Optically induced voltage was studied in carbon nanotube films configured as two-terminal resistive elements and operating as junctionless photocells in the infrared. The photovoltage is found to appear only for asymmetric/off-contact illuminations and the effect is explained based on photogenerated heat flow model. The engineered cell prototypes were found to yield electrical powers of ∼30 pW while demonstrating improved conversion efficiency under high-flux illumination. The cell is also shown to act as uncooled infrared sensor with its dark-to-photocurrent ratio improving as temperature increases. The concept might enable nanotube’s use in applications ranging from heat recycling to self-powered infrared sensors.

In this work the authors introduce and provide details of the synthesis and spectral characterization of single-crystal nanowires in less common, high performance, group II-V semiconductors such as Cd(3)As(2). The growth mechanism critically deviates from a known vapor-liquid-solid one by being completely non-catalytic and involving only two states: vapor and solid. The resultant nanowires range from ∼50 to 200 nm in diameter and reach lengths up to tens of micrometers, with their fast growth direction being normal to the (112) crystal planes. According to infrared (IR) optical absorption measurements, the nanowires have several IR active direct type light absorption transitions at 0.11, 0.28 and 0.54 eV, suggestive of their possible utility in low cost optoelectronic devices and photodetectors operating in the long wavelength range of the electromagnetic spectrum.

A series of photoluminescence and photoluminescence-excitation spectroscopies have been performed to probe the processes regulating defect-assisted light emission from one-dimensional ZnO nanowire phosphors in a wide temperature range of 123–463 K. The observed nonmonotonic change of the integral defect-photoluminescence intensity as well as its peak position with temperature are explained based on the interplay of competing effects of thermal quenching and carrier redistribution over radiative channels. A temperature-induced broadening of the defect photoluminescence band is observed and attributed to the appearance of ∼2.1 eV band, the intensity of which is also found to quench quickly with the onset of higher temperature. The results of photoluminescence-excitation measurements show that band-to-band excitations remain a primary excitation channel of defects especially at low and moderate temperature range, whereas the role of direct, one-photon absorption channel is found to progress as temperature approaches ∼500 K.

The mechanism of near-band-edge (NBE) emission from crystalline ZnO (c-ZnO) nanorods grown on c-Si by a catalyst-assisted vapor-liquid-solid method has been investigated by performing temperature-, power-, and time-dependent photoluminescence (PL) measurements at a temperature (T) range of 143–503K. In contrast to previous reports, we find that the NBE PL is primarily associated with free exciton emission, whereas the contribution of band-to-band and free-to-bound radiative recombinations remains negligible up to the highest T studied. A spectral evolution of the NBE band with T was further analyzed within the framework of a three-parameter model, proposed recently, with the results presented and discussed. Finally, the ratio of excitonic-to-defect luminescence intensity has been observed to change nonmonotonically with T, which is explained based on the difference in the quenching mechanisms of exciton and defect PL.

368and strength of the chemical bonds of wide-band gap semiconductors, photodetectors engineered based on most of metal-oxides can withstand highly elevated T and hostile environments. Despite the fact that carrier mobilities are much smaller in cases of metal oxides compared with those of many conventional semiconductors, owing to the drastically increased dielectric strength of metal oxides, much larger carrier velocities can be readily achieved by applying much higher electric fields/device biases. The property remains critical for reducing the photogenerated carrier transit time and thus improving gain characteristics of the photodetectors. Advances in nanofabrication methodologies now allow growing many metal-oxide nanowires, including in ZnO as dislocation-free, highly faceted single crystals, which according to the above-made discussion show significant promise for diverse nanophotodetector device as well as light-emission applications. At the same time, compared to cSi, ZnO nanowires typically exhibit a very limited intrinsic sensitivity to visible and infrared radiation, whereas the sensitivity to short-wavelength photons also tends to be reduced as a result of their small diameter and relative increase in the number of the surface defect states. In this chapter, we provide a brief review on the progress in engineering highresponsitivity ZnO nanowire photodetectors operating in an extended, i.e., ultravioletvisible spectral range. Particular attention is paid to the use and role of transition metal dopants to enhance the light sensitivity of ZnO nanowires/nanorods grown by seeded vapor-transport methods. Detailed consideration is given to several key aspects pertaining to the transport, photoconduction, and time-response characteristics of two-terminal metalsemiconductor-metal nano-photodetectors operating at both pre-avalanche and avalanche regimes. This review might be important to scientists working in with high-sensitivity and multispectral oxide-based nano-photodetectors, optical switches, and sensors.