We have fabricated a novel type of ultracompact spectrometer without dispersive element(s) suitable for the use in smartphones. It comprises a waveguide with a linear photodetector array on top. The photosensitive layer features a steep chemical concentration gradient, fabricated from (MgxZn1-x)O, allowing for spectral detection in the UV. The dimensions of the device make it ultracompact with a volume of less than 1 cubic millimeter.
Recently, immense interest in the semiconductor Ga₂O₃ arose due to its large bandgap and high predicted electrical breakdown field. By alloying Ga₂O₃ with In₂O₃ or Al₂O₃, its bandgap can be tuned over a large range, allowing possible applications in heterostructure devices or devices with an adjusted absorption energy. For this purpose, property screening over a large composition range is crucial.
In this contribution, we present electrical, optical and structural properties of (Ga,In)₂O₃ and (Ga,Al)₂O₃ thin films grown by continuous composition spread pulsed laser deposition. The influence of growth parameters on phase boundaries were investigated and unipolar devices were fabricated.
We demonstrate that exceptional points exist in fully transparent, optically ”effectively” biaxial, anisotropic micro-cavities, fabricated using an uniaxial cavity material with its axis inclined to the Bragg mirror growth direction. This is similar to the existence of singular (optic) axes in absorbing biaxial crystals, but the lack of time reversal symmetry is mediated by the mode broadening, i.e. the photon escape from the – in principle – open cavity system. As a consequence the eigenmodes are generally elliptically polarized, and completely circularly polarized eigenmodes are expected in certain directions. Via geometric and chemical composition design degrees of freedom, the spectral and angular position of these chiral modes can be rationally designed. Possible applications arise from the use of such directions for circularly polarized emission without the use of spin injection or internal or external magnetic fields. Also the coupling of such modes to excitons, adding oscillator strength to the system, seems a promising avenue of research.
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