Laserprocessing at the WSI

Material processing with lasers takes advantage of all the characteristics of laser light. The high energy density and directionality achieved with lasers permits strong localized heat- or photo-treatment of materials with spatial resolution below one micrometer. The pulsed and monochromatic light allows the control of depth of heat treatment or selective excitation. The laser beam can be moved to process large areas, is a sterile tool and is no subject to wear and tear.

Fig. 1: Nd:YAG-Laser system

In our group we use a Nd:YAG laser system as shown in Fig 1. The laser beam intensity profile is Gaussian. We process semiconductors using the primary beam ("homogeneous laser processing"), apply interferenc effects to generate periodic intensity profiles as shown in Fig. 2a,b or use digital holograms shown in Fig. 3a,b.


Fig. 2 a) Intensity pattern generated by two interfering beams b) Intensity pattern generated by interference of three beams


Fig. 3 a) Digital Hologram and b) the Intensity pattern generated by the hologram shown in Fig. 3a.

Some examples of laser processed semiconductors

Laser processing is applied to manufacture laterally structured electrodes (Fig. 4) for solar cells which improve the built-in electric field of thin film solar cells and give rise to light trapping. An other application is the photo chemical processing of DFB gratings for InP and GaN laser (Fig. 5). Large grain silicon for photovoltaic and display applications is grown on glass as shown in Fig. 6 by the scanning interference laser crystallization. Laser beam induced lift-off of GaN from sapphire substrates is applied to generate free standing thin film GaN substrates, LEDs or other electronic devices (see Fig. 7).


Fig. 4: Periodic structured microcrystalline Si electrode for thin film solar cells


Fig. 5: GaN DFB structure generated by photo chemical laser processing. The period is 240 nm.


Fig. 6: Scanning interference laser crystallized silicon on glass. Large Si grains are grown which extend several microns in scanning direction and about 1 micron perpendicular to it.


Fig. 7: Free standing GaN of about 100 micrometer Thickness. It has been lifted from the sapphire substrate by pulsed laser illumination


Review article on laser lift-off: "Freestanding GaN-substrates and devices" (pdf-file). 

Publications

See list of recent publications

Contact

Prof. Dr. Martin Stutzmann

TUM Technische Universität München TUM Technische Universität München Physik Department Elektrotechnik und Informationstechnik TUM Technische Universität München
 

Events & News

17 Jan 2018

ERC Consolidator Grant for Gregor Koblmüller   more

16 Jan 2018

Light-steering of spin-polarized currents in topological insulators   more

10 Aug 2017

Best Poster Awards for Ganpath Veerabathran and Alexander Andrejew at iNOW 2017   more

27 Jun 2017

Best Poster Award at Nanowire Week for Jochen Bissinger   more

15 Mar 2017

Dr. Kai Müller admitted to the “Junges Kolleg” of the Bavarian Academy of Sciences   more

Seminars

March 12, 2018

Two-dimensional coherent spectroscopy of a semiconductor microcavity   more

March 05, 2018

Diamond-organic photovoltaics   more