First X-Ray Evidence of Heterogeneous Impurity Correlations in Very Highly Doped n-GaAs

Abstract

Measurements of X-ray scattering from very highly doped GaAs:Te single crystals as a function of doping level and thermal treatment (annealing temperature) are reported. Reversible diffuse X-ray scattering occurs after sample annealing below a certain temperature. Presented results indicate an inhomogeneous arising of impurity-impurity correlations in GaAs:Te solid solution. Observed features of diffuse X-ray scattering in reciprocal space can be well understood within Krivoglaz theory of scattering due to spatial fluctuations of solute atoms pair correlation function and related 1attice deformations. Good coincidence of diffuse X-ray scattering with the free electron concentration changes caused by an annealing is reported. Free electron concentration drop accompanying impurity correlation strongly suggests a certain form of impurity bonding.PACS numbers: 61.72.-y, 61.10.-i, 71.55.-i Highly doped semiconductors are routinely approximated by ideal solid solutions. Many experimental phenomena not consistent with such a model are accounted by introducing point defects (e.g. vacancies) and treating a semiconductor as double ideal solution. Here we briefly present X-ray scattering arguments that highly doped GaAs:Te exhibits properties of nonideal solid solution, i.e. one with spatial correlations of solute atoms.In the investigations of critical phenomena the scattering experiments supply the fundαmentαl information on microscopic correlations, order parameters and fluctuations [1,2]. Measurements of the critical scattering [3], with its intensity dependence on temperature of the type I α (Τc -T)x, Τ is a critical temperature and x a certain index, allowed to derive many well-known conclusions on phase transitions [1,2]. The best known are the density fluctuations which occur close to gas-liquid critical point, detected by light scattering (critical opalescence). Another one is neutron scattering detection of the order of atomic magnetic moments, which occurs in a ferromagnet when Curie temperature is approached from above.