Influence of hydrogen on the volt-ampere and volt-farad characteristics of mis silicon tunnel diodes

The results of a joint analysis of volt-ampere and volt-farad characteristics of aPd−SiO _x -n-Si structure with a thin (3.7 nm) oxide tunnel layer are presented. It is shown that the forward-bias region of the volt-ampere characteristic can be used to identify the dependence of the surface potential ϕ_δ inSi on the voltage with consideration of the dielectric layer inhomogeneity as a function of the dielectric thickness. The probability of tunneling through theSiO _x layer is estimated for local regions with the least thickness equal to 1.3 nm. When the voltage increases from 0.1 to 0.7 V, the probability of tunneling decreases from 0.78 to 0.40, whereas the potential barrier height increases from 0.04 to 0.08 eV with consideration of the mirror image forces (given that the relativeSiO _x permittivity is equal to 3.9). In going from the room atmosphere to a gas mixture comprising 50 vol.% of hydrogen, the positive-charge density in the dielectric increases by 8·10⁻⁷ C/cm². Moreover, the voltage on flat bands and j _s decrease for local regions of a specimen with thin dielectric layers much more weakly than for most of the field electrode. V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 3–11, September, 1999.     

Room Temperature Spin Accumulation Effect in Boron Doped Si Created by Epitaxial Fe<Subscript>3</Subscript>Si/<Emphasis Type="Italic">p</Emphasis>-Si Schottky Contact

To study spin-dependent transport phenomena in Fe₃Si/p-Si structures we fabricated 3-terminal planar microdevices and metal/semiconductor diode using conventional photolithography and wet chemical etching. I?V curve of prepared diode demonstrates rectifying behavior, which indicates the presence of Schottky barrier in Fe₃Si/p-Si interface. Calculated Schottky barrier height is 0.57 eV, which can provide necessary conditions for spin accumulation in p-Si. Indeed, in 3-terminal planar device with Fe₃Si/p-Si Schottky contact Hanle effect was observed. By the analysis of Hanle curves spin lifetime spin diffusion length in p-Si were calculated, which are 145 ps and 405 nm, respectively (at T = 300 K). Spin lifetime strongly depends on temperature which can be related to the fact that spin-dependent transport in our device is realized via the surface states. This gives a perspective of creation of spintronic devices based on metal/semiconductor structure without need for forming tunnel or Schottky tunnel contact.     

Investigation of HfO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/<Emphasis Type="Italic">n</Emphasis>-Si(001)-based MOS structures via ballistic electron emission microscopy

(Au, Pt)/HfO₂/SiO₂/n-Si(001) metal-oxide-semiconductor structures with a thin (≈0.5 nm) SiO₂ layer, which is formed between HfO₂ and Si during atomic layer deposition of oxide layers, have been investigated via ballistic electron emission spectroscopy. The potential barrier heights at the (Au, Pt)/HfO₂ interfaces have been determined experimentally. The peculiarities observed in the curves of dependence of the collector current on the voltage between a scanning tunneling microscope probe and a metallic electrode are related to electron transport through the vacancy defect region of HfO₂ and the quantum-mechanical interference of electron waves arising from multiple reflections at the interfaces of the two-layer dielectric and at the interfaces of dielectric with a substrate and a metallic electrode.     

Properties of an Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si interface

The phase chemical composition of an Al₂O₃/Si interface formed upon molecular deposition of a 100-nm-thick Al₂O₃ layer on the Si(100) (c-Si) surface is investigated by depth-resolved ultrasoft x-ray emission spectroscopy. Analysis is performed using Al and Si L_{2, 3} emission bands. It is found that the thickness of the interface separating the c-Si substrate and the Al₂O₃ layer is approximately equal to 60 nm and the interface has a complex structure. The upper layer of the interface contains Al₂O₃ molecules and Al atoms, whose coordination is characteristic of metallic aluminum (most likely, these atoms form sufficiently large-sized Al clusters). The shape of the Si bands indicates that the interface layer (no more than 10-nm thick) adjacent to the substrate involves Si atoms in an unusual chemical state. This state is not typical of amorphous Si, c-Si, SiO₂, or SiO_x (it is assumed that these Si atoms form small-sized Si clusters). It is revealed that SiO₂ is contained in the vicinity of the substrate. The properties of thicker coatings are similar to those of the 100-nm-thick Al₂O₃ layer and differ significantly from the properties of the interfaces of Al₂O₃ thin layers.     

Metal-oxide-semiconductor characteristics of lanthanum cerium oxide film on Si

Metal-organic decomposed lanthanum cerium oxide (La _x Ce _y O _z ) film had been spin-coated on n-type Si substrate. Effects of post-deposition annealing temperature and time on the metal-oxide-semiconductor (MOS) properties of the film were studied. As temperature increased from 400 to 1000°C for 15 minutes dwell time, La _x Ce _y O _z demonstrated a decrease in interface trap density (D _it) and total interface trap density (D _total), which were related to the formation of SiO _x /silicates interfacial layer (IL). The lowest leakage current density and highest dielectric breakdown voltage (V _B) was obtained in 1000°C-annealed sample. When longer annealing times (30–120 minutes) were studied on the 1000°C-annealed sample, the sample annealed at 1000°C for 120 min showed the best MOS characteristics with V _B of 30 V. Reasons contributing to such observation were discussed.     

Anomalous temperature dependence of photoluminescence in GeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films and GeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiO<Subscript>2</Subscript> nano-heterostructures

The optical properties of GeO _x film and GeO _x /SiO₂ multilayer heterostructures (with thickness of GeO _x layers down to 1 nm) were studied with the use of Raman scattering and infrared spectroscopy, ellipsometry and photoluminescence spectroscopy including temperature dependence of photoluminescence. The observed photoluminescence is related to defect (dangling bonds) in GeO _x and interface defects for the case of GeO _x /SiO₂ multilayer heterostructures. From analysis of temperature dependence of photoluminescence intensity, it was found that rate of nonradiative transitions in GeO _x film has Berthelot type, but anomalous deviations from Berthelot type temperature dependence were observed in temperature dependences of photoluminescence intensities for GeO _x /SiO₂ multilayer heterostructures.     

Surface morphology of DyxOy films grown on Si

The crystalline structure and surface morphology of Dy_xO_y dielectric films grown on Si substrates were studied by grazing incidence diffraction and absorption with use of synchrotron radiation and by atomic force microscopy. The crystalline structure and the roughness of Dy_xO_y films were found to be strongly dependent on the deposition rate. The dielectric-silicon interface depends on the type of gas used in the annealing process. Moreover, results from the near edge X-ray absorption studies, have revealed that none of the examined films has a stoichiometry close to the Dy₂O₃. The level of stoichiometry is determined by the technological conditions. Nevertheless, MOS structures with Dy_xO_y films (EOT ∼ 23 Å) have shown a rather good Dy_xO_y-Si interface properties, which can be further improve by thermal annealing, and introducing of several additives, therefore Dy_xO_y films can be considered as suitable candidates for gate dielectric in MOS devices.     

Inherent diode isolation in programmable metallization cell resistive memory elements

The feasibility of a storage element with inherent rectifying or isolation properties for use in passive memory arrays has been demonstrated using a programmable metallization cell structure with a doped (n-type) silicon electrode. The Cu/Cu–SiO₂/n-Si cell used in this study switches via the formation of a nanoscale Cu filament in the Cu–SiO₂ film which results in the creation of a Cu/n-Si Schottky contact with soft reverse breakdown characteristics. The reverse bias leakage current in the on-state diode is dependent on the programming current employed as this influences the area of the electrodeposit and hence the area of the Cu/n-Si junction. The programming current also controls the on-state resistance of the device, allowing multi-level cell (MLC) operation, in which discrete resistance levels are used to represent multiple logical bits in each physical cell. The Cu/Cu–SiO₂/n-Si elements with heavily doped silicon electrodes were readily erasable at voltage less than −5 V which allows them to be re-programmed. Lightly doped silicon electrode devices were not able to be erased due to their very high reverse breakdown voltage but exhibited extremely low leakage current levels potentially allowing them to be used in low energy one-time programmable arrays.     

Electrical and dielectric properties of Al/HfO2/p-Si MOS device at high temperatures

The temperature dependence of capacitance–voltage (C–V) and conductance–voltage (G/w–V) characteristics of Al/HfO₂/p-Si metal-oxide-semiconductor (MOS) device has been investigated by considering the effect of series resistance (R_s) and interface state density (N_ss) over the temperature range of 300–400 K. The C–V and G/w–V characteristics confirm that the N_ss and R_s of the diode are important parameters that strongly influence the electric parameters in MOS device. It is found that in the presence of series resistance, the forward bias C–V plots exhibits a peak, and its position shifts towards lower voltages with increasing temperature. The density of N_ss, depending on the temperature, was determined from the (C–V) and (G/w–V) data using the Hill–Coleman Method. Also, the temperature dependence of dielectric properties at different fixed frequencies over the temperature range of 300–400 K was investigated. In addition, the electric modulus formalisms were employed to understand the relaxation mechanism of the Al/HfO₂/p-Si structure.     

Constant bias-temperature and constant charge-temperature agings for silicon oxide films of MOS devices

Effects of the conventional constant bias-temperature aging and newly reported constant charge-temperature aging on the silicon oxide films of MOS devices are theoretically and experimentally compared. Under the positive field condition, it is found that the movement of mobile ionic charges is different between these agings. In constant bias-temperature aging there appears an increasing peak electric fieldE _P at the SiO₂-Si interface and a constant gate voltageV _G during aging, while in constant charge-temperature aging there appears a constantE _p and a decreasingV _G .The time dependencies of the flatband voltageV _FB for both cases are consistent with the experimental results. Under the negative field condition, the trapping of the holes from Si into SiO₂ is important. It is found that the variation of the electric fieldE _i at the SiO₂-Si interface depends strongly on the aging method. An aging with constantE _i excludes the field variation effect during annealing, and can be achieved by the successive charge-temperature technique. Experimental results of these agings are given for comparison.     

Effect of ultrasonic treatment on the defect structure of the Si–SiO2 system

The effect of ultrasonic treatment (UST) on the defect structure of the Si–SiO₂ system by means of electron spin resonance (ESR), metallography, MOS capacitance technique and secondary ions mass-spectroscopy (SIMS) is presented. The non-monotonous dependence of the defect densities on the US wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres has been studied. It is shown that observed changes in the ESR intensity are caused by vibrational dissipative mechanisms which are a function of defect centre type and crystallographic orientation. The influence of the UST on the Si–SiO₂ interface properties depends on the time of oxidation. The density of point defects at the Si–SiO₂ interface can be reduced and its electrical parameters improved by an appropriate choice of the UST and oxidation conditions.     

Theoretical analysis of the gate capacitance inn-channel inversion layers on ternary chalcopyrite semiconductors in the presence of a quantizing magnetic field

An attempt is made to study theoretically, the dependence of the gate capacitance inn-channel inversion larges on ternary chalcopyrite semiconductors on a quantizing magnetic field, takingn-channel inversion layers on CdGeAs₂ as an example. It is found, on the basis of a newly derived electron energy spectrum of the above class of semiconductors, that the gate capacitance exhibits spiky oscillations with changing magnetic field and the oscillatory behaviour is in qualitative agreement with the experimental observation reported in the literature for the MOS structure of Hg_1–x Cd _x Te.     

Study of density of interface states in MOS structure with ultrathin NAOS oxide

The quality of the interface region in a semiconductor device and the density of interface states (DOS) play important roles and become critical for the quality of the whole device containing ultrathin oxide films. In the present study the metal-oxide-semiconductor (MOS) structures with ultrathin SiO₂ layer were prepared on Si(100) substrates by using a low temperature nitric acid oxidation of silicon (NAOS) method. Carrier confinement in the structure produces the space quantization effect important for localization of carriers in the structure and determination of the capacitance. We determined the DOS by using the theoretical capacitance of the MOS structure computed by the quantum mechanical approach. The development of the density of SiO₂/Si interface states was analyzed by theoretical modeling of the C-V curves, based on the superposition of theoretical capacitance without interface states and additional capacitance corresponding to the charges trapped by the interface states. The development of the DOS distribution with the passivation procedures can be determined by this method.     

The Au-SiO x -a-Si:H structures with very thin anodic oxide layers

Au-SiO _x -a-Si:H MIS structures with anodic oxide layers of thickness from 1.4 to 7.2 nm are investigated. The formation of the superthin SiO _x layers enables us to obtain photosensitive diode structures. These structures have a high photocurrent-to-dark current ratioi _ph/i _d >10⁴ and the dark resistanceR10¹⁰ for the reverse bias. The analysis of IR reflectance absorption spectra in the region of longitudinal Si-O stretching modes allows us to make a conclusion on the dependence of structure-chemical properties of superthin anodic oxids on their thickness.We thank Ing. J. Stuchlík from Czechoslovak Academy od Sciences for kindly manufacturing the a-Si:H films for us.     

Investigation of dielectric and electrical behaviour of nanocrystalline Zn1−xMnxO (x=0 to 0.10) semiconductors synthesized by mechanical alloying

The results on the measurement of electric and dielectric behaviour and capacitance–voltage characteristics of Zn_1−xMn_xO (x=0 to 0.10) nanocrystalline semiconductors are reported. Direct current conductivity increases with the increase Mn concentration and its thermal behavior can be explained by adiabatic polaronic hopping model. The alternating current conductivity obeys a power law of temperature and frequency. The temperature exponent p strongly depends on Mn concentration. The temperature dependence of frequency exponent s suggests that the overlapping large polaron conduction model is the appropriate conduction mechanism for the investigated samples. The interfacial boundaries and grain contribution to the dielectric properties can be identified by the analysis of complex impedance. Relaxation behaviour of the samples can be explained from the analysis of the electric modulus. Formation of Schottky diode can be described from capacitance–voltage characteristic of the samples and different diode parameters can be extracted from it.     

Anomalies of the static dielectric constant of Pb1−x Ge x Te

The static dielectric constant of Pb_1–x Ge _x Te (0x0.05) has been determined from differential capacitance measurements on Schottky-barriers in the temperature range of 4.2–300 K. A comparison with data deduced from the phonon frequencies via the Lyddane-Sachs-Teller relation shows substantial discrepancies which are attributed to lattice defects.Work supported by Jubiläumsfonds der Österreichischen Nationalbank     

Hole‐extraction layer dependence of defect formation and operation of planar CH3NH3PbI3 perovskite solar cells

Three planar CH₃NH₃PbI₃ (MAPbI₃) solar cells having the same structure except a hole‐extraction layer (HEL) showed distinctive difference in operation characteristics. Analysis of frequency‐dependent capacitance and dielectric‐loss spectra of the three MAPbI₃ devices showed two types of recombination‐loss channels with different time constants that we attributed respectively to interface and bulk defects. Discrepancy in defect formation among the three devices with a HEL of PEDOT:PSS, NiO_x, or Cu‐doped NiO_x was not surprising because grain‐size distribution and crystalline quality of MAPbI₃ can be affected by surface energy and morphology of underlying HELs. We were able to quantify interface and bulk defects in these MAPbI₃solar cells based on systematic and simultaneous simulations of capacitance and dielectric‐loss spectra, and current–voltage characteristics by using the device simulator SCAPS.

     

Electroluminescence properties of light emitting devices based on silicon nanocrystals

We have fabricated MOS devices where the dielectric layer consists of a substoichiometric SiO_x (x<2) thin film, annealed at 1100°C for 1 h to induce the separation of the Si and SiO₂ phases, with the formation of silicon nanocrystals (nc) embedded in the insulating matrix. We have studied the electroluminescence (EL) properties of such devices as a function of the current density and of the temperature. We have evaluated the excitation cross section of Si nc under electrical pumping at room temperature and at low temperature (12 K). Moreover, we have used the experimental EL intensities and decay times to evaluate the radiative rate as a function of the temperature.     

Burning carbon monoxide in the settling chamber of a hotshot wind tunnel for obtaining the CO<Subscript>2</Subscript> test gas

A method of formation and heating of CO₂ as a test gas in the settling chamber of a hotshot wind tunnel is considered. To form and heat CO₂, the chamber is filled with a source gas mixture of CO, O₂, and CO₂, and after initiation, these substances participate in an exothermic chemical reaction in accordance with the formula CO + 0.5 O₂ + xCO₂ = (1 + x)CO₂. A stoichiometric ratio of the concentrations of carbon monoxide CO and oxygen is used. Variation of the number of moles x of ballast CO₂ in the left part of the chemical formula allows changing the temperature of the resultant test gas in a wide range. Experiments in the IT-302M hotshot wind tunnel carried out at ITAM SB RAS have shown that a pressure increase during an isochoric process in the settling chamber due to the joint effect of heat released in the reaction CO + 0.5 O₂ and an electric charge provides the completeness of CO combustion almost equal to unity. The time of reaction completion at its initiation by an electric arc is no more than several milliseconds.     

Compositional effect of bcc Co100−x Fe x electrodes on magnetoresistance in AlO x -based magnetic tunnel junctions

The effect of the composition of ferromagnetic bcc Co_100−x Fe _x electrodes on tunneling magnetoresistance (TMR) of Co_100−x Fe _x /AlO _x /Co_100−x Fe _x /IrMn magnetic tunnel junctions was studied. The epitaxial growth of the bottom Co_100−x Fe _x electrode leads to a high-quality electrode and interface, which significantly enhances the TMR ratio and the desired effect for study. Other factors that could also affect TMR, such as interface roughness, tunneling barrier properties, and exchange-bias properties, were kept the same within the uncertainty of the experiment in order to minimize their effects. The observed TMR dependence on composition is attributed to the variation of the s-like electron densities of state of the bcc Co_100−x Fe _x electrodes with different compositions.