CHARACTERIZATION OF SIGE QUANTUM-WIRE STRUCTURES BY CATHODOLUMINESCENCE IMAGING AND SPECTROSCOPY

SiGe quantum wire (QWR) structures grown by gas source molecular beam epitaxy have been characterized by cathodoluminescence (CL) imaging an d spectroscopy. At T approximate to 5 K, the CL spectra obtained with a focused beam contain SiGe luminescence features associated with elec tron-hole plasma recombination. When the electron beam is defocused th ree separate SiGe no-phonon luminescence features and their transverse optic phonon replicas are observed. These features are related to rec ombination in the SiGe (100) quantum wells (QWs), SiGe (111) QWs, and the SiGe QWRs. The high generation rates associated with the focused e lectron beam quenches the luminescence and results in electron-hole pl asma recombination in the adjacent SiGe (100) QWs, and saturation of t he radiative processes. Defocusing the electron beam reduces the injec tion level and nonradiative processes, enabling the SiGe bound exciton features to be observed. Monochromatic CL imaging of the SiGe (100) Q Ws show that at low temperatures the CL image is broadened by exciton diffusion and becomes sharper at higher temperatures (T=50-70K) reflec ting nonexcitonic recombination. (C) 1995 American Institute of Physic s.