Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE) PDF Download

Zener Diode

A Zener diode is a p-n junction operated in the reverse biased mode to take advantage of its sharply defined breakdown voltage. The Zener voltage VZ is specified at some test value of current IZT, at which the diode will exhibit some dynamic impedance Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE)  which depends upon the zener voltage of the diode and the level of Zener current.

Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE)

Operation: A Zener diode may be used to regulate the load voltage at the value VZ by acting as a bypass value to counteract line voltage or load current variations. Diodes having a breakdown voltage below about 6V rely on the true Zener effect (high electric field moves electrons from bonds), while the avalanche effect is responsible for reverse current above 6 V. Zener diodes have a temperature coefficient, αZ which generally is negative for VZ below about 6 V but positive above 6V, and is expressed in per cent of VZ per °C, with the change in Zener voltage given by the equation.

Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE)

Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE)Zener diode Characteristics

Zener Regulator

When Zener diode is forward biased, it works as a diode and drop across it is 0.7 V. When it works in breakdown region, the voltage across it is constant (VZ) and the current through diode is decided by the external resistance. Thus, Zener diode can be used as a voltage regulator in the configuration shown in figure.
The load line of the circuit is given by:

Vs = RsIs + Vz

Zener diode as regulatorZener diode as regulator

V-I Characteristics of Zener diodeV-I Characteristics of Zener diode

To operate the zener in breakdown region Vs should always be greater than VZ. Rs is used to limit the current
The Zener on state resistance produces more IR drop as the current increases. As the voltage varies from V1 to V2 the operating point shifts from Q1 to Q2,
The voltage at Q1 is V1= I1 RZ + VZ
and at Q2, V2 = I2 RZ + VZ
Thus, change in voltage is
V2 – V1 = (I2 – I1)RZ; ΔVZ = ΔIZRZ

Operating point in V-I Characteristics of Zener diodeOperating point in V-I Characteristics of Zener diode

  • Reference Zener diodes are available with αz as low as O.0005 % °C.
  • The admission of a small amount of mercury gas increases the current capability of a hot cathode gas filled tube.
  • A cold cathode or glow discharge diode may be used as a DC voltage regulator in a similar manner to a Zener diode.

Optoelectronic Devices

Modern solid state devices, which include emitters, sensors and collectors, usually are known as optical electronic devices or optoelectronics.

  • The radiations from a tungsten lamp is mostly in the infrared region, with relatively little in the visible region. It is often used as a source of infrared radiation.
  • Illumination is a measure of the visible radiation on a surface and is measured in foot candles or lumens/sq-ft.
  • Irradiance is a measure of the total radiation on a surface and is measured in watt/cm2.

1. Light Absorption and Emission: Light absorption and emission in a semiconductor is known to be heavily dependent on the detailed band structure of the semiconductor.

2. Direct Bandgap Semiconductors: Direct bandgap semiconductors, i.e., semiconductors for which the minimum of the conduction band occurs at the same wave vector k, as the maximum of the valence band, have a stronger absorption of light as characterized by a larger absorption coefficient.

3. Indirect Bandgap Semiconductors: Indirect bandgap semiconductors, i.e., semiconductors for which the minimum of the conduction band does not occur at the same wave vector as the maximum of the valence band, are known to have a smaller absorption coefficient and are rarely used in light emitting devices.

Photon absorption in a direct bandgap semiconductorPhoton absorption in a direct bandgap semiconductorIndirect bandgap semiconductor assisted photon absorptionIndirect bandgap semiconductor assisted photon absorption Indirect bandgap semiconductor assisted by photon emission Indirect bandgap semiconductor assisted by photon emission

4. Photo-diode: The photo conductors which are junction type, are photo-diodes or photo transistors where in one or more p-n junction are used under reverse bias. Electron hole pairs resulting from photons incident on the p-n junction add to the minority carriers due to the reverse bias.

Symbol of Photo-diodeSymbol of Photo-diodeNote: Silicon and germanium photo sensors have their peak spectral response in the infrared region, with their response in the visible only approximately 40% of maximum.

  • The inherent current gain of a transistor provides the photo transistor with a high current gain in the region of 1 mA/mW/cm2.
  • By adding a second conventional transistor, a photo Darlington amplifier results, with even higher sensitivity.
  • Photo-diodes and photo transistors may be operated as switching devices in light-operated relays, shaft encoders, paper tape readers, brush less DC motors, etc.

Variations of the basic p-n photo-diode are

  • PIN photo-diode (Ultrafast response),
  • Avalanche photo-diode (Higher current sensitivity and fast response),
  • Photo-diode (Inexpensive higher current sensitivity but slower response)

5. Photovoltaic Sensors: Photovoltaic sensors, usually either silicon or selenium, generate a voltage under open circuit conditions of typically 0.5V. When operated in the short-circuit mode, the current is proportional to the illumination and can be used to provide a direct reading foot-candle metre. Photovoltaic sensors may be series parallel interconnected to provide large area solar power cells.

6. Light Emitting Diodes (LEDs): It is a special type of p-n junction device that under forward conditions can emit external spontaneous radiation in ultraviolet, visible and infrared regions of electromagnetic spectrum. Light Emitting Diodes may emit visible radiation when the p-n junction is diffused in GaAsP, infrared if constructed from GaAs, and a laser beam if sufficiently highly pulsed current is applied to a GaAs junction. A popular alphanumeric display is the LED seven segment device, which can provide high brightness for only a few milliwatts of input power per segment.

Basic Structure of light Emitting Diode (LED)Basic Structure of light Emitting Diode (LED)

7. Photovoltaic (Solar Cells)

The solar cells are semiconductor junction devices which are used for converting optical radiation (sunlight) into electrical energy. The generated electric voltage is proportional to the intensity of incident light. Due to their capability of generating voltage they are called as photovoltaic cells. p-n junction solar cells are currently used to supply electrical power for many space satellites.
When a photon of light energy collides with the valence electron either in p-type material or n-type material, it imparts sufficient energy to the electron to leave its parent atom. As a result, free electrons and holes are generated on each side of the junction. In p-type material, the newly generated electrons are minority carriers.

Circuit diagram of photo voltaic cellCircuit diagram of photo voltaic cell

These electrons move freely across the junction with no applied bias. Similarly, in n-type material, the newly, generated holes are minority carriers
These holes move freely across the junction with no applied bias. The result is an increase in minority carrier flow. In this way, the depletion region potential causes the photocurrent to flow through the external load.

  • The solar cell is a self-generating device i.e., it does not require any external power source.
  • The internal emf and current generated by the solar cell is enough which can be measured by the galvanometer.
  • A solar cell can't convert all solar radiation into electric energy.
The document Semiconductor Devices | Electronic Devices - Electronics and Communication Engineering (ECE) is a part of the Electronics and Communication Engineering (ECE) Course Electronic Devices.
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FAQs on Semiconductor Devices - Electronic Devices - Electronics and Communication Engineering (ECE)

1. What are semiconductor devices in electronics and communication engineering?
Semiconductor devices are electronic components made from semiconductor materials, such as silicon or germanium, that can control the flow of electric current. These devices are used in various applications in electronics and communication engineering, including amplifiers, diodes, transistors, and integrated circuits.
2. How do semiconductor devices work?
Semiconductor devices work based on the properties of semiconductors. Semiconductors have an intermediate level of electrical conductivity, greater than insulators but lower than conductors. By manipulating the material properties and adding impurities, such as doping, semiconductor devices can exhibit desired electrical characteristics. For example, a transistor consists of three layers of semiconductor material, with each layer having specific doping to control the flow of current.
3. What is the importance of semiconductor devices in electronics and communication engineering?
Semiconductor devices play a crucial role in electronics and communication engineering. They enable the miniaturization of electronic components, leading to smaller and more efficient devices. These devices are essential for signal amplification, switching, and digital processing. Additionally, semiconductor devices are used in various communication systems, such as wireless networks, satellite communication, and fiber optics.
4. What are some common types of semiconductor devices used in electronics and communication engineering?
There are several common types of semiconductor devices used in electronics and communication engineering, including: 1. Diodes: Diodes allow current to flow in only one direction and are commonly used for rectification, signal modulation, and in power supply circuits. 2. Transistors: Transistors are three-layer devices that can amplify or switch electronic signals. They are widely used in amplifiers, oscillators, and digital logic circuits. 3. Integrated Circuits (ICs): ICs consist of numerous interconnected semiconductor components on a single chip. They are used in computers, smartphones, and various electronic systems. 4. Optoelectronic Devices: These devices combine semiconductor materials with light-emitting or light-detecting properties. Examples include light-emitting diodes (LEDs), laser diodes, and photodiodes.
5. What are the challenges faced in the development of semiconductor devices in electronics and communication engineering?
The development of semiconductor devices in electronics and communication engineering faces several challenges, including: 1. Miniaturization: As technology advances, there is a constant demand for smaller and more powerful devices. Developing semiconductor devices with reduced sizes while maintaining their performance and reliability is a significant challenge. 2. Heat Dissipation: As semiconductor devices become more powerful, they generate significant heat. Efficient heat dissipation mechanisms need to be implemented to prevent overheating and ensure device longevity. 3. Power Efficiency: With the increasing energy consumption of electronic devices, power efficiency is a critical factor. Developing semiconductor devices with low power consumption and high energy efficiency is a continuous challenge. 4. Integration and Compatibility: As different electronic systems and devices need to work together seamlessly, ensuring compatibility and integration of semiconductor devices with various platforms and technologies is a challenge. 5. Reliability and Durability: Semiconductor devices should be reliable and durable, withstanding various environmental conditions and long-term usage. Developing robust devices that can withstand stress, temperature variations, and other factors is an ongoing challenge for engineers.
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