Study On The Electrical Behavior Of Copper And Silver In Single Crystalline Germanium

Germanium is an important semiconductor material. As the development of semiconductor industry, study on germanium has become a popular subject. Similar with silicon, germanium-based materials are easily contaminated by transition metals in cleaning and fabrication processes. In order to reduce or avoid the damage caused by metallic impurities,it is necessary to study the electrical behavior of transition metals in the single crystalline germanium.In this work, based on systematic review of the application of germanium-based materials and research on the electrical behavior of transition metals in germanium, it is found that the electrical behavior of copper and silver in single crystalline germanium processed by RTP has not been studied yet. First, we compare resistivities of copper contaminated germanium processed by conventional heat treatment and rapid heat treatment. By XRD and infrared transmission, the electrical behavior of copper and silver in germanium was analysed. Then the conduction type, resistivity and minority carrier lifetime of germanium processed by rapid heat treatment in different atmosphere, temperature and time are measured. The states of germanium are analyzed by the measurement of the spread resistance and correlated theory. Finally, we do the same experiment on silver contaminated germanium. This work fills research voids of the effect of transition metals on electrical properties of single crystalline germanium processed by RTP.Experimental results show that, when the heat treatment temperature is low, whether in conventional heat treatment or rapid thermal conditions, the diffusion of copper from the surface into germanium is slow. Cu₃Ge is generated at the surface of germanium. The diffusion of copper from the surface into germanium is fast when the heat treatment temperature is higher than 800℃and Cu mainly exists in the form of acceptor in gemanium, which is stable at room temperature. It is also found that the diffusion of copper under the conditions of rapid thermal treatment is much greater than that of conventional heat treatment.The resistivity of copper contaminated germanium increases at first and then decreases with increasing RTP temperature. The resistivity of copper contaminated germanium shows same trend with increasing RTP time. When the RTP temperature and RTP time is enough, the conduction type of germanium changes from N-type to P-type. Analysis indicates that this is caused by copper diffusion and its single acceptor states in germanium during the solid solving process. The precipitation time constant of copper in germanium decreases with decreasing copper concentration. Therefore, during the rapid thermal process, copper is more difficult to form precipitation. Minority carrier lifetime of germanium with the RTP time remained relatively stable after the first drop. Analysis shows that this phenomenon is not caused by the precipitation of copper, and may be caused by Cu_s^2-, and the concentration of Cu_s^2- kept constant when RTP time is more than 30 seconds.The electrical behavior of silver in germanium is similar to that of copper. However, the silver concentration in the germanium is much less than the concentration of copper in germanium. The minority carrier lifetime of silver contaminated germanium decreases after RTP. When the silver concentration is low, the concentration ratio between the double-acceptor state of silver and single-acceptor state of silver is a constant. When the concentration of silver increases, the concentration of double-acceptor-state of the silver increases.