Behavior Of Iron Impurities In Boron And Gallium Co-doped Czochralski Silicon

Compared with other semiconductor materials,silicon has the obvious advantages of natural abundance,low material cost,easy growth process and high compatibility.These advantages make silicon become the most widely used material in photovoltaic industry.However,solar cells based on boron-doped crystalline silicon suffer from light induced degradation due to the formation of recombination-active boron-oxygen?B-O?complexes under illumination,which reduce the performance of related solar cells.The boron-gallium?B-Ga?co-doped silicon can not only alleviate the light induced degradation caused by the B-O,but also improve the strong resistivity variation for the Ga-doped silicon,which has a broad application prospect.Therefore,a systematic evaluation on co-doping effect is necessary,including the interaction between the acceptors?B,Ga?with other impurities,especially the iron?Fe?,which is one of the most common and important contaminants in silicon.This thesis focuses on the distribution of iron-acceptor pairs and their hydrogen passivation behavior of B-Ga co-doped Czochralski silicon?CZ-Si?,as well as the electrical properties of iron precipitation.The innovative results achieved in this thesis are addressed as following:?1?The distribution of iron-acceptor pairs,hydrogen passivation behavior and its thermal stability of B-Ga co-doped CZ-Si have been studied.Iron contamination was introduced by FeCl₃ solution and high-temperature annealing.It was found that H introduced by a piranha solution and RBA treatment can passivate both Fe-B and Fe-Ga pairs in B-Ga co-doped CZ-Si.In the study of thermal stability of hydrogen passivation,it is found that the hydrogen passivation will be partially invalid when annealed under 250?.Obvious dissociation of acceptor-hydrogen?Ac-H?pairs was observed when annealing temperature is above 160?.The temperature of highest failure fraction for H passivation on Fe-B and Fe-Ga pairs are 80?and 200?,respectively,indicating the thermal stability of passivated Fe-Ga is stronger.A mechanism was given that H atoms were released from the dissociation of Ac-H pairs,which would passivate Fe-B/Fe-Ga pairs again.?2?The electrical properties of Fe precipitation in B-Ga co-doped CZ-Si have been investigated,including the energy levels and defect types of the early stages on Fe precipitation,as well as the comparison with B-doped and Ga-doped CZ-Si.The samples were annealed above 200?to form the early stages of Fe precipitation.By deep level transient spectroscopy?DLTS?,it is found that the defects corresponding to the early stages of Fe precipitation in the three samples are all extended defects,but the energy levels of them are different.It can be related to the different dopants around the Fe precipitation.At the same time,it can be concluded that the precipitation process for Fe is that some iron atoms begin to grow to a large cluster containing many iron atoms.With the increase of the number of iron atoms in the clusters,they gradually form Fe precipitation.