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Vacuum Diodes and the Rise of p-n Junction Semiconductors

Explore the history of vacuum diodes and their eventual replacement by p-n junction semiconductors, leading to smaller and more compact electronic circuits. Discover the various types and applications of vacuum diodes and the advantages of p-n junction semiconductors.

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Vacuum Diodes and the Rise of p-n Junction Semiconductors

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  1. P-N JUNCTION ASHVANI SHUKLAManager(c & i)Bgr Energy

  2. Introduction • History of p-n Junction • In November 16, 1904 first vacuum tube was invented by Sir John Ambrose Fleming and it is called the Fleming valve, the first thermionic valve. There was no existence of p-n junction in electronics field. In October 20, 1906 Triode Tube had been developed by Dr. Lee de Forest. A conceptual figure of vacuum diode is shown below.

  3. Here the vacuum tube works mostly like modern diode. But its size is larger. It consists of a vacuum container with cathode and anode inside. This cathode and anode are connected across a high voltage source. Generally it works on principle of thermo ionic emission. This cathode is heated by filament an hence electron get emitted from cathode towards anode. So it is also known as thermionic tube. Current only flow from the anode to cathode i.e. unidirectional flow. The V-I characteristics of a vacuum tube is shown below.

  4. How does vacuum tube diode work?

  5. Filament creates heat to the cathode to emit electrons. Beam of electrons flows from cathode to anode through the space between cathode and anode. The voltage difference is created across the cathode and anode by applying high voltage across their terminal. The replacement of the electrons in the electrodes is happened by this voltage source. Under reverse bias this vacuum tube does not work or it does not have any breakdown. This vacuum tube was the basic component of electronics throughout the first half of the twentieth century. It was available and common in the circuit of radio, television, radar, sound reinforcement, sound recording system, telephone , analog and digital computers, and industrial process control.

  6. Gradually p-n junction semiconductor has come in the market and vacuum tubes got replaced by them. But till today somewhere vacuum tubes are being used widely. These fields for application of the vacuum tubes are in • Atomic Clocks • Audio Systems • Car Dashboards • Cellular Telephone Satellites • Computer Monitors • DVD Players & Recorders • Electromagnetic Testing • Electron Microscopes • Gas Discharge Systems • Gas Lasers • Guitar Amplifiers • Ham Radio • High-speed Circuit Switching • Industrial Heating • Ion Microscopes • Ion Propulsion Systems • Lasers • LCD Computer Displays • Lighting • Microwave Systems • Microwave Ovens • Military Systems • Mobile Phone, Bluetooth & Wi-Fi Microwave Components • Musical Instrument Amplifiers • Particle Accelerators • Photomultiplier Tubes • Plasma Panel Displays • Plasma Propulsion Systems • Professional Audio Equipment • Radar Systems • Radio Communications • Radio Stations • Recording Studios • Solar Collectors • Sonar Systems • Strobe Lights • Satellite Ground Stations • Semiconductor Vacuum Electronic Systems • TV Stations • Vacuum Electron Devices • Vacuum Panel Displays

  7. Types of Vacuum Diodes • The vacuum diodes are classified as 1. frequency range wise (audio, radio, microwave) 2. power rating wise (small signal, audio power) 3. cathode/filament type wise (indirectly heated, directly heated) 4. application wise (receiving tubes, transmitting tubes, amplifying or switching) 5. specialized parameters wise (long life, very low micro phonic sensitivity and low noise audio amplification) 6. specialized functions wise (light or radiation detectors, video imaging tubes)

  8. After the vacuum tubes, p-n junction semiconductor came in the market. The circuit gets lighter and more compact. The p-n junction semiconductor made of either Silicon or Germanium material which has four numbers of electrons in the valence band. From this valence band the electron transit to the conduction band penetration the energy gap of one electron volt approximately. Generally pure Silicon or Germanium has no extra electron available in their crystal structure. But applying of thermal energy to this crystal some bonds break and some electrons get available in the conduction band. But current is very small or in the order of microampere.

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