Preparation and Characterization of Some Semiconductors from Transition Metal Oxides

Abstract

Our technologically advanced way of life would not be possible without the semiconductor industry. The first semiconductor device known as a transistor was discovered at Bell Labs in the late 1940s, and was widely used shortly thereafter for radio electronics. Today, transistors are still pervasive in every microelectronic component such as CD/DVD players, cellular phones, modes of transportation (e.g. planes, automobiles, etc.), and computers. In fact, the dual-core chips released by Intel in early 2009 feature over 1.7 billion transistors – all on a surface that is smaller than a postage stamp. Investigation of the various types of semiconducting materials, focusing on the influence of their structure on overall properties were studied. The world therefore now demands a material that should possess inherent properties like larger band gap, higher electron mobility as well as higher breakdown field strength. So on making investigation about such a material the name of compound comes out is “Zinc Oxide” which is a wide gap semiconductor material very well satisfying the above required properties. Not only has this Zinc oxide possessed many versatile properties for UV electronics, spintronic devices and sensor applications but also ZnO has been commonly used in its polycrystalline form over hundred years in a wide range of applications. This ignites many research minds all over the world and creates enthusiasm to develop proper growth and processing techniques for the synthesis of Zinc oxide. Zinc oxide is also known as "Lu-Gan-Stone" in China and has been used in medical treatment for quite number of years. The research on ZnO is catching fire right from the beginning of 1950, with a number of reviews on electrical [1] and optical properties [2] like N-type conductivity, absorption spectra and electroluminescence decay parameter. The nature of excitonic molecule in semiconductors which was discussed by Haynes [3] aiding a key publication by Park et al concerned with excitonic emission of ZnO [4] is the first step put for the growth and development of ZnO research in the mid of 1960. In 1966 the Raman Effect study of ZnO by Damen and Porto [5] leads to the identification of ZnO phonon energies. A simpler ZnO devices like ceramic varistors, piezoelectric transd- ucers etc was manufactured in the decade of 1970 with a progress in the study of variety of characterization techniques such as cathode luminescence(CL), capacitance – voltage studies(CV), electrical conduction and so on [6-9]. A lot of work on high quality thin films of ZnO, metallo-organic chemical vapor deposition (MOCVD) [10], spray pyrolysis [11] and radio frequency magnetron sputtering (RF) [12] has been done extensively for growth procedure. The twilight of stars sprinkles and a new era for research of ZnO begins actually in 1990 with a uniform growth in number of publications related to both character- ization and growth techniques. In 1990’s, newer growth methods were used including pulsed laser deposition (PLD) [13] and molecular beam epitaxy (MBE) [14]. At the end of late 1990 large scale commercial ZnO comes to the picture. In the field of ZnO research the last decade was mainly concerned with optimization of different growth parameters and processing techniques. Thus currently research work related to production of high quality, reproducible P-type conducting ZnO for device application is the main focus. ZnO has now become one of most studied material in the last seven years as it presents very interesting properties for optoelectronics and sensing applications, in nano range synthesis.

1.2 Properties and types of semiconductors: