Physics of nanometer structure devices

Sub-band populations and the spatial distribution of electrons in GaAs/(Al,Ga)As modulation-doped quantum wells

“…Theoretical support for the above interpretation of the results on wide well samples comes from published self-consistent calculations [8, 101; for the widest case treated, a 500 8, wide QW [8], the results for a symmetric potential distribution show that the two lowest confined states are nearly degenerate in energy, and that each state has two equal probability density peaks, one close to each interface. Thus, in this case it is inappropriate to consider the electrons as being confined at one interface or the other, and the carriers in the two lowest sub-bands would be expected to have similar mobilities.…”

“…It is tempting, therefore, to assign the rapidlyvarying SDH oscillations to the electron density at the inverted interface, and the superimposed slower variation to a third sub-band, E', which is expected to be occupied in wide QWS [8]; this situation is illustrated in figure 5 ( d ) . Such a correspondence between nb and high field SDH oscillations is rather surprising, since although the conduction in this magnetic field region is essentially dominated by the low mobility channel [ 141, Reed 2ooF 100 I I…”

“…Thus, in this case it is inappropriate to consider the electrons as being confined at one interface or the other, and the carriers in the two lowest sub-bands would be expected to have similar mobilities. However, as shown in [8], application of an electric field across the well removes the symmetry of the structure, increases the energy separation of the sub-bands and produces one dominant probability density peak for each sub-band; the spatial position of this peak is different for each sub-band. Recent unpublished calculations [28,32] for an asymmetric 500 A QW structure show that the probability density for the lowest (Eo) sub-band is almost entirely located close to one interface, whilst that for the second ( E , ) sub-band is at the other interface.…”