Dielectric function of amorphous indium gallium zinc oxide (a-IGZO) thin films is found to shift significantly with the film thickness, which is attributed to the changes in both the bandgap and electron concentration of the IGZO thin films with the film thickness. The ultrathin films (film thickness < ∼20 nm) exhibit a bandgap expansion with reducing film thickness due to the quantum confinement effect; while the thicker films (thickness > ∼35 nm) demonstrate the free-electron effect, i.e. the Burstein-Moss shift and increase of free-electrons absorption with increasing electron concentration Amorphous indium gallium zinc oxide (a-IGZO) is a transparent semiconductor material that has promising application in next generation flat panel display due to its high electron mobility and high transparency in visible. 1,2 Although intensive electrical studies have been carried out on the IGZO thin films, 3-6 there is still lack of detailed optical study of the complex dielectric function, one of the fundamental optical properties, of the IGZO thin films. It has been shown in our early work that free-electron concentration of a metal oxide thin film could have a significant impact on the optical properties of the oxide film, in particular, the onset absorption near the band edge. 7 When the electron concentration reaches ∼10 18 -10 19 cm −3 , a semiconductor-to-metal transition occurs, and the conduction band of the oxide semiconductor is partially filled with free electrons, resulting in a bandgap expansion as a result of the Burstein-Moss effect. 8 The dependence of carrier concentration on film thickness could further complicate the situation. 9 On the hand, it has also been shown that when a crystalline oxide film scales down to the nanoscale regime (e.g., the film thickness is less than ∼20 nm), the nanoscale structures exhibit some unique properties different from their bulk counterparts due to quantum confinement effect. 10 Therefore, it is interesting to study the thickness-dependence of the complex dielectric function of a-IGZO thin films as both the free-electron and quantum confinement effects on the optical properties of the oxide films are dependent of the film thickness.In this work, we present a study of the evolution of optical properties of a-IGZO thin films with film thickness. The bandgap and complex dielectric function of the IGZO thin films with various film thicknesses have been determined with spectroscopic ellipsometry (SE) based on the Tauc-Lorentz-Drude (TL-Drude) model. 8 It is observed that the complex dielectric function is strongly dependent of the film thickness. The ultrathin films (thickness < ∼20 nm) show a blueshift of both the real and imaginary parts of the complex dielectric function and an expansion of bandgap with decreasing film thickness due to the quantum confinement effect; in contrast, the thicker films (thickness > ∼35 nm) exhibit both the Burstein-Moss shift and enhancement of free-electrons absorption with increasing film thickness, which are related to the increase of elec...

Blue light optical storage products will become the next generation devices for recording media in the near future. To increase the crystallisation speed of recording by 405 nm wavelength blue laser diode, bismuth (Bi) is applied to substitute small quantities of antimony (Sb) in a pseudobinary GeTe-Sb 2 Te 3 (GeSb 2 Te 4 ) alloy material. It is shown that the activation energies for crystallisation of Ge-Sb-Te-Bi are reduced by addition of Bi indicating the improvement of recording speed. The Ge-Sb-Te-Bi material is incorporated into actual blue light phase change optical disks and is found to provide good land and groove recording characteristics, cross-talk characteristics, and cross-erase characteristics. It is demonstrated a promising candidate for HD DVD-RAM applications.