Superlattices energy levels

If there is a superlattice, there is an additional group of forbidden energies similar to those connected with the main lattice reflections. Slater (17) has pointed out that the depression of the energy levels from the forbidden energies could be the source of energy for the formation of a superlattice if the Fermi level fell at a superlattice forbidden electron energy. He anticipated that order from this cause could be widespread. 

Figure 3.4 Energy levels of (a) multiple quantum wells and (b) superlattices. When the barriers are thick, the wells are isolated, there is no inter-well electronic coupling, and the quantised states are narrow. When the barriers are thin (<4 nm), inter-well electronic coupling occurs, the quantised states broaden, minibands form and electron delocalisation and transport can occur. Source Nozik and Memming (1996).

Energy levels in quantum wells, superlattices and quantum dots Quantum wells and superlattices... 

For superlattices, several approaches have been used to calculate the energy level structure of the minibands (Bastard, 1981 Altarelli, 1985 Bastard and Brum, 1986). One approach is to use a tight-binding model for the multiple wells, leading to a Bloch-like envelope function of the form (Dingle et al, 1975)... 

Figure 3.7 shows these DOS functions for bulk semiconductors, QWs, superlattices, quantum wires and quantum dots the DOS for quantum dots exhibits discrete values at the discrete quantised energy levels. 

In this paper, recombination processes of nonequilibrium charge carriers in the doped GaAs superlattices are examined. Self-consistent calculations of the electrostatic potential profile in the superlattices are presented. Transformation of electron energy levels and wave functions as well as variation of the overlap of... 

The electronic properties of the new superlattice materials help to shed light on some major fundamental questions in amorphous semiconductors. Quantum size effects in the case of crystalline superlattices raise the lowest allowed electron and hole energy levels and give rise to a density of states that increases in discrete steps. This structure in the density of states is reflected in... 

Fig. S. (a) Potential well model for the a-Si H/a-SiN H superlattice. Indicated in the figure are the energy levels AE and A , for the lowest quantum states for electrons and holes is the...

The quantum cascade laser is very different from the conventional semiconductor laser that has been described in this article, and is based on the intersubband transitions between the excited states of coupled quantum wells, or superlattice structures, and on the resonant tunneling between the wells as the pumping mechanism. This means that lasing action takes place between energy levels within the conduction band (not between the conduction and valance bands). More importantly, since the electron is still in the conduction band, novel bandgap engineering can provide for a transport mechanism that allows for this electron to be reinjected into another set of coupled quantum wells, and is therefore reused. As a result, one injected... 

TRTS is very sensitive to the degree of electronic coupling between nano-crystals. In the case where there are strong overlapping of QD energy level wavefunctions, carriers populating the QDs can hop between dots, giving rise to a real component of the complex conductivity even at frequencies below the intraband transitions of isolated QDs. " In disordered superlattices of InP QDs, Beard et reported an increase in the transient... 

Redistribution of the space-charge of the excited carriers is presented in Fig. 1. Therewith at low temperatures, as seen in Fig. 2, the tunable photoluminescence band maximum coincides with the difference of the quasi-Fermi levels AF, which in turn is close to the effective energy gap Eg of the doped superlattice. At... 

Figure 2. Dependence of the effective energy gap Eg on the quasi-Fermi level difference AF in the superlattice No. 4 at 20 K (a) and 300 K (b). Thin curves represent the quasi-Fermi level for electrons Fe relative to the top of the valence band, dashed curves correspond to the quantum energy of the spontaneous recombination spectrum maximum hvmax.

Fig. 13. Energy-band diagram for a-Si H/a-SiN , H superlattice showing the effect of pinning the Fermi level Ef by the substrate interface states is the band-bending potential, Xo the depletion width, and the discontinuity of the conduction bands at the a-Si H/a-SiN, H interface.

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