Semiconductor: silicon (Si), germanium (Ge), are the four elements,

Intrinsic semiconductor is 1% pure crystal structure of semiconductor,
The generation of free electrons in the covalent bond with an empty position, known as the hole, the positively charged, there is a free electrons have a hole, when the free electron and hole collision disappear at the same time, known as the compound,
Carrier is a carrying charge particles, less carrier, poor electrical conductivity,
Conductive and temperature on the performance of semiconductor devices, the higher the temperature, thermal motion increases, carrier concentration increases, the conductivity stronger,
2% impurities in two kinds of N and P type semiconductor
N type semiconductor participation pentavalent phosphorus, number of free electrons increases, reduced Numbers of holes,
P type semiconductor participation trivalent boron element, mainly by hole conduction,
3% PN junction formation: matter because the concentration difference of motion is called diffusion movement, have the gas liquid solid, P area hole concentration is much higher than N area, the N concentration of free electrons is much higher than P areas, within the contact surface to produce electric field, to participate in the number of carrier diffusion and drift motion is the same, to achieve dynamic balance, it formed the p-n junction,
P-n junction unique conductivity: forward biased narrow the depletion layer, the diffusion current, p-n junction conduction, p-n junction should have resistance to current limiting, reverse biased, depletion layer width, the formation of drift current minority carriers (movement), because the current is very small, can be approximately considered as, namely forward biased conduction, reverse biased cut-off, unidirectional conductivity ()

The temperature of the semiconductor poor stability,

P-n junction capacitance effect:
Barrier capacitance, when reverse biased, the equivalent capacitance change is very big, mainly displays in with reverse voltage, Cb
Diffusion capacitance is the forward voltage when the equivalent capacitance of Cd
Junction capacitance Cj=Cb + Cd, not a constant,
Plus if pn junction voltage high frequency to a certain degree, will lose a one-way electrical conductivity, so the p-n junction has a upper limit cut-off frequency,