Hydrothermal growth of ZnO nanostructures

Ultraviolet (UV) photodetection has drawn a great deal of attention in recent years due to a wide range of civil and military applications. Because of its wide band gap, low cost, strong radiation hardness and high chemical stability, ZnO are regarded as one of the most promising candidates for UV photodetectors. Additionally, doping in ZnO with Mg elements can adjust the bandgap largely and make it feasible to prepare UV photodetectors with different cut-off wavelengths. ZnO-based photoconductors, Schottky photodiodes, metal–semiconductor–metal photodiodes and p–n junction photodetectors have been developed. In this work, it mainly focuses on the ZnO and ZnMgO films photodetectors. We analyze the performance of ZnO-based photodetectors, discussing recent achievements, and comparing the characteristics of the various photodetector structures developed to date.

https://www.mdpi.com/1424-8220/10/9/8604/pdf

ZnO-Based Ultraviolet Photodetectors

Both n-type and p-type ZnO will be required for development of homojunction light-emitting diodes (LEDs) and laser diodes (LDs). It is easy to obtain strong n-type ZnO, but very difficult to create consistent, reliable, high-conductivity p-type material. The most natural choice of an acceptor dopant is N, substituting for O, and indeed several groups have been able to obtain p-type material by such doping. Surprisingly, however, other groups have also been successful with P and As, elements with much larger ionic radii than that of O. Although ZnO substrates are now available, most of the epitaxial p-type layers so far have been grown on sapphire, or other poorly-matched materials. The lowest p-type resistivity obtained up to now is about 0.5 Ω-cm, which should be sufficient for LED fabrication. In spite of the present availability of p-type ZnO, very few homojunction LEDs have been reported so far, to our knowledge; however, several good heterojunction LEDs have been demonstrated, fabricated with p-type layers composed of other materials. One such structure, with fairly strong 389-nm emission at 300 K, involves n-type ZnO and p-type AlGaN, grown on an SiC substrate. Also, an N + -ion implanted ZnO layer, deposited by chemical vapor deposition on Al 2 O 3 , exhibits 388-nm emission at 300 K and could be economical to produce.

P‐type doping and devices based on ZnO

This paper demonstrates a technique to form a lateral homogeneous 2D MoS2 p–n junction by partially stacking 2D h-BN as a mask to p-dope MoS2. The fabricated lateral MoS2 p–n junction with asymmetric electrodes of Pd and Cr/Au displayed a highly efficient photoresponse (maximum external quantum efficiency of ∼7000%, specific detectivity of ∼5 × 1010 Jones, and light switching ratio of ∼103) and ideal rectifying behavior. The enhanced photoresponse and generation of open-circuit voltage (VOC) and short-circuit current (ISC) were understood to originate from the formation of a p–n junction after chemical doping. Due to the high photoresponse at low VD and VG attributed to its built-in potential, our MoS2 p–n diode made progress toward the realization of low-power operating photodevices. Thus, this study suggests an effective way to form a lateral p–n junction by the h-BN hard masking technique and to improve the photoresponse of MoS2 by the chemical doping process.

Lateral MoS2 p-n junction formed by chemical doping for use in high-performance optoelectronics.

Compact, solid-state UV emitters have many potential applications, and ZnO-based materials are ideal for the wavelength range 390 nm and lower. However, the most efficient solid-state emitters are p-n junctions, and p-type ZnO is difficult to make. Thus, the future of ZnO light emitters depends on either producing low-resistivity p-type ZnO, or in mating n-type ZnO with a p-type hole injector. Perhaps the best device so far involves an n-ZnO/p-AlGaN/n-SiC structure, which produces intense 390 ± 1 nm emission at both 300 K and 500 K. However, development of p-ZnO is proceeding at a rapid pace, and a p-n homojunction should be available soon.

The Future Of ZnO Light Emitters

Optimizing n-ZnO/p-Si heterojunctions for photodiode applications

Characterization of films and interfaces in n-ZnO/p-Si photodiodes

Effect of calcium ion (cross-linker) concentration on porosity, surface morphology and thermal behavior of calcium alginates prepared from algae (Undaria pinnatifida)

We report on the photoresponse behavior of n-ZnO/p-Si photodiodes. Semiconducting n-ZnO films have been deposited on p-Si substrates at 480 °C using various Ar/O2 ratios, 2:1, 4:1, and 6:1, to fabricate n-ZnO/p-Si photodiodes. As a laser of 670 nm wavelength illuminated the photodiodes, a maximum responsivity of 0.286 A/W and a maximum quantum efficiency of 53% were obtained at a reverse bias of 5 V from a diode prepared with an Ar/O2 ratio of 6:1. The response time of the photodiode was as short as 35 ns as measured using pulse modulation of the illuminating laser.

Photoresponse characteristics of n-ZnO/p-Si heterojunction photodiodes

We report on the photo-response behavior of n-ZnO/p-Si photodiodes. Semiconducting n-ZnO films have been deposited on p-Si substrate by RF sputtering at 300, 480 and 550°C. An optimum static photo-response was achieved from the photodiode prepared at 480°C as characterized by photocurrent measurements using a continuous monochromatic red illumination. Temporal photo-response of 35 ns was obtained from the same n-ZnO/p-Si diode to which a high frequency modulation of 1.5 MHz was applied for the dynamic response measurements. It is concluded that the n-ZnO/p-Si photodiode has good detecting capabilities in both of the dynamic and static photo-responses.

https://iopscience.iop.org/article/10.1143/JJAP.42.1560/pdf

Joon-Bae Lee

Papers

Optimizing n-ZnO/p-Si heterojunctions for photodiode applications

Characterization of films and interfaces in n-ZnO/p-Si photodiodes

Effect of calcium ion (cross-linker) concentration on porosity, surface morphology and thermal behavior of calcium alginates prepared from algae (Undaria pinnatifida)

Photoresponse characteristics of n-ZnO/p-Si heterojunction photodiodes

Dynamic and Static Photo-Responses of n-ZnO/p-Si Photodiodes