Electronic structure and optical properties of (ZnSe)n∕(Si2)m (111) superlattices

Abstract

The electronic properties of (ZnSe)n∕(Si2)m (111) superlattices (SLs) are investigated theoretically in order to clarify the general features of the zone-folding and the band-mixing effects in superlattices composed of an indirect-band-gap semiconductor (Si). The detailed electronic structure of (ZnSe)n∕(Si2)m (111) SLs are studied with the range n=m=10–16, giving special attention to the role of the interface states at the Zn–Si and Se–Si polar interfaces. The presence of the electric field in the SL is totally ignored, i.e., “the zero-field model.” The degeneracy of the energy minima of the conduction band at the M point in the zinc-blende-type bulk material cannot be lifted by the zone-folding effects alone. The band-mixing effect through the interfaces between the two constituent materials plays an important role in determining the overall band lineup throughout the entire Brillouin zone. The states at the conduction- and valence-band edges are confined two dimensionally in the Si layers. Furthermore, we have found two interface bands in the lower and upper regions of the gap. The states of the lower interface band are located at the Zn–Si interface, while those of the upper interface band are located at the Se–Si interface. The energies of the interface states depend on the parameters representing the Zn–Si and Se–Si bond lengths and the valence-band discontinuity between ZnSe and Si, but the interface states do not disappear from the gap with reasonable choices of the parameters. The electronic structure of the superlattice turns out to be quite sensitive to the combination of the well and barrier layer thicknesses. This sensitivity suggests the possibility of designing suitable band structures for device applications. Furthermore, the absorption spectra of the superlattices are calculated and are found to be quite different from those of bulk ZnSe and Si but fairly close to their average. The electronic and optical properties suggest that superlattices composed of indirect-band-gap semiconductors offer great potential for application to optical devices.

Tight-binding calculations of ZnSe/Si wurtzite superlattices: Electronic structure and optical properties

“…This situation can be explained by the folding of the bulk WZ zone onto the WZ SL zone. When comparing to the band structure of the ͑ZnSe͒ 16 / ͑Si 2 ͒ 16 ͑111͒ ZB SL, 32 we observe a breaking of degeneracy ͓except for the ⌬ ͑⌫ → A͒ direction͔ due to the lower symmetry ͑hcp versus hexagonal͒ a nearly constant value of the top of the valence band along the ⌬ direction. One difference in the band structures is that the order of the levels at the top of the valence band is inverted.…”

“…1͒, whereas a transition from direct to indirect is found for ͑ZnSe͒ 16 / ͑Si 2 ͒ 16 ͑111͒ zinc-blende ͑ZB͒ SL. 32 In the case of direct-band-gap WZ SL, the CBM is found at the ZB ⌫-folded state; it exhibits mainly Si layers and is therefore highly isotropic. This can be seen from the dispersion curve of Fig.…”

“…However, the situation is different in the case of ZnSe/Si͑111͒ ZB SL where the vacant interface band lies below the conduction-band edge. 32 Furthermore, for the ͑0001͒ interface case with relaxed Si bonds where ⌬ = 0.5, the lowest conduction-band states are lowered in the band gap. Consequently, the interface band gives a large density of states ͑DOS͒ in the band gap.…”

Comparative study on the performance of exchange and correlation in wide-gap semiconductors: the case of BeS, BeSe, and BeTe

“…In addition, the optimized local potential method of the modified-Becke-Johnson pointed out by Blaha and coworkers [35] is pertinent to simulate the electronic properties of systems containing huge number of atoms that are beyond the capabilities of GW technique or hybrid functional. This may pave a new perspective of applications that are at this stage merely accessible by the most of semi-empirical methods, like semi-empirical pseudopotential approaches or tight-binding approximations [2][3][4][5][6][7][8][9][10][11][12]. To assess the performance of these methods, we compute the band structures of beryllium chalcogenide semiconductors via GW, hybrid, and MBJLDA functionals, which will be compared to the available experimental data.…”

“…Since three decades, beryllium chalcogenides have drawn great deal of attention because of their hardness, electronic properties, and their potential application in microelectronic and optoelectronic devices [1][2][3][4][5][6][7][8][9][10][11][12]. Among them, BeS, BeSe, and BeTe compounds have proven to be the most desirable semiconductors for the light emitting optoelectronic devices in the blue color spectrum [4,10].…”