Quantum well to quantum wire crossover in AlAs/GaAs/AlAs heterostructures induced by interface roughness increase

Abstract

Adopting a real-space tight-binding supercell approach, we i n vestigate interface roughness e ects in semiconductor heterostructures. AlAs GaAs AlAs 001 QWs of average width W are considered, in which one of the interfaces is planar and the other has a shape de ned by periodic steps with amplitude A and wavelength . The oscillator strength f of the fundamental transition in the well describes the optical nature of the heterostructures. By investigating the wavefunctions as a function of the interface parameter A, w e conclude that the f behavior with A is an optical signature of the quantum well to quantum wire crossover in the heterostructures. Recently, photoluminescence experiments showed that hydrostatic pressure produces an increase in the optical e ciency of heterostructures in which the interfaces present a high degree of roughness. In order to investigate this optical behavior, we discuss hydrostatic pressure e ects on rough-interface heterostructures. I IntroductionThe recent progress in crystal fabrication techniques allows the growth of heterostructures with semiconductor materials of di erent atomic compositions. The interface roughness e ects in AlAs GaAs heterostructures have been intensively studied in the last years 1 -2 . In spite of optical experiments suggesting that completely at interfaces can be generated from particular growth conditions, the advent of highly sensitive microscopy techniques, as STM and TEM, indicates that some interfaces exhibit roughness over a few monolayers 3 . The optical and electronic properties of the heterostructures are very sensitive to uctuations in interface width. A very interesting problem in this context is the investigation of interface roughness e ects on the electronic properties of semiconductor heterostructures.In this work we i n vestigate the quantum well to quantum wire crossover in AlAs GaAs heterostructures induced by i n terface roughness. The optical properties of such structures were obtained within a realspace tight-binding supercell approach 4 , with periodic boundary conditions p.b.c. , using the sp 3 s parametrization proposed by V ogl et al 5 .The optical behavior of the heterostructures is described by the oscillator strength f of the transition be- where m is the free electron mass and E = E e 1 , E h 1 is the energy di erence between je 1 i and jh 1 i, which also gives the well's energy gap. Results for at interfaces quantum wells QWs 6 show that narrow wells display indirect-gap behavior, i.e., f = 0, and an abrupt transition into direct bandgap f nite occurs for W = 10 ML monolayers; 1 ML = a 2 , where a is the conventional cubic cell parameter . For the value of W considered here 16 ML and in the absence of interfaces roughness, the rst optical transition in the well is dipole-allowed.Recent photoluminescence experiments 7 show that hydrostatic pressure produces an increase in the

An extended Hückel study of the electronic properties of III–V compounds and their alloys

“…10. For the Al and Ga atoms in an alloy, the values of their on-site energies were set equal to the same average, which implies that the atoms partially lost their individuality and become a pseudo atom with orbital energies between the former values, in a similar fashion to the Virtual Crystal Approximation (VCA) [11]. However, only the on-site energies were varied: the zetas and the expansion coefficients were kept at their original values given in the Table I. Random alloys, as were considered in this article, lack formal translational symmetry and thus k is not a good quantum number, leading an inadequacy of the language of bandstructure dispersion E(k) to describe the energy states of the alloys.…”

“…However, only the on-site energies were varied: the zetas and the expansion coefficients were kept at their original values given in the Table I. Random alloys, as were considered in this article, lack formal translational symmetry and thus k is not a good quantum number, leading an inadequacy of the language of bandstructure dispersion E(k) to describe the energy states of the alloys. Nevertheless, several theoretical approaches have been proposed in the literature [11][12][13][14][15][16], intending to restore the relation between the energy and k. The Virtual Crystal Approximation [11] (VCA) was one of the first approximation employed in the theoretical study of A x B 1−x C semiconductor alloys into the TB frame, where the A and B atoms are replaced by a fictitious atom, whose TB parameters are calculated as weighted averages of the AC and BC binary parameter values. More realistic approaches, where the atom identity is preserved, are based on the spectral decomposition of the alloys eigenstates [13,14] or the unfolding of the supercell Brillouin zone [12,15,16]: the former approach employing plane waves as basis set and the second localized orbitals.…”

Using the Hg x Mg (1− x ) Te ternary compound as a room temperature photodetector: The electronic structure, charge transport, and response function of the energetic electromagnetic radiation

“…It has been shown for different ternary compounds that the obtained results by super-cell and VCA methods have acceptable agreements. [20][21][22] The MCNP is a general-purpose Monte Carlo N-particle code that can be used for neutron, photon, electron or coupled neutron/photon/electron transport using cross-section data. Given some inputs, the MCNP returns the dose, flux, response function, etc.…”

“…One of the abilities of the MCNP code is the response function generation by the Monte Carlo method. [22] The photon energy regime in MCNP is from 1 keV to 1 GeV. Since the electromagnetic radiation in the x and gamma regions is used abundantly in industrial, medicine and research fields, we calculate the response function to the energetic electromagnetic radiations for the Hg 0.6 Mg 0.4 Te and Cd 0.9 Zn 0.1 Te by MCNP in these regions with 0.05 MeV, 0.2 MeV, 0.661 MeV and 1.33 MeV radiation energies.…”

Theoretical evidence of the piezoelectric property enhancement for ScY- or CaTi-codoped wurtzite AlN

“…Arkansas et al proposed that the magnitude and variation of the piezoelectric coefficient for ordered hyperunits could be replicated successfully by VCA. 29,30 Additionally, Lee et al mentioned that a disordered structure constructed by VCA could serve as a simple pseudo-potential scheme for effective point positions, and the approach yields reliable data when estimating the band structure of compound semiconductors. 31 In the succeeding work, a disordered alloy was constructed by the VCA method in order to compare with the traditional ordered alloys and obtain a more stable crystal structure.…”