K.M. Gupta

Advanced Semiconducting Materials and Devices

In this preliminary chapter discussing the fundamentals of semiconductor, the electrical and electronic materials are classified. Importance of semiconducting materials and their scope are elaborated. Conductors, semiconductors and dielectrics are differentiated from each other on the basis of energy bandgap. Different types of semiconducting materials, their merits and characteristics are listed. Various elemental form, compound and alloyed semiconductors are described. Basic semiconducting devices along with their working principles are briefed. Latest developments in the field of semiconducting materials have been included; the main among them are emerging and futuristic spintronic materials, ferromagnetic semiconductors, emerging wide bandgap semiconductors, left-handed materials, photocatalytic semiconductors, integrated circuit purpose semiconductors etc. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Excess Carriers in Semiconductors

Most semiconductor devices operate by creation of charge carriers which are in excess of the charge carriers available at thermal equilibrium. Conduction in semiconductors are dominated by these excess carriers. Therefore, in this chapter optical absorption and its mechanism, absorption coefficient and factors affecting it, are explained. Luminescence, phosphorescence, electro-luminescence, mechanism of excitation and recombination are discussed. Carrier lifetime and its derivation, indirect recombination, steady state carrier generation and quasi-Fermi levels are described. Photoconductivity and photoconductive devices, photoconductive cell, photo-multiplier tube, and factors affecting the selection of semiconductors for photo-conducting purpose are explained. Concepts of diffusion of carriers, analysis of drift and diffusion carriers, Einstein relation, continuity equation for diffusion and recombination are presented. Equations have been derived for diffusion and diffusion length. Solution has been provided for charge transport and impurity distribution by error function method and Gaussian distribution method. Long diode and short diode are also discussed. Quantum efficiency, trapping centre, dark resistance of photoconductor, and derivation of junction-voltage etc. are briefed through solved solutions. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Semiconductor Materials: Their Properties, Applications, and Recent Advances

In this preliminary chapter discussing the fundamentals of semiconductor, the electrical and electronic materials are classified. Importance of semiconducting materials and their scope are elaborated. Conductors, semiconductors and dielectrics are differentiated from each other on the basis of energy bandgap. Different types of semiconducting materials, their merits and characteristics are listed. Various elemental form, compound and alloyed semiconductors are described. Basic semiconducting devices along with their working principles are briefed. Latest developments in the field of semiconducting materials have been included; the main among them are emerging and futuristic spintronic materials, ferromagnetic semiconductors, emerging wide bandgap semiconductors, left-handed materials, photocatalytic semiconductors, integrated circuit purpose semiconductors etc. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Novel Nanoscale Materials and Devices for Wireless Communication and Networking Applications

In the last decade, there have been immense technological developments throughout the world leading to much advancement in the technologies used in wireless communication systems. Massive ongoing research at nanometer length is set to meet the rising demand of the communication industry. So nanoscale materials and devices will play a major role in intelligent communication system. In this paper, we envisage the current and future applications of nanoscale materials and devices for wireless communication systems. It discusses about novel materials and devices that are being designed to provide enhanced and improved quality of service in terms of long range communication, improved performance, less power consumption, smaller size, energy efficient and robustness. We harness the properties and applications of materials at nanoscale dimensions by integrating them with the current technological requirements in terms of extremely high speed, intelligence, large capacity and swift interconnections. Such materials and devices would certainly leverage the future direction of research in wireless communication systems.

Semiconductor Growth Techniques and Device Fabrication

This chapter presents a brief outline of the technology associated with semiconductor processing. The production of highly pure electronic-grade silicon from raw feedstock is presented. Different techniques of semiconductor crystal growth are given. Czochralski (CZ) method and Bridgman method are explained. Zone refining process is also described. Semiconductor fabrication technology, and thin film micro-electronic circuit fabrication are presented. Preparation of wafers, epitaxy, masking, photolithography, interconnection by metalizing are discussed. Methods of ion-implantation, molecular beam epitaxy (MBE), sputtering and etching are explained. Semiconductor p–n junction (diode) formed by different methods, are described. Stepwise procedure for the formation of a semiconductor p–n junction, and transistor manufacturing processes (of grown junction, alloy formation, diffusion) are briefly narrated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Nano-Structured Semiconducting Materials and Devices

The present era is of nanotechnology and nano-materials. Therefore, a large number of investigations are being carried out in nano-structured semiconductors also. Consequently, the newer nano-based semiconducting materials and devices are being researched. Many recent developments in this field are included briefly in this chapter by incorporating the published research papers. The main emerging nano-semiconducting materials and devices included here are: semiconductor nanowires, nano crystals, nanogap devices, nanoparticle- based organic photovoltaic devices, nanoscale semiconductor, artificial electronic skin, semiconductor nanomembranes, nano-structured tin-dioxide materials, nano-structures based solar energy applications, metal-semiconductor hybrid nanostructures, inorganic semiconductor nanostructures etc.

Special Semiconducting Materials in Vivid Fields (for Thermoelectrics, Integrated Circuits, Photocatalytics, Spintronic Devices, etc.), Plasmonic Solar Cell, and Photonics

Semiconducting materials are used in widely varying fields for specific applications. Therefore, they are special purpose semiconductors. Such semiconductors are described in this chapter, for example; three-dimensional semiconductor solar cell, optical semiconductor, thermoelectric semiconductors, integrated circuit purpose semiconductors. The photocatalytic semiconductors which are used to make the environment free of pollution, are also discussed. Transparent oxide semiconductors and semiconductor based spintronic devices are also explained. Spin-charge converter, spin injection materials, plasmonic solar cells, and photonic semiconductors are also elaborated. Plasmonic and photovoltaic kinds of semiconductors are introduced. Applications of plasmonic (photovoltaic) solar cells, photonic processor, photonic crystals, and superlattices are given. Future of photonics is also incorporated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Carrier Transport in Semiconductors

Role of valence electrons and free electrons in carrier transport through semiconductors is presented. Various electrons theories such as Free election theory, Energy band theory, and Brillouim zone theory are described. Mechanism of conduction by free electrons is elaborated. Fermi energy level, intrinsic and extrinsic semiconductors, energy diagrams of n-type and p-type semiconductors are given. Direct and indirect energy band semiconductors and effect of alloying on them are discussed. Concepts of effective mass, density of state, temperature dependence of carrier concentrations are developed. Drift of carriers under electric and magnetic fields, collision time, effects of temperature on mobility of carriers, effects of doping on mobility are explained. Degenerate semiconductors and effect of heavy doping are incorporated. The phenomenon of Hall Effect and its significance; Hall voltage, Hall angle, Hall coefficient etc. are described. Relation between Density of states and Fermi energy, momentum space, Fermi sphere, Fermi radius, Fermi velocity, Fermi momentum, Fermi temperature etc. are derived. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

P-N Junctions and Their Breakdown Mechanisms

P-N junction is an important control element for the performance of semiconductor devices. Devices such as amplifiers, rectifiers, linear and digital ICs etc. employ one or more P-N junctions for their working. Therefore, for a good understanding of all these, the P-N junction diode: their applications and working at equilibrium conditions are presented. In this chapter, relations have been established between contact potential and doping concentrations, for Fermi level at equilibrium, for the width of depletion region and penetration depth. Biased junctions: their working when not connected to a battery, forward-biased and reverse biased p-n junctions and their voltage-current characteristics are described. Poisson’s equation, junction breakdown mechanisms, Zener and avalanche breakdown, and junction capacitance are discussed. Rectifying diodes, half-wave rectifiers, Zener diode for electric meter protection and as peak clipper are given. The breakdown diode; specifications of p-n junction diode, their physical structures and terminal identifications are also elaborated. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.

Microwave Diodes (Varactor Diode, p-i-n Diode, IMPATT Diode, TRAPATT Diode, BARITT Diode, etc.)

Microwave diodes are used to provide amplification, oscillation and other functions at microwave frequencies. They have a large bandwidth, therefore more information can be transmitted in microwave frequency range. It is the current trend to use microwaves more and more in long distance communication such as telephony, TV network, space communication, radars, microwave ovens etc. Therefore in this chapter, the Varactor diode; its construction, characteristics, performance and applications are presented, different types of semiconductor photodiodes are classified, and the IMPATT diode, TRAPATT diode and BARITT diode are elaborated along with their operation, performance and applications. The construction, operational characteristics and applications of p-n photodiodes, p-i-n photodiode, avalanche photodiode, and mid-infrared photodiodes are described. The transferred electron mechanism, valleys in conduction band and dependence of electron velocity on electric field are discussed. The Gunn diode: its fabricational materials, dielectric relaxation time etc. are given. The Dovett diode is also discussed. Minute insight into the various topics are given through solved numerical and theoretical examples. Review questions, numerical problems and objective type questions are also given with their answers.