Electron-beam-induced current

Other indirect methods for measuring lifetimes often involve device structures such as p-n junctions. The electron-beam-induced current (EBIC) technique, for example, measures the increase injunction current as an impinging electron beam moves close to the junction, i.e., within a few minority-carrier diffusion lengths. If a diffusion constant can be estimated, say by knowledge of the minority-carrier mobility, then the minority-carrier lifetime can be calculated. However, SI GaAs does not form good junctions, so such methods are really not applicable. 

A powerful method for the characterization of the origin of losses on structured surfaces is provided by the EBIC (Electron Beam Induced Current) technique also known as charge collection microscopy (23. 24). 

However, the SEM contrast of CNT can be difficult to interpret as it depends on a lot of parameters (76) the primary beam energy landing, the history of imaging, if the CNT are lying on a substrate or suspended, the substrate electrical conductivity and the electron beam induced contamination during imaging. The contrast can for example be linked to potential differences between the CNT and the substrate (77), or to electron beam-induced current on the insulating substrate surface (78). 

Figure 75. Current filaments in p-Ge at various voltages, made visible by the EBIC technique (electron beam induced currents). 274 (Reprinted from K. M. Mayer, R. Gross, J. Parisi, J. Peinke, R. P. Huebener, Spatially Resolved Observation of Current Filament Dynamics in Semiconductors. , Solid State Commun., 63, 55-59. Copyright 1987 with permission from Elsevier.)...

Schottky contacts on ZnO were realized by the thermal evaporation of Ag, Au, Ni, or Pd, respectively. We used different surface preparation techniques prior to the deposition of the contact metal. For the single crystals a front-back contact configuration was used while a front-front configuration has to be used for thin films grown on insulating sapphire substrates. The homogeneity of the Schottky contacts depends on the surface preparation as revealed by electron beam induced current (EBIC) measurements (Fig. 6). 

Figure 6. Electron beam induced current scans on a) a sample treated with N2O plasma and b) a sample treated with HCl prior to the metal deposition.

The lower limit for short lifetimes in this technique is determined by the optical excitation source turn-off time to about 0.1 gs. For shorter lifetimes steady-state diffusion length measurements are more suitable. The diffusion leyth is related to the recombination lifetime by the equation L l/(Dt ). Suitable techniques are surface photovoltage and scanning electron microscope electron beam induced current. They lend themselves to lifetimes down to the nano-second range. 

Voltage contrast and Electron Beam Induced Current (EBIC), two electrical techniques usually used for circuit analysis, have proven useful for semiconductor materials characterization. 

Electron beam induced current (EBIC) has been used to... 

Correlations with EBIC and XRT. Thermal features that arise either from mechanical defects or from metallic grains and grain boundaries are usually easy to recognize. However, thermal features arising from more subtle crystalline disruptions and variations, such as those described above are more difficult to identify. Before thermal-wave microscopy can be accepted as a routine, standard analytical technique, one needs to establish a direct correlation of some of these less obvious thermal-wave images with those obtained with other more widely accepted techniques. Below, we discuss two such correlations, one with electron beam Induced current (EBIC) and the other with x-ray topography (XRT). 

What is impUed by unequal generation and recombination lifetimes The lifetime measurement techniques and the resulting lifetimes measured with them must be clearly understood to avoid confusion. For example, the recombination lifetime is measured by such methods as photoconductive decay, open-circuit voltage decay, diode reverse-recovery, surface photo voltage, electron-beam induced current and others. 

Figure 11 shows the DSD density of GaAs grown on Si substrate revealed by electron beam-induced current (EBIC) measurement for various TCA temperature. The DSD density decreases with increasing the TCA temperature gradually and is on the order of 10 cm at 1000 C. The crystal quality improvement by the relatively high TCA temperature... 

BSE = Backscattered electrons SE = Secondary electrons SC = Specimen current EBIC = Electron-beam-induced current ... 

The mean number ElEj of electron - hole pairs generated in semiconductors— with a mean formation energy of , = 3.6eV in silicon, for example—normally recombine. The electric field inside depletion layers separates the charge carriers, and minority carriers can diffuse to the depletion layer and contribute to the charge collection /eg or electron-beam induced current. Depletion layers can be formed by p-n junctions parallel or perpendicular to the surface or by Schottky barriers formed by a nonohmic evaporated metal contact. Therefore, a scanning electron probe becomes a useful tool for qualitative and quantitative analysis of junctions and semiconductor parameters [227], which is demonstrated by the following examples ... 

Fig. 7.12. Electron-beam-induced current (EBIC) images showing the plan view of (a) GeSi deposited on unpatterned Si substrates and (b) GeSi deposited on patterned Si substrates. The figures reveal changes in misfit dislocation densities in a Geo.19Sio.8i alloy on a (001) Si substrate. Adapted from Fitzgerald et al. (1991) and Fitzgerald (1995). Reproduced with permission from E.A. Fitzgerald, Massachusetts Institute of Technology.

EBIC Electron-beam-induced current E-SEM, ESEM Environmental scanning electron... 

Currently, there is a lack of EBIC experiments devoted to the electrical properties of dislocations in silicon. Experiments such as scanning transmission electron beam induced current (STEBIC) could be used to reinvestigate these electrical properties, especially those of perfect dislocations. 

FIGURE 12 Electron beam-induced current image of integrated circuit. 

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