Semiconductor diode (No Bias)

• PN junction diode possesses the properties of a rectifier
• PN Junction Possibilities

  1. No bias
  2. Forward bias
  3. Reverse bias
• Bias refers to the application of external voltage across the two terminals when
• Biasing. When we apply external voltage across these two terminals
• If we applied noise channel voltage it is called no bias
• BJT


  Bipolar Junction Transistor
• BJT a three terminal device. You can consider it as a device with two diodes in which one diode is biased by the current of other diode
• PN Junction constitutes a rectifier which permits the easy flow of charge in one direction but restrains the flow in opposite direction
• The minority charge carriers depends on the temperature and will not depend external voltage
• The process of movement of charge carriers from high concentration to low concentration is called diffusion
• Diffusion current is because of majority charge carriers
• Immobile ions will surface down because of diffusion
• Immobile ions surface out means uncovering the immobile ions
• Immobile ions are acceptor ions and donor ions
• Depletion region 


  No mobile charges but only uncovered immobile ions
• We call it depletion region because it is depleted of free carriers
• Depletion region is also called space charged region
• The width of depletion region is fixed
• Barrier potential 


  Potential is acting like a barrier to the movent of holes and electrons it is acting as barrier for the further movement of free charge carriers
• Drift current 


  Because of the drift of electrons towards positive layer and drift of holes towards negative layer
• Drift current is due to minority charge carriers
• Under steady state 


  Diffusion current us equal to drift current
• Net current is equal to zero in case of open circuited PN Junction Diode
• This region of uncovered positive and negative ions is called the depletion region due to the “depletion” of free carriers in the region
• In the absence of an applied bias across a semiconductor diode, the net flow of charge in one direction is zero.