Laser - R&D and QC

Piegdon et al. (2012) demonstrate all-optical tunable laser based on a hybride concept where a polyelectrolyte/semiconductor hybrid devices have been formed by embedding a GaAs-based microdisk inside bilayers of PEI and PAZO molecules using a spin assembly process. Imaging ellipsometry was used to characterize the surface momogenity oft he polyelectrolyte coating. The observed surface is of smooth quality, exhibiting a roughness as low as 2.3 nm.

Reference:

Piegdon KA, Lexow M, Grundmeier G, Kitzerow HS, Pärschke K, Mergel D, Reuter D, Wieck AD, Meier C (2012) All-optical tunability of microdisk lasers via photo-adressable polyelectrolyte functionalization. Optics express 20, 6060-6067

More details

Local electron triggered reactions of functional surface adsorbates were used as a maskless, dry, and minimally invasive nanolithography concept to stabilize the polarisation of individual vertical cavity surface emitting lasers (VCSELs) on a wafer in a post-processing step. Using a 30 keV focused electron beam of a scanning electron microscope and injecting volatile organo-metallic (CH₃)₂Au(tfa) molecules, polarisation gratings were directly written on VCSELs by dissociating the surface adsorbed molecules. The electron triggered adsorbate dissociation resulted in electrically conductive Au-C nano-composite material, with gold nanocrystals embedded in a carbonaceous matrix. A resistivity of 2500 µΩcm was measured at a typical composition of 30 at.% Au. This material proved successful in suppressing polarisation switching when deposited as line gratings with a width of 200 nm, a thickness of 50 nm, and a pitch of 500 nm and 1µm. Refractive index measurements, performed with an imaging ellipsometer suggest that the optical attenuation by the deposited Au-C material is much lower than by pure Au thus giving a low emission power penalty while keeping the polarisation stable.

Reference:

Utke I, Jenke MG, Röling C, Thiesen PH, Iakovlev V, Sirbu A, Mereuta A, Caliman A, Kapon E (2011) Polarisation stabilisation of vertical cavity surface emitting lasers by minimally invasive focused electron beam triggered chemistry. Nanoscale 3, 2718-2722

More details:

Laser Diodes (LD) consist of semiconducting materials e.g. GaAs or Si, which are doped with electron donors and electron acceptors in different layers. Doping atoms can be Al and In among many others. At the interface between layers with electron depletion and electron excess, electrons and holes can recombine and emit light if a voltage is applied between these layers. Coherent light emission out of the LD is obtained if more light is amplified by recombination than lost through the reflecting outer surfaces of the LD (facets) and by absorption in the LD. The properties of the LD i.e. emission wavelength, linewidth, power, stability, lifetime depend on the dispersion functions of refractive index n and extinction k of all materials of the LD and on the thickness of each layer on the LD. In order to control the quality of the LD those dispersion functions and thickness shall be measured. Especially important for the function of the LD are the optical properties of the anti-reflection coating on the emitting surface of the LD. In a quantum well laser the interface of the light emission is only a few nm thin. Spectroscopic ellipsometry is the ordinary method to measure these optical properties on large semiconducting wafers. Imaging ellipsometry is needed to measure on those tiny LDs, because high lateral resolution of a few μm is necessary.