Hydrogenated amorphous silicon (a-Si:H)-based infrared photodiodes were fabricated by coating a-Si:H thin-film p-i-n layers over hydrothermally-synthesized disordered zinc oxide (ZnO) nanowire (NW) networks. Due to enhanced light scattering, the reversed biased three dimensional (3-D) radial-junction NW diodes showed an ∼10× increase in photocurrent under a broad spectrum (800-2000 nm) infrared (IR) illumination compared to planar devices. The diodes were optimized by using InGaZnO (IGZO) transparent top contacts that had 20% higher optical transmission in the IR compared to Al-doped ZnO electrodes. Reverse-bias dark current was minimized by optimizing the area of the NW sidewalls and the a-Si:H shell layer thickness. The former reduces the effects of carrier recombination along the NW core-shell interface and the latter minimizes the tunnelling current across the radial-junction device. An enhancement of ∼100× was achieved for these devices compared to non-optimized diodes.

Hydrogenated amorphous silicon (a-Si:H) thin films were coated onto hydrothermally synthesized disordered zinc oxide (ZnO) nanowire networks to form three dimensional (3-D) hybrid nanowire/thin-film structures. The optical absorption of the hybrid structure was extended from the visible regime up to infrared wavelengths of 2.5 μm compared to a planar thin-film structure. By modulating the defect density of the a-Si:H shell, the optical absorption at 2.3 μm could be varied from 14% to 56%. The extended optical absorption was due to an increased effective thin-film thickness of the a-Si:H shell by three orders of magnitude through the 3-D ZnO-core/a-Si:H-shell structure and modulation of the defects within the a-Si:H shell layer.

A novel lateral infrared photodetector was demonstrated using 3-D structures comprising of zinc-oxide nanowire (NW) cores and hydrogenated amorphous silicon (a-Si:H) thin-film shell. The 3-D infrared photodetectors showed a low dark current of ~10−11–10−12 A and ~102–103 light-on/light-off ratio with both constant and pulsed 1.55- $\mu \text{m}$ wavelength light. A vertically integrated infrared sensor/thin-film transistor (TFT) device incorporating the 3-D infrared photodetector on the back channel of an a-Si:H TFT was fabricated, creating an integrated optical detector and a switch. The detector dark current was found to scale with the NW geometry on the TFT back channel and may be used to optimize the performance of the hybrid sensor-switch device.

Hydrothermally synthesized disordered ZnO nanowires were conformally coated with a-Si:H thin-films to fabricate three dimensional hybrid nanowire/thin-film structures. The a-Si:H layer formed a radial junction p-i-n diode solar cell around the ZnO nanowire. The cylindrical hybrid solar cells enhanced light scattering throughout the UV-visible-NIR spectrum (300 nm–800 nm) resulting in a 22% increase in short-circuit current density compared to the reference planar p-i-n device. A fill factor of 69% and a total power conversion efficiency of 6.5% were achieved with the hybrid nanowire solar cells using a spin-on indium tin oxide nanoparticle suspension as the top contact.

The electrical stability of flexible a-Si:H thin-film transistors (TFT) under mechanical bending is given. The electrical stability was found to be dependent on the strain state of the applied bending during dc-gate bias of the TFT. The heterogeneous integration of hybrid thin-film/nanowire structures on polyeth ylene napthalate substrates is also described. The a-Si:H coated nanowires were found to h ave approximately half of the optical reflectivity due to light scattering of the 3-D hybrid structures compared to planar thin films.

The optics of core / shell nanowire solar cells was investigated. The optical wave propagation was studied by finite difference time domain simulations using realistic interface morphologies. The interface morphologies were determined by a 3D surface coverage algorithm, which provides a realistic film formation of amorphous silicon films on zinc oxide nanowire arrays. The influence of the nanowire dimensions on the interface morphology and light trapping was investigated and optimal dimensions of the zinc oxide nanowire were derived.

AbstractA new architecture light emitting transistor combining the drive transistor, storage capacitor and light emitter into a single device promises to greatly reduce AMOLED manufacturing costs by dramatically reducing the backplane circuit complexity. Here we demonstrate device operation at 60 Hz using only a switching transistor and show remarkable stability under bias stress, despite use of an organic channel.