PHOTOLUMINESCENCE ABOVE THE EXCITATION-ENERGY IN ALPHA-SIH

Photoluminescence (PL) has been measured in hydrogenated amorphous sil icon (alpha-Si:H) at energies above the exciting light energy, E(x), f or E(x) = 1.33 and 1.38 eV. The shape of the PL at energies above E(x) , is essentially identical to the shape of the PL in the same spectral region when excited with E(x) above the optical gap (greater-than-or- equal-to 1.9 eV) and is also essentially independent of temperature ev en though the shape of the PL below E(x) exhibits a marked temperature dependence. Although the dependence of PL intensity above E(x) on exc itation power is only slightly greater than unity, we attribute the ex citation mechanism to a two-step process that proceeds through the man ifold of silicon dangling-bond states even in high-quality alpha-Si:H.