Stoichiometry and impurity concentrations in II–VI compounds measured by elastic recoil detection analysis (ERDA)

Abstract

Polycrystalline ZnSe will be used in a chemical vapour deposition process for thin-film solar-cell emitter layers. The precursor bulk material was characterised with respect to stoichiometry and impurity concentrations by the ERDA method, for which an experimental setup is installed at the Berlin Ion Beam Facility (ISL). The sample material was irradiated with high-energy Kr and Xe projectile ions of 120 and 250 MeV, respectively. The energy and time-of-flight (TOF) of the released sample atoms were detected. In contrast to the Rutherford backscattering technique the measurement of both parameters enables the separation of different masses not only in thin-films but also in bulk material. ERDA allows the simultaneous depth profiling of heavy and light elements including hydrogen. We found ZnSe bulk samples to exhibit an oxygen surface contamination with a Zn/O ratio of 1 : 2 and thickness of 27×10 15 at/cm 2. An accuracy in stoichiometry, i.e., Zn/Se ratio of better than 1% could be achieved and impurity concentrations could be detected down to the 100 ppm range. Detection limits of the ERDA technique and its capacity for concentration profiling in II–VI materials will be discussed.