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

Abstract

Our study is devoted to the theoretical investigation of the electronic and optical properties of ͑ZnSe͒ n / ͑Si 2 ͒ m ͑0001͒ wurtzite ͑WZ͒ superlattices ͑SLs͒ with the range n = m = 1 -18, giving special attention to the role of interface states at the Zn-Si and Se-Si polar interfaces. The calculations are performed by means of a semiempirical tight-binding model with an sp 3 s ‫ء‬ basis. The procedure involves the construction of a tight-binding Hamiltonian model of WZ SLs from the WZ bulk in the ͑0001͒ direction with different n and m layers. For ͑ZnSe͒ 16 / ͑Si 2 ͒ 16 SL, we found that the energy band gap is close to 1.665 eV, with the conduction-band minimum located at the ⌫ point. The states at the conduction-and valence-band edges are confined two dimensionally in the Si layers. For a valence-band discontinuity ⌬E v = 1.09 eV given by Harrison theory, the band gap between the confined band edges states increases ͑2.37 eV at the ⌫ point for n = m =2͒ by decreasing the superlattice period. It is shown that the heterointerface bond relaxation strongly affects interface band in the band gap. In the ͑ZnSe͒ 10 / ͑Si 2 ͒ 10 SL, the relaxed Si bonds at the heterointerface induce a vacant interface band and a filled interface band in the band gap. The band structures of ͑ZnSe͒ n / ͑Si 2 ͒m ͑0001͒ ͑WZ͒ ͑SLs͒ with different layer thickness are used to determine the electron and hole effective masses. Furthermore, the calculated absorption spectra of the superlattices are found to be quite different from those of bulk ZnSe and Si but fairly close to their average. The electronic structure of the superlattice turns out to be quite sensitive to the combination of the well and barrier layer thickness. This sensitivy suggests the possibility of designing suitable band structures for device application.

Electronic Structures and Transition Properties of BeSe and BeTe Molecules

“…Similarly, the Te atom was treated as a system of 6 valence electrons and 46 electrons within the core using the effective core potential ECP46MWB basis set 20 for s and p functions. The active space in the C 2v symmetry group then contains 5σ (Be: 2s, 2p 0 , 3s, and 3p 0 and Se: 4p 0 ), 2π (Be:2p ± 1 and Se: 4p ± 1), and 0δ (Be:0 and Se:0) and 7σ (Be: 2s, 2p 0 , 3s,3p 0 , 3d 0 , and 3d + 2 and Te: 5p0), 4π (Be:2p ± 1,3p ± 1, and 3d + 1 and Te: 5p ± 1), and 1δ (Be:3d − 2 and Te:0) orbitals distributed into the irreducible representation as 5a1, 2b1, 2b2, and 0a2 and 7a1, 4b1, 4b2, and 1a2, which correspond to [5,2,2,0] and [7,4,1,1] for the molecules BeSe and BeTe, respectively.…”

“…Solid-state beryllium chalcogenides (BeS, BeSe, and BeTe) exhibit several interesting physical properties related to their electronic structure; they present high bonding energy, hardness, and unusual electronic, mechanical, thermal, and optical properties. They are very interesting candidates for optoelectronic devices in the blue and UV spectral regions because of their high band gap energies. − …”

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].…”