XPS Analysis of Dopant Penetration in Joined p-n Silicon-Germanium Semiconductor

The penetration behavior of dopants, boron and phosphorous, across a p-n junction in a joined silicon-germanium semiconductor, which had been applied to a thermoelectric element, was elucidated by X-ray photoelectron spectroscopic (XPS) analysis. The p-n joined disk sample was prepared from Si, Ge and B (79.7:20.1:0.21 in atomic ratio for p-type semiconductor), and Si, Ge and P (79.8:20.0:0.18 for n-type) powders one on the top of the other at 1523 K for 180 s under 49 MPa by a pulse current sintering process. Then, the XPS measurement and surface grinding of the joined sample were carried out alternately, which gave a series of photoelectron spectra as a function of distance from the p-n junction. The binding energy differences for Si2s and Ge3d peaks between the p-type and the n-type sides were 0.5 and 0.6 eV, respectively. An interlayer with a thickness of approximately 2 mm was found just in the p-type side judging from the above energy differences. The binding energies inside the interlayer along the thickness varied gradually between the original value of p-type Si-Ge and that of the n-type. It was considered that both the dopants coexisted in the interlayer, caused by the migration of phosphorous of the n-type side into the p-type side. The long-distance migration of phosphorous more likely occurred according to the vaporization-condensation mechanism. XPS analysis was proved to be most effective for the characterization of the p-n junction of semiconductors.