning electron microscopy inspection revealed that the etching stops at the ALD-AlO layer. After 60 min of etching, we have not detected any V-pits on the surface (on the underneath Ga-face GaN), indicating etching suppression by the ALD-AlO layer. We have performed in-plane (112¯0) X-ray diffraction (XRD) measurements, atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging, electron-beam-induced-current (EBIC) investigations.

Modeling of the electron beam induced current signal in nanowires with an axial p-n junction

A tridimensional mathematical model to calculate the electron beam induced current (EBIC) of an axial p-n nanowire junction is proposed. The effect of the electron beam and junction parameters on the distribution of charge carriers and on the collected EBIC current is reported. We demonstrate that the diffusion of charge carriers within the wire is strongly influenced by the electrical state of its lateral surface which is characterized by a parameter called surface recombination velocity (v r). When the surface recombination is weak (i.e. low v r value), the diffusion of charge carriers occurs in one dimension (1D) along the wire axis, and, in this case, the use of bulk EBIC models to extract the diffusion length (L) of charge carriers is justified. However, when the surface effects are strong (i.e. high v r values), the diffusion happens in three dimensions (3D). In this case, the EBIC profiles depend on v r value and two distinct cases can be defined. If the L is larger than the nanowire radius (r a), the EBIC profiles show a strong dependency with this parameter. This gives evidence that the recombination of generated carriers on the surface through v r is the dominant process. In this situation, a decrease of two orders of magnitude in the EBIC profiles computed with a high and a low v r value is observed in neutral regions of the junction. For the case of L smaller than r a the dependency of the EBIC profiles on the v r is weak, and the prevalent recombination mechanism is the bulk recombination process.

Electrical properties of oxygen precipitate-related defects in Czochralski silicon

Oxygen precipitate-related defects in Czochralski (Cz) silicon have been studied by electron-beam-induced current (EBIC) and deep-level transient spectroscopy (DLTS). The EBIC results present that oxygen precipitates combined with dislocations can strengthen carrier recombination. The DLTS data reveals two levels of T 1 (E v + 0.43 eV) and T 2 (E v + 0.26 eV), which are related to the oxygen precipitates and dislocations, respectively. Hydrogen can partly passivate the recombination activity of oxygen precipitates and dislocations, as well as their induced electronic states. The results are of interest for deeply understanding the electronic properties of oxygen precipitates and their induced dislocations in Cz silicon used in the semiconductor industry.

Study of zinc oxide/porous silicon interface for optoelectronic devices

A study of the interface of the ZnO/PSi heterojunction with photoluminescense (PL), cathodoluminescense (CL) and Electron Beam Induced Current (EBIC) is presented. The fabrication process of the heterostructure consisted of three steps; First, it was formed the porous silicon (PSi) layer via electrochemical synthesis, it was followed by the growth of a ZnO thin film onto the Psi layer via RF-magnetron sputtering, Finally, a thermal annealing process at 700 °C was applied on the ZnO/PSi heterojunction device. The PL analysis revealed a widening of the luminescence spectrum (in a range of 350 to 850 nm) due to the application of a thermal annealing process which favored the crystallization of the ZnO/PSi structure. Monochromatic CL images were focused on the two main peaks of the CL spectra at 385 and 436 nm, showing the emission of the ZnO and the ZnO/PSi structure, respectively. EBIC characterization determined the electronic properties of the heterojunction such as deflection zone (50 nm) as well as the hole (Lp=55nm), and electron (Ln=60nm) diffusion lengths. Furthermore, EBIC characterization served to experimentally determined the density of donor impurity atoms in the ZnO film (Nd=3.75x1014cm−3).