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Gunn Diode ne ku çi ye?
Pêşnûmayî Gunn Diode
Gunn diode yek encam pasîv semikonduktor bi du termînal e ku ji materyal semikonduktor n-doped teşkilkirin, heta lê gelek diodên din jî p-n junctionan hene. Gunn diodên dikarin ji materyalan ve hatine kirin ku van materyalan ji kaniyên enerjiya cêrserbun, sererast yên vala, te destpêkirin, û wan materyalan şeviyên conduction band de hene, wek Gallium Arsenide (GaAs), Indium Phosphide (InP), Gallium Nitride (GaN), Cadmium Telluride (CdTe), Cadmium Sulfide (CdS), Indium Arsenide (InAs), Indium Antimonide (InSb) û Zinc Selenide (ZnSe).
Prosedeyê herêmî ya binihêriş dibe ku layer epitaxial ê li ser substrat degenerate n+ bibin da ku sê layer n-type semiconductor (Figure 1a) bin formikirin, yana layerên derbasîn tu berbiyayên din jî layera navendî, active layer, tê.
Li ser dibistana yekan Gunn diode metal contacts di du endan de nehatine kirin da ku biasing bêtir bike. Şekilî symbolî ya circuit ê ya Gunn diode wek Figure 1b hatine nîşan kirin û ji normal diode rê bêtir biguherîne da ku bi rêya absencî p-n junction be.
Heke voltage DC bi Gunn diode birêve bike, electric field di layeran de, bêtirîn di layera navendî, active region de, pirsa bide. Sêdî, conduction ji ber vegerina electronan ji valence band yanên valley lower ê ya conduction band de gir îrova dihe.
V-I plot û wateya nîşankirin û heye curve û Region 1 (pink colored) ya Figure 2. Lê, dema çi ke werdigere value threshold (Vth) reşike, conduction current û di Gunn diode de gir îrova dihe wek curve û Region 2 (blue colored) ya figure de nîşan kirin.
Çunki, bi voltajên zêde electronan ji valley lower ê ya conduction band yanên valley higher ê de gir îrovan, mobilityyan dikarin ji ber zêdetirina effective mass ûyan gir îrovan. Zêdetirina mobility conductivityyan gir îrovan û ji ber raya current flowing through the diode gir îrovan.
Birêre, diode negative resistance region di V-I characteristic curve de nîşan dide, ku ji Peak point yanên Valley Point de digire. Effect û wate transferred electron effect û Gunn diodes jî Transferred Electron Devices emandin.
Li vir, transferred electron effect jî Gunn effect emandin û li nav John Battiscombe Gunn (J. B. Gunn) emandin, ku bi discovery ûyan di 1963 de nîşan kirin ku microwave ûyan dikarin ji ber apply steady voltage across chip of n-type GaAs semiconductor bikin. Li vir important e ku materyal û wate use bikin da ku Gunn diodes dikarin n-type bin, ji ber transferred electron effect tenha ji electrons û naha ji holes reşike.
Ji ber ku GaAs poor conductor e, Gunn diodes heat zaf zaf bikin û need heat sink. Bi microwave frequencies, current pulse di active region de move kirin, ji specific voltage re start kirin. Move pulse potential gradient reduce kirin û prevent further pulse formation.
New current pulse dikare tenha ji ber previous pulse far end of active region re çawe, potential gradient increase kirin. Time û wate pulse travel across active region determine pulse generation rate û operational frequency of Gunn diode. Ji bo vary oscillation frequency, thickness central active region must be adjusted.
Li vir, nature negative resistance exhibited by Gunn diode enables it to work as both an amplifier and an oscillator, latter known as Gunn diode oscillator or Gunn oscaillator.
Advantages of Gunn Diode
Lies in the fact that they are the cheapest source of microwaves (compared to other options such as klystron tubes)
They are compact in size
They operate over a large bandwidth and possess high frequency stability.
Disadvantages of Gunn Diode
They have a high turn-on voltage
They are less efficient below 10 GHz
They exhibit poor temperature stability.
Applications
In electronic oscillators to generate microwave frequencies.
In parametric amplifiers as pump sources.
In police radars.
As sensors in door opening systems, trespass detecting systems, pedestrian safety systems, etc.
As a source for microwave frequencies in automatic door openers, traffic signal controllers, etc.
In microwave receiver circuits.
