HW-QA-2020 issues https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues 2020-07-30T10:18:19Z https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/51 L20 Clarification 2020-07-30T10:18:19Z atapia L20 Clarification ![Screenshot_2020-07-29_at_17.12.30](/uploads/5375c516200f630388d0bb868c70a87f/Screenshot_2020-07-29_at_17.12.30.png) Hi again, So in the highlighted section. I feel this sentence is slightly redundant. What continuity conditions are we talking about here? Are these simply, $(\bold{D}_N(x=0) - \bold{D}_P(x=0)) \bullet \bold{n} = \sigma = 0$ $\psi_N(x=0) - \psi_P(x=0) = 0 $ Also, what is the significance of having the same dielectric constant in both sides? What effect does this have on the continuity conditions? Thanks again, Andres ![Screenshot_2020-07-29_at_17.12.30](/uploads/5375c516200f630388d0bb868c70a87f/Screenshot_2020-07-29_at_17.12.30.png) Hi again, So in the highlighted section. I feel this sentence is slightly redundant. What continuity conditions are we talking about here? Are these simply, $(\bold{D}_N(x=0) - \bold{D}_P(x=0)) \bullet \bold{n} = \sigma = 0$ $\psi_N(x=0) - \psi_P(x=0) = 0 $ Also, what is the significance of having the same dielectric constant in both sides? What effect does this have on the continuity conditions? Thanks again, Andres https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/50 L19 Clarification 2020-07-29T15:13:16Z atapia L19 Clarification ![Screenshot_2020-07-27_at_19.22.43](/uploads/22ca82893c93d45b9b5e5a3a91e73f05/Screenshot_2020-07-27_at_19.22.43.png) ![Screenshot_2020-07-27_at_19.23.25](/uploads/64b3103f2d5829576a608ef1eb218daa/Screenshot_2020-07-27_at_19.23.25.png) Sorry but I am having troubling interpreting this diagram here and correlating it to the expression of the built-in potential. There are a few things that remain undefined when you introduced this diagram. What is $\phi_n$? Is there a direct relation between $\phi_{bi}$ and $\phi_{SB}$? if so what is it? Thanks again for your help. ![Screenshot_2020-07-27_at_19.22.43](/uploads/22ca82893c93d45b9b5e5a3a91e73f05/Screenshot_2020-07-27_at_19.22.43.png) ![Screenshot_2020-07-27_at_19.23.25](/uploads/64b3103f2d5829576a608ef1eb218daa/Screenshot_2020-07-27_at_19.23.25.png) Sorry but I am having troubling interpreting this diagram here and correlating it to the expression of the built-in potential. There are a few things that remain undefined when you introduced this diagram. What is $\phi_n$? Is there a direct relation between $\phi_{bi}$ and $\phi_{SB}$? if so what is it? Thanks again for your help. https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/49 L15 Question: Huckel Limit 2020-07-27T17:20:11Z atapia L15 Question: Huckel Limit ![Screenshot_2020-07-23_at_19.45.04](/uploads/e66630846c351440c191a748ba64c126/Screenshot_2020-07-23_at_19.45.04.png) **My doubt is about the text highlighted in yellow.** What is the significance of treating the particles (hereafter solute) as point charges? Is this to simply say that each individual particle will have an uniform (spherical/radial) electric field generated. Also, since we are using the DH approximation. To respect what are we computing the Debye screening length $\lambda_{DH}$? Is this quantity dependent on the concentration of solute we have? Or the concentration of electrolyte the solute is solvated in? It is not too clear what exactly is generating this boundary layer of ions. I believe it is the solvent, but I am not too sure... **Finally, a typo highlighted in blue** I believe here it should be $R_s\kappa << 1$ ![Screenshot_2020-07-23_at_19.45.04](/uploads/e66630846c351440c191a748ba64c126/Screenshot_2020-07-23_at_19.45.04.png) **My doubt is about the text highlighted in yellow.** What is the significance of treating the particles (hereafter solute) as point charges? Is this to simply say that each individual particle will have an uniform (spherical/radial) electric field generated. Also, since we are using the DH approximation. To respect what are we computing the Debye screening length $\lambda_{DH}$? Is this quantity dependent on the concentration of solute we have? Or the concentration of electrolyte the solute is solvated in? It is not too clear what exactly is generating this boundary layer of ions. I believe it is the solvent, but I am not too sure... **Finally, a typo highlighted in blue** I believe here it should be $R_s\kappa << 1$ https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/48 L14 Clarification 2020-07-27T17:20:48Z atapia L14 Clarification ![Screenshot_2020-07-23_at_17.31.25](/uploads/dede7f79c04f1f3c0035a339a5f78d50/Screenshot_2020-07-23_at_17.31.25.png) Hi again, Going through the lecture scripts again, I noticed this sentence is not very clear. The sentence seems somehow incomplete. What do you mean by considering the osmotic pressure? What are we considering about it exactly? From what I gathered we simply took how the electric force was defined in Lecture 13, but there is nothing to relate this to the osmotic pressure. Am I missing a point here? What should I consider about the osmotic pressure in this situation. ![Screenshot_2020-07-23_at_17.31.25](/uploads/dede7f79c04f1f3c0035a339a5f78d50/Screenshot_2020-07-23_at_17.31.25.png) Hi again, Going through the lecture scripts again, I noticed this sentence is not very clear. The sentence seems somehow incomplete. What do you mean by considering the osmotic pressure? What are we considering about it exactly? From what I gathered we simply took how the electric force was defined in Lecture 13, but there is nothing to relate this to the osmotic pressure. Am I missing a point here? What should I consider about the osmotic pressure in this situation. https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/47 L11 Clarification 2020-07-27T17:22:09Z atapia L11 Clarification ![Screenshot_2020-07-22_at_20.31.39](/uploads/a97e539d1d3f9f0a167317494cfae291/Screenshot_2020-07-22_at_20.31.39.png) Hi, Sorry but it is not too clear on this script. What is $\gamma^2_0$ ? Is not mentioned anywhere else in the script and makes it confusing to follow. Thanks again for the help! ![Screenshot_2020-07-22_at_20.31.39](/uploads/a97e539d1d3f9f0a167317494cfae291/Screenshot_2020-07-22_at_20.31.39.png) Hi, Sorry but it is not too clear on this script. What is $\gamma^2_0$ ? Is not mentioned anywhere else in the script and makes it confusing to follow. Thanks again for the help! https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/46 L8 Clarification 2020-07-22T15:37:28Z atapia L8 Clarification Hi I noticed that the lecture script has a missing figure. Figure 8.4 is missing and the formatting around that section is unclear. Hi I noticed that the lecture script has a missing figure. Figure 8.4 is missing and the formatting around that section is unclear. https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/45 Derivation in Darcy&#39;s law 2020-07-16T14:08:44Z etzoldk Derivation in Darcy's law I hope it is okay, if I ask a question considering the lecture here. Please let me know, if I should ask Prof. Shih directly. In Lecture 16 we discussed Darcy's law. In the beginning we had the formula $<v> = \frac{\kappa}{\mu L} \cdot \Delta P_{eff} = \frac{\kappa}{\mu L} \cdot \left( \Delta P - \Delta \Pi_{eff} \right)$. The final formula is then $<v> = \frac{-\kappa}{\mu L} \cdot \left( \Delta P - \sigma k_B T \Delta c \right)$ as it is also written in Eq. (16.5) in the script. Now I am wondering where this minus sign in the final formula is coming from. I hope it is okay, if I ask a question considering the lecture here. Please let me know, if I should ask Prof. Shih directly. In Lecture 16 we discussed Darcy's law. In the beginning we had the formula $<v> = \frac{\kappa}{\mu L} \cdot \Delta P_{eff} = \frac{\kappa}{\mu L} \cdot \left( \Delta P - \Delta \Pi_{eff} \right)$. The final formula is then $<v> = \frac{-\kappa}{\mu L} \cdot \left( \Delta P - \sigma k_B T \Delta c \right)$ as it is also written in Eq. (16.5) in the script. Now I am wondering where this minus sign in the final formula is coming from. celebik celebik https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/42 [HW5 2.5] What happens to Evac and Others 2020-06-06T13:31:09Z atapia [HW5 2.5] What happens to Evac and Others ![Screenshot_2020-06-03_at_16.26.09](/uploads/99aed9b997feaff54c3c5191a708ea0e/Screenshot_2020-06-03_at_16.26.09.png) For Lecture 20, we see that E_vac is shot up by the band bending on the p-side, and shot down in the n-side. Does this mean that E_vac is no longer at zero reference for one of the sides? How can we compute the new fermi level if our reference are no the same. In https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/38 You say that, > $E_{FB} = E_{CB}(x = \infty) - e\phi_{B}$ but then this assumes that evac is still at zero right? ![Screenshot_2020-06-03_at_16.26.09](/uploads/99aed9b997feaff54c3c5191a708ea0e/Screenshot_2020-06-03_at_16.26.09.png) For Lecture 20, we see that E_vac is shot up by the band bending on the p-side, and shot down in the n-side. Does this mean that E_vac is no longer at zero reference for one of the sides? How can we compute the new fermi level if our reference are no the same. In https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/38 You say that, > $E_{FB} = E_{CB}(x = \infty) - e\phi_{B}$ but then this assumes that evac is still at zero right? https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/40 Q 2.7 2020-06-06T13:31:20Z bpatel Q 2.7 Hi! I had a question regarding 2.7. Getting the values of the potentials is fine, but I'm a bit stuck with how to obtain the final Fermi level after contact, which is required to find the delta E2D? I can't seem to find any formula in the script. Hi! I had a question regarding 2.7. Getting the values of the potentials is fine, but I'm a bit stuck with how to obtain the final Fermi level after contact, which is required to find the delta E2D? I can't seem to find any formula in the script. https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/38 [HW5 Q2.5] 2020-06-06T13:31:24Z lcartocci [HW5 Q2.5] Hi, I'm unsure how to go about question 2.5 (and as far as I've seen, other people are having the same problem as well). I'm guessing it's the LHS of the conditions we have to rewrite, so I've managed to find a relation between both $E_{CB}(x\rightarrow\infty)$ and $E_{CB}(x=0)$ based on $\psi_{B0}$ but struggle to make use of the bandgap and especially $n_{B0}$ (do we even need it in the expression since B is intrinsic?). What I have so far is the following: $\psi_{B0}=-E_{FB}/e$ with $E_{FB}=E_{CB}-1/2*E_{gB}$ -- but here $E_{CB}$ corresponds to conduction band energy before contact, so this is where I get stuck (unless we can assume that it's equal to the $E_{CB}$ far from the interface after contact??)... Could you please let me know if I'm going in the right direction, or if there's something wrong in my reasoning? Hi, I'm unsure how to go about question 2.5 (and as far as I've seen, other people are having the same problem as well). I'm guessing it's the LHS of the conditions we have to rewrite, so I've managed to find a relation between both $E_{CB}(x\rightarrow\infty)$ and $E_{CB}(x=0)$ based on $\psi_{B0}$ but struggle to make use of the bandgap and especially $n_{B0}$ (do we even need it in the expression since B is intrinsic?). What I have so far is the following: $\psi_{B0}=-E_{FB}/e$ with $E_{FB}=E_{CB}-1/2*E_{gB}$ -- but here $E_{CB}$ corresponds to conduction band energy before contact, so this is where I get stuck (unless we can assume that it's equal to the $E_{CB}$ far from the interface after contact??)... Could you please let me know if I'm going in the right direction, or if there's something wrong in my reasoning? https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/35 [HW5 Q3.3] 2020-05-31T13:30:00Z lcartocci [HW5 Q3.3] Hi, I have a question about the band diagram asked in Q3.3. Firstly, I have trouble understanding how it should be fundamentally different from Figure 3 given in the homework. In addition, I don't see how this could fulfill the condition where the conduction band offset $\Delta E_C$ should remain the same (before contact $\Delta E_C > 0$, after contact - as shown in Fig.3 - it seems that $\Delta E_C > 0$). Thanks! Hi, I have a question about the band diagram asked in Q3.3. Firstly, I have trouble understanding how it should be fundamentally different from Figure 3 given in the homework. In addition, I don't see how this could fulfill the condition where the conduction band offset $\Delta E_C$ should remain the same (before contact $\Delta E_C > 0$, after contact - as shown in Fig.3 - it seems that $\Delta E_C > 0$). Thanks! https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/33 HW5 Q1.1 2020-05-28T08:31:23Z arshah HW5 Q1.1 In Q 1.1, are we supposed to simplify the PBE in different regions? (For e.g. for x<xn, xn<x<xp, and x>xp) or are we just expected to re-write the PBE and leave it in the form of equation 19.2 in the script? In Q 1.1, are we supposed to simplify the PBE in different regions? (For e.g. for x<xn, xn<x<xp, and x>xp) or are we just expected to re-write the PBE and leave it in the form of equation 19.2 in the script? vaglig vaglig https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/32 HW5 Q1.4 2020-06-06T13:31:27Z aandreotti HW5 Q1.4 Dear Tian, When I derive eq 1.4 I don't get the minus sign in front of it. This is why I consider Na=Nd (concentration of dopants). Indeed from the plot 1.a I see at x=xn Nd=-a*xn>0 and at x=xp Na=a*xp>0. Is there another reason for the minus sign or should I consider Na=-Nd? Thank you in advance! Best regards Alessandro Andreotti PS: In Q1.5 it's written er=11.0 Did you mean 110 or 11 is correct? One curiosity about the band diagram in Q2 what does the energy line Evac represent? Dear Tian, When I derive eq 1.4 I don't get the minus sign in front of it. This is why I consider Na=Nd (concentration of dopants). Indeed from the plot 1.a I see at x=xn Nd=-a*xn>0 and at x=xp Na=a*xp>0. Is there another reason for the minus sign or should I consider Na=-Nd? Thank you in advance! Best regards Alessandro Andreotti PS: In Q1.5 it's written er=11.0 Did you mean 110 or 11 is correct? One curiosity about the band diagram in Q2 what does the energy line Evac represent? vaglig vaglig https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/30 [HW5 Q3.4] Determining power conversion efficiency 2020-05-25T09:29:21Z lcartocci [HW5 Q3.4] Determining power conversion efficiency Hi again, I have a question regarding the solar cell power conversion efficiency. According to the lecture, to calculate this value, we should also take into account the photons that are not absorbed by the semiconductor due to their energy being lower than the bandgap. However, in the question itself, it says to calculate the number of photons radiated by the blackbody as a function of frequency "which are all absorbed by the solar cell" -- I take this as meaning we should only consider the energy of the photons within the light frequency range referred to in Question 3.2. Which approach should we take here? In principle I would assume we should consider the entire solar spectrum (ie. including the energy of photons which do not get absorbed) to compute the overall conversion efficiency... I hope this makes sense! Hi again, I have a question regarding the solar cell power conversion efficiency. According to the lecture, to calculate this value, we should also take into account the photons that are not absorbed by the semiconductor due to their energy being lower than the bandgap. However, in the question itself, it says to calculate the number of photons radiated by the blackbody as a function of frequency "which are all absorbed by the solar cell" -- I take this as meaning we should only consider the energy of the photons within the light frequency range referred to in Question 3.2. Which approach should we take here? In principle I would assume we should consider the entire solar spectrum (ie. including the energy of photons which do not get absorbed) to compute the overall conversion efficiency... I hope this makes sense! https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/29 [HW5 Q2.1] Calculation of Fermi energies 2020-06-02T16:14:32Z lcartocci [HW5 Q2.1] Calculation of Fermi energies Hi, I have a question with respect to Question 2.1, where we have to calculate the Fermi energies of A (n-doped) and B (intrinsic). In principle, to do this we would need the density of states of the conduction and valence bands Nc and Nv, which are in turn related to the effective carrier masses... Can we assume those to be the same in those calculations, such that Nc=Nv? If not, I would be unsure how to proceed in order to answer the question. Hi, I have a question with respect to Question 2.1, where we have to calculate the Fermi energies of A (n-doped) and B (intrinsic). In principle, to do this we would need the density of states of the conduction and valence bands Nc and Nv, which are in turn related to the effective carrier masses... Can we assume those to be the same in those calculations, such that Nc=Nv? If not, I would be unsure how to proceed in order to answer the question. https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/27 Doubt in Q3.5 2020-05-19T12:43:59Z bpatel Doubt in Q3.5 I had a doubt in Q3 part 5 of the assignment. Are we supposed to get the equation of dP/dx and subsequently attempt to find the values of the limits (see the word doc attached). Or are we just supposed to express dP/dx in terms of the limits? Which I am not very sure how to do?[Q3_part_5_doubt.docx](/uploads/fbb55468c1ec6e1bbeb3a8b0271c4109/Q3_part_5_doubt.docx) I had a doubt in Q3 part 5 of the assignment. Are we supposed to get the equation of dP/dx and subsequently attempt to find the values of the limits (see the word doc attached). Or are we just supposed to express dP/dx in terms of the limits? Which I am not very sure how to do?[Q3_part_5_doubt.docx](/uploads/fbb55468c1ec6e1bbeb3a8b0271c4109/Q3_part_5_doubt.docx) https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/26 HW4 Q3.5 Setting up dP/dx 2020-05-12T19:34:25Z etzoldk HW4 Q3.5 Setting up dP/dx I managed to set up $\eta \nabla^2 v_\mathrm{f} = \frac{\partial p}{\partial x} + c \frac{\partial U}{\partial x} = \frac{\Delta p - \Delta \Pi_\mathrm{eff}}{L} = \frac{\Delta P}{L}$ but now I am stuck because I don't know how I should set up $dP/dx$. Could you give me a hint? I managed to set up $\eta \nabla^2 v_\mathrm{f} = \frac{\partial p}{\partial x} + c \frac{\partial U}{\partial x} = \frac{\Delta p - \Delta \Pi_\mathrm{eff}}{L} = \frac{\Delta P}{L}$ but now I am stuck because I don't know how I should set up $dP/dx$. Could you give me a hint? https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/25 [HW4] Q3.4 2020-05-19T12:43:34Z Gianluca Lombardini [HW4] Q3.4 Hi, at some point I get the equation $\frac{d^2 g(x)}{d x^2} - \beta\frac{d g(x)}{d x}\frac{d U(x)}{d x} = 0$. Could you tell if I am on the right path? An if yes, could you maybe give a hint on how to solve it analytically? Thanks! Hi, at some point I get the equation $\frac{d^2 g(x)}{d x^2} - \beta\frac{d g(x)}{d x}\frac{d U(x)}{d x} = 0$. Could you tell if I am on the right path? An if yes, could you maybe give a hint on how to solve it analytically? Thanks! celebik celebik https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/24 Q3.1 2020-05-08T08:26:42Z aandreotti Q3.1 Dear TAs, Can I ask you a question regarding the derivation in Q3.1? In my derivation, I have one term that is int[-beta exp[-beta U(x)] g(x) dU]. At this point, can I take g(x) out of the integral? If I do so, I get this solution for w: =exp(-beta U(L/2)) x<=-L/2 =exp(-beta U(-L/2)) x>=L/2 But now can I generalize and say w=exp(-beta*U(x))? Otherwise, it doesn't make sense to have an expression only outside the membrane (of course if I can take out g(x) from the integral). Thank you in advance for your help and your time! Kind regards Alessandro Dear TAs, Can I ask you a question regarding the derivation in Q3.1? In my derivation, I have one term that is int[-beta exp[-beta U(x)] g(x) dU]. At this point, can I take g(x) out of the integral? If I do so, I get this solution for w: =exp(-beta U(L/2)) x<=-L/2 =exp(-beta U(-L/2)) x>=L/2 But now can I generalize and say w=exp(-beta*U(x))? Otherwise, it doesn't make sense to have an expression only outside the membrane (of course if I can take out g(x) from the integral). Thank you in advance for your help and your time! Kind regards Alessandro https://gitlab.ethz.ch/IEM-course/2020-iem-hw-qa/-/issues/23 [Lecture 16] Eq. 16.5 and [HW4] Q3.1 2020-05-19T12:43:51Z aandreotti [Lecture 16] Eq. 16.5 and [HW4] Q3.1 Dear Tian, Can I ask you a question about eq. 16.5 of Lecture 16? During the lecture Prof. Shih provided us with this expression for the solute flux N=-w*D/L*delta(C)+w*c*v Why eq.16.5 has the term D/L that multiplies c*v too? In other words, the solute carried by the solvent isn't independent from diffusion? And sorry, for what concerns the term delta(c), on the assignment it is written that it is c1-c2. But in this case, when c1>c2 the first term on the right hand side is negative but the diffusive flux is from reservoir 1 to 2. So shouldn't it be delta(c)=c2-c1? Thank you in advance! Best regards Alessandro Andreotti Dear Tian, Can I ask you a question about eq. 16.5 of Lecture 16? During the lecture Prof. Shih provided us with this expression for the solute flux N=-w*D/L*delta(C)+w*c*v Why eq.16.5 has the term D/L that multiplies c*v too? In other words, the solute carried by the solvent isn't independent from diffusion? And sorry, for what concerns the term delta(c), on the assignment it is written that it is c1-c2. But in this case, when c1>c2 the first term on the right hand side is negative but the diffusive flux is from reservoir 1 to 2. So shouldn't it be delta(c)=c2-c1? Thank you in advance! Best regards Alessandro Andreotti vaglig vaglig