Luminescence Property And Physical Structure Of Dislocations Induced By Electron Irradiation In Silicon

It is well known that silicon is one of the most important semiconductor materials which is widely used for microelectronic devices. The silicon photoelectric monolithic integration can provide a large bandwidth optical interconnects, inexpensive manufacturing for optoelectronic devices. These advantages make the silicon-based optoelectronics become one of the hotspots of the international semiconductor research. However, the lack of silicon-based light source which is compatible with the current IC manufacturing process has been the most important issue of silicon optoelectronics. The luminescence based on defects in silicon, especially the light-emitting in the infrared band based on silicon dislocations has become one of the most important paths to silicon-based light source.In this dissertation, the electron beam irradiation technique has been creatively and successfully applied to inducing dislocations in silicon and its generation mechanism, physical structure and properties have been systemetically investigated. The photoluminescence and electroluminescence properties of different irradiated silicon samples (Czochralski silicon, float-zone silicon and cast quasi-single crystalline (QSC))silicon have been studied intensively. In the following, the primary achievements in this work are described.(1) The method of electron beam irradiation can induce dislocations into silicon with densities up to～107cm-2. The method has good controllability, one can selectively generate localized dislocations at a specific area by controling the position and angle of the electron beam. The dislocation structure is fragmented and localized. By increasing of the irradiation time, the macro-and micro-strain increase. The dislocations and other defects will react with each other by forming more complex structures. We believe that the silicon lattice expansion and contraction caused by thermal stress introduced under the the electron beam irradiation is the main reason for the induced dislocations. The method of electron beam irradiation is a new method to induce dislocations in silicon, which offters the new option for the study of defects in silicon and the silicon-based light-emitting materials.(2) The photoluminescence of dislocations in Czochralski silicon induced by electron beam irradiation are studied extensively by applying a wide range of temperature and time combinations. By applying the1050℃12h single step annealing, the Dl luminescence center has been successfully enhanced and stabilized and its quenching temperature has been substantially increased to room temperature. The D1peak activation energy is almost the same before and after heat treatment, which is-86meV. It is first reported that there is an abnormal energy movement of D1peak in the temperature range of170K-210K, which proves the existence of the reconstruction of D1luminescence center. Structural studies reveal that silicon point defects could participate in the reconstruction of the dislocation structure in the high temperature and long time annealing, thereby forming a complex dislocation-point defect structure. It is the reconstructed D1luminescence center which can strongly enhance and stabilize D1emitting at room temperature.(3) The origin of the0.78eV line has been investigated systematically by comparing the photoluminescence of the electron irradiated float zone silicon and Czochralski silicon. The activation energy of0.78eV line is-13meV which is much smaller than that of D1/D2lines. The0.78eV line has its unique dependence of the intensity on temperature, which reveals its nature is different than that of D1/D2lines. It is shown that the0.78eV luminescence center has no relation with the silicon oxygen atoms in the clusters, neither in the form of the thermal donor nor the oxygen precipitates. The0.78eV line may come from specific reconstructed dislocation structure which is easily influenced by point defects and temperature.(4) By preparing the silicon light emitting diodes, the power-dependent and temperature-dependent electroluminescence property of the electron irradiated silicon sample have been studied extensively. The strong Dl line around1.6μm is successfully achieved at room temperature. Studies show that the D1luminescence center is easily activated at15K, while the band-to-band luminescence requires a higher injection level. It reveals the competition of the Dl line and the band-to-band luminescence. It is also found that the～0.86eV peak beside the D1line in the electroluminescence spectra which only exist in the larger injected power. The power-dependent electroluminescence spectra study shows the D1center is composed by several dislocations induced energy levels. Compared to the band-to-band radiative recombination, the injected electron and hole will preferentially recombine near the D1luminescence center.(5) The photoluminescence of as-grown dislocations and irradiated dislocations in the QSC silicon have been investigated extensity. It is found that the distribution of the native dislocations in the same QSC silicon wafer is widely varied, and the luminescence properties show significant differences in different regions. There are identical dislocation related D1～D4lines in the as-grown dislocations. The dependence of D1/D2peak positions on the temperature is different with the single crystalline silicon. The D1and D2lines envelope together as a large peak after the high temperature and long time annealing. There is a phenomenon that the peak position first blue shifts than redshifts with the increase of the temperature. In the QSC silicon, there is a complex reaction of as-grown dislocations and irradiated dislocations with the impurities and point defects, which exerts great effects on the D1luminescence center. The heat treatment will make the impurities and point defects form atmosphere bubbles around the dislocation stress field; when the temperature increases, the bubbles move, resulting in the abnormal peak movement of D1line. It reveals the fact that the dislocations luminescence centers is very susceptible to the influence of point defects.