Localized States in Amorphous and Polycrystallized Si

Optical and electrical properties of electron-beam deposited amorphous Si films have been measured in a wide range of annealing temperatures to investigate the nature of localized states. Polycrystallization of Si films was found to be accompanied by an abrupt decrease in the refractive index and film thickness. The localized state density near the Fermi level is obtained to be ∼10 20 cm -3 eV -1 for as-deposited samples from capacitance measurements of a-Si/SiO 2 /p + Si tunnel junctions. Field effect results showed that this density is reduced to ∼10 18 cm -3 eV -1 by annealing at 650°C and subsequently to ∼10 17 cm -3 eV -1 after polycrystallization. On the other hand, the density at ∼0.21 eV above the Fermi level remains almost unchanged around 5 × 10 19 cm -3 eV -1 irrespective of annealing and polycrystallization, suggesting the presence of a common structural defect in amorphous and polycrystalline Si.