STM-BASED LUMINESCENCE SPECTROSCOPY ON SINGLE QUANTUM DOTS

The ability to fabricate quantum dots using the Stranski-Krastanow gro wth technique has improved dramatically during the last number of year s. Due to the large number of dots formed (typically 10(8)-10(9) cm(-3 )) the emission linewidth is inhomogeneously broadened. We have grown quantum dots of InP in between barriers of GaInP, as well as on top of GaInP, having a low density of dots in order to perform single-dot sp ectroscopy. These dots have been studied by photoluminescence and scan ning tunneling luminescence. We find in photoluminescence that the ful ly formed dots have well-defined, sharp (0.04-1 meV) emission lines, w hich are very similar from dot to dot. In scanning tunneling luminesce nce we find that we can very locally excite only a few partially forme d dots which have sharp emission lines (0.1 meV at 77 K). These emissi on lines display a quantum confined Stark effect when the applied tip to sample bias is varied. We can carefully determine the onset of exci ton formation as a function of applied bias. The applied bias which is necessary for impact ionization is found to agree well with simple th eory.