The charge neutrality level in w-AlxGa1−x N solid solutions

Abstract

537.311.322Energy positions of the charge electroneutrality level (CNL) and neutral vacancy levels of nitrogen are calculated for w-GaN, w-AlN, and w-Al x Ga 1-x N versus solid-solution composition x in the virtual-crystal approximation. It is shown that within the whole range of the w-Al x Ga 1-x N compositions, the CNL is located in the upper half of the band gap, which results in the n-type conductivity of this material upon exposure to high-energy radiation.The concept of local charge electroneutrality (the "neutral" point) is widely used for analyzing energy-level diagrams of unstressed interfaces, estimating electrophysical characteristics of defect semiconductors, and calculating equilibrium levels of doping materials by chemical impurities [1][2][3][4][5][6][7]. The charge electroneutrality level acts as a fundamental crystal parameter identical for all isotype semiconductors with similar type of chemical bonds. Thus, within a unified concept, we can obtain the most important parameters of interfaces (Schottky-barrier height and band discontinuities in semiconductor heteropairs), calculate the electrophysical properties (conductivity type, limiting Fermi level, and specific-resistance rate) of defect semiconductor materials upon exposure to high-energy radiation or severe plastic deformation, and estimate the limiting equilibrium levels of semiconductor doping by hydrogen-like (shallow) chemical impurities. That is why this problem currently attracts considerable attention.In recent years, the group A 3 N nitrides including solid solutions and heterostructures on their basis are of great interest as candidate materials for rf electronics and semiconductor optics. However, the practical use of these compounds is limited by the high concentration of growth defects, mainly in the nitrogen sublattice (~10 19 cm -3 ), caused by high synthesis temperatures and volatility of the nitrogen components. The exposure to high-energy radiation is known to change the electron characteristics of materials (conductivity type, specific-resistance rate, and Fermi-level position) due to the formation of defect states in the band gap of the semiconductor crystal. This is widely used in radiation technology to control electrophysical, optical, recombination, and other properties of semiconductors. These studies are of great importance for investigations into tolerance of semiconductor materials and devices to high-energy radiation. Hence, studying the intrinsic lattice defects and their influence on the properties of wide-band A 3 N group nitrides is one of the most topical problems of materials science and technology.In this work, the energy dependence of the local charge electroneutrality level in w-GaN, w-AlN, and solid solutions on their bases is studied using the calculation methods we developed earlier. The correlation between the CNL position and the energy positions of neutral vacancy levels for nitrogen (neutral nitrogen vacancy is one of the major growth defects in these compounds) is analyzed.The band structure of w...

A model of the intimate metal-semiconductor Schottky-barrier contact

“…By this is meant that the model is incorrect in the general case. A new model of intimate contact is proposed, according to which the Fermi-level pinning at the contact is due to high density of electron surface states of one or another origin [2,[4][5][6][7][8][9] in equilibrium with the metal, whereas the distortions of IV characteristics (deviations from ideality) are due to the continuous (and/or discrete) spectrum of the NSS states in equilibrium with the semiconductor, which are energy-and coordinate distributed in the general case. The distortions of IV characteristics are directly caused by the barrier-height variation (due to the barrier-shape variation) resulting from the change in the NSS charge when a bias voltage is applied.…”

“…Further, we can lean upon a traditional mechanism of the Fermi-level pinning due to high density of "purely"electron surface states of one origin or another [2,[4][5][6][7][8][9] in equilibrium with the metal and consider the effect of NSS on the IV characteristics of contacts within this modified model.…”

“…However, the well-known data (see, for example, [4]) show that the contacts manufactured by means of certain techniques (molecular-beam epitaxy or interphase interaction under thoroughly prepared conditions) show no foreign inclusions (insulating layers) at the MS-interface, and we deal with intimate MSSBCs. This fact was widely used in construction of more recent models of metal-semiconductor contacts explaining the mechanism of the Fermi-level pinning in intimate contacts [4][5][6][7][8].…”

Correlation between energy positions of deep intrinsic point-defect levels and a limiting fermi level in irradiated III–V semiconductors

“…In estimations of the "neutral" point energy position in crystals using different heuristic models, the position is identified with 1) the position of local-charge electroneutrality level E lnl for defect (gap) states of the crystal [2,3], 2) the energy position of the model amphoteric local gap state E all [4], and 3) the energy position of the deepest (most localized) defect state E DL of the crystal within the limits of its dielectric gap [5]. The energy positions of the corresponding model levels calculated using these data are in good agreement with the experimental values F lim for the irradiated semiconductors [3][4][5].…”

Effect of electron irradiation on InAs〈Sn〉 microcrystals grown by chemical transport method

“…In fact, according to theoretical investigations, the value of F lim in a defect semiconductor is the intrinsic (fundamental) parameter of a crystal and is identified with the positions of charge-neutrality level of the defect states of the semiconductor (E cnl ) [8], level of a local amphoteric defect (E lnl ) [9], level of the deepest crystal defect (E dl ) [10] in the energy interval in the vicinity of its forbidden band, or with the midgap between the conduction and valence bands of the crystal averaged over the first Brillouin zone (<E G >/2) [8].…”