M. Badylevich

Composition influence on the physical and electrical properties of SrxTi1−xOy-based metal-insulator-metal capacitors prepared by atomic layer deposition using TiN bottom electrodes

In this work, the physical and electrical properties of SrxTi1−xOy (STO)-based metal-insulator-metal capacitors (MIMcaps) with various compositions are studied in detail. While most recent studies on STO were done on noblelike metal electrodes (Ru, Pt), this work focuses on a low temperature (250 °C) atomic layer deposition (ALD) process, using an alternative precursor set and carefully optimized processing conditions, enabling the use of low-cost, manufacturable-friendly TiN electrodes. Physical analyses show that the film crystallization temperature, its texture and morphology strongly depends on the Sr/Ti ratio. Such physical variations have a direct impact on the electric properties of SrxTi1−xOy based capacitors. It is found that Sr-enrichment result in a monotonous decrease in the dielectric constant and leakage current as predicted by ab initio calculations. The intercept of the EOT vs physical thickness plot further indicates that increasing the Sr-content at the film interface with the bottom TiN...

Band alignment and electron traps in Y2O3 layers on (100)Si

Y2O3 films deposited by atomic vapor deposition on (100)Si with a 2 or 5 nm thick pregrown thermal SiO2 are investigated as possible charge trapping layers. Analysis of these structures using spectroscopic ellipsometry, photoconductivity, and internal photoemission reveals that Y2O3 has a 5.6 eV wide optical bandgap and a 2.0 eV conduction band offset with silicon. Photo(dis)charging experiments show that the optical energy depth of most of the traps exceeds 1.5 eV with respect to the Y2O3 conduction band, explaining the observed charge retention time of ∼108 s at room temperature, even in the absence of a blocking insulator.

Impact of magnetite nanoparticle incorporation on optical and electrical properties of nanocomposite LbL assemblies

Optical and electrical properties of polyelectrolyte/iron oxide nanocomposite planar films on silicon substrates were investigated for different amount of iron oxide nanoparticles incorporated in the films. The nanocomposite assemblies prepared by the layer-by-layer assembly technique were characterized by ellipsometry, atomic force microscopy, and secondary ion mass-spectrometry. Absorption spectra of the films reveal a shift of the optical absorption edge to higher energy when the number of deposited layers decreases. Capacitance-voltage and current-voltage measurements were applied to study the electrical properties of metal-oxide-semiconductor structures prepared by thermal evaporation of gold electrodes on nanocomposite films. The capacitance-voltage measurements show that the dielectric constant of the film increases with the number of deposited layers and the fixed charge and the trapped charge densities have a negative sign.

Electronic structure of the interface of aluminum nitride with Si(100)

The band alignment at the interfaces of Si(100) with amorphous (a-) and crystallized (c-) AlN layers was analyzed using internal photoemission and photoconductivity spectroscopy. The bandgap of thin a-AlN layers grown using atomic layer deposition is found to be 5.8±0.1 eV, widening to 6.5±0.2 eV after annealing induced crystallization into the wurtzite phase. Internal photoemission of electrons from the Si valence band to the AlN conduction band was found to exhibit the same energy threshold of 3.2±0.1 eV in amorphous and crystallized AlN. The energy band diagrams of a-AlN/Si(100) and c−AlN/Si(100) interfaces are established.The band alignment at the interfaces of Si(100) with amorphous (a-) and crystallized (c-) AlN layers was analyzed using internal photoemission and photoconductivity spectroscopy. The bandgap of thin a-AlN layers grown using atomic layer deposition is found to be 5.8±0.1 eV, widening to 6.5±0.2 eV after annealing induced crystallization into the wurtzite phase. Internal photoemission of electrons from the Si valence band to the AlN conduction band was found to exhibit the same energy threshold of 3.2±0.1 eV in amorphous and crystallized AlN. The energy band diagrams of a-AlN/Si(100) and c−AlN/Si(100) interfaces are established.

Electron Trap Energy Distribution in ALD Al2O3, LaAl4Ox, and GdyAl2-yO3 Layers on Silicon

The energy distribution of electron trap density in atomic layer deposited Al2O3, LaAl4Ox and GdyAl2-yO3 insulating layers was studied by using the exhaustive photodepopulation spectroscopy. Upon filling the traps by electron tunneling from Si substrate, a broad energy distribution of trap levels in the energy range 2?4 eV is found in all studied insulators with trap densities in the range of 1012 cm?2eV?1. The incorporation of La and Gd cations reduces the trap density in aluminate layers as compared to Al2O3. Crystallization of the insulator by the post-deposition annealing is found to increase the trap density while the energy distribution remains unchanged. The similar trap spectra in the Al2O3 and La or Gd aluminate layers suggest the common nature of the traps, probably originating from imperfections in the AlOx sub-network.

Electronic structure of NiO layers grown on Al2O3 and SiO2 using metallo-organic chemical vapour deposition

Analysis of electron states in nanometer-thin NiO layers grown by metallo-organic chemical vapor deposition on SiO2 or Al2O3 by means of spectroscopic ellipsometry and internal photoemission measurements points to the presence of a metal-like electron density, in correlation with the enhanced electrical conductivity of the films. These metallic states are suggested to be related to Ni clusters formed by partial reduction of NiO by hydrogen-containing by-products of the deposition reaction.

The effect of composition on the bandgap width in insulating NbxTayOz nanolayers

The bandgap width in niobium tantalate (NbxTayOz) films with Ta/(Ta+Nb) ratio of 10.7, 41.9, and 68.4 % are studied in this work. The samples were prepared by atomic layer deposition on (100)Si/TaN substrates, some of them subjected to crystallization annealing. Two photoconductivity spectral thresholds are found in all the studied samples: one at around 4.2 eV and another in range 3.2–3.8 eV, which may be correlated with the bandgaps associated with TaOx and NbOx sub-networks, respectively. The observed preservation of the narrowest bandgap of NbOx despite the addition of the Ta cation indicates that electron states of Nb and Ta have insufficient mutual interaction to affect the gap width of two oxide sub-networks.

Injection and trapping of electrons in Y2O3 layers on Si

We have investigated yttrium oxide (Y2O3) as a charge trapping layer for nonvolatile memory cells. The Y2O3 films of 7 to 55 nm thick were deposited by atomic vapour deposition on (100)Si with a 2 or 5−nm thick pregrown thermal SiO2 serving as a tunnel dielectric. Analyses of these structures using spectroscopic ellipsometry, photoconductivity and internal photoemission reveal that Y2O3 has a 5.6−eV wide optical bandgap and a conduction band offset of 2.0 eV with respect to silicon. Upon electron tunneling, an efficient oxide charging was observed. Photo-(dis)charging experiments reveal that the optical energy depth of most of the electron traps exceeds 2 eV with respect to the Y2O3 conduction band.

Integration of low dimensional crystalline Si into functional epitaxial oxides for next generation solar cell application

Si quantum dots (QD) embedded into Gd2O3 and Si quantum wells (QW) with epitaxial Gd2O3 as the barrier layers were grown on Si substrates. With decreasing dot size down to the 2-nm range, the optical absorption exhibits a spectacular shift in spectral threshold upto 2.9plusmn0.1 eV, as compared to the 1.12 eV absorption edge of the bulk Si crystal. Such shift suggests a significant influence of quantum confinement on the nanocrystal/oxide interface band diagram; the effect of which was observed to be predominantly caused by the upshift of the nanocrystal conduction band. Also, the Pt/Gd2O3/Si MOS capacitors comprised with Si nanoclusters display large hysteresis (~1.5-2 V) in capacitance-voltage measurements making them potential candidate of nonvolatile memory devices.