Electron Beam Induced Current Technique Research Articles

Use of Electron Beam-Induced Current Technique to Characterize Transport Properties of Narrow-Gap-Energy Materials for IR Detection

AbstractThe electron beam-induced current technique (EBIC) developed at CEA-Leti has been a valuable tool for studying the transport properties of minority carriers in HdCdTe. Indeed, previous work has demonstrated the use of this technique for estimating diffusion length from the exponential decay of EBIC as a function of junction distance, as well as direct measurement of the modulation transfer function (MTF) of small pixel pitch diodes. In this work, a modulated electron beam and a lock-in amplifier are used to measure the variation in current and phase shift with the scan distance to the junction. This work is focused on the estimation of the minority carrier lifetime from the linear evolution of the phase shift as a function of junction distance.

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.

Impact of Electron Injection and Temperature on Minority Carrier Transport in Alpha-Irradiated ß-Ga2O3 Schottky Rectifiers

The effect of electron injection on minority carrier transport in Si-doped β-Ga2O3 Schottky rectifiers with 18 MeV alpha particle exposure (fluences of 1012–1013 cm−2) was studied from room temperature to 120°C. Electron Beam-Induced Current technique in-situ in Scanning Electron Microscope was used to find the diffusion length of holes as a function of duration of electron injection and temperature for alpha-particle irradiated rectifiers and compared with non-irradiated reference devices. The activation energy for electron injection-induced effect on diffusion length for the alpha-particle irradiated sample was determined to be ∼ 49 meV as compared to ∼74 meV for the reference sample. The decrease in activation energy of the electron injection effect on diffusion length for irradiated sample is attributed to radiation-induced generation of additional shallow recombination centers closer to the conduction band edge.

Electron injection-induced effects in Si-doped β-Ga2O3

The impact of electron injection, using 10 keV beam of a Scanning Electron Microscope, on minority carrier transport in Si-doped β-Ga2O3 was studied for temperatures ranging from room to 120°C. In-situ Electron Beam-Induced Current technique was employed to determine the diffusion length of minority holes as a function of temperature and duration of electron injection. The experiments revealed a pronounced elongation of hole diffusion length with increasing duration of injection. The activation energy, associated with the electron injection-induced elongation of the diffusion length, was determined at ∼ 74 meV and matches the previous independent studies. It was additionally discovered that an increase of the diffusion length in the regions affected by electron injection is accompanied by a simultaneous decrease of cathodoluminescence intensity. Both effects were attributed to increasing non-equilibrium hole lifetime in the valence band of β-Ga2O3 semiconductor.

Impact of temperature and gamma radiation on electron diffusion length and mobility in p-type InAs/GaSb superlattices

The minority carrier diffusion length was directly measured by the variable-temperature Electron Beam-Induced Current technique in InAs/GaSb type-II strain-layer-superlattice infrared-detector structures. The Molecular Beam Epitaxy-grown midwave infrared superlattices comprised 10 monolayers of InAs and 10 monolayers of GaSb to give a total absorber thickness of 4 μm. The diffusion length of minority electrons in the p-type absorber region of the p-type/barrier/n-type structure was found to increase from 1.08 to 2.24 μm with a thermal activation energy of 13.1 meV for temperatures ranging from 77 to 273 K. These lengths significantly exceed the individual 10-monolayer thicknesses of the InAs and GaSb, possibly indicating a low impact of interface scattering on the minority carrier diffusion length. The corresponding minority electron mobility varied from 48 to 65 cm2/V s. An absorbed gamma irradiation dose of 500 Gy halved the minority carrier diffusion length and increased the thermal activation energy to 18.6 meV, due to creation of radiation-induced defect recombination centers.

Catastrophic Optical Bulk Damage – A New Failure Mode in High-Power InGaAs-AlGaAs Strained Quantum Well Lasers

ABSTRACTHigh-power single-mode (SM) and multi-mode (MM) InGaAs-AlGaAs strained quantum well (QW) lasers with emission wavelengths of 910 − 980 nm are extensively used in various fiber lasers and amplifiers for both telecom and defense applications. In particular, underseas and satellite communication systems require stringent reliability from these lasers. Since these lasers predominantly fail by catastrophic and sudden degradation due to COD, it is crucial especially for space satellite applications to investigate reliability, failure modes, and degradation mechanisms of these lasers. Catastrophic optical mirror damage (COMD) was known to be the only failure mode until our group reported a new failure mode in MM and SM InGaAs-AlGaAs strained QW lasers in 2009 and 2016, respectively. Our group reported that bulk failure due to catastrophic optical bulk damage (COBD) has become the dominant failure mode of both SM and MM lasers. Since there have been limited reports on COBD compared to COMD, the intent of this paper is to introduce our studies on COBD that have spanned the last decade. We investigated reliability, failure modes, and degradation processes in SM and MM InGaAs-AlGaAs strained QW lasers by performing short-term step-stress tests and long-term accelerated life-tests as well as failure mode analyses using various nondestructive and destructive micro-analytical techniques including electron beam induced current (EBIC), time-resolved electroluminescence (EL), deep level transient spectroscopy (DLTS), focused ion beam (FIB), and high-resolution TEM. EBIC and EL techniques were employed to study dark line defects generated in degraded lasers stressed under different test conditions. Time-resolved EL techniques were employed to study initiation and progressions of dark spots and dark lines in real time as lasers were aged. DLTS techniques were employed to study electron traps in both pristine and degraded lasers. Lastly, FIB and high-resolution TEM were employed to prepare cross sectional and plan view TEM specimens to study DLD areas in post-aged lasers. We also report our current understanding on degradation mechanisms responsible for COBD in both SM and MM lasers.

Effect of 1.5 MeV electron irradiation on β-Ga2O3 carrier lifetime and diffusion length

The influence of 1.5 MeV electron irradiation on minority transport properties of Si doped β-Ga2O3 vertical Schottky rectifiers was observed for fluences up to 1.43 × 1016 cm−2. The Electron Beam-Induced Current technique was used to determine the minority hole diffusion length as a function of temperature for each irradiation dose. This revealed activation energies related to shallow donors at 40.9 meV and radiation-induced defects with energies at 18.1 and 13.6 meV. Time-resolved cathodoluminescence measurements showed an ultrafast 210 ps decay lifetime and reduction in carrier lifetime with increased irradiation.

Modified electron beam induced current technique for in(Ga)As/InAsSb superlattice infrared detectors

Electron beam induced current (EBIC) measurements provide a powerful tool for characterizing semiconductor based materials and devices. By measuring the current generated by the electron beam of a scanning electron microscope (SEM), EBIC allows us to extract the minority carrier diffusion length (L) and the surface recombination velocity to diffusivity ratio (S/D) of a material. When combined with information on minority carrier lifetime (τ), for instance from time-resolved photoluminescence measurements, the minority carrier mobility of the material can be extracted. However, the EBIC technique relies heavily on the accurate modeling of the carrier generation and collection process. Traditionally, this was achieved using a combination of empirical analytical expressions (and later Monte Carlo simulations) for carrier generation and analytical diffusion/recombination expressions for carrier collection. This approach introduces significant uncertainties into the extracted material parameters. Here, we present a numerical approach to EBIC modeling which improves the spatial resolution of our model, while also retaining information regarding the relative EBIC signal as a function of incident beam energies and currents. We apply this technique to investigate the temperature dependent minority carrier mobility of InAs/InAsSb and InGaAs/InAsSb strained layer superlattice infrared detectors and compare our results to the values obtained using external quantum efficiency measurements of the same samples. Our approach not only allows for an improvement in the uncertainty of the extracted material parameters, but also offers insight into the material and device behavior as a function of nonequilibrium carrier concentration. The technique presented here offers potentially improved characterization of not only infrared detectors, but a range of semiconductor-based devices.

Microscopic Analysis of Inherent Void Passivation in Perovskite Solar Cells

The presence of voids in perovskite solar cells influences the efficiency because of accelerated charge recombination. The induced electric field near voids due to band bending attracts photogenerated electrons and holes toward the voids, leading to carrier recombination. However, if the surface of the voids is coated by materials with a band gap higher than that of the perovskite layer, the strong electric field induced near the voids in the opposite way prevents carriers from recombining. We identified voids in the perovskite layer by using an electron beam-induced current technique and found the influence of field-assisted passivation by organic materials on the efficiency of the solar cell.

On a better estimate of the charge collection function in CdTe solar cells: Al2O3 enhanced electron beam induced current measurements

The electron beam induced current technique (EBIC) was applied to substrate configuration CdTe solar cells in order to estimate the current density loss due to incomplete charge collection. In order to improve the measurement accuracy a thin Al2O3 layer was deposited on the device cross section by atomic layer deposition. Absorption coefficients and internal quantum efficiency (IQE) of the CdTe absorber layer and device were derived from reflection and transmission measurements. An estimate for the IQE was then calculated from EBIC measurements for devices with and without Al2O3 coating. The comparison of this estimate to the measured IQE shows that the Al2O3 enhances the accuracy of the EBIC measurements. Details of the EBIC profile and an estimate for the residual IQE i.e. current loss are discussed. Finally, a tentative explanation for the improved accuracy of the Al2O3 enhanced EBIC measurement is presented.

Comparative study of different metals for Schottky barrier diamond betavoltaic power converter by EBIC technique

In order to improve the performance of betavoltaic converters based on synthetic IIb diamond Schottky structure, we performed comparative studies of converters with Al, Hf, Pt, and Au metals forming the Schottky barrier by means of the electron beam‐induced current (EBIC) method. Nearly full collection of generated electron–hole pairs was found for all fabricated structures. The aluminum contact showed the lowest energy loses due to negligible electrons absorption and backscattering. But the conversion efficiency of the Al‐contact Schottky diode was just about 2% because of its low open‐circuit voltage. We attributed the reduction of the Schottky barrier height to local defects observed by EBIC. The diamond cells with platinum contact showed the best performance of about 6% with a relatively high open‐circuit voltage >1 V and a good incident beam multiplication factor. Thereby platinum forms the most stable and effective Schottky barrier contact for diamond betavoltaic cells.

EBIC and LBIC studies of the properties of extended defects in plastically deformed silicon

The results of comparative experimental studies of one- and two-dimensional defects in plastically deformed silicon by the electron-beam-induced current (EBIC) and light-beam-induced current (LBIC) techniques are reported. It is shown that the contrast of two-dimensional defects (dislocation trails) in the LBIC method can by much more pronounced than that in the EBIC technique, which is in good agreement with the results of calculations. The higher sensitivity of the LBIC technique is mainly due to deeper penetration of the optical beam into the material in comparison to the penetration of the electron beam of a scanning electron microscope.

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.

Direct Electronic Property Imaging of a Nanocrystal-Based Photovoltaic Device by Electron Beam-Induced Current via Scanning Electron Microscopy.

Scanning electron microscopy (SEM) electron beam-induced current (EBIC) studies were performed on the cross-section of a nanocrystal-based hybrid bulk heterojunction photovoltaic device. Using these techniques, the short circuit carrier collection efficiencies are mapped with a better than 100 nm resolution. Electronically deficient and proficient regions within the photoactive layer are determined. The results show that only a fraction of the CdSe nanorod:P3HT layer (P3HT = poly-3(hexylthiophene)) at the Al cathode interface shows primary collection of charged carriers, in which the photoactivity decreases exponentially away from the interface. The recombination losses of the photoactive layer away from this interface prove that the limiting factor of the device is the inability for electrons to percolate between nanoparticles; to alleviate this problem, an interparticle network that conducts the electrons from one nanorod to the next must be established. Furthermore, the EBIC technique applied to the nanocrystalline device used in this study is the first measurement of its kind and can be applied toward other similar architectures.

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.

Measurement of Beta Particles Induced Electron-Hole Pairs Recombination in Depletion Region of GaAs PN Junction

PN junctions and schottky diodes are widely employed as electron-hole pair collectors in electron beam induced current (EBIC) techniques and betavoltaic batteries, in which the recombination in depletion regions is ignored. We measured the beta particles induced electron-hole pairs recombination in the depletion region of a GaAs P+PN+ junction, based on comparisons between measured short currents and ideal values. The results show that only 20% electron-hole pairs in the depletion can be collected, causing the short current. This indicates an electron-hole pair diffusion length of 0.2μm in the depletion region. Hence, it is necessary to evaluate the recombination in the EBIC techniques and betavoltaic design.

Minority carrier transport in p-ZnO nanowires

In this work, we explore the minority carrier diffusion length in zinc oxide nanowires, using the electron beam-induced current technique. Systematic measurements as a function of temperature were performed on p-type, Sb-doped ZnO film, containing a 4 μm thick nanowire layer. The minority carrier diffusion length exhibits a thermally activated increase with the energy of 74±5 meV. Electron beam irradiation also causes the diffusion length increase with the activation energy of 247±10 meV, likely related to SbZn–2VZn acceptor-complex.

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.

The detection of electron-beam-induced current in junctionless semiconductor

The scanning electron microscope is a versatile tool and its electron beam techniques have been widely used in semiconductor material and device characterizations. One of these electron beam techniques is the electron-beam-induced current (EBIC) technique. One of the limitations of the conventional EBIC technique is that it requires charge collecting junctions which may not be readily available in junctionless samples such as bare substrates unless some special sample preparation procedure such as the fabrication of a diffused junction is done on the junctionless sample. In this paper, the technique of detecting EBIC current in junctionless samples with the use of a two-point probe is presented. It is found that the EBIC current is independent from its physical parameter when the sample thickness is greater than 4L; the width to the right of probe 2 and the width to the left of probe 1 are greater than 2L and 8L, respectively. The parameters affecting this technique of detecting the EBIC current such as the depth of the generation volume, probe spacing, and the applied bias are also discussed in this paper. A commercially available two-dimensional device simulator was used to verify this technique.

Correlation between Thermal Oxide Breakdown and Defects in n-Type 4<i>H</i>-SiC Epitaxial Wafers

In this work, the correlation between thermal oxide breakdown and dislocations in n-type 4H-SiC epitaxial wafers has been investigated. Thermal oxide was grown by oxidation in N2O at 1250°C followed by annealing in NO atmosphere. The electron beam induced current (EBIC) technique was employed to find correlations between the electrically active defects in epitaxial layers and regions where the oxide breakdowns occurred. The test measurements of leakage currents in MOS devices were performed in order to correlate the leakage currents with number of defects in the epi-layer detected by EBIC technique.