Structural and photoluminescence properties of porous GaP formed by electrochemical etching

The structural and optical properties of porous GaP have been studied by scanning electron microscopy, spectroscopic ellipsometry, and photoluminescence (PL) spectroscopy. Porous GaP layers were fabricated by anodic etching in HF:H₂O:C₂H₅OH=1:1:2 electrolyte on n-type (100) and (111)A substrates. The morphology of the porous GaP layer is found to depend strongly on the surface orientation. Apart from the red emission band at ∼1.7 eV, a supra-band-gap (E_g^X) emission has been clearly observed on the porous GaP (111)A sample. The anodic porous layer on the (100) substrate, on the other hand, has shown only the red emission at 300 K and both red and green donor-acceptor pair emissions at low temperatures. The correlation between the PL properties and the porous morphology is discussed. An optical transition model is also proposed for the explanation of the PL emission properties of the porous GaP samples.