189 research outputs found
Theory of ion beam induced charge measurement in semiconductor devices based on the Gunn's theorem
Abstract Ion beam induced charge collection (IBIC) is a powerful experimental technique to characterise semiconductor materials and devices. It is based on the measurement of the charge induced in a given electrode by the motion of charge carriers generated by MeV ions. The problem of IBIC pulse formation is usually solved by the Shockley–Ramo theorem in which charge carriers are moving in presence of an electric field and all the electrodes are maintained at constant potentials. This theoretical model was demonstrated according to basic electrostatic principles and was first applied to evaluate the induced currents in vacuum tubes and then in semiconductor devices even in presence of stationary space charge. However, the basic assumption underlying such theorems is the independence of the space charge distribution on the applied bias voltage. Such a hypothesis is clearly not valid in partially depleted semiconductor devices where the extension of the depletion region depends on the conditions of the boundary electrodes. We present in this paper a new theoretical approach based on a general expression for electrostatic induction deduced by J.B. Gunn in 1964, which overcomes any limitation on space charge distribution. The resulting simple new formalism reduces to the Ramo–Shockley theorem as a special case. In order to clarify this theoretical approach, some simple IBIC experiments on semiconductor p–n and Schottky diodes are presented and discussed
4H-SiC Schottky diode radiation hardness assessment by IBIC microscopy
We report findings on the Ion Beam Induced Charge (IBIC) characterization of
a 4H-SiC Schottky barrier diode (SBD), in terms of the modification of the
Charge Collection Efficiency (CCE) distribution induced by 20 MeV C ions
irradiations with fluences ranging from 20 to 200 ions/um2. The lateral IBIC
microscopy with 4 MeV protons over the SBD cross section, carried out on the
pristine diode evidenced the widening of the depletion layer extension as
function of the applied bias and allowed the measurement of the minority
carrier diffusion lengths. After the irradiation with C ions, lateral IBIC
showed a significant modification of the CCE distribution, with a progressive
shrinkage of the depletion layer as the fluence of the damaging C ions
increases. A simple electrostatic model ruled out that the shrinkage is due to
the implanted charge and ascribed the perturbation of the electrostatic
landscape to radiation-induced defects with positive charge state
A new diamond biosensor with integrated graphitic microchannels for detecting quantal exocytic events from chromaffin cells
The quantal release of catecholamines from neuroendocrine cells is a key
mechanism which has been investigated with a broad range of materials and
devices, among which carbon-based materials such as carbon fibers, diamond-like
carbon, carbon nanotubes and nanocrystalline diamond. In the present work we
demonstrate that a MeV-ion-microbeam lithographic technique can be successfully
employed for the fabrication of an all-carbon miniaturized cellular bio-sensor
based on graphitic micro-channels embedded in a single-crystal diamond matrix.
The device was functionally characterized for the in vitro recording of quantal
exocytic events from single chromaffin cells, with high sensitivity and
signal-to-noise ratio, opening promising perspectives for the realization of
monolithic all-carbon cellular biosensors
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