Organic semiconductor distributed feedback (DFB) laser pixels fabricated via nanograting transfer and ink-jet printing

Summary form only given. Organic semiconductor distributed feedback (DFB) lasers are of particular interest as tunable visible laser light sources. They are becoming promising candidates as excitation sources integrated in photonic lab-on-a-chip (LOC) or other sensing systems [1-3]. For bringing those to market, the established device fabrication methods and large-area thin film deposition may not fulfil the functionality and flexibility required by miniaturised LOC applications. We demonstrate two novel inexpensive fabrication methods to implement spatially defined organic semiconductor DFB lasers with a high yield and without negative influences on surrounding microstructures, e.g., passive photonic components. We applied nanograting transfer as a convenient method to fabricate localized organic small molecule DFB lasers. The fabrication process of the DFB laser device is depicted in Figs. 1(a) and (b). The cyclic olefin copolymer (COC) mold with a small molecule layer on top was pressed onto the unstructured plane active layer under high pressure. The previously deposited layer was subsequently detached from the mold and transferred to the plane substrate [4]. A scanning electron microscope (SEM) image of the grating on the final device is shown in Fig. 1(c). Fig. 1(d) shows the laser emission and laser threshold of the fabricated device. For solution processing of localized organic polymer DFB lasers, we used ink-jet printing to deposit the active conjugated polymer solutions onto the predefined DFB grating regions [5]. Utilizing a mixture of high-boiling and low-boiling solvents for dissolving the polymer, the ink-jet printed film profile was optimized, thus creating uniformly emitting organic lasers. With precise control of jetting duration, frequency, slew rate and firing voltage, the spatial accuracy of printing and thus the laser emission from the device can be improved. We demonstrate the accurate lateral positioning of ink-jet printed laser pixels on a polymer substrate with 500 μm × 500 μm grating fields (see Fig. 2(a), (b) and (c)).