Electron Beam Induced Current Research Articles

What Limits the Open-Circuit Voltage of Bromide Perovskite-Based Solar Cells?

High band gap Pb bromide perovskite (APbBr3)-based solar cells, where A is a mixture of formamidinium, methylammonium, and Cs, show significantly higher, relative, VOC losses than their iodide analogs. Using photoluminescence-, quantum efficiency-, and surface photovoltage-spectroscopy measurements, we show the absence of any significant electronically active tail states within the bulk of the (FA0.85MA0.1Cs0.05)PbBr3 absorber. All methods confirm that EG = 2.28 eV for this halide perovskite, HaP. Contact potential difference measurements for this HaP, on different substrates, reveal a Z-shape dependence between the substrate work functions and that of the HaP, deposited on it, indicating that the HaP is relatively low doped and that its Fermi level is affected by the substrate onto which it is deposited. We confirm results from electron beam-induced current (EBIC) and other measurements that most voltage loss of cells, made with these HaP films, is at the HaP/selective-contact interface, specifically the...

From EBIC images to qualitative minority carrier diffusion length maps

A novel method is presented with the aim to perform minority carrier diffusion length map on cross-sectional samples. The method is based on one Electron-Beam Induced Current (EBIC) acquisition and on the analyze of the EBIC signal slope variation on each scanned points. This method is applied on a pinned photodiode array realized on a low doped silicon epitaxy, and the electron diffusion length map which is extracted is in good accordance with our expectation taking into account the doping distribution of the device. A TCAD simulation also confirms quantitatively the measured diffusion length map. Advantages and drawbacks of this method are discussed in this study.

Axial p‐n junction design and characterization for InP nanowire array solar cells

AbstractIn this work, InP nanowire (NW) array solar cells with different axial p‐i‐n junction designs were investigated. The optical properties of the different NW structures were characterized through a series of microphotoluminescence measurements to extract important material parameters such as minority carrier lifetimes and internal quantum efficiencies. A glancing angle sputtering deposition technique has been developed to enable a direct visualization of the p‐n junctions in the vertical array of InP NW solar cells (NWSCs) using electron beam‐induced current (EBIC) technique. Based on EBIC and electrical simulation, it is found that the background doping in NWSC significantly affects the junction position. By modifying the junction design, the width and position of the p‐n junction can be varied effectively. By employing a p‐p−‐n structure, a high junction position (>1 μm from the substrate) and wide depletion width have been achieved as confirmed by EBIC measurement. Moreover, the NW growth substrate does not show any influence on the device behavior due to the fully decoupled junction position, indicating a promising structural design for future development of high‐performance, low‐cost flexible NW devices.

Axial EBIC oscillations at core/shell GaAs/Fe nanowire contacts

Electron beam induced current (EBIC) measurements were carried out in situ in the scanning electron microscope on free-standing GaAs/Fe core–shell nanowires (NWs), isolated from the GaAs substrate via a layer of aluminum oxide. The excess current as a function of the electron beam energy, position on the NW, and scan direction were collected, together with energy dispersive x-ray spectroscopy. A model that included the effects of beam energy and Fe thickness predicted an average collection efficiency of 60%. Small spatial oscillations in the EBIC current were observed, that correlated with the average Fe grain size (30 nm). These oscillations likely originated from lateral variations in the interfacial oxide thickness, affecting the resistance, barrier potentials, and density of minority carrier recombination traps.

STEM Imaging with Beam-Induced Hole and Secondary Electron Currents

Transmission electron microscopy excels at determining a sample's physical structure---the locations and identities of its constituent atoms---, but is typically blind to electronic structure. A combination of electron-beam-induced current (EBIC) imaging with scanning transmission electron microscopy (STEM), however, does reveal electronic properties by detecting the emission of both secondary electrons and the corresponding holes, for differential contrast that is otherwise inaccessible. Thus STEM EBIC can provide high-resolution images of the properties that govern the function of nanoelectronic devices.

Analytical and numerical simulation of electron beam induced current profiles in p-n junctions

The electron beam induced current (EBIC) mode of a scanning electron microscope (SEM) is a widely used technique for the quantitative assessment of minority carrier diffusion length and surface recombination. Point source (one-dimensional) and extended source (two-dimensional) analytical models are two widely used approaches to assess this information in geometry where the electron beam (e-beam) is parallel to the p-n junction. In this article, a two-dimensional (2D) analytical model is evaluated and compared with 2D finite element numerical simulations, where the electron beam-solid interaction is modeled using a Monte Carlo simulation coupled with a drift-diffusion solver. The simulations are computed for both low and high level injection conditions. The effect of an e-beam injection level on the shape of EBIC profiles is analyzed to evaluate limitations of the analytical models.

An STM – SEM setup for characterizing photon and electron induced effects in single photovoltaic nanowires

Vertical arrays of semiconductor nanowires show great potential for material-efficient and high-performance solar cells. The characterization and correlation between material structure and properties of the individual nanowires are crucial for the continued performance improvement of such devices. In this work, we developed a method with a scanning tunneling microscope (STM) probe inside a scanning electron microscope (SEM) to enable the studies of single photovoltaic nanowires. The STM probe is used to contact individual nanowires in ensembles. We combine the STM-SEM with an in situ light emitting diode (LED) illumination source to study both the electrical and photovoltaic properties of vertical GaAs nanowires with radial p-i-n junctions. We also illustrate that the local charge separation ability within the nanowires can be studied by electron beam induced current (EBIC) measurements. The in situ SEM setup allows the correlation between properties and nanowire structure. The data show that the quality of the electrical contact to the semiconductor nanowire is crucial to be able to investigate the inherent properties of the nanowires. We have established a procedure to make high-quality ohmic contacts to the nanowires with the STM probe. We also show that the effect of mechanical strain on the electrical properties can be investigated by the STM-SEM setup.

Investigation of Si Dendrites by Electron-Beam-Induced Current

This paper reports on electron-beam-induced current (EBIC) characterization of special multicrystalline Si ingot by dendritic growth under high undercooling. Grain boundaries (GBs), dislocations, and their interaction with carbon related precipitates were investigated. The difference between grains from dendrite and non-dendrite growth was compared. In dendrite grains, parallel twins were frequently found. In non-dendrite grains, irregular GBs of various characters co-existed. Both parallel twins and irregular GBs exhibited dark EBIC contrast at room temperature, indicating the presence of minority carrier recombination centers due to impurity contamination. However, sometimes in non-dendrite grains GBs were visualized with bright EBIC contrast with enhanced collection of charge carriers. The origin of the abnormal bright EBIC contrast was explored and it turned out to be SiC related precipitates, which made GBs conduction channels for electron transport.

Secondary Electron Contrast in STEM Electron Beam-Induced Current (EBIC): a Path Towards Mapping Electronic Structure

Secondary Electron Contrast in STEM Electron Beam-Induced Current (EBIC): a Path Towards Mapping Electronic Structure

You Do What in Your Microprobe?! The EPMA as a Multimode Platform for Nitride Semiconductor Characterization

While the use of electron probe microanalysis (EPMA) is widespread in the geological and metallurgical sciences, it remains less prevalent in the field of semiconductor research. For these materials, trace element (i.e. dopant) levels typically lie near or beneath the detection limit of wavelength-dispersive Xray (WDX) spectrometers, while alloy compositions of ternary mixtures and multilayer structures can more readily be determined using X-ray diffraction techniques. The electron beam measurements more commonly applied to semiconductors remain transmission electron microscopy (for structural characterization), and scanning electron microscopy (topographic, optical and electrical information). Despite this, there are many aspects of the EPMA that make it an attractive platform for all of thesetypes of semiconductor characterization, particularly when combining compositional information fromWDX with complementary and simultaneously-acquired signals. These advantages include: built-inlight optics; a stable, quantified and high-current beam; and a combined large-area and high-resolutionmapping capability. This allows the measurement of cathodoluminescence (CL), electron beam-inducedcurrent (EBIC) and electron channelling contrast imaging (ECCI) signals alongside WDX, which weapply to the investigation of visible and UV AlxInyGa1-x-yN materials, devices and nanostructures.

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.

Surface Dielectric Tunnel Barrier Induced by Mn Doping in SnO2 Micro‐ and Nanostructures

Electrical properties of undoped and Mn doped SnO2 microplates and rods are studied by electron beam induced current (EBIC) in a scanning electron microscope (SEM), and I–V curves acquired at room temperature. AFM measurements reveal the formation of numerous terraces at the (−101) surface of the analyzed Mn‐doped SnO2 microplates, which also exhibit high carrier recombination processes at their central region, as confirmed by combined EBIC and cathodoluminescence (CL) measurements. A diffusion length for minority carriers about 205 nm is obtained by EBIC measurements. Different electrical conduction mechanisms, such as Fowler‐Nordheim, direct tunneling and Poole‐Frenkel, are evaluated in the electrical analysis of the samples. Mn doped microplates show lower conductivity than the undoped microds. Moreover the height of the surface tunnel barrier is increased by Mn doping, as confirmed by the analysis of the I–V curves acquired under transversal configuration. A value of the relative dielectric constant ϵr about 7.3 is estimated for the probed SnO2 microstructures.

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.

Diffusion length of non-equilibrium minority charge carriers in β-Ga2O3 measured by electron beam induced current

The spatial distribution of electron-hole pair generation in β-Ga2O3 as a function of scanning electron microscope (SEM) beam energy has been calculated by a Monte Carlo method. This spatial distribution is then used to obtain the diffusion length of charge carriers in high-quality epitaxial Ga2O3 films from the dependence of the electron beam induced current (EBIC) collection efficiency on the accelerating voltage of a SEM. The experimental results show, contrary to earlier theory, that holes are mobile in β-Ga2O3 and to a large extent determine the diffusion length of charge carriers. Diffusion lengths in the range 350–400 nm are determined for the as-grown Ga2O3, while processes like exposing the samples to proton irradiation essentially halve this value, showing the role of point defects in controlling minority carrier transport. The pitfalls related to using other popular EBIC-based methods assuming a point-like excitation function are demonstrated. Since the point defect type and the concentration in currently available Ga2O3 are dependent on the growth method and the doping concentration, accurate methods of diffusion length determination are critical to obtain quantitative comparisons of material quality.

Cathodoluminescence studies of chevron features in semi-polar (112¯2) InGaN/GaN multiple quantum well structures

Epitaxial overgrowth of semi-polar III-nitride layers and devices often leads to arrowhead-shaped surface features, referred to as chevrons. We report on a study into the optical, structural, and electrical properties of these features occurring in two very different semi-polar structures, a blue-emitting multiple quantum well structure, and an amber-emitting light-emitting diode. Cathodoluminescence (CL) hyperspectral imaging has highlighted shifts in their emission energy, occurring in the region of the chevron. These variations are due to different semi-polar planes introduced in the chevron arms resulting in a lack of uniformity in the InN incorporation across samples, and the disruption of the structure which could cause a narrowing of the quantum wells (QWs) in this region. Atomic force microscopy has revealed that chevrons can penetrate over 150 nm into the sample and quench light emission from the active layers. The dominance of non-radiative recombination in the chevron region was exposed by simultaneous measurement of CL and the electron beam-induced current. Overall, these results provide an overview of the nature and impact of chevrons on the luminescence of semi-polar devices.

Effects of Iron Contamination and Hydrogen Passivation on the Electrical Properties of Oxygen Precipitates in CZ-Si

Oxygen precipitates (OPs) are unavoidably formed in Czochralski silicon (CZ-Si) containing relatively high concentrations of oxygen. The recombination behavior of such defects is also vital for bulk devices like solar cells as they can reduce the minority carrier lifetime and degrade the cell performance. In our experiments, the characteristics of oxygen precipitation in n-type CZ-Si are systematically investigated by means of Fourier transform infrared spectroscopy (FTIR), deep level transient spectroscopy (DLTS) and electron beam induced current (EBIC). It is found that the iron contamination in n-type CZ-Si can strongly influence the OPs generation and their electrical properties, whereas the hydrogen passivation can effectively reduce the recombination activity of OPs.

The Effect of Threading Dislocation on Current-Voltage Characteristics of 3.3kV 4H-SiC Schottky Barrier Diode

Silicon carbide (SiC) is an attractive semiconductor for high-power, high-temperature, and high-frequency electronic devices due to its wide bandgap, high breakdown electric field, and high thermal conductivity. However, the development and commercialization of SiC-based devices are slow due to SiC defects. SiC growth technology has also been developed so much that killer defects, including micropipes, triangular defects and basal plane dislocation that degrade device performance, have been reduced. Although many researches have reported the degradation of devices performance caused by various crystal defects in SiC, the studies on the effect of threading dislocations (TDs) is still insufficient [1,2]. In this paper, we studied the effect of TDs on current-voltage (I-V) characteristics of 3.3 kV 4H-SiC Schottky barrier diodes (SBDs). The 3.3 kV SBDs were fabricated on a n-type 4H-SiC epitaxial wafer. The thickness of epitaxial layer was 28 um and its doping concentration 1 × 1015 cm-3. The boron (NA: 2.0 × 1018 cm-3) was implanted to form the junction termination extension (JTE) that helps to reduce electric field crowding at Schottky metal edge. The aluminum (ND,max: 5.0 × 1019 cm-3) was implanted to form ohmic contact for robust reverse blocking at the periphery of active region. The ion-implanted samples were annealed at 1700 °C for 60 m in Ar ambient. Nickel (Ni) was firstly depotied to form the front-side ohmic contact and cathod electrode, and annealed at 950 °C. Schottky metal, Ni, is deposited and then wet-etched to define the active regions. Post-annealing was performed at 300 °C. The crystal defects and process defects caused during diode fabrication on the active region were observed using electron beam induced current (EBIC) and X-ray topography (XRT). The I-V measurement were performed for forward and reverse I-V charateristics. To study the effet of dislocation on electrical properties of fabricated SBDs, I-V characteristies were analyzed. The Schottky barrier height (SBH) and ideality factor (IF) were extracted from forward characterisitics. The extracted average SBH and IF of SBDs were 1.5 eV and 1.05, respectively. The average leakage current was about 10-12 A at the reverse bias of -100V. The breakdown voltages increased with the length of JTE. The observed maximum breakdown voltage was 4.6 kV. The defects in acvitve region of all measured devices were analyzed using XRT technique to compare with electrical characteristics. The TDs did not affect the forward I-V charcteristecs. However the process defects degraded the forward characteristics, such that the ideality factor was increased from 1.05 to 1.4. These process defect significantly increased the leakage current to 10-7 A and reduced the breakdown below 1 kV. Therefore, the process defects during fabrication are fatal to the device performance. The leakage current of the devices observed TDs at active region increased compared with devices without defect. The breakdown voltage of fabricated 3.3 kV SBDs was not significantly affected by crystal defects. This meas that the TDs are not fatal defect for SBDs having rating breakdown voltage of 3.3 kV. Nevertherless, the increase in the leakage current of a device having the TDs may cause long-term reliability issues. Therfore, it is necessary to determine allowable type of defects and their defect density for highly reliable SiC power devices. [1] H. J. Jung, S. B. Yun, I. H. Kang, J. H. Moon, W. J. Kim, W. Bahng, Mater. Sci. Forum, 821-823 (2015) 563-566. [2] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, T. Endo, Appl. Phys. Lett., 100 (2012) 242102. Figure 1

Electrical and Material Properties Analysis of 5kV 4H-SiC Schottky Barrier Diodes

Silicon carbide is an attractive material for next-generation power devices, it has wide band gap and high thermal conductivity. SiC power devices can operate at higher temperatures and voltages compared to silicon devices. But, electrical characteristics of the SiC power devices can be deteriorated by SiC defects. The killer defects such as micropipes and stacking faults have been reduced through the development of SiC growth technique. But still the threading dislocations (TDs) and basal plane dislocations (BPDs) lowered the breakdown voltage and increased the leakage current during device operation [1]. In this study, we fabricated the 5 kV 4H-SiC Schottky barrier diode (SBD) to study the effect of SiC defect on electrical properties of SiC SBDs. The thickness of epitaxial layer was 50 um and the doping concentration is 1E15 cm-3. The device was fabricated with various length of junction termination extension (JTE). Ion implantation was performed to form p surge (Al, 500 °C, 5E19 cm-3) and JTE (B, 500 °C, 2E18 cm-3) regions. Activation annealing was performed at 1700 °C for 60 m. 100 and 30-nm-thick Ni were deposited as the cathode and front-side ohmic metal respectively, and then annealed at 950 °C for 90 s in RTA system. Finally, 100-nm-thick Ni was sputtered on front-side as a Schottky contact metal. We investigated the forward, reverse characteristics, and reverse breakdown voltage of the fabricated 4H-SiC SBDs. The diode characteristics, ideality factor (IF) and Schottky barrier height (SBH) were obtained from the forward electrical characteristics, about the 1.23 and 1.3 eV, respectively. The relative highly ideality factor may be due to rough surface of thick epitaxial layer. The breakdown voltage was obtained above 5 kV with JTE length longer than 60 um. During reverse characteristics the electrically weak points were observed using electroluminescence (EL). The EL spot was mainly aroused from electrically leaky points, it mostly observed at the edge of JTE. Some EL spots were observed inside the JTE or active region. The defects of the fabricated 4H-SiC 5 kV SBDs were analyzed using non-destructive analysis method, X-ray topography (XRT) and electron beam induced current (EBIC). We tried to determine the correlation between the electrical characteristics of the device and the crystal defects in the device. [1] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, and T. Endo, Appl. Phys. Lett. 100, 242102 (2012). Figure 1

The Effect of Threading Dislocation on Current-Voltage Characteristics of 3.3 kV 4H-SiC Schottky Barrier Diode

We investigated the relationship between threading dislocation and current-voltage (I-V) characteristics of 3.3 kV 4H-SiC Schottky barrier diodes (SBDs). The crystal defects were observed using non-destructive methods. X-ray topography (XRT) and electron beam induced current (EBIC) were used to compare the current-voltage characteristics of fabricated SBDs with defects. The surface and process defects were found to be fatal to devices performance such as ideality factor and leakage current increased and the breakdown deterioration. However, the threading dislocations rarely affected forward I-V characteristics and blocking voltage of fabricated 3.3 kV SBDs. The leakage current of the SBDs with threading dislocations in active region was increased by 103 compared with those of the SBDs without defect.

Reducing Zn diffusion in single axial junction InP nanowire solar cells for improved performance

In this work axial n-i-p junction InP nanowires were grown by selective-area metal organic vapor phase epitaxy (SA-MOVPE) technique with the growth sequence starting from n-segment. The optical properties and carrier lifetimes of the n-, i- and p-type segments were studied and compared using time-resolved photoluminescence (PL) and cathodoluminescence (CL) measurements. We demonstrate for the first time that CL is capable of resolving the electrical profile of the nanowires, namely the varied lengths of the n-, i- and p-segments, providing a simple and effective approach for nanowire growth calibration and optimization. The CL result was further confirmed by electron beam induced current (EBIC) and photocurrent mapping measurements performed from the fabricated single nanowire solar cell devices. It is revealed that despite a non-optimized device structure (very long n-region and short i-region), the n-i-p nanowire solar cells show improved power conversion efficiency (PCE) than the previously reported p-i-n (growth starts with p-segment) single nanowire solar cells due to reduced p-type dopant (Zn) diffusion during the growth of n-i-p solar cell structure.