Low temperature photoluminescence properties of p- and n-type AlxGa1-xAs with x > 0.42

The photoluminescence (PL) spectra of n- and p-type AlxGa1-xAs (x > 0.42) g rown by metalorganic vapor phase epitaxy (MOVPE) and liquid phase epitaxy s how typically a broad PL band (BB) centered about 300 meV below the near ba nd-gap PL lines. In the MOVPE grown samples the BE is composed out of four lines. The BE intensity increases with the doping level and dominates the s pectrum at concentrations > 10(17) cm(-3). The temperature dependence of th e BE intensity shows two distinct maxima at approximate to 19 K and approxi mate to 80 K. Hydrogenation of MOVPE grown samples at 170 degrees C reveal an effective passivation of the shallow accepters and the centers associate d with the BE line. On the contrary hydrogenation at temperatures > 250 deg rees C leads to an increase in the BE intensity which is related with the e vaporation of As from the surface and the generation of Vn, in the layers a t these temperatures. Our results suggest that the BE is related with isoel ectronic centers formed when V-As and C-As or Si-As associate to form next nearest neighbor ion pairs. The PL is then due to a recombination of excito ns in analogy to the case of (Zn,O) isoelectronic complexes in Gap.