We propose a dielectric rod waveguide antenna (DRW) integrated with a photomixer as a THz emitter. This represents a different approach as opposed to the classical solution of a substrate lens. Main goals are an inexpensive alternative to substrate lenses, reduction of both reflections on the semiconductor-air interface and scattering of terahertz-generated power into the substrate. A radiation pattern measured at 137 GHz is shown as a proof-of-concept. In order to increase radiated power, the improvement of the rod antenna is discussed. Finally, as an application example, evanescent coupling of the DRW into a high index whispering gallery mode resonator is shown

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Near-surface GaN/GaInN quantum wells (QWs) were investigated as optical transducers for the detection of hydrogen sulfide. The heterostructure sensors were grown by metal organic vapor phase epitaxy and later covered by a thin layer of Au by electron beam evaporation. The QW photoluminescence (PL) is sensitive to changes in the sensor surface potential. By the adsorption of hydrogen sulfide (H 2 S) on the Au cover layer, downward near-surface band bending results in an increase of the quantum confined Stark effect in the GaInN QW producing a red shift in its luminescence. Unexpectedly, an increase in PL intensity is also observed. A concentration of 0.01 parts per million of H 2 S in nitrogen has been successfully detected. This phenomenon may be helpful to detect trace amounts of H 2 S present in the human breath for early detection of diseases.

Herein, the optimization of (In)GaN heterostructures for chemical sensing is presented. The metalorganic vapor phase epitaxy (MOVPE)‐grown sensor consists of an InxGa1−xN quantum well (QW) placed close to the surface of a GaN substrate with a thin GaN cap layer on top. The photoluminescence (PL) wavelength of this QW is sensitive to surface potential changes and thus its optical signal is used as sensor response. Simulations are performed with nextnano to improve its sensitivity. Sensor parameters such as the cap layer thickness d, QW thickness Lz, background buffer layer doping concentration N, and indium concentration x of the QW are varied. It is found that a thin cap layer, together with high background doping and medium QW thickness, is ideal. The indium content does not show a strong influence on sensitivity. The trends found in the simulations are mostly confirmed in real‐world experiments performed in a chemical sensing setup, yet quantitative deviations exist.

The development of sensitive biosensors, such as gallium nitride (GaN)-based quantum wells, transistors, etc., often makes it necessary to functionalize GaN surfaces with small molecules or even biomolecules, such as proteins. As a first step in surface functionalization, we have investigated silane adsorption, as well as the formation of very thin silane layers. In the next step, the immobilization of the tetrameric protein streptavidin (as well as the attachment of chemically modified iron transport protein ferritin (ferritin-biotin-rhodamine complex)) was realized on these films. The degree of functionalization of the GaN surfaces was determined by fluorescence measurements with fluorescent-labeled proteins; silane film thickness and surface roughness were estimated, and also other surface sensitive techniques were applied. The formation of a monolayer consisting of adsorbed organosilanes was accomplished on Mg-doped GaN surfaces, and also functionalization with proteins was achieved. We found that very high Mg doping reduced the amount of surface functionalized proteins. Most likely, this finding was a consequence of the lower concentration of ionizable Mg atoms in highly Mg-doped layers as a consequence of self-compensation effects. In summary, we could demonstrate the necessity of Mg doping for achieving reasonable bio-functionalization of GaN surfaces.