Diodes I. Pre-viewing tasks 1. Look through the words and expressions given below and guess what this film can be about. Write down several sentences expressing your viewpoint on possible contents of the film. P-N junction ++ Semiconductor --- electrons +++ Holes +++ Impurities --- Bias ++ direct current --- alternating current --- Resistance +++ Capacitance +++ 2. Write down types of diodes that will be mentioned in the film. Photodiodes, Light Emitting Diode (LED), Laser diode 3. Watch the film and make sure that the choice you made is correct. II. While-watching-the-film tasks a). Watch the film "Diodes" and mark the following sentences as true or false. 1. Photodiodes are used in road signals. --2. Laser diodes are used in security alarms. +++ 3. The cathode acts as a positive terminal. +++ 4. The depletion region contains only positive ions on the P-side and negative ions on the N-side of the junction. --5. The motion of electrons doesn't stop immediately after the formation of the depletion region. +++ 6. Junction potential is 0.6 V for germanium and 0.2 V for silicon. --- 7. If a diode is operated in the forward-bias mode, we connect the positive terminal of the battery to the anode and the negative terminal to the cathode of a P-N junction diode. +++ 8. In the reverse bias case the majority charge carriers cross the depletion region setting up the current flow. +++ 9. When the diode is operated in DC voltage, the resistance of the diode is called dynamic resistance. --10. Resistance takes a very high value of Mega Ohms during reverse bias. +++ b). Watch the film again and answer the following questions. 1. Who and when coined the term diode? What is the origin of the word diode? William Henry Eccles was the first who coined the term diode, in 1919. Origin of the word diode from the Greek roots di, meaning “two”, and ode, meaning “electrode”. 2. What material is used to form the p-n junction? Silicon and germanium 3. What impurities are used if we want to get semiconductors of N-type and P-type? P-type: Borum atom N-type: Phophorus Atom 4. What is diffusion? Electrons from the N-side get attracted to the holes of the P-side, these electrons cross over the junction recombine with the holes and sees to be free carriers, this process called diffusion 5. What is junction potential? Charged ions level up electric fields in the depletion region known as Junction potential 6. What process is called biasing? Biasing – process of applying external voltage to an electronic device or a system to establish suitable working conditions 7. How can you define a drift current and a leakage current? -electrones move from anode to cathode, setting up the flow of current from anode to cathode, this current called as a drift current. - the current that the diode will leak when a reverse voltage is applied to it is called leakage current 8. What is breakdown voltage? Breakdown voltage is a parameter that defines the largest reverse voltage that can be applied to a diode without damaging the material. 9. How does a Zener diode work? Zener diode- is a diode that permits current to flow in either a forward or reverse direction. It has heavily doped p-n junction. 10. What is Diffusion capacitance? What is Transition capacitance? Diffusion capacitance is defined as a change in charge due to change in voltage during forward bias operation of a diode Transition capacitance is defined as a change in charge due to change in voltage during reverse bias operation of a diode c) Complete the sentences with the correct ending. 1. P-N junction diodes act as a base for all these diodes (LED, photodiodes, laser diodes) 2. The boron atom, being trivalent, accepts one electron from a neighboring silicon atom and creates vacancy or hole in the silicon structure. 3. As the phosphorus atom donates one electron, it loses its neutrality and becomes positively charged immobile ion. 4. As electrons cross the junction, they get repelled by the negative ions of the P-side . 5. Diodes are operated in two modes: Forward bias and Reverse Bias. 6. If a diode is operated in the reverse-bias mode, we apply the positive end of the battery to an Anode and the negative end of the battery to a cathode of the p-n junction diode . 7. In order to prevent a diode from breaking down, a diode should be doped in a very controlled manner. 8. Zener diodes find many applications in voltage regulated circuits. 9. We select diodes according to their specifications such as DC resistance, AC resistance, Diffusion capacitance, Transition capacitance. 10. Static resistance plays a vital role in the analysis of Clipping circuits or Rectifier circuits. III. Post-viewing tasks Below you will find a mind map that can be used while delivering an introductory lecture on diodes. a) Extend this mind map. Write down key words and expressions for each heading. Make up sentences using these words and expressions. b) Use your notes to summarize the video in 200 words. Origin of the word diode Applications of diode Construction of P-N junction diode Diodes Zener diode Parameters of diode Biasing of diode A) Origin of the word diode William Henry Eccles, in 1919 Diode from Greek roots : di+ode( di mean two, ode mean electrode) Application of a diode As switch or in rectifiers Construction of P-N junction diode Semiconductor device formed by doping the P and N-type semiconductors into silicon or germanium semiconductors. Biasing of Diode When in forward bias its equivalent resistance increases to few Ohms When in reverse bias its equivalent resistance increases to few Mega Ohms, no current Parameters of diode Capacitances: -diffusion capacitance (during forward bias) -transition capacitance (during reverse bias) Zener diode Zener diode is a heavily doped p-n junction diode, which is used for its current conduction in reverse bias method and control breakdown voltage B) This video is about diodes, types of diodes and how they work. Term “diode” was coined in 1919 by William Henry Eccles. Origin of the word diode from the Greek roots di, meaning “two”, and ode, meaning “electrode”. This video tells us about 3 types of diodes: photodiodes, Light Emitting diode (LED), Laser diodes. LED’s are used in road signals, Laser diodes are used in security alarms, photodiodes are used in smoke detectors. All these diodes make up p-n junction diodes. P-n junction diode consists of P-type semiconductor and N-type semiconductor. Boron atoms are used to get P-type semiconductor and Phosphorus atoms are used to get Ntype semiconductor. Also video tells us about biasing. Biasing – process of applying external voltage to an electronic device or a system to establish suitable working conditions. There are 2 types of current: leakage current and drift current. Electrons move from anode to cathode, setting up the flow of current from anode to cathode, this current called as a drift current. The current that the diode will leak when a reverse voltage is applied to it is called leakage current. Breakdown voltage is a parameter that defines the largest reverse voltage that can be applied to a diode without damaging the material. Zener diode is a diode that permits current to flow in either a forward or reverse direction. It has heavily doped p-n junction.
