Hi, I'm learning about diodes and the formation of the PN junction, but there are a few things i'm unclear on.
It is my understanding that the PN junction forms when electrons in the conduction band of the N region move across and combine with the holes in the valence band of the P region. This leaves positive ions on the N side and negative ions on the P side near to the junction, and this creates an electric field which is eventually strong enough to prevent any more electrons from moving across from N to P. The energy required (per unit charge) to move additional electrons is called the barrier potential. So we have the before and after energy diagrams as follows:
According to the book i'm reading, the barrier potential is usually something like 0.7V, and they take this as the minimum forward bias required to establish a current. This will allow electrons in the conduction band of the N region to get over the barrier potential. Am I correct in thinking they then flow into the conduction band of the P region, and immediately combine with the holes in the valence band? This is where I start to get a bit confused.
Firstly, this sounds a bit stupid, but why can't the electrons just go from conduction band in the N type to valence band in the P type? Why do they have to go from conduction band to conduction band? The lazy ones wouldn't have to bother getting over the barrier potential then
Secondly, in the diagram above, where is the barrier potential? Is it the energy difference between the conduction bands in the two regions? That is what I was thinking it was for a few weeks, but then I thought about it some more and became convinced that this is incorrect. For example, if I forward bias the diode with a battery equal to the barrier potential I will give the electrons just enough energy to get up over this barrier and into the conduction band of the P region. They then immediately combine with holes in the valence band and lose a load of energy (does this energy go to heat or something?) and travel out through the wire. But with this view of the barrier potential, the battery will not give them enough energy to get back up into the conduction band of the N type, then back up into the conduction band of the P type to start over again. As far as I can see, the only way you can get a continuous current is if the battery gives the electrons an amount of energy equal to the energy difference between the conduction band and valence band in the P region. So is this the barrier potential
Those are my two main questions for now. Sorry for being a bit long-winded, but hopefully I explained my confusion clearly.
Thanks for any help!
Jon.
Oh and Merry Christmas!!!!
It is my understanding that the PN junction forms when electrons in the conduction band of the N region move across and combine with the holes in the valence band of the P region. This leaves positive ions on the N side and negative ions on the P side near to the junction, and this creates an electric field which is eventually strong enough to prevent any more electrons from moving across from N to P. The energy required (per unit charge) to move additional electrons is called the barrier potential. So we have the before and after energy diagrams as follows:
According to the book i'm reading, the barrier potential is usually something like 0.7V, and they take this as the minimum forward bias required to establish a current. This will allow electrons in the conduction band of the N region to get over the barrier potential. Am I correct in thinking they then flow into the conduction band of the P region, and immediately combine with the holes in the valence band? This is where I start to get a bit confused.
Firstly, this sounds a bit stupid, but why can't the electrons just go from conduction band in the N type to valence band in the P type? Why do they have to go from conduction band to conduction band? The lazy ones wouldn't have to bother getting over the barrier potential then
Secondly, in the diagram above, where is the barrier potential? Is it the energy difference between the conduction bands in the two regions? That is what I was thinking it was for a few weeks, but then I thought about it some more and became convinced that this is incorrect. For example, if I forward bias the diode with a battery equal to the barrier potential I will give the electrons just enough energy to get up over this barrier and into the conduction band of the P region. They then immediately combine with holes in the valence band and lose a load of energy (does this energy go to heat or something?) and travel out through the wire. But with this view of the barrier potential, the battery will not give them enough energy to get back up into the conduction band of the N type, then back up into the conduction band of the P type to start over again. As far as I can see, the only way you can get a continuous current is if the battery gives the electrons an amount of energy equal to the energy difference between the conduction band and valence band in the P region. So is this the barrier potential
Those are my two main questions for now. Sorry for being a bit long-winded, but hopefully I explained my confusion clearly.
Thanks for any help!
Jon.
Oh and Merry Christmas!!!!
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