Photoluminescence

Pulsed photoluminescence spectroscopy of Si surfaces: A fast and contact-less method to measure surface recombination

Pulsed photoluminescence (PL) is a fast and contact-less tool to measure passivation and surface recombination after or during modification of Si surfaces even at room temperature. Fig. 1 and Fig. 2 show the experimental set-up which is optimised for Si due to the use of an interference filter instead of a monochromator. The excitation wavelength ranges from 360 nm upto 920 nm by means of a nitrogen laser pumped dye laser.

Theoretical calculations reveal that the integrated PL intensity (IPL) is inverse proportional to the amount of nonradiative recombination centres, ns. The set-up can be calibrated by means of SiO2 layers on c-Si which are differently annealed to obtain a variation in the interface state density measured by standard rf-CV. The resulting plot of IPL vs. Dit from rf-CV is shown in fig. 4 (right) at different excitation densities. The resulting slope of -1 leads to the assumption that the measure of IPL can be used as an express method to characterise the Si surface with respect to ns. Additionally, the comparison of measured and calculated PL transients leads to values for the surface recombination velocity, So, as plotted in fig. 4 (left).

Fig. 5 shows an example for in-situ PL measurement during etching of an electrochemicaly prepared SiO2 layer on Si by concentrated NH4F solution. The SiO2 layer is formed by switching the potential from -1.5 to +7V for about 10 sec in the etching solution. IPL decreases strongly when the worse passivation wet oxide layer is formed and increases again after several seconds due to the H-termination of the Si surface which is a well passivation layer.

A second set-up is used to measure PL spectra in the range from 360 nm to 1700 nm by pulsed excitation from a dye laser. PL spectra of some Si based samples are plotted in fig. 6 and show the dynamic range of the set-up used.

References

[1] In situ Monitoring of Electrochemical Processes at the (100) p-Si/Aqueous NH4F Electrolyte Interface by Photoluminescence;
J. Rappich, V.Yu. Timoshenko and Th. Dittrich; J. Electrochem. Soc. 144, 493-496 (1997)
[2] In Situ Photoluminescence During (Electro-) Chemical Etching of Silicon Oxides and Silicon in Acidic NH4F Solutions;
J. Rappich; Electrochem. Soc. Proc. Vol. 97-20, 238-245 (1997)
[3] Quantitative Analysis of Room Temperature Photo­luminescence of c-Si Wafers Excited by Short Laser Pulses;
V. Yu. Timoshenko, A.B. Petrenko, M.N. Stolyarov, Th. Dittrich, W. Füssel, and J. Rappich; J. Appl. Phys. 85(2), 4171-4175 (1999)
[4] Express characterisation of Indirect Semiconductor Surfaces by in situ Photoluminescence During Chemical and Electro­chemical Treatments;
V.Yu. Timoshenko, J. Rappich, Th. Dittrich; Appl. Surf. Science 123/124, 111-114 (1998)
[5] In-situ characterization of the surface state density by Photoluminescence during electrochemical treatments of silicon surfaces;
Th. Dittrich, V.Yu. Timoshenko and J. Rappich; Mat. Res. Soc. Symp. Proc. Vol. 451 (1997) 203-208
[6] Photoluminescence characterization of non-radiative defect density on silicon surfaces and interfaces at room temperature;
V. Yu. Timoshenko, A.B. Petrenko, Th. Dittrich, W. Füssel, and J. Rappich; Thin Solid Films 364, 196-199 (2000)
[7] Passivation of an anodic oxide/p-Si interface stimulated by electron injection;
Th. Dittrich, T. Burke, F. Koch, and J. Rappich; J. Appl. Phys. 89 (2001) 4636-4642