Lab 4 and 5: PN junctions and Solar Cells

Summary

This video lecture provides a concise overview of PN junction diodes and their operation. It explains the basic concepts of diodes as electronic components that allow current to flow in one direction, akin to a plumbing valve. The lecture revisits the principles of p-type and n-type semiconductors, the formation of depletion regions, and the role of built-in electric fields. It also touches on forward and reverse biasing of diodes, leading to their rectification properties, which are crucial for various semiconductor devices. The lecture concludes with a brief mention of upcoming topics on solar cells.

Takeaways

• 📘 The lab focuses on experiments with PN junction diodes and solar cells, with a brief theory recap.
• 🧠 A diode is compared to a one-way valve in plumbing, allowing current to flow in one direction while blocking it in the opposite direction.
• ⚙️ A diode is made from p-type and n-type semiconductor materials, typically silicon, which are joined together to form a junction.
• 🔋 In intrinsic silicon, there are no free electrons, making it an insulator; doping silicon with trivalent or pentavalent atoms turns it into p-type or n-type silicon, respectively.
• ⚡ P-type silicon has an excess of holes (positive charge carriers), while n-type silicon has an excess of electrons (negative charge carriers).
• 🔄 When p-type and n-type silicon are joined, electrons and holes diffuse across the junction, creating a space charge region or depletion region where no free carriers exist.
• ⚖️ The built-in electric field created by the separation of charges in the depletion region prevents further diffusion, maintaining equilibrium.
• ➡️ Applying a forward bias (positive on p-side, negative on n-side) reduces the built-in electric field, allowing current to flow.
• ⬅️ Applying a reverse bias (negative on p-side, positive on n-side) strengthens the built-in electric field, blocking current flow.
• 📈 In the forward bias, the current increases exponentially with voltage, while in reverse bias, the current remains negligible and constant.

Q & A

What is the primary function of a diode?

A diode acts as an electronic switch, allowing current to flow in one direction (forward bias) and blocking current flow in the opposite direction (reverse bias).

What happens when a P-type and an N-type semiconductor material are brought into close contact?

When a P-type and an N-type semiconductor material are brought into close contact, a PN junction is formed. This junction creates a depletion region where the majority of free charge carriers (electrons and holes) are depleted due to diffusion of electrons from the N-side to the P-side and holes from the P-side to the N-side.

Why is silicon commonly used as a semiconductor material?

Silicon is commonly used as a semiconductor material because it is a group 4 element with four valence electrons, which allows for the formation of a perfect lattice structure. It can be easily doped to create P-type or N-type semiconductors by adding impurities like boron (trivalent) or phosphorus (pentavalent).

How does doping with a trivalent atom like boron create a P-type semiconductor?

Doping with a trivalent atom like boron creates a P-type semiconductor because boron has three valence electrons, which leaves an unpaired 'hole' when it bonds with neighboring silicon atoms. This hole can move through the lattice and act like a positively charged entity, thus creating P-type material.

What is the role of the built-in electric field in a PN junction?

The built-in electric field in a PN junction acts as a barrier to prevent further diffusion of charge carriers (electrons and holes). It is generated due to the separation of charges in the depletion region and helps maintain equilibrium in the system.

What is the effect of applying a forward bias to a PN junction diode?

Applying a forward bias to a PN junction diode reduces the barrier created by the built-in electric field, allowing current to flow more easily from the P-side to the N-side. This results in an exponential increase in current with increasing voltage.

How does reverse bias affect the current flow in a PN junction diode?

Applying a reverse bias to a PN junction diode strengthens the built-in electric field, which further prevents the flow of charge carriers. This results in a very small, almost negligible, and constant current flow that does not significantly change with voltage.

What is the significance of the depletion region in a PN junction?

The depletion region in a PN junction is significant because it is devoid of free charge carriers (electrons and holes). This region is crucial for the diode's rectification property, allowing current to flow in one direction and blocking it in the other.

What will be observed during the lab experiment with PN junction diodes?

During the lab experiment with PN junction diodes, students will observe the IV characteristics of the diode. In forward bias, they will see an exponential increase in current with voltage, while in reverse bias, the current will remain negligible and almost constant.

What is the difference between equilibrium and non-equilibrium conditions in a PN junction?

In equilibrium conditions, no external bias is applied, and the system is in a balanced state with a built-in electric field preventing further diffusion of charge carriers. In non-equilibrium conditions, an external bias is applied, which can either counteract (forward bias) or strengthen (reverse bias) the built-in electric field, affecting the flow of current.

Outlines

00:00

🔬 Introduction to PN Junction Diodes and Solar Cells

This paragraph serves as an introduction to the lab session, focusing on experiments with PN junction diodes and solar cells. The speaker briefly revisits the basic theory of these topics, highlighting their importance and explaining that while detailed theory will be covered in a later course, the provided information is sufficient for conducting the experiments.

05:02

🛠️ Basics of Diodes: Electronic Valves

The speaker introduces the concept of a diode, comparing it to a valve in plumbing that controls the direction of flow. In electronics, diodes allow current to flow in one direction (forward bias) while blocking it in the reverse direction. The paragraph emphasizes the importance of diodes in creating controlled circuits and discusses their ideal versus real characteristics, which will be explored in the lab through IV measurements.

10:03

🧪 Understanding P-Type and N-Type Semiconductors

This paragraph explains how doping silicon with trivalent or pentavalent atoms creates P-type and N-type semiconductors, respectively. It describes how replacing a silicon atom with boron introduces holes (P-type), and replacing it with phosphorus introduces free electrons (N-type). The paragraph underscores the maintenance of overall charge neutrality in both types of semiconductors despite the presence of these charge carriers.

15:04

🔄 Diffusion and Space Charge Region in PN Junctions

The focus here is on the diffusion process when P-type and N-type silicon are joined, leading to the formation of a space charge region or depletion region. The speaker explains how holes and electrons diffuse across the junction, resulting in a separation of charges and the creation of an internal electric field. This field opposes further diffusion, stabilizing the junction in equilibrium.

20:07

⚡ Built-In Electric Field and PN Junction Equilibrium

This paragraph discusses the role of the built-in electric field in a PN junction at equilibrium, where no external bias is applied. The electric field, generated by the separation of charges, prevents further diffusion of charge carriers. The speaker sets the stage for discussing non-equilibrium conditions by explaining how the internal electric field maintains the junction's stability.

25:07

🔌 Forward and Reverse Bias in PN Junctions

The speaker explains how applying an external bias affects the PN junction. In forward bias, the external field opposes the built-in field, reducing its effect and allowing current to flow easily. In reverse bias, the external field strengthens the built-in field, further inhibiting the flow of charge carriers. The paragraph outlines how these behaviors lead to the rectifying properties of diodes, with forward bias allowing exponential current increase and reverse bias resulting in minimal current flow.

📝 Summary and Conclusion on PN Junction Diodes

This final paragraph recaps the main points about PN junction diodes, focusing on how the space charge region and built-in electric field create the diode's rectifying behavior. The speaker concludes with a preview of the next lab session, which will cover solar cells, and encourages the audience to understand these foundational concepts before moving forward.

Keywords

💡PN Junction

A PN junction is the boundary between p-type and n-type semiconductor materials. It is a fundamental component in devices like diodes and solar cells. In the video, the PN junction is described as a key structure that enables rectification by allowing current to flow in one direction while blocking it in the opposite direction.

💡Diode

A diode is an electronic component made from a PN junction that allows current to flow in one direction but not in the reverse. In the video, the diode is compared to a one-way valve in plumbing, controlling the direction of current flow based on biasing conditions.

💡Forward Bias

Forward bias refers to the condition where a positive voltage is applied to the p-side of the diode and a negative voltage to the n-side, reducing the barrier and allowing current to flow. The video explains that under forward bias, the internal electric field of the diode is counteracted, leading to increased current flow.

💡Reverse Bias

Reverse bias is the condition where a negative voltage is applied to the p-side and a positive voltage to the n-side of the diode, enhancing the built-in electric field and preventing current flow. The video mentions that in reverse bias, only a very small leakage current flows, demonstrating the diode's rectifying property.

💡Depletion Region

The depletion region is the area around the PN junction that is depleted of free charge carriers (electrons and holes). It forms due to the diffusion of carriers across the junction, creating a region with immobile charged ions. In the video, this region is crucial for the diode's rectifying behavior, as it determines how easily current can flow through the device.

💡Built-in Electric Field

The built-in electric field is an internal field created by the separation of charges in the depletion region of a PN junction. It prevents further diffusion of charge carriers across the junction. In the video, this electric field is fundamental to the functioning of the diode, controlling the flow of current under different biasing conditions.

💡Doping

Doping is the process of intentionally adding impurities to a semiconductor to modify its electrical properties. P-type doping adds elements with fewer valence electrons, creating 'holes,' while n-type doping adds elements with more valence electrons, providing extra electrons. The video describes how doping creates p-type and n-type materials, which form the PN junction.

💡Rectification

Rectification is the process of converting alternating current (AC) to direct current (DC). In the video, the diode's ability to allow current to flow in only one direction under forward bias and block it under reverse bias is highlighted as the basis for rectification in electronic circuits.

💡Semiconductor

A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. The video uses silicon as an example, explaining that its electrical properties can be altered through doping, making it suitable for creating electronic components like diodes and solar cells.

💡Diffusion

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. In the context of the video, diffusion describes the movement of electrons and holes across the PN junction, leading to the formation of the depletion region and the built-in electric field.

Highlights

Introduction to lab experiments on PN Junction diodes and solar cells.

Recap of PN Junctions and solar cells theory from 11th and 12th grade studies.

Explanation of a diode as an electronic switch, allowing current flow in one direction.

Description of forward bias and reverse bias in diodes.

Composition of a diode from P-type and N-type semiconductor materials.

The role of doping in creating P-type and N-type semiconductors.

Mechanism of hole and electron movement in PN Junctions.

Formation of the depletion region and its effect on charge carrier movement.

The concept of charge neutrality in PN Junctions despite local charges.

Diffusion of charge carriers and the creation of the space charge region.

The built-in electric field's role in preventing further diffusion of charge carriers.

Equilibrium condition in PN Junctions without external bias.

Impact of forward bias on reducing the built-in electric field and increasing current flow.

Exponential increase in current under forward bias due to reduced internal electric field.

Application of reverse bias and its effect on strengthening the internal electric field.

Negligible current flow in reverse bias due to strengthened internal electric field.

Practical lab measurements of IV characteristics of PN Junction diodes.

Overview of the rectification process in PN Junction diodes.

预告下一周将讲解太阳能电池的更多细节。

Transcripts

so hello and welcome to the lab four and

five

uh in ae2301e2501

uh in this particular lab we will be

doing a few experiments

on PN Junction diodes and solar cells so

before we do the experiments it might be

worthwhile to

recall or revise a little bit of theory

and that is what the objective of this

short video lecture will be

so you might have already studied about

PN Junctions and solar cells in your

11th and 12th I'll just recap

uh the key Concepts whereas you have but

please note that your

detailed Theory would be covered in your

semiconductor device fundamentals course

but the stuff that I'm going to discuss

today will suffice in helping you do the

experiment so let us begin

so

so we begin with PN Junctions to create

these device called diodes

so this is the base very basic and most

fundamental semiconductor device that

you can build in the lab so what is a

diode a diode is nothing what I would

call is nothing but an electronic wolf

right so as you know in your water

Plumbing Systems you suppose you have a

pipe in most cases you need to build

these so-called walls

and these walls what their primary

functionality is to

uh they are built something like this so

as you can see the primary functionality

of the wall is to allow the flow of

water in this direction but to disallow

the flow of water in this particular

direction right

so similarly it is also very important

to have diodes which act as electronic

words so what what does what the diode

essentially does is allows the flow of

current so if I draw a corresponding

electronic

counterpart for a plumbing wall what I

would do is I have voltage and I have

current so the job of a diode in the

forward

quadrant or in the first quadrant is to

allow the flow of current as you know

and in the reverse quadrant is to block

the flow of current so this is

therefore called forward bias

and this is called reverse price right

so what we are going to do is try to see

that this is your ideal characteristics

that you want from a dial

but as you know when you start making

semiconductor devices hardly anything is

ideal so the question that we will try

to ask is uh what does an actual

semiconductor diode look like

so before we ask that question what we

will do is and not just ask the question

we will also make measurements on a

common diode uh which will be given to

you in the lab we will make certain IV

measurements and see how diodes

characteristics looks like

but what is a diode made up of so a

diode as you know might be as you might

know is made up of a b type

semiconductor material and an type

semiconductor material brought in close

content so when a junction is formed

between

a p-type semitone P type semiconductor

let's assume that the semiconductor is

is the commonly known silicon and an

n-type semiconductor

and type silicon when you bring the n t

type and N type Semiconductor in this

case happens to be silicon the most

common semiconductor together

you are able to construct or you are

able to make a diode okay so how does

this work is what we will try to explore

right now

so let's try to recall what we know or

what we understand by P and N type

doping uh so as you know silicon

is a group 4 element

so it has

four valence electrons which is bonded

to other silicon atoms as well

and in its intrinsic Case by intrinsic

case I mean that you have a perfect

silicon lattice

with no impurities this B has more or

less like a

insulator why because all the electrons

are bound to each other and there is no

movement of electrons for it to become a

conductor as you know how conductors and

insulators are distinguished is from the

fact that in conductors you have very

high conductivity because of presence of

free electrons as you can see if you

have a

perfect lattice of silicon all silicon

atoms are bonded uh to neighboring four

silicon atoms and therefore there is no

presence of any free electrons therefore

we can assume that a silicon's perfect

lattice will behave more like an

insulator and that is what we generally

see it's insulin it has very uh High

Resistance or very low conductivity so

but however we want current to flow

through certain system through this

particular material and that is what

makes semiconductor so special that you

can alter or you can dope the material

or dope the semiconductor such that it

can either conduct electrons or holes

right this is what we have been studying

in our 11th and 12th standard also so

how does that happen what you

essentially do is you replace one of the

Silicon atoms with a pentavalent atom or

a trivalent atom so let's try to do that

so if we replace this particular silicon

if we delete off this particular silicon

and you replace it with a

if you replace this with a

atom which is you substitution you

substitute the silicon atom which was on

the right hand side with a trivalent

atom such as Boron you will see boron

will have three

valence electrons only and because boron

has three valence electrons it will bond

to only three neighboring atoms of

silicon right so suppose it goes and

bonds with three neighboring atoms of

silicon and what you have remaining if

you look carefully is this

extra electron which is unpaired

right and as we were discussing that

there is no

atom there is no electron from Boron to

compensate for this missing

one extra electron in the Silicon so

what we have in

this place is an absence of an electron

which is also called a hole

and as we know this particular hole can

Traverse through the lattice

on application of an electric field and

act like a like a positively charged

entity and therefore we call that this

has become a

p-type silicon

on the other hand if I have the same

silicon lattice

and I replace one of the silicons

with a pentavalent atom

pentavalent

let's say phosphorus

what will happen the phosphorus has five

the phosphorus atom has five

electrons which will bond to its

neighboring silicon atoms

and what remains is this extra electron

and this extra electron

which I will Mark with

red

can Traverse through the lattice

and this extra electron is what gives

this silicon

just an n-type silicon characteristics

so as we just discussed p-type silicon

has an excess of holes

and the n-type Silicon has an excess of

electrons please remember that although

you have electrons and holes which are

positively uh and negative uh positive

negatively and positively charged

respectively overall the charge

neutrality of the system remains why is

that the case because of an electron

leaves this particular side and moves

around in the lattice and equivalent

positive charge is created on the

phosphorus atom

so please never get confused that n type

and p-type silicon atoms are negatively

and positively charged yes locally they

might have some charge but overall

charge neutrality is maintained okay so

now that we understand what P type and

n-type silicon is or an n-type and

p-type semiconductor is let's see what

happens when you join both PN and type

silicon together

so what happens when you join p and N

type silicon together is the following

so I'm sure you might have studied about

this law called the law of diffusion or

the fixed law

remember what the fixed law used to tell

you which was nothing but the law of

diffusion

it just says that

if there is some

quantity which can move around in space

a best example to give is probably a gas

molecule if a gas molecule can move

around its space and you have a high you

open a bottle which has a high

concentration of this particular gas

molecule it could be a perfume it will

diffuse into space what does that mean

that it will move from region of

higher concentration to a area of lower

concentration and this is what exactly

happens when you join an p and n-type

silica material together so please

recall you had P silicon and N silicon

and when you the P silicon had an excess

of holes

which I'm marking with red and the N

silicon had an excess of electrons

which I am marking with green

so if there are excess of electrons and

holes what essentially will happen if

electrons will move or diffuse from the

n-type Silicon to the p-type Silicon

and

holes will move from p-type Silicon to

n-type Silicon right

so this diffusion will happen because

holes are higher in concentration and B

side compared to enzyme and electrons

are in higher concentration in inside

compared to the P side this is very

simple but the question we ask is will

this diffusion

happen continuously or there will be an

opposite Force to prevent this

particular diffusion so the answer is

that please remember that earlier n-type

silicon and p-type silicon where overall

charge neutral however if electrons

start flooding out from the inside what

will they leave behind as we discuss it

will leave behind these

positively charged donor atoms which is

phosphorus in this case so what will

happen is as

diffusion progresses in this particular

system

what you will notice is the near the

junction near the metrological junction

or the physical Junction where you have

made the p and ends silicon you have

made an intimate contact between p and N

silicon what essentially happens is

there is a positive charge which starts

forming on the inside

and the negative charge

with forms on the P side please recall

where what is the source of this

positive and negative charge as we

discussed previously

this electron if it

if phosphorus

overall it looks neutral right however

however if the electron starts moving

very far away from the

phosphorus atom there will be the

uncovering of phosph the phosphorus

which was neutral with five electrons

now it has lost an electron the electron

has moved away so a local positive

charge will develop over this phosphorus

and that is why as we discussed a

positive charge develops over because of

the uncovering of donor atoms at the

inside and uncovering of acceptor atoms

at the P side there is a resultant

negative charge so now let's see what

happens because of this uh specific

distribution of chart so earlier you had

the material was which was completely

neutral but now you have regions where

there is a separation of charge and

therefore this area is called

chart separation area

also please note that this particular

region earlier had lot of electrons on

the right hand side and holes on the

left hand side but since they are devoid

of electrons and holes why the electrons

from the right hand side have moved to

the left hand side and holes have moved

from the right hand side to the left

hand side because of this there are

devoid of free charge carriers and

therefore this area is also called

depletion

region so these are the two regions

there these are the two kind of names by

which we denote this particular region

which I have shaded out

so this area is also called the

depletion region because it is depleted

of mobile or free carriers which is

electrons and holes and because they

have moved away and diffused into the

other side what essentially has happened

is they have uncovered the donor atoms

and therefore this is called the chart

separation area or the space charge

region and this as you will see is the

main functional reason why the diode is

able to give you a rectification

property or it allows current to flow in

One Direction and not in the other

direction so how does that happen let's

have a closer look

why did we start this discussion we were

trying to understand what happens when

there is a space charge region so what

happens essentially when there is a

space charge region because you as you

know from gauss's law Whenever there is

a separation in charge it will give a

equivalent electric field as you know

electric field is always from the

positive side to the negative side so in

this in this particular example there

will be an equivalent equal electric

field which will get generated in this

direction

so you will have an electric field let

me Mark it with

a different color

so there will be an electric field in

this particular direction right so if

you want to draw on top of this electric

field will be from

positive charge to the negative charge

now what does this electric field do

please remember why the space charge

region was created the space charge

region was created because of diffusion

of holes from P side to inside and

diffusion of electrons from the inside

to the P side this created the space

chart region which in turn created this

electric field this electric field is

called the built-in electric field

the electric field built-in electric

field is created because of the

separation of charges and what does

these built-in electric Fields do please

remember

it will prevent electrons from flowing

from n-type to P type why because

electric field electrons in general move

opposite to the direction of electric

field so if there is an electric field

in this direction it will prevent the

movement of electrons from right hand

side to left hand side and it will

prevent the movement of holes from the

left hand side to the right hand side or

from the P side to the inside

and this built-in electric field is what

finally brings equilibrium to the system

the 10th in in short what I mean to say

is that the built-in electric field is

created

to prevent the further diffusion of

holes from the inside to the P side and

therefore there is a limited space

charge region so this is what a PN

Junction looks in equilibrium what does

equilibrium mean that you have not

applied any external bias to the P side

or the inside so the equilibrium if we

Define clearly is nothing but

the external bias

we bias is equal to 0 is nothing but

the

that the system is in equilibrium okay

so in equilibrium what we understood is

there will be a built-in electric field

and this built-in electric field will

prevent the further uh diffusion of

electrons from inside and holes from the

P side okay so in this equilibrium

condition what we will understand we

will understand how the rectification

happens so let me just draw the two

cases

what happens when we move away from

equilibrium or we move to so called

non-equilibrium condition

so in non-equilibrium condition what

essentially happens is either you can

apply a positive bias

or you can apply a negative bias

and what we will do is does the applied

bias strengthen the built-in electric

field which is there even at zero bias

which is at equilibrium condition or

does it oppose the electric field right

so that is what we will try to uh check

so please remember what we studied till

now we had the p-type material

and we had the n-type material

in both the cases

and because of the separation of charges

there was a built-in electric field

and this built-in electric field created

due to the separation of charges was

preventing further diffusion of

electrons and holes now what we say is

this is the story in or this is a

picture in the equilibrium condition

what happens in the non-equilibrium

condition in the non-equilibrium

condition we apply a positive bias

especially in the forward case in the

forward equilibrium condition what we do

is we apply a positive bias

to the B side and the negative bias

to the N side right so in forward bias

we apply a positive to the B side and a

negative to the N sign so what happens

so this was your e internal electric

field

and what you are essentially with what

was the internal electric field doing it

was preventing the flow of carriers

right mobile carriers and if we apply a

external electric field in this case

which

is in the opposite direction so this is

e external so the EA internal was the

internal electric field the built-in

electric field of the diode this by

applying a positive bias we are

counteracting or we are suppressing the

internal electric field so if we add

both of them you will see that

you the extent of the electric field

internal electric field the E net

goes down substantially

because the e-net goes down

substantially what happens is now

current concussion why can current

gushing in this direction from the P

side to the inside because the effective

internal electric field or the built-in

field is counteracted by the external

electric field and therefore and

therefore in the positive half or in

forward bias

you see an increase in current

of course this increasing current is not

ah

linear in nature but it is exponential

in nature so if I need to draw it well

it will look like this Y is is

exponential in nature we will study in

detail in some other course like

semiconductor device fundamentals it

requires understanding of the band

diagrams and type picture but we will

not get into that at the moment we will

just very roughly try to understand why

applying an external electric field

in the forward bias reduces the net

internal electric field allowing

carriers to flow through so now it might

have been also very apparent to you by

applying

reverse bias or a negative on the P side

and a positive

on the inside

strengthens this internal electric field

and the net electric field becomes

really big and prevents further movement

of carriers right and therefore what you

see is that in the reverse bias when you

apply a negative bias to the P side and

a positive bias to the N side you see

because of the further strengthening of

the external internal electric field

from the external source

there is a very slow amount of current

which flows through right so this is in

summary

what we were the basics of why uh PN

Junctions work atom in a nutshell so in

the lab what we will try to do is in

essence measure the ID characteristics

of this PN Junction diode and we will

see that the IB characteristics of a PN

Junction diode in forward bios looks

like an exponential whereas in Reverse

bias we will not go to very high reverse

biases or as you know there can be some

kind of a breakdown also we will not go

into that region for a small range of

reverse bias around 10 volts whichever

diode which will be supplied you can

handle you see that the amount of

current that flows through uh the uh

through the terminal in the reverse

biases not just very negligible but also

you will see that it can in essence it

it does not change with voltage it is

more or less flat width voltage it

doesn't change with voltage

and this property we will be using in

detail to explain how transistors work

so please note that in forward bias you

see an exponential change in current as

you apply the bias so let me just apply

V and I just Mark V and I but in the

reverse bias irrespective of how much V

you apply the current remains quite

negligible and also it remains constant

so this is a brief introduction about a

PN Junction diodes why do they work in a

nutshell

they work because

the movement of free electrons from the

inside to the P side

the electrons from the diffusion of

electrons from n side to psi and vice

versa of holes from PSI to n side create

this particular depletion charge region

or chart separation region which has an

which induces an internal electric field

or a built-in electric field

how do you make the diode conduct in One

Direction You counteract this built-in

electric field and therefore which was

preventing the flow of free carriers you

reduce that barrier of flow of free

carriers and therefore there is a smooth

oh smooth current carrying capability in

the forward bias whereas in the reverse

bias you strengthen this built-in

electric field which prevents the flow

of carriers and therefore uh you have a

condition where current does not flow so

this is the basics of rectification in

the PN in Junction uh diode in the next

week I will explain a few more details

of solar sets which you will also be

working on thank you