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XPS Se 3d Peak at 59 eV for Na Diffused in Bridgman CuInSe2+x
S. Park, C.H. Champness, I. Shih
CuInSe2, Diffusion, Sodium, XPS, Bridgman-grown
Subtopic: CdTe, CIS and Related Ternary and Quaternary Thin Film Solar Cells and Modules
Event: 31st European Photovoltaic Solar Energy Conference and Exhibition
Session: 3DV.1.33
1238 - 1242
ISBN: 3-936338-39-6
Paper DOI: 10.4229/EUPVSEC20152015-3DV.1.33
0,00 EUR
Document(s): paper, poster


Using stoichiometric p-type samples of Bridgman-grown CuInSe2, elemental sodium was diffused into the surface, within an ampoule under vacuum, causing conversion of the samples to n-type to a depth of more than 100 microns from the surface. The amount of Na diffused in was monitored by the intensity of the XPS Na 1s peak at a binding energy of 1,071 eV. As a result, a single XPS Se 3d peak was observed at 54.5 eV but, after subsequent annealing the same samples in air in a sealed ampoule at 200 °C for 1 hour, a second Se 3d peak appeared at a binding energy of 59 eV. This peak was also seen earlier in Bridgman CuInSe2, where Na was introduced into the melt prior to compound synthesis, for ingots stored for a long time in air. The 59 eV peak has been assigned to Na2SeO3, created by oxidation of Na2Se, itself formed by the combination of sodium with selenium destined for the creation of the CuInSe2. As a consequence, the resulting chalcopyrite becomes stoichiometrically selenium deficient and hence n-type. From the measured n/p junction depths, an estimate of the diffusion coefficient was made in the range of 10-10 to 10-8 cm2/sec for sodium in multi-crystalline CuInSe2 at 250 °C.