ELECTROLUMINESCENCE, PHOTOLUMINESCENCE, AND PHOTOCURRENT STUDIES OF SI SIGE P-I-N HETEROSTRUCTURES/

Comparative electroluminescence and photoluminescence measurements wer e performed on Si/Si-0.7-Ge-0.3 p-i-n single quantum well structures, and on one p-i-n and one undoped multiple quantum well structure in a wide temperature range. The samples were grown pseudomorphically by mo lecular beam epitaxy, and mesa diodes for electroluminescence and phot ocurrent measurements were fabricated. In electroluminescence, optical emission comes primarily from the SiGe quantum wells whereas no emiss ion from Si is observed except for high temperatures of approximate to 200 K and up. All p-i-n structures exhibit maximum emission intensiti es in a temperature range between 80 K and 220 K, depending on the qua ntum well width. This temperature characteristic is very different fro m undoped quantum well samples. A model is discussed that accounts sat isfactorily for all observed temperature dependent data. As an essenti al feature, the model includes Auger recombination in addition to radi ative recombination in the n(+) and p(+) sides of the junctions and in the SiGe quantum well due to the high electron or hole densities in t hese regions. Photocurrent spectra due to single quantum wells are mea sured showing the SiGe absorption threshold in addition to the Si thre shold. Quantitative fits to these spectra yield threshold energies for SiGe and Si consistent with the electroluminescence spectra. The ques tion of how photogenerated excess holes that are bound in a quantum we ll can escape the well at 4.2 K to yield the measured photocurrents is discussed. (C) 1996 American Institute of Physics.