DETERMINATION OF NITROGEN CONCENTRATION IN GAP EPITAXIAL LAYERS BY 2 INDEPENDENT METHODS

The nitrogen concentration in GaP is determined by optical absorption in the A‐line at T = 77 K. The concentration of the isolated nitrogen atoms is given for T = 77 K by the modified LIGHTOWLERS' relation [NA] cm−3 = 8.2 · 1014 phαmax, where α is measured in cm−3, h in meV. p is a dimensionless line shape factor. It is shown that at higher N concentrations considering only the A‐line absorption the impurity density is underestimated because the nitrogen atoms included in NNi pairs give no contribution to the absorption. The measurements have been made in the range from [N] = 5 · 1016… 1019 cm−3 in layers grown by vapour phase epitaxy. The results are compared with nitrogen concentrations obtained by precision lattice parameter measurements. The change of the lattice parameter is calculated using VEGARD's law. The good agreement between the nitrogen densities obtained by two different independent methods reveals (i) that the LIGHTOWLERS' calibration factor is valid also at higher N‐concentrations and (ii) that the nitrogen atoms are predominantly incorporated into P‐lattice sites. Copyright © 1979 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim