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8
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0039874864
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T. Ishibashi, S. Tarucha, and H. Okamoto, in Proceedings of the International Symposium on GaAs Related Compounds
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(1981)
Inst. Phys. Conf. Ser.
, vol.63
, pp. 587
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15
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0001307296
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(1982)
Appl. Phys. Lett.
, vol.41
, pp. 221
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Gibbs, H.M.1
Tarng, S.S.2
Jewell, J.L.3
Weinberger, D.A.4
Tai, K.5
Gossard, A.C.6
McCall, S.L.7
Passner, A.8
Wiegmann, W.9
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24
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0000014253
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In this paper we observed broadening and shift of the exciton peaks which we ascribed to fields parallel to the layers. However, with the improved sample geometries used in the present work, we now believe that these early results showed a combination of parallel and perpendicular fields together with some ohmic heating of the sample. In our present work, we have taken care to eliminate heating as a cause of any of the effects, and contacts have been improved to eliminate the formation of Schottky barriers which could give perpendicular fields in the parallel field sample.
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(1983)
Appl. Phys. Lett.
, vol.42
, pp. 864
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Chemla, D.S.1
Damen, T.C.2
Miller, D.A.B.3
Gossard, A.C.4
Wiegmann, W.5
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26
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84927199643
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M. Erman, P. Frijlink, J. B. Theeten, C. Alibert, and S. Gaillard, Proceedings of the 11th International Symposium on GaAs and Related Compounds, Biarritz, 1984, edited by J. A. Revill (Hilger, Bristol, U. K., in press).
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28
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0000741042
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This independent work provides a complementary but closely related calculation to that reported by ourselves briefly in Ref. 20 and in greater detail in the present paper for the perpendicular field electroabsorption. The wave functions used are slightly different, but excitonic effects are included in a manner similar to our own calculations. We have also carried out more direct calculations of the tunneling time of carriers out of the wells and obtained good absolute agreement of theory and experiment for the shifts, and in the present paper we have also repeated the calculations for the 57:43 split of the band discontinuities which has recently been favored.
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(1985)
Phys. Rev. B
, vol.31
, pp. 3893
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Brum, J.A.1
Bastard, G.2
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31
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71049128027
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edited by, D. H. Auston, K. B. Eisenthal, Springer, New York
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(1984)
Ultrafast Phenomena IV
, pp. 162-165
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Knox, W.H.1
Fork, R.L.2
Downer, M.C.3
Miller, D.A.B.4
Chemla, D.S.5
Shank, C.V.6
Gossard, A.C.7
Wiegmann, W.8
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56
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84927199641
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There are some semantic problems and physical paradoxes associated with the use of the term ``exciton binding energy'' in this context which deserve some comment. First, the principal semantic problem is that there are no bound states of a system in a uniform electric field because the system can always tunnel to lower energy states and with the charged particles nearer to the ``electrodes.'' However, it is reasonable to talk of an exciton as being a particle if it lives long enough to produce a recognizable resonance, which ``orbits'' before the exciton is destroyed;
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57
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84927199640
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this is already the working definition even without field, because the exciton is not stable in the presence of phonons, and at room temperature in the quantum well the resonance is only just resolvable due to the phonon broadening. The use of the approximate separable wave function [Eq. (3)] also makes the problem of the definition of exciton binding energy deceptively simple, as the energy of the system as a whole then separates into the sum of three energies, Ee, Eh, and EB. However, this is an artifact of the approximation;
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58
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84927199639
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it encourages us to think that we can always conceive of the total shift of the exciton resonance as being the shift of the band gap (Ee + Eh ) plus the change of exciton binding energy. In reality, the shift of the band gap and the shift of the exciton peak position are separate problems;
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59
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84927199638
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it just happens that with this separable wave function the solution of the exciton problem involves the solution of the band-gap problem. Furthermore, the high-lying exciton states are probably not bound in any sense in the presence of the fields used here;
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60
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84927199637
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hence, if we use the definition of binding energy as being the separation of the lowest bound state and the first unbound state, the first unbound state would not be the original lowest continuum state and EB as used here would not be the binding energy. We refer to EB as the exciton binding energy here for brevity and because it has a simple correspondence with the zero-field case. One physical paradox which arises from the separation of the problem is that the binding energy EB actually reduces with field, tending to shift the exciton energy upwards. This is paradoxical because for a physical system of this symmetry the first consequence should be a reduction of energy. (If the exciton wave function were to remain totally unchanged in the presence of the uniform perpendicular field, its energy would not change because of its mirror symmetry;
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61
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84927199636
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hence, given that the physical system always seeks the lowest energy state, the energy of the system cannot increase.) The resolution of this paradox is that the energy of the exciton as a whole does decrease;
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62
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84927199635
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there is no requirement that an arbitrary contribution to that energy should decrease. Because of the arbitrariness of the binding energy, it is important to emphasize that the (Stark) shifts, which we discuss, are the total shifts of the exciton peaks, not the shifts in binding energy;
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63
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84927199634
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there is, thus, no physical problem in having Stark shifts larger than the zero-field binding energy.
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75
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84927199633
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The computer solution for the particle transmission of quantum-well structures was developed and provided by G. A. Baraff.
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