Structural and Optical Properties of the Thermally Stable Amorphous Si 1-x B x Alloy
- PDF / 1,839,809 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 6 Downloads / 205 Views
STRUCTURAL AND OPTICAL PROPERTIES OF THE THERMALLY STABLE AMORPHOUS Sim-iB, ALLOY. JOHAN R. A. CARLSSON, X.-H. LI, S. F. GONG, AND H. T. G. HENTZELL Thin Film Division, Department of Physics and Measurement Technology, Linkdping University, S-581 83 Linkbping, Sweden
ABSTRACT Thin amorphous Sil-xBx films were co-evaporated onto pre-oxidized (100) Si wafers and quartz substrates, by using a high vacuum system with 2 electron guns. Films were deposited in a composition range from x=O to x=0.5. In order to study how the structural and optical properties depended on concentration and annealing temperature, heat treatments were carried out at temperatures from 400 up to 1000 'C. The films were characterized by means of transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and light absorption spectrophotometry. It is shown that the amorphous Sil-xBx alloy is stable up to 1000 'C at certain compositions and that the optical band gap of the alloy increases gradually with increasing annealing temperature up to 700 - 900 'C, and then increases rapidly when annealed at a higher temperature by about 0.5 eV. These changes can be associated with microstructural alterations. The relationship between the microstructure and the band gap of the films is discussed.
1. INTRODUCTION We have previously shown1 that a stable amorphous silicon-boron (a-Si1-x.Bx) alloy with x=0.3 can exist even after annealing at temperatures as high as 1100 TC. This very high thermal stability has been the driving force for us to conduct more careful studies of the microstructure and properties of these films since amorphous alloys are very seldom stable at high temperatures. For example, pure amorphous Si crystallizes at about 630 0C 2 and the relatively stable amorphous Si-Ti alloy crystallizes at 580 °C. 3 Boron is a non-metal and a p-type dopant in crystalline silicon, and its effects on the solid phase epitaxial regrowth of polycrystalline silicon (polysilicon) has been shown before. 1 In this work, the structural and optical band gap properties of the amorphous silicon-boron (a-Sil.xBx) alloys and their dependence on annealing temperatue and composition have been studied by utilizing transmission electron microscopy (TEM), Auger electron spectroscopy (AES), and light absorption spectro-photometry. In this work, we reveal the correlation between the microstructure and the optical band gap of the alloys. Furthermore, the mechansim of the alloy formation and the changes in the optical band gap associated with composition and annealing temperature are discussed.
II. EXPERIMENTAL DETAILS The samples used in this study, with x=0, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5, were subsequently annealed at temperatures between 400 and 1000 TC for the study of temperature and concentration dependence on the structural and optical band gap properties. All samples were deposited onto pre-oxidized Si wafers and quartz substrates. The Si and quartz substrates were first cleaned with the RCA treatment4 and then oxidized at 1100 TC for 60 min wi
Data Loading...
