Electron beam induced current detection of sub-surface two-dimensional charge reservoir

Abstract

In conjunction with metal-semiconductor-metal heterostructure (HMSM) devices, the electron beam induced current (EBIC) detection method is ideal in two-dimensional sheet charge detection. Using a delta modulation-doped heterostructure, a scan-line plot comparison to its undoped structural equivalent exposes the electrical effects of the sheet charge existence. While electrically biasing both heterostructure types, each were placed in an SEM chamber and electrode-to-electrode scan-line plots were taken at different biasing levels. Based on experimental results, dark currents for the delta modulationdoped device are detrimental to its EBIC signal-to-noise ratio but its electron-hole pair collection rate is more effective in EBIC signaling than its undoped counterpart at higher biasing levels. Bypassing the charge transport limitation of a saturated group drift velocity in the active region, charge carriers are swept to the highly conductive twodimensional sheet charge in the doped structure resulting in higher EBIC signaling; the sheet charge shields the active region from the drift-current limitations by modifying the carrier transport path within the active region. Supported by experimental EBIC characterization data, biased delta modulation-doped HMSM device simulations predicted the presence of the two-dimensional sheet charge would effectively simulate smaller finger-gapped devices but without sacrificing its active region volume. Improvements in electron beam control, most notably beam depth within a sample, can aid in the development of a non-destructive EBIC method to determine sheet charge uniformity; an added feature to the established device failure and defect analysis EBIC techniques used today. Theoretical electrical dissimilarities with modulation-doped and undoped in-plane Schottky contact devices are discussed to support the EBIC method and its application; the advantages and/or disadvantages of using degenerate devices of this type in substitution of its undoped structural equivalent are demonstratd.%%%%M.S., Electrical Engineering – Drexel University, 2008