Optical characterization of ultra‐pure GaAs

Abstract

The problem of ultra-pure thick GaAs layers has been important for a long time. Growth of such material is an important technological problem and the basis of application in electronic devices. Epitaxial (100–1000) μm thick GaAs layers were grown by vapour phase epitaxy in a chloride system (HVPE) on N+ and semi insulating 2″ substrates horizontally; the growth zone extended over ∼19 cm with a temperature gradient of ∼3 °C/cm. The total impurity concentration N was in the range ≤ 1012–1014 cm–3. These epilayers have been investigated using low temperature photoluminescence (LTPL), C–V, and Hall measurements. However, estimation of the electro-physical parameters of ultra-pure (N ≤ 1012 cm–3) GaAs often causes difficulties. Because of the low concentration of impurities (N ≤ 1012 cm–3) electro-physical measurements are difficult in many cases or even impossible. In those cases where electro-physical measurements proved feasible a direct relationship was established between the variation of the electro-physical parameters and the evolution of the LTPL spectra at 2 K. By extrapolating the obtained data to regions of lower impurity concentration, ND and μe values corresponding to certain values of the parameters of the LTPL spectra could be found. Thus, analysis of the LTPL spectra can yield estimates of ND and μe when direct determination is difficult or impossible. We consider that from a detailed analysis of LTPL spectra at 2 K the concentration of deep levels in ultra-pure GaAs can be determined.