I'm currently working on quantum transport in a heterostructure with 2 quantum wells. To offer a physical explanation of the behavior of the I-V curve, I plotted the LDOS inside each well. For the left well, I obtained something I don't know how to fully explain: when I increment the voltage, the states do not just shift up in energy but also peak in value.
I mean, for thermal equilibrium (0V) the max value of LDOS was 0.7[/eV], but when I reached 0.66V, the value peaked to 5[/eV]. I understand that when the barriers shift, some of the initial bounded states scape to the continuum, but I don't understand this peak. The curious part is that at this voltage, the current is very low (I guess the peak is not in the energy range between the Fermi levels at each contact). I attach some plots for review
I do not understand all the parameters here, but this is what happens when a potential change causes a strongly localized (quasi-bound) state to appear in the left well. In this case, you should see quite a sharp threshold voltage beyond which the LDOS increases dramatically, and you may be able to relate this to a simple infinite-well model.
Thank you very much for your answers. I think I get the point both of you are making. What still intrigues me, however, is why this quasi-bound state appear. I'm supposed to observe bound states in equilibrium, but when the potential starts to change, shouldn't some of these states scape to the continuum? (the barriers won't be at the same energy level, and the left one is higher than the right one). And why doesn't this quasi-bound state appear in the right well too? My system is a triple-barrier (double quantum well) InAs/InP heterostructure. Both wells are symetric and the middle barrier is a bit wider than the outer ones.
Thanks again!
Thanks! I think I get your point. I'm using a 1D model with a single-band effective mass Hamiltonian, and for calculating all the quantities of interest, I'm using Green's functions (For the DOS, the Spectral function obtained from the NEGF). What seems strange to me is the fact that this sharp peak just in the left well, despite of the fact that both wells are symmetric, and have the same witdth, and depth, and the potential profile is changed linearly with the voltage (see attached figure)
Sorry, I don't understand how do you lebelled DOS by Left or Right. Is it an approximation for low energy states localized in the correspondent well? In any case I believe that the absence of symmetry is a kind of mistake in your calculation. Why don't you try to solve the effective mass Hamiltonian problem by superposition of several plane waves as it ussually promt by any textbook?
Yes it is an approximation for the states with lower energy inside each well. Well the idea of my work is to obtain the LDOS (and other properties) usind the NEGF formalism. I did find an error in my calculation: a typo in the effective mass. Thanks for the help :)
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