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Chemical vapor deposition grown MoS2 single crystals were transferred onto the edge of a p-Si/SiO2 wafer, forming an abrupt heterogeneous junction diode at the MoS2/p-Si interface. When electrically characterized as a field effect transistor, MoS2 exhibits an n-type response and can be doped in the presence of ultraviolet (UV) light. As a diode, it operates satisfactorily in air, but has higher currents in vacuum with a turn on voltage of ∼1.3 V and an on/off ratio of 20 at ±2 V. UV irradiation increases the diode on state current, decreases the turn-on voltage, and reduces the ideality parameter below 2. These changes are reversible after annealing in air as desorption of electron trapping species like O2− and H2O− are believed responsible for this effect. A circuit integrating this diode was used to rectify a 1 kHz signal with an efficiency of 12%. Its simple design, coupled with the ability to clip AC signals, sense UV light, and reversibly tune these diodes, makes them inexpensive, multifunctional, and usable as active or passive circuit components in complex electronics.

Fibers of the biopolymer poly(lactic acid) (PLA) and the p-type semiconducting polymer poly(3-hexylthiophene) (P3HT) were fabricated using the electrospinning technique at low PLA concentration (5 wt%) in CHCl 3 . The fibers were several millimeters long and had diameters in the range 100 nm-4 m. Nanofibers containing 63%/37% of PLA/P3HT were electroactive, and therefore were used to construct p-n diodes whose ideality parameter was 2.4 and rectification (on/off) ratio was 400 at ±1 V. These diodes were also able to sense UV radiation and remain operable with an increase in the on/off ratio and a lowering of the turn-on voltage. By fabricating reusable and low-cost multifunctional diodes from PLA/P3HT, the applications of PLA as a biocompatible and biodegradable polyester are expanded to include electronic device fabrication with low environmental impact.

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