Monte Carlo simulation of CL and EBIC contrasts for isolated dislocations

Electron beam-induced current (EBIC) and cathodoluminescence (CL) are widely used to investigate semiconductor materials and devices, particularly to obtain information on the recombination properties and the geometry of defects. This report describes a simple formulation of CL and EBIC contrasts based on the Born approximation of excess carrier density in the presence of a pointlike defect. Quantitative interpretation of the CL and EBIC images is often difficult because of a lack of accurate theory treating simultaneously both the details of the electron beam penetration in the semiconductor and the generation of EBIC and CL signals. To overcome this difficulty, the Monte Carlo approach to the phenomenon of the electron beam penetration in solids has been developed to calculate the CL and EBIC signals during a simulation of the electron trajectory. Results for an inclined dislocation in GaAs are presented.     

A theoretical study of the determination of the depth of a dislocation by combined use of EBIC and CL technique

We propose a method for the determination of the depth of a macroscopical lattice defect, e.g., a dislocation, in a semiconductor diode using EBIC and CL contrast measurements from the same defect. The method requires restrictions neither with respect to the value of the bulk diffusion length nor with respect to the shape of the generation region of electron-hole pairs.     

High-resolution scanning near-field EBIC microscopy: application to the characterisation of a shallow ion implanted p+-n silicon junction

High-resolution electron beam induced current (EBIC) analyses were carried out on a shallow ion implanted p⁺–n silicon junction in a scanning electron microscope (SEM) and a scanning probe microscope (SPM) hybrid system. With this scanning near-field EBIC microscope, a sample can be conventionally imaged by SEM, its local topography investigated by SPM and high-resolution EBIC image simultaneously obtained. It is shown that the EBIC imaging capabilities of this combined instrument allows the study of p–n junctions with a resolution of about 20 nm.     

Scanning microscopies of indented MgO crystals

The combination of scanning electron microscopy (SEM) and scanning optical microscopy (SOM), including a computer-controlled signal detection system, is promising in the study of a variety of materials, especially such alkaline-earth oxides with a rock salt structure, such as MgO. Among the SEM modes of this technique used to investigate deformed zones in indented MgO single crystals are: secondary electrons (SE), cathodoluminescence (CL) (total, pointal, color), electron beam-induced current (EBIC), electron beam-induced voltage (EBIV), as well as both polarized and transmitted light modes in SOM. The present experiments were designed to clarify the correlation between the optical, luminescent, electrical, and plastic properties of deformed MgO. An attempt has been made to explain the results in terms of dislocations created during deformation.     

Scanning-DLTS,EBIC, and CL Investigations of Diamond Indentations in GaAs p+n Junctions

Diamond indentations have been carried out on Zn-diffused GaAs p⁺n junctions on (100) oriented material. Electron-beam induced current (EBIC) investigations revealed the well-known dislocation slip bands in 〈110〉 directions. Scanning deep level transient spectroscopy (SDLTS) imaging proved a deformation-induced point-defect level at E_y + 0.5 eV, which is preferentially concentrated in the dislocation-free regions between the slip bands rather than within the slip bands. Monochromatic cathodolumines-cence (CL) imaging at 10K using different wavelengths revealed only the dislocation-induced recombination activity but not any point-defect luminescence corresponding to the 0.5 eV level found by SDLTS.     

Scanning electron microscopy studies of double-layer silicon structures prepar by epitaxy and direct bonding

The electrical properties of multilayer structures obtained by direct bonding of silicon wafers and epitaxial growth have been investigated. The measurements were made by scanning electron microscopy (SEM) in either secondary electron or electron beam-induced current (EBIC) regime, using cross sections of the structures with a p-n junction formed in the subsurface region of the active layer. The measurements of defect recombination activity were made using Schottky diodes formed on the active layer surfaces. Parasitic p-n junctions in some samples under a small direct voltage have been observed and the reason for the appearance of such parasitic junctions has been established. Two types of defects with different distribution densities and amplitudes of EBIC contrast have been detected.     

Observation of current-density filamentation in multilayer structures by EBIC measurements

The total current-voltage characteristics of the p⁺-n⁺-p-n^? and n⁺-p-n-p^? diodes under investigation show branches of negative differential resistance. Accompanied by the appearance of negative differential resistance is a filamentation of current-density and electric-field distribution. Electron beam-induced current (EBIC) measurements were used to examine the properties of filamentation from the point of view of self-organized pattern formation. Besides the detection of the spatial distribution of the electric field, EBIC measurements give information on current-density filamentation. Furthermore, the perturbation by the electron beam gives information on the dynamic behavior of the filamentary structure.     

EBIC and luminescence studies of defects in solar cells

Electron beam-induced current (EBIC) can be used to detect electronic irregularities in solar cells, such as shunts and precipitates, and to perform physical characterization of defects by, e.g. measuring the temperature dependence of their recombination activity. Recently also luminescence methods such as electroluminescence (EL) and photoluminescence (PL) have been shown to provide useful information on crystal defects in solar cells. In this contribution it will be shown that the combined application of EBIC, EL and PL may deliver useful information on the presence and on the physical properties of crystal defects in silicon solar cells. Also pre-breakdown sites in multicrystalline cells can be investigated by reverse-bias EL and by microplasma-type EBIC, in comparison with lock-in thermography investigations.     

GaP LPE半导体材料的扫描电子显微镜研究

本文论述了用扫描电子显微镜研究GaP LPE半导体材料,二次电子像用于分析样品的表面形貌,电子束感生电流像(EBIC)用于显示p-n结的位置,定量EBIC用以确定少子扩散长度和表面复合速度等重要参量。     

The interpretation of EBIC images using Monte Carlo simulations

Charge collection microscopy, usually known by the acronym EBIC (Electron Beam Induced Current) imaging, is a powerful technique for the observation and characterization of semiconductor materials and devices in the scanning electron microscope. Quantitative interpretation of EBIC images is often difficult because of the problem of accurately representing the electron-beam interaction with the semiconductor. This paper uses a Monte Carlo technique to simulate the electron-beam interaction, and it is shown that this permits simple analytical point-source solutions to be generalized to fully represent the experimental situation of an extended, non-uniform, carrier source. The model is demonstrated by application to EBIC imaging in the Schottky barrier geometry.     

Advanced semiconductor diagnosis by multidimensional electron-beam-induced current technique

We present advanced semiconductor diagnosis by using electron-beam-induced current (EBIC) technique. By varying the parameters such as temperature, accelerating voltage (V(acc)), bias voltage, and stressing time, it is possible to extend EBIC application from conventional defect characterization to advanced device diagnosis. As an electron beam can excite a certain volume even beneath the surface passive layer, EBIC can be effectively employed to diagnose complicated devices with hybrid structure. Three topics were selected to demonstrate EBIC applications. First, the recombination activities of grain boundaries and their interaction with Fe impurity in photovoltaic multicrystalline Si (mc-Si) are clarified by temperature-dependent EBIC. Second, the detection of dislocations between strained-Si and SiGe virtual substrate are shown to overcome the limitation of depletion region. Third, the observation of leakage sites in high-k gate dielectric is demonstrated for the characterization of advanced hybrid device structures.     

Direct assessment of recombination noise in semiconductors using electron beam-induced conductivity

The level of internal noise of the transistors, diodes, and other semiconductor components limits the successful design of any low noise electronic system. All types of noise, namely, Johnson, 1/f, and so forth, are generated due to activity of crystalline defects such as vacancies, dislocations, and others. The intensity of the electron scattering and recombination processes, inflicted by defects (traps), controls the level of noise. Dependent on the dynamic operation condition of semiconductor devices, such as external biases and level of current injection, the traps will generate certain type and level of noise. Material growth or device processing technologies could introduce all kind of defects. Therefore, characterization of the semiconductor wafer in the early stages of processing (at least before packaging) could help to predict the level of noise due to the type and density of defects present on the wafer. Sorting out bad semiconductor chips could save money and effort in the radio frequency design of low-noise circuits. This current study focuses on 1/f noise modeling, which involves most powerful generators of noise and linear defects, named dislocations. The study also examines the possibility of assessing this noise by quantitative electron beam-induced conductivity (EBIC) measurements. These defects could be found in the bulk as well as at the epitaxial interfaces of a semiconductor device. The nanoscale size of these defects makes the scanning electron beam an instrument of choice for the proposed study. Conventional EBIC produces images of the defects, where contrast is proportional to the recombination rate at the site of a defect. Since contrast is measured as a fraction of one percent, the relative nature of contract value precludes quantitative measurements of the recombination rate, thus making quantitative assessment of 1/f noise impossible. In our model, using the Boltzman continuity equation, the recombination-generation processes per unit of length of a dislocation was defined for two operational conditions of EBIC, namely, for low and high intensity of an electron beam. The experimental technique of the quantitative measurement of carrier recombination (Mil'shtein 2001) consists of taking two EBIC scans along the selected defect at two different beam intensities, digitally subtracting the first scan from the second one and normalizing the result to the size of the electron range. The value of the recombination rate, extracted from the model, could then be used to predict the level of 1/f noise in the tested semiconductor sample.     

Characterization of defects in semiconductors by combined application of SEM(EBIC) and SDLTS*

Besides the characterization of the geometrical structure of defects in semiconductors by TEM the estimation of their electrical activity is of importance. SEM(EBIC) and SDLTS (scanning deep level transient spectroscopy) are especially suitable for this purpose; they allow the inspection of electronic properties with a spatial resolution in the micron-range. On the one hand, SEM(EBIC) yields information on the recombination efficiency of defects in the crystal volume adjacent to a pn junction or a Schottky barrier; on the other hand, SDLTS enables the detection to be carried out of the distribution and the energetic levels of deep level defects lying in the space charge region. Accordingly, the combined application of these techniques is very promising for investigating physical processes implying an inhomogeneous incorporation of deep level defects in semiconductor crystals. In comparison to the widely used SEM(EBIC) technique SDLTS has only rarely been applied, a fact that is due to the high detection sensitivity necessary for measuring capacity transients. The application of a highly sensitive (10^—6 pF) micro-computer-controlled SDLTS system in combination with a conventional EBIC system allows a reliable inspection of semiconductor materials and devices, based on A₃B₅ compounds and on silicon. A typical application of the above technique is the investigation of the impurity distribution around extended crystal defects, like dislocations and precipitates, to study their gettering activity.     

Observation of dislocations and microplasma sites in semiconductors by direct correlations of STEBIC,STEM and ELS

A high voltage electron microscope, equipped with scanning transmission (STEM) attachment, electron beam induced conductivity (EBIC) facilities, and electron energy loss spectrometer (ELS), has been used to investigate semiconductor devices. The capability of STEM to produce, simultaneously or sequentially, conductive and transmission images of the same specimen region, which can also be ELS analysed, is exploited in order to establish direct and unambiguous correlations between EBIC and STEM images of defective regions (dislocations and microplasma sites) in silicon devices. The results obtained are discussed in terms of correlations, resolution, contrast, and radiation damage; in addition, a comparison is made between this method and the other correlation methods based on EBIC/SEM (scanning electron microscope) and TEM (transmission electron microscope).     

Low-voltage cross-sectional EBIC for characterisation of GaN-based light emitting devices

Electron beam induced current (EBIC) characterisation can provide detailed information on the influence of crystalline defects on the diffusion and recombination of minority carriers in semiconductors. New developments are required for GaN light emitting devices, which need a cross-sectional approach to provide access to their complex multi-layered structures. A sample preparation approach based on low-voltage Ar ion milling is proposed here and shown to produce a flat cross-section with very limited surface recombination, which enables low-voltage high resolution EBIC characterisation. Dark defects are observed in EBIC images and correlation with cathodoluminescence images identify them as threading dislocations. Emphasis is placed on one-dimensional quantification which is used to show that junction delineation with very good spatial resolution can be achieved, revealing significant roughening of this GaN p-n junction. Furthermore, longer minority carrier diffusion lengths along the c-axis are found at dislocation sites, in both p-GaN and the multi-quantum well (MQW) region. This is attributed to gettering of point defects at threading dislocations in p-GaN and higher escape rate from quantum wells at dislocation sites in the MQW region, respectively. These developments show considerable promise for the use of low-voltage cross-sectional EBIC in the characterisation of point and extended defects in GaN-based devices and it is suggested that this technique will be particularly useful for degradation analysis.     

SEM and TEM studies of defects in Si-doped GaAs substrate material before and after Zn diffusion

Si-doped GaAs slices after Zn diffusion exhibited a marked decrease in luminous efficiency and a large increase in p-n junction depth when the initial carrier concentration due to the Si was > 3·5 times 10²⁴ m^?3. SEM studies using the CL and EBIC methods, and TEM examinations using plan-view and cross-section specimens, showed that these behaviours were associated with high densities of structural defects, interpreted as Zn precipitation. Reasons for these behaviours in terms of nucleation behaviour and diffusion mechanisms are suggested.     

The effect of electron range on electron beam induced current collection and a simple method to extract an electron range for any generation function

The effect of electron range on electron beam induced current (EBIC) is demonstrated and the problem of the choice of the optimal electron ranges to use with simple uniform and point generation function models is resolved by proposing a method to extract an electron range-energy relationship (ERER). The results show that the use of these extracted electron ranges remove the previous disagreement between the EBIC curves computed with simple forms of generation model and those based on a more realistic generation model. The impact of these extracted electron ranges on the extraction of diffusion length, surface recombination velocity and EBIC contrast of defects is discussed. It is also demonstrated that, for the case of uniform generation, the computed EBIC current is independent of the assumed shape of the generation volume.     

Combined cathodoluminescence and X-ray analysis of paint pigments

The suitability of cathodoluminescence (CL) measurements for differentiating between different paint pigments is demonstrated with an example of a combined energy-dispersive X-ray (EDX) and CL analysis of different zinc oxide (ZnO) pigments in a paint fragment where the EDX spectra are virtually identical, but where the CL spectra show significant differences. Consequently, it is possible to distinguish different pigments on the basis of CL spectra and monochromatic CL micrographs.     

Electron-beam-induced current decay measurements in electron probe instruments using a multichannel analyzer

A simple method for decay measurements of the charge collection mode (commonly referred to as electron-beam-induced current or EBIC) of an electron probe instrument is presented. The decay, which occurs at continuous electron irradiation, should be distinguished from a decay measurement due to the electron beam blanking. This method could be applied to other modes of an electron probe instrument, e.g., cathodoluminescence, in studying electron-beam-sensitive semiconductors. An example of the decay of the EBIC signal in a hydrogenated amorphous silicon device is presented.     

Application of a new detector for cathodoluminescence measurements in the wavelength range to 1.8 μm

The energetic gap structure of semiconductors or insulators can strongly be influenced by the local appearance of inhomogenities, impurities, dopants or vacancies. A high spatial resolution cathodoluminescence (CL) measuring technique makes it possible to investigate this gap structure via spectral analysis of the emitted CL. This can lead to a detailed knowledge of the local defect distribution. The wavelength range which could be detected by CL measurements has, up to the present, been limited to values less than 1 μm, because no detectors were available for higher wavelengths. By use of a new germanium detector, the measuring range could be extended to 1.8 μm. This makes it possible to analyse the CL properties, both of materials with small gap energies and of deep impurities. The detector properties which are important for CL measurements are presented. The efficiency of the detector is demonstrated by CL investigations of barium titanate ceramics and silicon. The results are discussed and compared to results obtained using conventional detectors.