Dependence on the atmosphere of preparation of the Iuminescence of spark processed porous GaAs

We report on the preparation of photoluminescent porous GaAs by the application of high voltage spark discharges in atmospheres of pure oxygen, pure nitrogen, and in mixed N₂:O₂ ratios of 4:1 and 1:4. The spark-processed porous (spp) samples were characterized by the observation of their visible photoluminescence (PL) when illuminated with UV monochromatic radiation. Some differences are observed in the initial PL spectra of the spp-GaAs according to the atmosphere of preparation under similar sparking and time conditions. The PL consists of two dominant bands, a yellow-green band between ∼2.2 and 2.6 eV and a blue-violet band, centered at 3.1 eV. Comparison with Raman and PL results from As₂O₃ and As₂O₅ indicates that the PL in the spp-GaAs is produced by the formation of these compounds by exposure to oxygen during the preparation. This is reinforced by energy dispersive x-ray spectroscopy measurements that indicate that the spp-GaAs is always oxidized, even when prepared under a nitrogen flow. The blue-UV emission at 3.1 eV suggests that we cannot rule out confinement as a contributing mechanism for this PL. Raman spectra indicate that for samples prepared in pure nitrogen, the resulting material consists of amorphous As and GaAs, and the cubic form of As₂O₃, arsenolite. PL and Raman indicate that there exists an increasing degree of amorphization of the resultant material with the introduction of nitrogen in the preparation atmosphere.