This letter presents studies of multiwavelength flexible photodetectors on a plastic substrate by use of printing transferred single-crystal germanium ͑Ge͒ membranes. Ge membranes of 250 nm thickness with selectively ion-implantation doped regions were released from a germanium-on-insulator substrate and integrated with a 175-m-thick polyethylene terephthalate substrate via a dry printing technique. Photodiodes configured in lateral p-i-n configuration using the flexible Ge membranes with an intrinsic region width of 10 m exhibit an external quantum efficiency that varies from 5% at 411 nm to 42% at 633 nm under −1 V bias condition. These results demonstrate the potential of utilizing single-crystal Ge-membrane photodiodes for imaging applications and as solar cells on objects with arbitrary curvatures and shapes.

A bacteriorhodopsin (bR)-silicon n-channel metal-oxide field-effect transistor (NMOSFET) monolithically integrated photoreceiver is demonstrated. The bR film is selectively formed on an external gate electrode of the transistor by electrophoretic deposition. A modified biasing circuit is incorporated, which helps to match the resistance of the bR film to the input impedance of the NMOSFET and to shift the operating point of the transistor to coincide with the maximum gain. The photoreceiver exhibits a responsivity of 4.7 mA/W.

A monolithically integrated bacteriorhodopsin-semiconductor phototransceiver is demonstrated for the first time to the authors' knowledge. In this novel biophotonic optical interconnect, the input photoexcitation is detected by bacteriorhodopsin (bR) that has been selectively deposited onto the gate of a GaAs-based field-effect transistor. The photovoltage developed across the bR is converted by the transistor into an amplified photocurrent, which drives an integrated light-emitting diode with a Ga0.37Al0.63As active region. Advantage is taken of the high-input impedance of the field-effect transistor, which matches the high internal resistance of bR. The input and output wavelengths are 594 and 655 nm, respectively. The transient response of the optoelectronic circuit to modulated input light has also been studied.

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