Intro to Semiconductor devices & Diodes Electronics 1 CVHS

Semiconductors  A material with four free or valence electrons  Usually silicon or germanium, these materials do not allow the free flow of electrons like a conductor, but also do not prevent electron flow like an insulator

Semiconductor Doping  Silicon and germanium start out as a pure semiconductor crystal  In order to be useful, the crystalline structure must be “doped”  Doping replaces some of the atoms in the crystal with atoms from different elements  These “replacement” atoms contain more or less free electrons than the pure semiconductor material

Semiconductor Doping  If atoms with more free electrons are used, N-Type material is created  The added free electrons in N-Type material are called carriers  If atoms with fewer free electrons are used, P-Type material is created  The missing free electrons in P-Type material are called holes

Semiconductor Properties  Once their internal structure has been altered, semiconductors can act as an insulator or a conductor  This property is controlled with current, and allows the semiconductor device to either block almost all of the current, or allow almost all of the current to pass through (semiconductor can act as an insulator or conductor)

Diodes  Diodes only allow current to travel in one direction  A diode is made of an anode (+) and a cathode (-)  The diode will permit current flow when it is forward biased (anode connected to + and cathode connected to -)  The diode will prevent current flow when it is reverse biased (anode connected to - and cathode connected to +)

Diodes  Internally the diode is composed of two differently doped materials, N-material and P-material.  In between these two materials is a thin layer called the “depletion region”  The depletion region is neither P nor N, but made up of the pure crystalline semiconductor structure

Forward Bias  When a positive charge is on the anode (P- material) and a negative charge is on the cathode (N-material) the diode will conduct  This occurs because likes repel each other, and the N-Type & P-Type close over the depletion region

Reverse Bias  When a negative charge is on the anode (P- material) and a positive charge is on the cathode (N-material) the diode will not conduct  This occurs because opposites attract each other, and the N-Type & P-Type widen the depletion region

Forward Operating Voltage & PIV  All semiconductor devices require a forward operating voltage. This is the amount of forward bias voltage required for the component to start conducting Germanium ~ 0.3vdc Silicon ~ 0.6vdc  Diodes also have a Peak Inverse Voltage Rating (PIV) This is the amount of reverse bias voltage a diode can handle without breaking down A higher voltage will cause the diode to conduct in reverse bias (avalanche current)

Rectification  One of the most common uses of diodes is for rectification  Rectification is changing AC to DC  A single diode can be used to transform AC into a rough DC signal (only converts half of the AC signal to DC)

Bridge Rectifier  Because a single diode produces such a crude DC signal, a bridge rectifier is more commonly used  A bridge rectifier allows all of the AC signal to be converted into DC  Bridge rectifiers still produce a pulsating DC signal, so a filter (cap) must be used to further improve the signal

LED’s  LED stands for Light Emitting Diode  Like a diode, an LED will only allow current flow in one direction  LED’s can only handle a limited amount of current (must include a current limiting resistor)

Review  Semiconductors have how many valence electrons?  What procedure is used to produce N-Type and P-Type material?  What are N-Type & P-Type?  What is a depletion region?  What is forward bias?  What is reverse bias?  What is forward operating voltage?  What is PIV?  What is rectification?  What is an LED?