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5HETEROSTRUCTURES OF ANTIMONIDE-BASED SEMICONDUCTORS
Islombek Arabboevich Muminov, Shalola Yunusali kizi Akhmedova, Dilnoza Akhmadjon kizi Sobirjonova, Doniyorjon Kahramonjon ugli Khomidjonov
Farg 'ona davlat universiteti islomjon_muminov1990@mail.ru
ABSTRACT
The article is devoted to semiconductors with low-dimensional systems, which are actively developing and are a relatively new direction. The concept of quantum wells, quantum threads, and quantum dots is revealed in the paper. The concept of Quantum States is important for active device technology, for example the behavior Quantum well lasers, Photo detectors, Resonant Tunneling Diodes etc. can be explained by means of this concept.
Keywords: Molecular beam epitaxy, Quantum wells, effective mass, potential well, Schrodinger equation, finite barrier.
INTRODUCTION
Molecular beam epitaxy allows routine production of heterostructures where composition changes over atomic length scales. The interface of a heterostructure may serve as a barrier to electrons and/or holes because of the change in band gap and the nature of the band alignments. Semiconductor alloys can have band gaps and alignments spanning their constituent semiconductor components. The band gap, Eg.
is plotted against the lattice parameter for several semiconductors and their alloys in Fig. 1. The data is taken from reference [1].
Figure 1: Band gap and lattice constants of several compound semiconductors and their ternary alloys. Band parameters were taken from Vurgaftman et al. [1 ].
The functional dependence of band parameters on chemical composition is not necessarily linear as suggested by Vegard's law. Bowing of band parameters is accounted for in the curves representing the band gaps of semiconductor alloys.
When a thin narrow band gap material is sandwiched between wider band gap materials electrons or holes may be confined within the narrow gap material if the alignment of conduction or valence bands produce a potential well [16]. The carriers become trapped in the confining potential; their motion along the growth direction is restricted and the continuous band is quantized into sub-bands. Their motion in the plane of the well is unrestricted, and they behave two-dimensionally. Quantum wells (QWs) are critical structures in many electronic and opto-electronic devices. They are also important in the field of condensed matter research, where they provide a system in which carrier density, density of states, confinement energy, band structure and spin-orbit coupling can be controlled and modified.
1 0 0.4
p ( eV1 • nm !)
Figure 2: (a) An AlSb/InAs/AlSb heterostructure viewed along the [2-30]
crystal-lographic direction. (b) The band structure along the [001] growth axis of the het-erostructure shown in (a), the bound state energy levels and wavefunctions. (c) The electronic subband dispersion of the bound states (d) The two-dimensional density of states.
DISCUSSION
Quantum mechanics predicts the properties of particles confined to quantum heterostructures. Solving the Schrodinger equation for a one-dimensional particle in an infinitely deep well of width a produces energy eigenvalues,
1 /fmnr\2
2m
where m = m"me, and rn is the effective mass. In reality confinement potentials have finite barrier heights, as in the case of an AlSb/InAs/AlSb heterostructure, Fig. 2a. The confinement potential for electrons is the conduction band offset between InAs and AlSb. The bound-state electron wavefunctions are able to penetrate the finite potential barriers and a change in the energy levels with respect to the infinitely deep well of the same width is observed. The energy levels and wavefunctions are determined numerically by a self-consistent solution of the Schrodinger-Poisson equations [17]. The band edges and wavefunctions are shown in Fig. 2b. The conduction sub-band dispersion relation, Fig. 2c, describes the allowed quantum mechanical states as a function of in-plane wavenumber (momentum),
for electrons confined in the growth direction but free in the plane of the quantum well.
Confinement alters the density of states from the parabolic form for three dimensional electrons to a step-like density of electronic states of the form m/rarft2, starting at £n, shown in 2d. The number of occupied subbands depends of the density of electrons and the temperature.
CONCLUSION
Electronic structure of the heterostructures is discussed, as well as the impact of defects on electronic properties and the application of these heterostructions for their use in different area.
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