K. D. Shcherbachev

Metastable centers in AlGaN/AlN/GaN heterostructures

A set of AlGaN/AlN/GaN high electron mobility transistor structures with Al composition in the AlGaN barrier changing from 20% Al to 50% Al was grown by metalorganic chemical vapor deposition on sapphire and studied by capacitance-voltage (C-V) measurements, admittance spectroscopy, and deep level transient spectroscopy. C-V and admittance measurements were performed in the dark and after illumination. The results suggest the presence of high concentrations of deep negatively charged traps in the AlGaN barriers, producing shifts of the C-V characteristics to more positive voltages. The density of negatively charged centers can be increased by cooling at high reverse bias. These centers have a high barrier for the capture of electrons. Their thermal activation energy is estimated as 0.85 eV, while the optical ionization energy is ∼1.7 eV.

The microstructure of Si surface layers after plasma-immersion He+ ion implantation and subsequent thermal annealing

A set of complementary methods (high-resolution X-ray reflectivity, high-resolution X-ray diffraction, transmission electron microscopy and atomic force microscopy) were used to study structural changes in the surface Si layer after high-dose low-energy (2 keV) He+ plasma-immersion ion implantation and subsequent thermal annealing. This combination is proved to be a powerful tool for complete structural diagnostics of nanoscale He+ ion implanted Si layers, especially in the ultra-low-energy implantation regime.

Effect of energy density on the target on SnO2:Sb film properties when using a high-speed particle separator

SnO2:Sb thin films are grown by pulsed laser deposition with high-speed particle separation on quartz-glass substrates without post-deposition annealing under different deposition conditions in the range of the energy densities on the target from 3.4 to 6.8 J/cm2. Their optical, structural, and electrical properties are studied. It is found that the energy density on the target affects the SnO2:Sb film conductivity and transmittance. The optimum conditions of film growth by the droplet-free pulsed laser deposition method are determined. A resistivity minimum of 1.2 × 10–3 Ω cm is observed at an energy density on the target of 4.6 J/cm2, a substrate temperature of 300°C, and an oxygen pressure of 20 mTorr in the vacuum chamber during deposition.

Specific features of formation of radiation defects in the silicon layer in “silicon-on-insulator” structures

Specific features of formation of radiation defects in thin silicon layer of silicon-on-insulator (SOI) structures have been studied. It is shown that there are differences between variations in the structural and electrical properties of the thin silicon layer and those in bulk silicon crystals (with similar electrical characteristics) subjected to the same radiation effect. It is established that the embedded insulator in the SOI structure represents a barrier for motion of radiation-induced intrinsic interstitial silicon atoms, which brings about an increase in the dose of bombarding ions, which leads to the loss of single-crystallinity of the silicon layer in a SOI structure. It is shown that γ-ray irradiation with doses unaffecting the electrical conductivity of bulk silicon crystals appreciably affects the conductivity of the silicon layer in the SOI structures. In addition, variation in the conductivity of silicon layer is related to variation in the density of surface states at the interface between the silicon layer and the built-in insulator, rather than to generation of conventional radiation-induced structural defects in silicon.

Formation of nanoparticles containing zinc in Si(001) by ion-beam implantation and subsequent annealing

The formation of nanoparticles containing zinc in Si(001) substrates by the implantation of 64Zn+ ions and subsequent annealing in dry oxygen at 800 and 1000°C for 1 h is studied. The structure of the samples is studied by high-resolution transmission electron microscopy, X-ray diffraction, and photoluminescence spectroscopy. 20-nm zinc nanoparticles located at a depth of about 50 nm are revealed in the as-implanted sample. 10–20-nm pores are observed in the surface layer. Annealing leads to oxidation of the Zn nanoparticles to the Zn2SiO4 state. It is shown that the oxidation of Zn nanoparticles begins on their surface and at an annealing temperature of 800°C results in the formation of nanoparticles with the “соre–shell” structure. The X-ray diffraction technique shows simultaneously two Zn and Zn2SiO4 phases. ZnO nanoparticles are not formed under the given implantation and annealing conditions.

Defect structure transformation after thermal annealing in a surface layer of Zn-implanted Si(001) substrates

A combination of high-resolution X-ray diffractometry, Rutherford back scattering spectroscopy and secondary-ion mass spectrometry (SIMS) allowed the influence of structural transformations in the damaged layer of Zn-doped Si(001) substrates after a multistage thermal treatment to be revealed. The shape of the Zn SIMS profiles correlates with the crystal structure of the layer and depends on the presence of factors influencing the mobility of Zn atoms.

Structural changes induced by neutron irradiation and heat treatments in InSb single crystals

Structural transformations in InSb crystals exposed to fast neutrons (with energies E > 0.1 MeV) and to full-spectrum reactor neutrons with the ratio between the flux densities of slow and fast neutrons ϕsn/ϕfn ≈ 1 are studied. It is shown that, in regard to the effect of fast neutrons on the lattice spacing, two portions can be distinguished in its dependence on the irradiation dose. At small fluences of fast neutrons (Ffn < 2.5 × 1017 cm−2), no increase in the lattice spacing is observed. As follows from the diffuse X-ray scattering data, in this region of fluences, the clusters of vacancies dissociate and the number of small-sized interstitial-type clusters increases. At Ffn > 2.5 × 1017 cm−2, the lattice spacing increases linearly with increasing fluences of neutrons, and numerous small-sized vacancy clusters and interstitial clusters capable of trapping the Sn dopant atoms are formed. Heat treatment of the exposed samples at temperatures up to 400°C results in complete restoration of the lattice spacing.

Influence of annealing temperature and its atmosphere on the properties of zinc implanted silicon

The presented results characterize nanoparticle formation in n-Si(100) samples implanted with 50-keV 64Zn+ ions (the dose is 5 × 1016 cm‒2) at room temperature followed by heat treatment in an oxygen or nitrogen atmosphere at temperatures of 400–900°C. Defects and zinc concentration profiles are investigated via the Rutherford backscattering spectroscopy with the help of the channeling technique, in which 1.7-MeV He+ ions are scattered at an angle of 110°. The silicon surface layer is visualized using a transmission electron microscope equipped with an energy-dispersive microanalyzer. The surface topology of the implanted and annealed samples is studied via atomic-force microscopy. The implantation process is accompanied by the formation of a 150-nm-thick amorphous Si surface layer containing Zn nanoparticles with an average size of 4 nm, below which a radiation-damaged layer 50 nm thick is generated. After 800°C annealing in an oxygen atmosphere, a recrystallized single-crystal silicon layer with a complex ZnO/Zn2SiO4 phase is formed. After 800°C annealing in a nitrogen atmosphere, a recrystallized polycrystalline Si layer involving Zn nanoparticles is created.

Evolution of structural properties of Si(001) subsurface layer containing He bubbles by low temperature annealing

Transformation of microstructure of the buried He bubbles of silicon surface layer after He+ low energy plasma immersion ion implantation and subsequent low-thermal annealing were studied by high resolution X-ray diffraction and reflectivity, Rutherford backscattering spectroscopy, transmission electron and atomic force microscopy methods. The ion energies varied in the range 2 – 5 keV at constant exposure ion doses 5×·1017 cm-2. Formation of a three-layer structure (amorphous a-SiOx layer at the surface, amorphous a-Si layer with helium bubbles and buried helium bubbles heavy damaged tensile strained crystalline c-Si layer) that is retained after annealing was observed. Helium-filled bubbles are observed in an as-implanted sample. Evolution of the multilayer structure and the bubbles due to annealing are revealed and comparing with the structural parameters of an as-implanted sample was done. The bubbles are shown to trend into two-model distribution after annealing. The characteristic bubble size is determined to be in a range of 2–20 nm. Large size helium-filled bubbles are located in the amorphous a-Si layer. Small size bubbles are revealed inside the damaged crystalline Si layer. These bubbles are a major source of tensile strain in c-Si layer.

Mo/Al/Mo/Au-based ohmic contacts to AlGaN/GaN heterostructures

Mo/Al/Mo/Au metallization scheme as an ohmic contact to undoped AlGaN/GaN heterostructures was investigated. The optimal thicknesses of the metal layers were determined: Mo (10 nm)/Al (60 nm)/ Mo (50 nm)/Au (50 nm). The specific contact resistance of the fabricated ohmic contact is 4.7 × 10–7 Ohm cm2 (0.14 Ohm mm). The microstructure of the contact after annealing was investigated using scanning and transmission electron microscopy, X-ray diffractometry and energy-dispersive X-ray spectroscopy. It is shown that a noticeable alloying of metallization into semiconductor upon annealing does not occur, but strong mixing of metals takes place. X-ray diffraction analysis demonstrated the presence of interfacial compounds, namely, Al2Au, Al3 + xMo1–x, AlMo3, Al12Mo, GaMo3 and GaAu2. Investigations of the phase composition of films depending on the thickness ratio of the metallization layers have shown that the formation of Al2Au phase has a negative effect on the contact surface morphology, and the formation of GaMo3, AlxMoy phases likely plays the most important role in the ohmic contact formation, which was also confirmed by the method of energy-dispersive analysis.