A semiconductor material has an electrical conductivity value falling between a conductor (such as metallic copper) and an insulator (such as glass). Lattice structure and atomic structure of constituent elements decide whether a particular material will be insulator, metal or semiconductor.
Energy Bands
- There are two distinct band of energies (called valence band and conduction band) in which electrons in a material lie. Valence band energies are low as compared to conduction band energies. All energy levels in the valence band are filled while energy levels in the conduction band may be fully empty or partially filled.
- The electrons in the conduction band are free to move in a solid and are responsible for the conductivity. The extent of conductivity depends upon the energy gap between the top of valence band and bottom of conduction band.
- The electrons from valence band can be excited by heat, light or electrical energy to the conduction band and thus, produce a change in the current flowing in a semiconductor.
CLASSIFICATION OF SEMICONDUCTORs
Based on material
- Elemental semiconductors: Silicon (Si) and (Ge)
- Compound semiconductors:
- Inorganic: CdS, GaAs, CdSe, InP etc.
- Organic: Anthracene, Doped pthalocyanines etc.
Most of the currently available semiconductor devices are based on elemental semiconductors Silicon or Germanium (Ge) and compound inorganic semiconductors. However, after 1990s, a few semiconductor devices using organic semiconductors and semi-conducting polymers have been developed.
Based on purity
- Intrinsic semiconductor: They are pure semiconductors with no impurities. They have no or zero conductivity at very low temperatures. However, as temperature rises, the conductivity of these materials increases.
- Extrinsic semiconductor: When a small quantity of small impurity is added to pure semiconductor, the conductivity of the semiconductor is increased manifold. These semiconductors are called extrinsic or impurity semiconductors. The deliberate addition of a desirable impurity is called doping and the impurity atoms are called dopants.
Wide Bandgap semiconductor
- They are semiconductors materials which have a larger band gap than conventional semiconductors. Conventional semiconductors like silicon have a bandgap in the range of 1-1.5 EV (silicon and gallium arsenide), whereas wide-bandgap materials have bandgaps in the range above 2 EV.
- Examples of wide-bandgap semiconductors: Boron nitride, Diamond, Zinc, Gallium nitride, Zinc Oxide, Tin dioxide, Aluminum phosphide, Cadmium sulfide, Silicon carbide
Benefits of wide bandgap semiconductors:
- Permits devices to operate at much higher voltages and frequencies.
- Devices can operate at higher temperatures of the order of 300o C.
- Higher temperature tolerance allows these devices to operate at much higher power levels.
- Applications: They are key components to make green and blue LEDs and lasers, certain radio frequency applications notably military radars.
Gallium Nitride
- It is a very hard, mechanically stable widegap bandgap semiconductor. It was commonly used in blue light-emitting diodes since the 1990s.
- Ministry of Electronics and IT (Meity) and IISc have jointly established GaN based Development Line Foundry facility called Gallium Nitride Ecosystem Enabling Centre and Incubator (GEECI), especially for radio frequency and power applications, including strategic applications.
Benefits of Gallium Nitride
- Higher breakdown strength
- Faster switching speed leading to faster devices
- Higher thermal conductivity
- Lower on-resistance giving lower conductance losses.
- Less power needed to drive the circuit.
- Ability to make smaller devices taking up less space on the printed circuit board.
- Lower cost
RISC-V Microprocessors
- Ministry of Electronics and Information Technology (MeitY) has launched Digital India RISC-V Microprocessor (DIR-V) Program. This Program aims to enable the creation of the microprocessors for the future in India, for the world and achieve industry-grade silicon and design wins by December 2023.
About RISC-V
- RISC-V is an open standard Instruction Set Architecture (ISA) based on established RISC principles. Each computer hardware will support a particular ISA.
- Unlike most other ISA designs, RISC-V is provided under open-source licenses that do not require fees to use. RISC-V can be extended or customised for a variety of hardware or application requirements.
- ARM and x-86 are two such instruction set architectures- one of which is licensed and the other is sold, where the industry consolidated in the earlier decades. However, RISC-V has emerged as a strong alternative to them in the last decade, having no licensing encumbrances, enabling its adoption by one and all in the semiconductor.
- industry, at different complexity levels for various design purposes. India has developed two series of microprocessors:
- SHAKTI series of microprocessors by IIT Madras.
- VEGA microprocessors by C-DAC.