Temperature Dependent Line-Shape of the Silicon Dangling Bond EPR-Resonance in Polycrystalline Silicon
- PDF / 394,802 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 37 Downloads / 215 Views
N. H. NICKEL Hahn-Meitner-Institut Berlin, Rudower Chaussee 5, 12489 Berlin, F. R. Germany. E. A. SCHIFF Department of Physics, Syracuse University, Syracuse, New York 13244, USA.
ABSTRACT The temperature dependence of the silicon dangling-bond resonance in polycrystalline (poly-Si) and amorphous silicon (a-Si:H) was measured. At room temperature, electron paramagnetic resonance (EPR) measurements reveal an isotropic g-value of 2.005 5 and a line width of 6.5 and 6.1 G for Si dangling-bonds in a-Si:H and poly-Si, respectively. In both materials spin density and gvalue are independent of temperature. While in a-Si:H the width of the resonance did not change with temperature, poly-Si exhibits a remarkable T dependence of A~p In unpassivated poly-Si a pronounced decrease of AHpv is observed for temperatures above 300 K. At 384 K AJIpp reaches a minimum of 5.1 G, then increases to 6.1 G at 460 K, and eventually decreases to 4.6 G at 530 K. In hydrogenated poly-Si AHpp decreases monotonically above 425 K. The decrease of AJIpp is attributed to electron hopping causing motional narrowing. An average hopping distance of 15 and 17.5 A was estimated for unhydrogenated and H passivated poly-Si, respectively.
1. INTRODUCTION Electrical and optical properties of polycrystalline silicon (poly-Si) are dominated by grainboundary defects. These defects have been measured by electron paramagnetic resonance (EPR) and identified as silicon dangling-bonds with an average g-value of 2.0055.1 In order to obtain technologically usefu~l material, grain-boundary defects must be passivated. Commonly, this is achieved by exposing poly-Si to a hydrogen plasma at elevated temperatures. Hydrogen effectively passivates silicon dangling-bonds and thus improves the electrical properties of the material. 2 Defect passivation is diffu~sion limited and eventually the spin density saturates. 3 The silicon dangling-bond defect has also been detected in amorphous silicon, 4 at Si-Si0 2 interfaces, 5 and divacencies. 6 In contrast to crystalline silicon, amorphous silicon samples are characterized by an isotropic distribution of the defect symmnetry-axes with respect to the external magnetic field. This causes inhomogeneous broadening of the natural line-width. In this paper we present a temperature dependent change of the width of the dangling-bond resonance in unpassivated and hydrogenated polycrystalline silicon. With increasing temperature the line width decreases which is indicative of motional narrowing. We propose that this effect is due to el.ctron hopping between dangling-bond sites.
2. EXPERIMENTS Undoped polycrystalline silicon films were prepared by two different methods using quartz wafers as substrates. A set of fine grain poly-Si films was deposited by low-pressure chemical 1019
Mat. Res. Soc. Symp. Proc. Vol. 452 ©1997 Materials Research Society
vapor deposition at 625 'C to a thickness of 0.55 gm. Cross-sectional transmission electron microscopy revealed that the films were composed of columnar grains extending from the substrate t
Data Loading...
