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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 ≤ 10 12-10 14 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 ≤ 10 12 cm -3 ) GaAs often causes difficulties. Because of the low concentration of impurities (N ≤ 10 12 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 electrophysical parameters and the evolution of the LTPL spectra at 2 K. By extrapolating the obtained data to regions of lower impurity concentration, N D and µ e 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 N D and µ e 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.

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