Silicon-based structures for IR light emission

Abstract

There is a lot of interest in obtaining efficient infra-red (IR) light emission from Si-based structures for use in optoelectronics. Although it has been theoretically predicted that Sim/Gen atomic layer superlattices can have a quasi-direct bandgap, the experimental studies have not yet given very high luminescence intensities, particularly at room temperature, from such structures. So far, the most efficient method to have IR light emission at room temperature is to process Si/Si1-xGex superlattices or quantum well structures into narrow (<60nm diameter) columnar structures. After planarization with insulating material it has been possible to fabricate LEDs using these columns. While the results are very promising there are also a number of unsolved problems concerning the mechanism allowing for efficient light emission and concerning the passivation of the surfaces of the columns to have a long-term stability of the emission. Another way to have IR light emission at room temperature and possibly obtain a Si-based laser is to use Er-doped material. For Er-doped LEDs, most of the work has been done on ion-implanted structures. It has been found that to have the Er-related emission at 1.54 μm it is necessary to also have co-dopants like O or F to activate the Er. Since a high temperature step is necessary to anneal out implantation damage it has been difficult to have high concentrations of Er/O without precipitation, as the required concentration for useful devices is far above the solid solubility of Er in Si. Low temperature growth using MBE is a promising method to achieve high Er/O or Er/F concentrations without precipitation and intense room-temperature electroluminescence has very recently been reported from a reverse biased Er/O-doped LED grown by MBE.