Luminescence study of the disorder in polycrystalline InP thin films

InP films have been deposited on amorphous sapphire substrate by means of t he metallorganic chemical vapour deposition technique with and without PH3/ H-2 plasma preactivation. Polycrystalline materials, having average grain s izes of about 40 nm, which, however, vary according to the growth parameter s, were obtained. The structural and compositional disorder strongly influe nce the optical and electrical properties. The most structurally disordered films present the largest photoluminescence (PL) efficiency and a blue-shi ft of the whole PL spectra. Radiative recombinations of carriers confined i n crystallites having the smallest sizes are proposed to explain such an an omalous behaviour. The temperature dependence of the bandgap follows the we ll known phenomenological models except for the hydrogenated samples, in wh ich a blue-shift of the intrinsic luminescence band is observed with increa sing temperature. This anomalous effect is related to phonon-assisted trans itions between nanoclusters with different sizes. Electrical conductivity m easurements show different conductivity mechanisms in two different ranges of temperature. In particular, for temperatures lower than 200 K the conduc tion mechanism is due to a variable-range hopping process.