Preface

Photodetectors are devices which sense light or electromagnetic energy and convert it into a response, usually electrical. As part of photonics systems, they are developing very fast with photonics applications, e.g. photosensors, telecommunications, information processing, metrology, spectroscopy, medicine, military technology, laser material processing, biophotonics, agriculture, robotics.

There are different types of photodetectors: optical and chemical detectors, photoresistors, photodiodes, thermocouples, phototubes, solar cells, etc. The choice of a particular detector depends on the requirements of a specific application – e.g. the wavelength of the light, the sensitivity, the speed of response. The variety of photodetectors is so wide, that it is impossible for a single book to cover the state-of–art, the latest developments and the new trends in the field including the theoretical aspects, design and simulation, experimental results, and applications of all photodetectors.

In this book some recent advances in photodetectors and photodetection systems for specific applications are examined. The book is divided into three sections.

*Section 1* includes nine chapters where recent developments on different photodetectors and their characteristics are described. In *Section 2* a theoretical model and some simulations are presented*.* In *Section 3* eight examples of photodetection systems for different applications are given: imaging, particle size analysis, transfers of time, and measurement of vibrations, magnetic field, polarization of light, and particle energy.

The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies.

> **Dr. Sanka Gateva** Associate Professor, Institute of Electronics, Bulgarian Academy of Sciences, Bulgaria

**Part 1** 

**Photodetectors** 

**Part 1** 

**Photodetectors** 

**1** 

*Malaysia* 

**ZnO Metal-Semiconductor-Metal UV Photodetectors on PPC Plastic with** 

N.N. Jandow\*, H. Abu Hassan, F.K. Yam and K. Ibrahim *Nano-Optoelectronics Research and Technology Laboratory School of* 

The unique and attractive properties of the II-VI compound semiconductors have triggered an enormous incentive among the scientists to explore the possibilities of using them in industrial applications. Zinc Oxide (ZnO) is one of the compound semiconductors of the II– VI family with a direct band gap of 3.37 eV at room temperature, and a large excitation binding energy (60 meV). ZnO is low cost and easy to grow. It is also sensitive to the UV region because of its ultra violet absorbance and has high photoconductivity (Young et al., 2006). These properties make ZnO a promising photonic material for several applications, such as transparent conducting electrodes, surface acoustic wave filters, gas sensors, light emitting diodes, laser diodes and ultraviolet detectors (Kumar et al., 2009; Lim et al., 2006; Janotti et al., 2009; Bang et al.,2003). ZnO is of value and importance due to wide chemistry, piezoelectricity and luminescence at high temperatures. In industry, it can be used in paints, cosmetics, plastics and rubber manufacturing, electronics, and pharmaceuticals

Films of ZnO, indium tin oxide (ITO), and cadmium oxide (CdO) have recently been investigated as transparent conducting oxide (TCO) due to their good electrical and optical properties, their abundance in nature, their optical transmittance (>80%) in the visible

ZnO crystallizes in two different crystals structural. The first is the hexagonal wurtzite lattice with lattice constants of a = 3.249 Å and c = 5.207 Å which is mainly used in thin film industry as a transparent conducting oxide (TCO) or as a catalyst in methanol synthesis (Jin, 2003). The second structure, which is well known to geologists, is in the form of rock salt

ZnO possesses very similar properties to the nitride-based semiconductors such as GaN; yet it has many advantages over GaN (Koch et al., 1985; Paul et al., 2007). For examples: firstly, the growth of high quality single crystal of ZnO is a well understood technology; whereas

structure which is used in understanding the earth's lower mantle (Hussain, 2008).

**1. Introduction** 

 \*

Corresponding Author

[http://www.navbharat.co.in/Clients.htm].

region, and they are non-toxic (Angelats, 2006).

 **Various Metal Contacts** 

 *Physics Universiti Sains Malaysia, Minden, Penang* 
