Schematic diagram of the setup. By varying the pinhole diameter the spatial detection profile can be adjusted. For pinhole sizes of 100 and are used. The signal is detected from the point of excitation. The excitation is represented by the dotted line, the detected signal by the bold bright line. The objective has a 50× magnification with and is optimized between 500 and 2000 nm wavelength. The sample is illuminated by a 532 nm laser with a power of 19.5 mW on the sample.
Simulated electron density for a of and at a -type doping of . The injection densities above satisfy high injection condition. This simulation shows, that within from the excitation center high injection conditions are fulfilled, which allows us to assume high injection conditions. The laser is focused on the sample surface. The inserts show the line scans along the arrows.
Simulation of the emitted BB PL radiation at 1100 nm. Similar to the injection density, the emitted BB PL decreases rapidly from the center of excitation. Due to the approximately quadratic dependence of the BB PL emission on the injection density at high injection the decrease with distance is steeper. The inserts show the line scans along the arrows.
Detection profiles of the set for pinhole sizes of and (note the different scales). The detection profiles are measured by scanning the light of a point source in and direction. The hole is at . Positive is below the surface.
Simulation of the spatially resolved contribution to the detected PL radiation at 1100 nm with the small pinhole size of . The detected BB PL decreases even stronger than the emitted BB PL with distance from the point of excitation, which is due to the confocal setup of . The inserts show the line scans along the arrows.
Experimental quotient and a representative PL spectrum against the wavelength for a representative set of . is constant over a 50 nm range around 1100 nm, which proves that the wavelength dependence of does not significantly influence our results.
Graphical representation of the calibration table for against for between 10 and for a doping level of . is monotonically increasing with which allows the determination of from . The simulations shows, that for high lifetimes does not depend on due to the dominating Auger recombination in this area. Therefore a global can be extracted from high lifetime regions, where is practically independent from .
Measurement and simulation of for high lifetime samples with different doping concentrations. The measurement is in agreement with the simulation but the accuracy is not high enough to show the decrease in with . From the scattering of the experimental data the measurement error for can be estimated to be ±0.3. For the simulation is and is .
Qualitative overview mapping of the sample for the identification of a region of interest (see marked square) with recombination active defects. The dark straight lines are surface scratches due to the polishing.
Measurement of the spatially resolved for the region of interest in Fig. 8. is clearly decreased at two of the three grain boundaries. The insert shows along the arrow crossing the left grain boundary and the denuded zones.
Calibrated quantitative high-resolution lifetime map of the region of interest of Fig. 9 from in Fig. 10. The measurement reveals a micron wide denuded zone around the left grain boundary (arrow). The lower right grain boundary is highly recombination active and the lifetime varies along the grain boundary which is an indication for a locally increased impurity decoration.
PLI image of the sample of Figs. 9–11 at low level injection conditions. The image shows a good qualitative agreement to Fig. 11 (square) and also to the high injection overview scan in Fig. 9. The recombination activity of the three grain boundaries is qualitatively the same. A quantitative comparison is not feasible due to the strongly differing injection conditions. The mirror-inverted “W60” originates from the laser mark on the backside.
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