Amorphous phase formation in InxGa1-xAs, InxGa1-xP and Si1-xGex

Abstract

Amorphous semiconductors have found uses in an increasing variety of electronic and photonic devices over the last few decades, many of which are now commonplace. The ubiquitous Thin Film Transistor (TFT) LCD/LED flat panel display is a multibillion dollar per annum industry. Other examples include photovoltaic cells and night vision systems. A thorough understanding of the physical characteristics of this class of materials is of commercial, military, scientific and technological interest. In particular, a deeper understanding of the amorphisation process may assist in accelerating the uptake of this technology. This thesis investigates the amorphisation kinetics of three semiconducting materials, InxGa1-xAs, InxGa1-xP and Si1-xGex, to gain an understanding of the damage production process in these materials via ion implantation. Ion implantation is a commonly used technique in the semiconductor industry for rendering materials amorphous due to the precise control it offers over the implanted ion fluence and ion species. All three of these materials are of technological importance for their use and development in fields such as solar cells for space applications, quantum well FETs, wireless LAN and GPS applications. Ion implantation was performed using Ge ions to render InxGa1-xAs, InxGa1-xP and Si1-xGex amorphous. Implantation induced disorder was quantified with Rutherford backscattering spectroscopy in the channelling configuration (RBS-C). EXAFS measurements were preformed to study the local atomic structure of the crystalline material. Parameters such as bond length, bond angle and structural disorder were deduced from the EXAFS measurements. These results were then correlated to RBSC to help explain the amorphisation behaviour observed in InxGa1-xAs, InxGa1-xP and Si1-xGex. It was found that distortion in both bond length and bond angle distribution was apparent for both InxGa1-xAs and InxGa1-xP with the structural disorder primarily being accommodated by bond angle distribution. This leads to the presence of local regions of strain acting as preferential sites for stimulated amorphisation. The amorphisation kinetics observed in InxGa1-xAs and InxGa1-xP are attributed to these pre-existing local strain regions. The structural disorder observed in crystalline Si1-xGex was much reduced in comparison to the InxGa1-xAs and InxGa1-xP. Hence, amorphisation kinetics observed in Si1-xGex differ from those observed in InxGa1-xAs and InxGa1-xP. It is hoped that the insights gained by this thesis into the amorphisation kinetics of these materials will help open up more avenues and application for the use of these and materials similar to these in the electronics industry.