Room-temperature Near-infrared Electroluminescence From Boron-diffused Silicon Pn Junction Diodes

As the development of integrated circuits (IC), the disadvantages of traditional metal interconnection structure, such as interlayer interference, energy dissipation and signal delay, have become a bottleneck restricting the development of ultra-large-scale integration circuits (USLIC). Optical interconnection which uses photons to transform information will be an ultimate solution for future progress in USLIC. Due to silicon being an indirect-band-gap semiconductor and fundamentally unable to emit light efficiently, achieving efficient silicon-based light source compatible with the current IC manufacturing technology has become the key issue of silicon optoelectronics. As their structure is simple and fabrication process totally compatible with CMOS technology, silicon pn junction diodes have attracted much attention. The past few years has seen great advances in the development of silicon pn junction diodes. The near-infrared luminescence of silicon pn diodes has shown great application potential in silicon optoelectronics.In this thesis, silicon pn diodes with different doping concentrations and junction depths have been fabricated by boron-diffusion in the manner of rapid thermal processing (RTP) and furnace processing (FP). Their electroluminescence (EL) and luminescence mechanism have been carefully studied. Additionally, improving the EL efficiency of silicon pn diodes by surface texture processing has been systematically investigated. The primary achievements are summarized as follows:(1) Silicon pn diodes with different doping concentrations and junction depths are achieved by boron diffusion. The carrier concentration of silicon pn diodes made by RTP is about1016cm-3～1017cm-3and the junction depth is about200nm-500nm, while those of silicon pn diodes made by FP are1017cm-3～1020cm-3and2μm～5μm. All silicon pn diodes show good rectifying properties.(2) The room-temperature near-infrared EL performance of silicon pn diodes is studied. The result shows that the doping concentration and junction depth have great influence on the optical properties of silicon pn diodes. In the room-temperature near-infrared EL spectra of lightly doped diodes only band-to-band emission (BB-line,～1.1eV) is observed, while in that of heavily doped diodes the0.78eV luminescence is observed besides BB-line under the condition of high power injection. In addition, the peak intensity of the0.78eV emission increases exponentially with the injection power with no observable saturation. The turn-on power of the0.78eV luminescence could be decreased by increasing the doping concentration while keeping the junction depth.(3) Strong0.78eV emission at room temperature is achieved and its origination is carefully investigated. In the low-temperature photoluminescence (PL) spectra of the relevant pn diodes no dislocation-related luminescence is found. And in the cross-sectional transmission electron microscope (TEM) no dislocations or dislocation loops are found. We deduce the0.78eV emission originates from the irradiative recombination at the strain regions caused by large number of boron atoms diffusing into silicon lattice.(4) Extremely heavily doped silicon pn diodes with dislocations are achieved by boron diffusion. In the TEM image of those diodes, short dislocations are found in the region2μm～3μm close to the surface. And in the low-temperature PL spectra, typical dislocation-related luminescence bands (D1-D4) are observed. In the room-temperature EL spectra, only strong0.78eV emission is found. Strong0.78eV electroluminescence from both silicon pn diodes with and without dislocations is achieved.(5) Surface texture processing is used to improve the EL efficiency of silicon pn diodes. The dependence of pyramids’size on the light extraction efficiency is studied both from the theoretical and practical aspects. Through FDTD simulation, large and closely packed pyramids have strong improvement effect on the extraction efficiency, which can reach2.6times as that of planar silicon pn diodes. The experiment results show that pyramid-structured surface can improve the EL intensity of silicon pn diodes and large size pyramids do more good. In addition, the highest power conversion efficiency we get from surface textured silicon pn diodes is about1.6times as that of planar silicon pn diodes.