TOPIC OF PRESENTATION Gunn Diode GUNN DIODE Definition • History • Construction • Definition: Such type of semiconductor device which have only N type doped (semiconductor) material, is called “Gunn Diode.” It’s a unique component. Gunn Diode is also known as: Transferred Electron Device (TED). Microwave Semiconductor Device. Symbols for Circuit Diagram: History: Gunn diode was invented by a Physicist, John Battiscombe Gunn, in 1963, in IBM. Transferred Electron Effect was first published by: Ridley and Watkins in 1961. Further work by Hilsum in 1962, Finally J.B. Gunn, observed it, using GaAs semiconductor, in 1963. Construction: Gunn diodes are fabricated from a single piece of n-type semiconductor, Source Material: Tri-methylgallium and arsenic (10% in H2). Most Common Materials : Gallium Arsenide (GaAs) and Indium Phosphide (InP). Three main areas: Top/Upper Area, Middle Area, Bottom Area. Middle area (Active layer) has a doping level between 1014 cm-3 to 1016 cm-3 . Substrate has doping density n = 1.3x10 ^18 cm-³. Thickness varies according to the frequency required. Metal contacts consist of three layers, namely a 80 nm layer of AuGe sandwiched between two layers of 10 nm of Ni. Additional AuGe is evaporated on the existing contacts to a depth of 0.7μm. Use Of Gold. Its relative stability, and high conductivity. Requirements: The material must be defect free , and it must also have a very uniform level of doping. Types of Materials Used For Gunn Diodes To Get Different Frequencies: Gallium arsenide for frequencies up to 200 GHz, Gallium nitride can reach up to 3 THz. GUNN DIODE Negative Resistance In Gunn Diode GaAs (Galliam Arsenide ) has a property of negative resistance. ) The negative resistance in Gunn diode is due to (a) electron transfer to a less mobile energy level (b) high reverse bias (c) electron domain formation at the junction (a) How electron move into low mobility ? According to Einstien Equation E=mc2 (b) High reverse bias (c) Electron domain formation at the junction EFFECT OF NEGATIVE RESISTANCE ON CURRENT GUNN DIODE Gunn Effect GUNN DIODE WHICH HAS A DYNAMIC RESISTANCE. NEGATIVE GRAPH BETWEEN RESISTANCE AND VOLTAGE As a result we arrange that average voltage on the Gunn diode is as illustrated in figure. The diode is said to be biased into the negative resistance region. CHANGE IN ENERGY R= RL + R(V) WHEN R >0 THE ENERGY OF ANY OSCILLATION TENDS TO BE REDUCED BY RESISTIVE DISSIPATION. WHEN R <0 The oscillation energy tends to be increased. According to law of conservation of energy The amount of energy at r > 0 = The amount of energy at r < 0 GRAPH BETWEEN RESISTANCE AND CURRENT WORKING OF GUNN DIODE COAXIAL CAVITY In this case, each diode induced fluctuation travels up the cavity and reflected from the far end, returning to the diode after a time L = length of cavity c= speed of light The oscillator may therefore oscillate at any frequency such that. n= the “number of half- waves” FOR A BETTER RESULT n=1 The system won't oscillate at a lower frequency because the cavity is too short to permit it. It can't oscillate at a higher frequency because the diode is ‘too slow’, hence we ensure a single-valued oscillation frequency. Real Gunn devices have a response time which varies with the applied voltage, hence we can electronically tune the oscillation frequency by slightly adjusting the bias voltage GUNN DIODE Difference between Gunn diode and P-N junction DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION Gunn diode Construction It only consists of N type semiconductor material It has N+ n N+ material No depletion region is formed P-N junction diode It consists of P & N type semiconductor material It has P type,N type and depletion region between these materials DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION Gunn Doiode P-N junction Diode DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION Symbols of Gunn Diode P-N junction DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION Gunn Doiode P-N junction Diode DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION Gunn Doiode P-N junction Diode DIFFERENCE BETWEEN GUNN DIODE AND P-N JUNCTION I-V characteristics Of Gunn diode I-V characteristics Of P-N junction Diode GUNN DIODE Applications A Gunn diode can be used to amplify signals because of the apparent "negative resistance". Gunn diodes are commonly used as a source of high frequency and high power signals Sensors and measuring Instruments Anti-lock brakes Sensors for monitoring the flow of traffic Pedestrian safety systems Distance traveled" recorders Traffic signal controllers Automatic traffic gates AUTOMATIC DOOR OPENERS CAR SPEED DETECTORS SENSORS TO AVOID DERAILMENT OF TRAINS MOTION DETECTOR RADIO AMATEUR USE GUN OSCILLATOR Thanks!