Characteristic diode valve splice

1) Law of the splice:

If a type semiconductor is had n and they create of the braces gap-electron in x=0, it is had that it changes appreciably only the concentration of the minority bearers of type "p" which diffusing diminish until stretching to the value of equilibrium p₀ therefore obtain that the concentration of the minority bearers in x is being the free medium way of the gaps (…D_p is the constant of spread of gaps while t_p the time is the medium time of life of the gap that is that in average elapses before its ricombinazione) while P₀ is the equilibrium value which it stretches the exponential and p' (0) it is the gap concentration in x = 0, in particular if the iniettate charges are due to a tension applied in x=0 have dictate law of the splice.

 

2) It upgrades them of âBuilt inâ?:

If we have a semiconductor of drugged type "n" in not uniform way generates one spread current and, in absence of external sollicitations, the current must be null total that it implies that the spread current must be balanced from one current of equal and opposite conduction, considering gaps is had from which the electric field can be gained of built-in which being conservativo it admits upgrades them to scale V that is function only of the point that is from which integrating between x₁ and x₂ is had . Being function only of the points it begins them and final the not varied formula if instead of an only semiconductor to not uniform concentration we have a splice pn for which the concentration of gaps in the type region "p" is while in the type region "n" it is , is had quindi .

 

3) Splice pn to empty:

The region "p" is characterized from trivalenti atoms of impurità represents from ione a negative with neighbor a gap to you while the region "n" is characterized from pentavalenti atoms of impurità represents from one ione positive with neighbor an electron to you. For effect of the concentration gradient the gaps muoveranno from sx to dx and free electrons in the opposite back, that determine a region of horse emptying of wide splice 0,5mm, in it not are free bearers but single the Ionian ones more do not neutralize to you. A double layer is created therefore of loads that it gives to place to an electric field who opposes itself to the spread currents, its value is obtained integrating the equation of Poisson and, for successive integration is obtained also upgrades them being from which famous as to the ends of the emptying zone there is just they of contact upgrades itself.

 

4) direct Polarization of the splice pn:

Connecting of the generator to the drugged semiconductor of type "p" it increases the gap number and also the free electron number presents in the type region "n" therefore increases the spread current through the splice that is one current of minority bearers. On the band charts this corresponds to a lowering of the tension of built-in that therefore it facilitates the spread.

 

5) inverse Polarization of the splice pn:

Connecting of the generator to the drugged semiconductor of type "n" it is had analogous that present the free electrons in it come remove you from the splice, and - of the generator connected to the drugged semiconductor of type "p" it attracts contained gaps in it, the result is that the emptying zone is expanded. In theory since the bearers are in ended number, the current to regimen would have is null however has one small current due to the minority bearers who are generate to you thermally and are attracted from the pole of the battery situated from the other part of the splice.

On the band charts an elevation of the tension of built-in that is had therefore it inhibits the motion for spread of the majority bearers while it does not influence the flow of the minority bearers generates to you thermally.

 

6) Equation of the diode valve:

where_{the 0} are the current of inverse saturation and h is the idealità factor and holds account that in the silicon can be had generation phenomena and recombination also in the transition region therefore h is worth 2 for the silicon and 1 for the germanium. It is observed that the â?"1 it is necessary so that for v = 0 0 are i =.

 

7) logaritmica Characteristic:

The if â?"1 he is negligible invites to write it in logaritmica shape, graficando they must be had of the straight ones but to high tension the tension applied to the clips does not coincide with the tension applied on the splice in how much has one fallen in the resistance of mass of the semiconductor and therefore the increase of the current with the applied tension is to delineate that instead exponential .

 

8) Tension of threshold:

From the characteristic tension-current of the famous diode valve that is a value of the tension under which the current that crosses it is smaller of 1% of the maximum value in order then instead to increase quickly, such tension of threshold v_g is worth 0,2V for the germanium and 0,6V for the silicon, such following difference is due to the two reasons:

to)       _{the 0} for GE it is of the order of the mTo while for one is of the order of the hTo ci² has had to the fact that the energy gap of the germanium is inferior to that one of the silicon.

b)       in the current it is increased more slowly in how much for tensions of little tenth ones of volt h= 2 and therefore the effect of the exponential is less marked.

 

9) Effect of the temperature on one splice pn:

In the it is had that _{the 0} double every 10°C while V_T diminishes of 2,5mV every °C, this totally correspond to an increase of the current of inverse saturation_{the 0} pars to 7% for every °C, theoretically instead would have to be greater, the reason of the discordanza are that in the theoretical calculation the member of _{the 0} neglects itself who disperses itself on the surface.

 

10) Linearizzazione at times:

The circuit equivalent of the diode valve sees the series of a direct resistance R_f , one battery V_g and one ideal diode valve, all in parallel to the inverse resistance R_i , this last and R_f coincides with the dynamics resistance of the diode valve that is with the tangent to its characteristic curve, such value is almost constant and the equation of the diode valve is obtained deriving regarding v, and therefore and for R _i is had analogous: .

 

11) Ability to transition:

A splice to step with the region is had totally "p" much drug addict regarding the region "n"…(N _To > >N _D) therefore having the diode valve to be neutral, the transition region is the much widest one in the region "n" that in the region "p" W _n> > W _ptherefore it will not be able to be neglected W _pand that is to be said that the region of transition in the diode valve is wide W = W_n. Integrating two times the equation of Poisson finds that W depends on the square root of the applied tension and with it also the ability to transition that is the same ability to a condenser to flat faces therefore is like if the charges instead of being to the inside of the transition region they are distributed on its extremities.

 

12) Diode valve varactor:

Increasing the inverse tension to the heads of the diode valve the region of W transition is expanded and therefore the ability to transition diminishes, in such a way pu² therefore to change the frequency of resonance of a come to an agreement circuit, in the circuit an inductance and a condenser of block are also present that serves to avoid that continuous the necessary one in order to polarize the varactor catches up the oscillating circuit.

 

13) Method of the control of loads:

A splice pn in which the region is had "p" much more it is drugged of the region "n", pu² therefore to neglect the injection of loads that it derives from the free electrons that they diffuse in the region "p" and to consider the sun gaps that they diffuse in the region "n", it loads iniettata is that one under the curve and the density of spread current is obtained integrating of the rest is and therefore the spread current is that, estimated in x = 0, and replacing p' (0) gives back con has that is a linear relation between applied tension and loads and therefore he is simpler that not the exponential relation between I and V.

It is important to notice that if the diode valve is polarized directly then Q is positive, otherwise is negative.

 

14) Ability to spread:

The spread ability is introduced for a directly polarized splice, if it can some make an appraisal is statics that dynamics:

Static appraisal

replacing ha where I have replaced the resistance they of the diode valve differs, observes themselves like to growing of the current in the diode valve increases the C_D that is approximately 100 times larger of the C_T .

Dynamics appraisal

Beginning from a direct polarization increases the directed tension to the heads of the diode valve, that provokes an increase of the gap concentration on the splice, but they find it hard to diffuse for which to the time t Dt the two abilities to transition will have been only iniettata load inferior Q' to load Q iniettatato®the time t ¥ therefore are also various.

 

15) Times of commutation:

A diode valve polarized directly to the tension v _F is had , in it slides the current where R_L is cargo the supposed resistance the much largest one of the direct resistance of the diode valve. Applying one tension - V_R the diode valve inversely turns out polarized however the current to its heads immediately does not catch up the value_{the 0} in how much majority bearers who were diffuse in the region in which they are minority bearers completely need a Pò of time before being riassorbi, sin when that does not happen is only had that the sign of the tension is changed and therefore changes the back of the current, solo when the density of minority bearers in excess has been reduced to 0 the current comes down esponenzialmente until to the value_{the 0} . The time of recombination can be reduced or inserting of the centers of recombination in gold or increasing inverse the tension applied.

 

16) Diode valve zener:

It comes used laddove demands a stable tension to the heads of a cargo, in short it is a polarized diode valve inversely, is had that when the inverse tension increases, the current that slides in the initially constant diode valve to the value_{the 0} it begins to increase to tension V almostconstant _Z abruptly, the mechanisms that are to the base are:

Effect avalanche

He is based on the fact that in regimen of inverse polarization, a minority bearer who comes down from the barrier of upgrades remarkablly is accelerated them, for which hitting against a ione of the reticulum is in a position to fornirgli sufficient energy in order to break off a covalent bond and to create a brace electron-gap that in its turn will come accelerated and hitting with other Ionian ones of the reticulum creates other braces gap-electron and therefore via.

Zener Effect

In regimen of inverse polarization we have that the applied tension can be such to break off of the covalenti ties and to create of the braces electron-gap which go to increase the inverse current.

It is had that under the 6V the Zener effect prevails in as far as growing of the applied inverse tension increases the dimensions of the emptying region and therefore diminishes the responsible electric field of the Zener effect moreover for inferior values of tension to 6V is had that to growing of the temperature the tension of Zener diminishes in how much increases the energies of valence electrons and therefore they can be extracted more easily.

Above the 6V the effect prevails avalanche in how much the minority bearers acquires greater energy from the barrier of upgrades them however to growing of the temperature the tension of Zener increases in how much the Ionian ones oscillates mainly around to the equilibrium positions and hitting with the minority bearer sufficient speed embezzles it speed impedendogli to catch up one to break off for collision a covalent bond.

 

17) Diode valve Tunnel:

It is a fast diode valve much that is based on the realization of a splice much drug addict and therefore of thickness much small, so small one that the quantistica mechanics says to us that the electron can pass equally through it.

The characteristic is that typical one of a device to negative resistance of N type and therefore it is a lot used in the realization of oscillating.

 

18) Fotodiodo to semiconductor:

The part of the characteristic of the diode valve that interests is 3° the quadrant that is inverse polarization, has that the cancellation incident creates of the braces electron-gap, if they do not recombine themselves before crossing the splice, gives to place to one current_{the s} that sum to the current of inverse saturation_{the 0} therefore =_{s the 0} .

The intensity of the current is greater if it is succeeded to concentrate the spot in correspondence of the splice in how much in such a way reduces the probability that the bearers it generates to you are recombined before crossing the splice.

 

19) photovoltaic Cells:

The part of the characteristic of the diode valve that interests is 4° the quadrant that is inverse polarization but with an inferior positive tension to the threshold tension, the cancellation that affects the splice creates of the braces electron-gap that they increase the minority current, of the rest if the splice pn is to empty, the current total must be 0 therefore us must be an equal increment of the current of majority bearers, but if this happens it wants to say that the barrier has been reduced of upgrades them and therefore to the heads of the diode valve it is had just upgrades them photovoltaic par to the intensity of which the barrier has been reduced of upgrades them, such value is 0,1V for GE and 0,5V for therefore in order obtaining a usable tension it is necessary to put more elements in series, but every cell has one its inner resistance therefore obtains that great part of the generated electric power is dispersed in thermal energy, in order to resolve the problem stà being tried to come true dispositive you that they work to low tensions. It is of the rest important to succeed to extract from the cell the maximum power that it is come true trying between the hyperbolas to constant power the that tangent with the characteristic of the cell, combining point of ceiling with the origin desume the optimal cargo resistance.