The technology breakthrough
a ultrafast 4D scanning electron microscope

We developed a new measurement tool for semiconductor nanostructures that combines both high spatial and high temporal resolution. We transformed a scanning electron microscope so that it acquired picosecond temporal resolution besides its intrinsic nanometer spatial resolution. This goal was achieved by replacing the original electron source by an ultrafast pulsed electron gun and a time-resolved detection line. Results we obtained on this tool have been acknowledged by the scientific community by main publications in Nature and Applied Physics Letters.

This breakthrough is very similar to the invention of the movie camera after the film camera, except it does not bring time to the real world but to the nanoworld.

Pulsed electron gun

Attolight's 4D microscope performs excitation spectroscopy. Electron excitation spot can be chosen with a precision of 50nm. An exciting pulse arrives every 12ns on the sample (80MHz repetition rate) and last 10ps. In average the system delivers one electron per pulse, which makes it useable for single electron injection.

Light collection and detection

The light coming out of the structure (cathodoluminescence) is collected by a parabolic mirror mounted above the sample. It is then detected as a function of time and energy by our time-resolved detection line (PicoMaster). Our pattented detection line consists of a monochromator with two exits ports. One exit is coupled to a STREAK camera for time-resolved detection and the other exit is coupled to a photomultiplier for continuous cathodoluminescence measurements.

Data treatment

Knowing the typical energies of the nanostrucutures under investigation determined by standard CL or optical methods one can deduce the excited carriers diffusion paths.

Applications

Transport measurement

The vertical quantum wire at the center of the pyramid is charecterized by a lower energy than the lateral quantum wire. The farther we move the excitation point away from the vertical quantum wire, the lower gets the rise time of its luninesence signal. This directly indicates carrier diffusion to the vertical quantum wire. Fitting this signal yields excited carrier diffusion coefficient and mobility.

The graphs show time-resolved spectra of a vertical quantum wire connected to the lateral quantum wire.

For more details see Nature, 438 p.479 Nov. 2005 (Restricted link)

Local lifetime study

Local time-resolved luminescence spectra show lifetime variations indicating the predominence of non radiative recombinations in the vicinity of threading dislocations.

Not yet published