SILICON-BASED STRUCTURES FOR IR LIGHT-EMISSION

There is a lot of interest in obtaining efficient infra-red (IR) light emission from Si-based structures for use in optoelectronics. Althoug h it has been theoretically predicted that Si-m/Ge-n atomic layer supe rlattices can have a quasi-direct bandgap, the experimental studies ha ve not yet given very high luminescence intensities, particularly at r oom temperature, from such structures. So far, the most efficient meth od to have IR light emission at room temperature is to process Si/Si1- xGex superlattices or quantum well structures into narrow (<60 nm diam eter) columnar structures. After planarization with insulating materia l it has been possible to fabricate LEDs using these columns. While th e results are very promising there are also a number of unsolved probl ems concerning the mechanism allowing for efficient light emission and concerning the passivation of the surfaces of the columns to have a l ong-term stability of the emission. Another way to have IR light emiss ion 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-rel ated emission at 1.54 mu m it is necessary to also have co-dopants lik e O or F to activate the Er. Since a high temperature step is necessar y to anneal out implantation damage it has been difficult to have high concentrations of Er/O without precipitation, as the required concent ration for useful devices is far above the solid solubility of Er in S i. Low temperature growth using MBE is a promising method to achieve h igh Er/O or Er/F concentrations without precipitation and intense room -temperature elec troluminescence has very recently been reported from a reverse biased Er/O-doped LED grown by MBE.