AVS 47th International Symposium
    Surface Science Wednesday Sessions
       Session SS-WeP

Paper SS-WeP16
X-ray Photoelectron Spectroscopy Measurements of Mid-gap Density of States in Amorphous Hydrogenated SiC Thin Films

Wednesday, October 4, 2000, 11:00 am, Room Exhibit Hall C & D

Session: Poster Session
Presenter: F.S. Ohuchi, University of Washington
Authors: F.S. Ohuchi, University of Washington
M.-H. Lee, University of Washington
D.A. KuKuruznyak, University of Washington
Correspondent: Click to Email
Optical properties of amorphous Si-C thin films are directly related to electronic structure. The most significant optical parameters in amorphous systems are the optical band gap, E@sub g@, and the steepness parameter of the exponential absorption edge called Urbach energy, E@sub u@. In amorphous materials such as amorphous hydrogenated SiC (a-Si@sub 1-x@C@sub x@:H) thin films, the absorption edge is not clearly defined, and the Urbach tails further complicate the electronic band structure due to the mid-gap energy states. By fabricating metal-semiconductor junctions, electrons can be externally supplied to the mid-gap states. When an insulating layer further exists between the metal and a-Si@sub 1-x@C@sub x@:H thin film, occupied electrons in the mid-gap states will induce charges in the insulator, resulting in a shift in the electron binding energy at the interface, thus the density of mid-gap states can be measured by X-ray photoelectron spectroscopy (XPS). In this talk, a new method to evaluate the mid-gap density of states is proposed and applied to a-Si@sub 1-x@C@sub x@:H thin films. Experimentally, a-Si@sub 1-x@C@sub x@:H was deposited on the top of Au surface on Si by DC plasma enhanced chemical vapor deposition. Very thin oxide (SiO@sub 2@) and Au layers with the thickness of below electron penetration depth were grown subsequently. The shift in difference between Au 4f and Si 2p core-level binding energies was measured by XPS as a function of the bias voltage. The energy distribution of mid-gap DOS was obtained from analyzing the amount of the bias-induced binding-energy shift, and the measured mid-gap DOS was further compared to optical absorption measurements in an attempt to elucidate the relationship between the optical property and electronic structure in a-Si@sub 1-x@C@sub x@:H thin films.