COMPARISON OF ROOM-TEMPERATURE PHOTOLUMINESCENCE DECAYS IN ANODICALLY OXIDIZED CRYSTALLINE AND X-RAY-AMORPHOUS POROUS SILICON

The photoluminescence (PL) decay after pulsed YAG:Nd excitation at 353 nm of anodized p-type porous silicon layers (either PECVD-deposited X-ray-amorphous or bulk crystalline) has been studied as a function of PL wavelength in the ns to ms time range. The decays are similar for both materials, being strongly non-exponential with a slow (typically 10-100 mu s) and a fast (<50 ns) component, the latter being stronger in X-ray-amorphous films. The only major difference occurs at large wavelengths (above 750 nm), where the slow component of the decay in the amorphous layer becomes quite different from the ''universal'' [1] line shape observed in its crystalline counterpart, which is shown here to be that of a stretched exponential. These observations are borne out by delayed PL spectra obtained with a boxcar integrator in the same time range. We discuss various decay analysis procedures leading to an effective recombination rate distribution and compare the results derived for both types of material.