One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

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One-dimensional ZnO nanostructures: Solution growth and functional properties

Physical Concepts of High‐Field, Thin‐Film Electroluminescence Devices

Visible light LEDs are produced having a layer of conjugated polymer which is cast directly from solution or formed as a gel-processed admixture with a carrier polymer The LEDs can be formed so as to emit polarized light

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Visible light emitting diodes fabricated from soluble semiconducting polymers

The previously postulated production of holes during the electrical breakdown of varistors has been directly verified. In some compositions band‐gap (3.2 eV) luminescence from the recombination of these holes with free electrons has been observed. The intensity of this luminescence is greater in varistor compositions exhibiting higher nonlinearity coefficients. It is also proportional to the square of the current which implies hole creation by impact ionization in the depletion region near the grain boundaries. This study used varistors of relatively simple chemical composition.

Electroluminescence in ZnO varistors: Evidence for hole contributions to the breakdown mechanism

ZnSe p‐n junction diodes have been formed by nitrogen ion implantation. MIS diodes have also been made using a film of ZnSe oxidized in H2O2 solution for the insulator layer. Blue electroluminescence has been observed from both the diodes in forward bias at room temperature. The external quantum efficiency is about 10−5. The emission may originate from a bound exciton.

Blue electroluminescence from ZnSe diodes

Schottky diodes consisting of a metal contact on n -type ZnSe emit light when biased in the forward direction if there is a layer of insulating or semi-insulating material between the metal and the semiconductor. The electroluminescence spectrum is characteristic of luminescent centres in the ZnSe. There is a threshold voltage for electroluminescence which corresponds to the difference between the metal Fermi level and the top of the valence band of the semiconductor. For gold on ZnSe the threshold voltage is 1·3 V. Characteristics of the device differ from those of similar MIS systems because the oxide used here has appreciable conductivity.

Electroluminescence in forward-biased zinc selenide Schottky diodes

Schottky diodes consisting of a metal layer in contact with an n-type ZnSe crystal are electroluminescent when biassed in the reverse direction. Electrons tunnel from the metal into the semiconductor, are accelerated in the depletion layer field and then impact-ionize luminescent centres. Experiments confirming each of these mechanisms are described. A simple theory is propounded to give a quantitative understanding of the processes and of the performance of the diodes as light sources.

A.W. Livingstone

Papers

Electroluminescence in forward-biased zinc selenide Schottky diodes

Electroluminescence in reverse-biassed zinc selenide Schottky diodes