Deep levels and compensation effects in sulfur-doped GaPN layers grown by organometallic vapor phase epitaxy

Abstract

Two GaPN epilayers, with different N contents of 0.3% and 0.9%, i.e., at the low-doping level and in the dilute-content range, respectively, have been examined by deep level transient spectroscopy (DLTS) and thermal admittance spectroscopy (TAS). DLTS revealed a main peak below 200K and a low-intensity broad signal above 250K. For the dominant peak, Arrhenius plots revealed an activation energy of 0.4eV below the conduction band and a corresponding trap density above 1017cm−3, in both the samples. The higher N-content sample features for this level a broader line shape and about one-order-of-magnitude larger cross section, as compared with the low N-content epilayer. TAS Arrhenius plots yielded a compressed discrepancy between the signatures of this trap in the two samples, pointing to a common physical origin, likely corresponding to N-split interstitials, and to a possible incidence of Poole–Frenkel effect on this trap behavior. However, the main discrepancy between the results from the two techniques lay in the concentrations as calculated for the signal above 250K. It was found that DLTS underestimates its intensity by at least one order of magnitude. Based on the extension of TAS data at high temperatures, this controversial signal resulted to correspond to Ga interstitials, which can also form complexes and can thus account for the strong compensation effects observed in these epilayers.