P. Saring

Current-voltage characteristics of manganite-titanite perovskite junctions

Summary After a general introduction into the Shockley theory of current voltage (J–V) characteristics of inorganic and organic semiconductor junctions of different bandwidth, we apply the Shockley theory-based, one diode model to a new type of perovskite junctions with polaronic charge carriers. In particular, we studied manganite–titanate p–n heterojunctions made of n-doped SrTi1− yNbyO3, y = 0.002 and p-doped Pr1− xCaxMnO3, x = 0.34 having a strongly correlated electron system. The diffusion length of the polaron carriers was analyzed by electron beam-induced current (EBIC) in a thin cross plane lamella of the junction. In the J–V characteristics, the polaronic nature of the charge carriers is exhibited mainly by the temperature dependence of the microscopic parameters, such as the hopping mobility of the series resistance and a colossal electro-resistance (CER) effect in the parallel resistance. We conclude that a modification of the Shockley equation incorporating voltage-dependent microscopic polaron parameters is required. Specifically, the voltage dependence of the reverse saturation current density is analyzed and interpreted as a voltage-dependent electron–polaron hole–polaron pair generation and separation at the interface.

Electronic and structural properties of femtosecond laser sulfur hyperdoped silicon pn-junctions

The structural properties of femtosecond laser sulfur hyperdoped silicon pn-junctions are correlated to electronic transport characteristics at the interface. The depth of the planar space charge region obtained from cross-sectional electron beam induced current analysis is in good agreement with the sulfur concentration depth profile, derived from secondary ion mass spectroscopy. EBIC signals from the crest regions of the laser structured surface reveal increased recombination activity. Using transmission electron microscopy, we show that such recombination is related to dislocations, which are most probably highly decorated with sulfur.

Transmission Electron Microscopy Investigations of Metal-Impurity-Related Defects in Crystalline Silicon

This contribution summarizes recent efforts to apply transmission electron microscopy (TEM) techniques to recombination-active extended defects present in a low density. In order to locate individual defects, electron beam induced current (EBIC) is applied in situ in a focused ion beam (FIB) machine combined with a scanning electron microscope. Using this approach defect densities down to about 10cm-2 are accessible while a target accuracy of better than 50nm is achieved. First applications described here include metal impurity related defects in multicrystalline silicon, recombination and charge collection at NiSi2 platelets, internal gettering of copper by NiSi2 precipitates and site-determination of copper atoms in NiSi2.

Characterization of Electrical Contacts on Silicon (100) after Ablation and Sulfur Doping by Femtosecond Laser Pulses

This paper investigates the influence of different number of laser pulses on contact behavior and conductivity of the surface layer of femtosecond laser microstructured, sulfur-doped silicon. Single shot laser processed silicon (Pink Silicon) is characterized by low surface roughness, whereas five shot laser processed silicon (Grey Silicon) has an elevated sulfur content with a surface roughness low enough to maintain good contacting. To laterally confine the laser induced pn-junction part of the Grey Silicon sample surface is etched off. The etching depth is confirmed to be sufficient to completely remove the active n-type sulfur layer. While Pink Silicon shows little or no lateral conductivity within the laser processed layer, Grey Silicon offers acceptable conductivity, just as expected by the fact of having incorporated a higher sulfur dopant content. Recombination dominates the irradiated regions of Pink Silicon and suppresses excess charge carrier collection. Grey Silicon, while showing sufficient lateral conductivity, still shows regions of lower conductivity, most likely dominated by the laser irradiation-induced formation of dislocations. According to our results, the optimum laser pulse number for electrical and structural properties is expected to be in the range between one and five laser pulses.

Spatially Resolved Defect Analysis in Cz-Silicon after Copper-Nickel Co-Precipitation by Virtue of Light-Beam-Induced Current Measurements

We report on a light-beam-induced current (LBIC)-analysis of metal silicide defects arising from co-precipitation of copper and nickel in Cz-silicon-bicrystals produced by wafer direct bonding. Large colonies of silicide precipitates in the one wafer emerging from undisturbed growth from few nucleation sites were observed in different orientations with respect to the surface which correspond to Si {110} planes. From this, the colonies formed during copper-nickel co-precipitation reveal the same attributes as those colonies typical for copper precipitation in the absence of nickel. Oxygen related defects associated with a higher defect distribution in the other wafer were characterized by means of high resolution Transmission Electron Microscopy (TEM) and their temperature dependent LBIC signal.