Electronic Devices: Steady state injection - Diffusion length

[@TheBrucekee]

Thanks for the videos! this one and the generation and recombination are a huge help. you rock

[@HeyZeus096]

Duuuude thank you so much! I was stumped on how to get Lp for a homework problem!

[@ioannaathineos5269]

You are a savior !

[@xvels01vutbr44]

What happened with the factor which involves dp/dx? at 3:14

[@crediblehuman9753]

Can someone tell me what he says at 1:16 . Del n and Dep p are equal for ....... reasons.

[@arpitgupta843]

in your video number 23 at time @5:08 you have written that the net recombination rate is "R-G(thermal generation)" and you have taken condition of dp/dt=0. IN this video at @4:05 you have written net recombination rate to be " R-G(but there G is not thermal generation)" and here the condition taken is also dp/dt=0. You have also mentioned that the generation and combination are equal at the quillibrium.

[@techgurukula]

Hi Arpit, in steady state/equilibrium (loosely used) generation and recombination should be equal, if not the carrier concentration should keep on increasing or decreasing - not possible (charge cannot disappear or appear from no where. Hence dp/dt = 0 and dn/dt = 0. when carrier are injected (carrier concentration increased beyond equilibrium concentration), imbalance is created between generation and recombination, but as time progresses over steady state/equilibrium (loosely used) generation and recombination should be equal dp/dt=0 and dn/dt=0. It's only during that transition the imbalance is present. Thanks, Techgurukula.

[@arpitgupta843]

@@techgurukula Thank you for replying me. Also what happened to the dp/dx factor. @3:21

[@buvansrinivasan8711]

anybody has an idea whats software he used to derive it.

[@abhishekbose825]

What happened to the dp/dx term from continuity equation? Why is it not considered here?

[@devbratsrivastava9987]

dp/dx equation comes from drift current. At steady state, since there is no new carrier injection, both electron and hole drift current will be zero.

[@abhishekbose825]

@@devbratsrivastava9987 Thanx for the reply 😀. I forgot about this question. Let me tell you what I understood. Firstly, dp/dx is concentration gradient which results into diffusion current. You can see diffusion current equation. It is not due to drift current. Now, since the light intensity is kept constant, the excess holes which were generated due to low level injection and are moving from high concentration region to low concentration region(i.e. from x=0 to x=infinity), will recombine with majority carriers(electrons) such that the hole concentration will become constant throughout the semiconductor at steady state. Therefore dp/dx is neglected at steady state.

[@devbratsrivastava9987]

​@@abhishekbose825 So, d2p/dx2 should also be 0, right?

[@abhishekbose825]

@@devbratsrivastava9987 thanx for rectifying me brother. I checked the derivation again. Yes that term is indeed a part of drift equation. We are not considering dp/dx=0 rather that whole term is neglected because the device is electrically neutral at steady state(E=0). Is that what you were trying to say?

[@devbratsrivastava9987]

@@abhishekbose825 Yes exactly! :)

[@زينبناظم-ر1و]

Thanks alot

[@AS-nx9fu]

Lmaoo the fake accent here😭😭😂😂

[@omarelmekawy6044]

its called steady state because the light injection is constant ?

[@techgurukula]

steady state because the carrier concentration is not dependent on time (dp/dt = 0). Yes, in a way the input light is assumed to be constant hence the generation, recombination constant - as a result the carrier concentration changes w.r.t to space but not time.

[@sunilyadav-im9of]

why u dnt consider del(p/x) expression from continuity equation..??????

[@chenyuhwu]

'Cause there is no electric field applied.

[@vineethreddy9708]

what is Tp or Tn

[@cschandu123]

Vineeth Reddy its minority carrier life time, watch his previous video on recombination and generation

[@jiahooilow7842]

what is Dp

[@techgurukula]

+jiahooi low Dp is Diffusion Coefficient of Holes.

[@nikolafc2491]

jiahooi low It's the diffusion coefficient of holes which can be derived from Einstein relation.

[@himanchalpatel788]

You skiped steps. Why

[@amarendrathumati4943]

Thanks bro