PAGE 186
Low Temperature Photolithography
selected applications for cryogenic confocal microscopy
Laser
750 nm
PL signal
Laser
532 nm
Objective
Resist
layer
QDs
(Scheme courtesy of Pascale Senellart, LPN, CNRS, Paris,France)
Optical image of an in-situ lithography pattern
centred on a single QD (see [4] for details)
Very sophisticated new techniques in device fabrication have greatly
benefited from the possibility of cryogenic in-situ optical lithography. For
example, to manufacture microcavities around single quantum dots, an
appropriate photoresist has to be exposed while the luminescence signal
of those single quantum objects is monitored, which requires cryogenic
sample temperatures. The French group around Dr. Pascale Senellart at
the Laboratory for Photonics and Nanostructures at CNRS has pioneered
this technique by combining confocal microscopy with in-situ optical
lithography at low temperature. This way they managed to embed a sin-
gle quantum object into a lithographically designed device with a yield
approaching 100%. Prior to this revolutionary technique, hit rates rarely
exceeded 1:10000, making previous approaches pain staking and ineffi-
cient. Based on their remarkable work [1-4], attocube is now offering a
commercial three channel cryogenic confocal microscope, capable of sim-
ilar high yields. Using the attoCFM I with three channels, low temperature
quantum devices such as quantum dots can now be individually selected
and addressed using their photoluminescence fingerprint. A sophisticated
closed loop control system allows users to determine (and relocate) the
position of each quantum device with a repeatability better than 10 nm.
While two channels are used for laser excitation and detection of the
quantum dot emission, a second laser – connected to the third channel
– allows lithography tasks on the nanometer scale at the location of the
previously located quantum device. This technique allows the researcher
to create pillar-shaped micro cavities or other sophisticated structures
around the quantum dot.
In fact, Dr. Senellart has recently received the 2014 Silver
Medal of Physics from the CNRS for her pioneering work. The
joint development of the “cryogenic scanning stage laser litho-
grapher” has resulted in a heavily used instrument in her laboratory.
This has helped to boost the production of quantum dot based quantum
devices for research purposes. Many researchers in the world are currently
benefiting from this device production.
[1] Dousse et al., Phys. Rev. Lett. 101, 267404 (2008)
[2] Dousse et al., Appl. Phys. Lett. 94, 121102 (2009)
[3] Dousse et al., Nature 466, 217-220 (2010)
[4] A. K. Nowak et al., Nature Communications 5, 3240 (2014)
Emission intensity map of the connected pillar (see [4] for details)
For more information on the instruments used in this
application, please refer to page 58: Breadboard
add-on with free-beam coupling.