We improved organic light-emitting transistors (OLETs) characterized by aluminum-doped zinc oxide (AZO) layer insertion between organic and gate insulator layers using organic oligomer semiconductor crystals. (i) To ensure firm contact between the crystal and the AZO layer, we shaped the AZO layer into a rectangle (250 × 500 µm2) and covered it with a vapor-phase-grown crystal. (ii) To enhance contact between the crystal and the AZO layer, we placed the crystal used as a mask on the patternless AZO layer and etched parts of AZO not covered with the crystal with hydrochloric acid vapor. We completed OLETs by forming electron- and hole-injection contacts on the crystal. We modified these contacts with an oxide and/or a carbonate. The devices showed bright light emission from the part of the crystal sandwiched between the electron- and hole-injection contacts located on the AZO layer.

We have succeeded in directly engraving one-dimensional diffraction gratings on the surface of organic semiconducting oligomer crystals by using focused ion beam (FIB) lithography and laser ablation (LA) methods. The FIB method enabled us to shape the gratings with varying periods down to ~150 nm. With the LA method a large-area grating with a ~500-nm period was readily accessible. All the above crystals indicated spectrally-narrowed emission (SNE) lines even in the case of shallow groove depths ~2-4 nm. In particular, we definitively observed the SNE pertinent to the first-order diffraction with the crystal having the diffraction grating of a 148.3-nm average period. The present results indicate utility of the built-in gratings that can directly be fabricated on the surface of the crystals.