Growth and characterization of Al_xGa_1-xAs obtained by metallic-arsenic-based-MOCVD¹

In this work reports results related to growth and characterization of Al_xGa_1-xAs epilayers, which were grown in a metallic-arsenic-based-MOCVD system. The gallium and aluminium used precursors were trimethylgallium (TMGa) and trimethylaluminium (TMAl), respectively. By photoluminescence measurements observed, that only samples grown at temperatures above 800°C display photoluminescence. Hall measurements on the samples showed highly compensated material. Samples grown at temperatures lower than 750°C were highly resistive. Independently of the V/III ratio; the samples grown at higher temperatures were n-type. As the temperature is increased the layer compensation decreases. The Al_xGa_1-xAs epilayers resulted n-type with an electron concentration of 1×10¹⁷ cm^-3 and a corresponding carrier mobility of ~2200 cm²/V×s. Raman spectra show vibrational bands associated to TO-GaAs-like (262 cm⁻¹), LO-GaAs-like (275 cm^-1), TO-AlAs-like (369 cm^-1) and LO-AlAs-like (377 cm^-1). The Raman spectra show the epilayers become more defective as the growth temperature is increased. The chemical composition was studied by SIMS exhibit the presence of silicon, carbon and oxygen as main residual impurities. The silicon concentration of ~1.0×10¹⁷ cm^-3 is very close to the carrier concentration determined by the van der Pauw measurements. The residual oxygen detected on the samples maybe responsible of the weak photoluminescence signal of the Al_xGa_1-xAs layers.