The combination of inorganic semiconductors with organic thin films promises new strategies for the realization of complex hybrid optoelectronic devices. Oxidative chemical vapor deposition (oCVD) of conductive polymers offers a flexible and scalable path towards high-quality three-dimensional inorganic/organic optoelectronic structures. Here, hole-conductive poly(3,4-ethylenedioxythiophene) (PEDOT) grown by oxidative chemical vapor deposition is used to fabricate transparent and conformal wrap-around p-type contacts on three-dimensional microLEDs with large aspect ratios, a yet unsolved challenge in three-dimensional gallium nitride technology. The electrical characteristics of two-dimensional reference structures confirm the quasi-metallic state of the polymer, show high rectification ratios, and exhibit excellent thermal and temporal stability. We analyze the electroluminescence from a three-dimensional hybrid microrod/polymer LED array and demonstrate its improved optical properties compared with a purely inorganic microrod LED. The findings highlight a way towards the fabrication of hybrid three-dimensional optoelectronics on the sub-micron scale.
(Al,In)GaN-based laser diodes with ridge widths broader than a few micrometer tend to show filamentation effects in the lateral direction. By time-resolved scanning near-field optical microscopy, we find different kinds of filaments depending on ridge width and lateral position. We investigate these effects systematically and compare them to the results of corresponding simulations, which are based on a simple rate equation model including the lateral dimension. By this comparison we find a consistent and reasonable set of material parameters that can describe the laser diode. Furthermore, we discuss several reasons for filamentation dynamics like ridge asymmetry or spatial hole-burning, as well as critical temperatures that induce filamentation.
The lateral mode profile of pulsed broad ridge 405nm (Al, In)GaN laser diodes grown on GaN and SiC substrates, respectively, is investigated by temporal and spectral resolved scanning near-field optical microscopy. During the first microsecond of the pulse, we observe changes both in the spatial mode profile and in the spectral regime caused by thermal and carrier induced modification of the waveguide refractive index, before stable filaments build up. In quasi-cw operation, a correlation between the lateral mode profile and the corresponding spatial resolved longitudinal mode pattern can be found. The results show that different filaments have different effective refractive indices and thus build up separate longitudinal mode combs.
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