Solid State Phenomena Vols. 205-206

Abstract: The lowest energetic configurations of metal impurities in 4^th row (Sc - Zn), 5^th row (Y - Cd) and 6^th row (Hf - Hg) elements in Ge crystals were determined with density functional theory calculations. It was found that the substitutional site is the lowest energetic configuration for most of the calculated metals in Ge. The most stable configurations of dopant (Ga, Sb) - metal complexes in Ge crystals were also investigated. Following results were obtained. (1) For Ga dopant, 1st neighbor T-site is the most stable for metals in group 3 to 7 elements while substitutional site next to Ga atom is the most stable for metals in group 8 to 12 elements. (2) For Sb dopant, substitutional site next to Sb atom is the most stable for all calculated metals. Binding energies of the interstitial metal M_i with the substitutional dopant D_s were obtained by the calculated total energies. The calculated results for Ge were compared with those for Si.

Abstract: The damaging factor of 15 MeV proton irradiation of n-Ge is investigated. The protons during irradiation went through thin samples and in this way effects of passivation are out of the scope of the report. As a result of irradiation, considerable losses of shallow donor states of group-V impurity atoms are observed. The removal rate of shallow donor states due to interactions of impurity atoms with intrinsic defects is found to be about 215 cm^-1. Most of the defects produced are electrically neutral in n-type material. The role of radiation-produced acceptors is of minor importance. The main stage of isochronal annealing is occurred over a temperature interval of T=250° to 400°C. After that point the electrical parameters are completely recovered. A model of generation processes of intrinsic defects under the proton irradiation is discussed.

Abstract: We present a model for charged dislocations effects on III-V compound semiconductor based FinFETs performance. The model is developed to obtain momentum relaxation time and, from it, key device performance parameters such as effective mobility, threshold voltage, and finally saturation drain current. We find out that charged threading edge dislocation density of a FinFET channel should be smaller than about 10⁷ cm^-2 to ignore the dislocation scattering impact on the device performance which is roughly one order more strict condition than previously known condition for wurtzite GaN.

Abstract: In this paper the effect of unstable luminescence in nitrides was studied, notably the phenomena of cathodoluminescent intensity rising under stationery electron beam irradiation with typical times of tens up to hundreds of seconds. Long-lasting impact by electron beam leads to changes of cathodoluminescence properties of irradiated area. The changes still remain even after keeping structures at room temperature for several days. Reversibility of this "memory effect" was examined. A model of effect observed was proposed and experimentally verified.

Abstract: The high-Al-content Al_xGa_1-xN alloys, x>0.70, and AlN is the fundamental wide-band-gap material system associated with the technology development of solid-state LEDs operating at the short wavelengths in the deep-UV (λ < 280 nm). Yet, their properties are insufficiently understood. The present study is intended to bring elucidation on the long-time debated and much speculated Si transition from shallow donor in GaN to a localized deep DX defect in Al_xGa_1-xN alloys with increasing Al content. For that purpose electron paramagnetic resonance is performed on a particular selection of high-Al-content epitaxial layers of Al_0.77Ga_0.23N, alternatively Al_0.72Ga_0.28N, alloy composition.

Abstract: The fabrication of thin-film transistor devices incorporating active semiconductors based on zinc oxynitride (ZnON) compound is presented. It is demonstrated that the addition of appropriate dopant, gallium, in ZnON, suppresses the formation of shallow donor, nitrogen vacancies, and significantly improves electrical characteristics of the resulting TFT. The Ga:ZnON devices with field-effect mobility values exceeding 50 cm²/Vs are achieved, which makes them suitable as switching or driving elements in next-generation flat-panel displays.

Abstract: Electronic properties of radiation damage produced in 4H-SiC by electron irradiation and its effect on electrical parameters of Junction Barrier Schottky (JBS) diodes were investigated. 4H‑SiC N‑epilayers, which formed the low‑doped N-base of JBS power diodes, were irradiated with 4.5 MeV electrons with fluences ranging from 1.5x10¹⁴ to 5x10¹⁵ cm^-2. Radiation defects were then characterized by capacitance deep-level transient spectroscopy and C-V measurement. Results show that electron irradiation introduces two defect centers giving rise to acceptor levels at E_C‑0.39 and E_C‑0.60 eV. Introduction rate of these centers is 0.24 and 0.65 cm^‑1, respectively. These radiation defects have a negligible effect on blocking and dynamic characteristics of irradiated diodes, however, the acceptor character of introduced deep levels and their high introduction rates deteriorate diode’s ON-state resistance already at fluences higher than 1x10¹⁵ cm^‑2.

Abstract: The aim of this work is study of point defects modification in silicon dioxide by a high power density electron beam. In this work we used the method which allows to estimate quantitative content of luminescent point defects by dependence of cathodoluminescence on current density. Content of point defects was evaluated and changing of point defect content in silicon dioxide under electron beam was assessed. It is shown that content of defect connected with silicon deficit decreases whereas content of defect connected with oxygen deficit increases. The model of point defects transformation was suggested on the basis of these results.

Abstract: Photon absorption in the solar energy range has been investigated in semiconductor nanostructures. Different synthesis techniques (magnetron sputtering, plasma enhanced chemical vapor deposition, ion implantation) followed by thermal annealing, have been employed to fabricate Si or Ge nanoclusters (1-25 nm in size) embedded in SiO₂ or Si₃N₄ matrices. The thermal evolution in the formation of Si nanoclusters (NCs) in SiO₂ was shown to depend on the synthesis technique and to significantly affect the light absorption. Experimentally measured values of optical bandgap (E_g^OPT) in Si NCs evidence the quantum confinement effect which significantly increases the value of E_g^OPT in comparison to bulk Si. E_g^OPT spans over a large range (1.6-2.6 eV) depending on the Si content, on the deposition technique and, in a most significant way, on the structural phase of NC. Amorphous Si NCs have a lower E_g^OPT in comparison to crystalline ones. The matrix effect on the synthesis and light absorption in semiconductor NCs was investigated for Ge NCs. Large difference in the Ge NCs synthesis occurred when using SiO₂ or Si₃N₄ matrices, essentially due to a much lower Ge diffusivity in the latter, which slows down the formation and growth of Ge NCs in comparison to silica matrix. Light absorption in NCs is also shown to be largely affected by the host matrix. Actually, Ge NCs embedded in Si₃N₄ material absorb photons in the solar energy range with a higher efficiency than in silica, due to the different confinement effect. In fact, Si₃N₄ host offers a lower potential barrier to photogenerated carriers in comparison to silica, thus a lower confinement effect is expected, leading to slightly smaller optical bandgap. These effects have been presented and discussed for potential application in light harvesting purposes.

Abstract: A possibility of formingquantum cones (QC) by Nd:YAG laser radiation on the surface of semiconductorssuch as Si and Ge crystals, and SiGe and CdZnTe solid solutions has been shown.A two-stage mechanism of quantum cone formation has been proposed. The first stage is generation and redistribution of point defects (impurity atoms and intrinsic point defects – vacancies and self-interstitials) in a temperature gradient field, the so-called thermogradient effect. As a result a new phase is formed on the irradiated surface, for example a Ge phase forms on the surface of a SiGe solid solution. The second stage is characterized by mechanical plastic deformation of the strained top layer leading to the formation of quantum cones, due to selective laser radiation absorption of the top layer. The first stage is more difficult for understanding of the physical processes which takeplace during of growth of QC, especially in pure intrinsic elementary semiconductors (Ge, Si) and compounds (CdTe, GaAs). Therefore, this research is focused on the investigation of the first stage of QC formation by laser irradiation. As a result of the investigation, a new mechanism for p-n junction formation in the elementary semiconductors and heterojunction in solid solutions by laser radiation as a first stage of QC formation is proposed.