Kinetics of Light-Induced Deffect Formation and Annealing in Hydrogenated Amorphous Silicon Alloyed with Sulfur
- PDF / 350,508 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 44 Downloads / 208 Views
ABSTRACT The creation and annealing kinetics of light-induced defects in a-SiS.:H are studied by ESR and LESR measurements. The dispersion of defect creation after prolonged illumination with white light is greater for a-SiSI:H than that for undoped a-Si:H. In addition, the saturated value of the dark spin density is slightly lower for a-SiSx:H than that for a-Si:H. The annealing behavior can be fitted with a Gaussian distribution of annealing activation energies as is the case for undoped a-Si:H. The incorporation of sulfur decreases the peak energy and increases the width of the distribution of activation energies. Light-soaking does not change the low temperature LESR spectrum and LESR spin density. INTRODUCTION One of the most serious problems in hydrogenated amorphous silicon (a-Si:H) is the metastability that is introduced after prolonged illumination with white light (normally called the Staebler-Wronski effect),' an effect that significantly limits the application of a-Si:H in devices. Although the fundamental mechanism of the Staebler-Wronski effect is not clear,2 efforts to improve the stability of the material have taken several approaches. One approach, the addition of chalcogen elements (S and Se) into a-Si:H, has resulted in a decrease of the degradation of conductivity and photoconductivity after light-soaking. Wang et al. 3 found a persistent photoconductivity (PPC) in a-SiS.,:H films, whose effect on both the conductivity and photoconductivity is opposite to the Staebler-Wronski effect. It is possible that the presence of the PPC effect may increase the stability of the materials and devices. Recent studies have shown that the Staebler-Wronski effect and the PPC effect occur on different time scales during light-soaking and anneal at different temperatures in a-SiS,:H and a-SiSe.:H.4 A similar phenomenon has also been observed in compensated a-Si:H samples doped with phosphine and diborane. 5 Although a model based on optically-induced activation of sulfur donors during lightsoaking has been proposed,6 there is still only weak experimental evidence to support the model. Sulfur can be a double donor in crystal silicon, and the lowest donor level is relatively deep.7 In addition sulfur donors can be passivated by hydrogen atoms. The situation is more complicated in the amorphous phase. First, the random network in amorphous silicon provides the possibility for chalcogen atoms to form two-fold-coordinated structures (the favorite coordination of chalcogen atoms), which is one factor that leads to the low efficiency of doping.' Second, the significant concentration of hydrogen in the materials may passivate the donors that are at substitutional sites In this paper, we report the kinetics of generation and annealing of light-induced defects in a-SiSX:H films and in undoped a-Si:H films. The defect density was measured by electron spin resonance (ESR) and light-induced ESR techniques.
453 Mat. Res. Soc. Symp. Proc. Vol. 507 0 1998 Materials Research Society
EXPERIMENTAL PROCEDURE The a-SiSx:H and undo
Data Loading...
