Electron-Beam-Induced Current and Cathodoluminescence

Abstract

Electron beams generate electron-hole pairs or minority carriers in semicon-ductors within a small volume. They are therefore excellent tools for measur-ing semiconductor-device parameters such as the diffusion length, the surface recombination velocity, the relaxation time, and the position and width of depletion layers by recording the charge-collection current or electron-beam-induced current in a depletion layer. Schottky barriers as well as diffused and ion-implanted p-n junctions can be studied. By modulating the CRT with the charge-collection current, images of depletion layers and of crys-tal defects, which influence the recombination of minority carriers, can be displayed. Cathodoluminescence (CL) is a further important source of information about semiconductors and allows the local composition, doping and tempera-ture in devices to be measured by recording the spectrum of the cathodolumi-nescence emission and the decay times. Defects can also be imaged in the CL mode. For mineralogical and biological specimens, CL provides a method of distinguishing phases and elemental concentrations and of localizing specific fluorescent stains. For recording light emission excited by cathodoluminescence, a light col-lection system of high efficiency must be employed, especially for spectro-scopic resolution and at low light levels. 7.1 Electron-Beam-Induced Current (EBIC) Mode 7.1.1 EBIC Modes and Specimen Geometry When electron-hole pairs are generated inside a depletion layer or when mi-nority carriers diffuse to the layer, the electric field of the depletion layer sep-arates the charge carriers and a charge-collection current Icc or an electron-beam-induced current (EBIC) can be measured externally. This effect has been discussed in Sect. 5.2.2 in connection with semiconductor detectors. However, the most important application of EBIC is in semiconductor tech-nology, where the EBIC signal can be used as a video signal for the imaging of p-n junctions and of crystal defects, since it is affected by differences in the