Fast Surface States Research Articles

Structural Properties of Al-Doped ZnO Films

In this study, the results of the investigation of the influence of Al atoms on the structural characteristics of ZnO films obtained by the sol-gel method are presented. It has been determined that the glass substrates consist of subcrystallites with dimensions of 28.6 nm, having cubic unit cells with lattice parameters a = 0.3336 nm, and their surfaces belong to the crystallographic orientation (111). It has been identified that the grown thin ZnO films consist of subcrystallites with dimensions of 39.5 nm, having a wurtzite structure with lattice parameters a = b = 0.3265 nm and c = 0.5212 nm, respectively. It has been determined that at the boundaries of the division of these subcrystallites, polycrystalline regions with sizes of 12.6 nm, 28.3 nm, 30 nm, and 33 nm are formed. Additionally, nanocrystallites with sizes of 56.8 nm self-assemble on the surface areas of the deposited films. The increase in the values of the “c”axis of the hexagonal crystal lattice of ZnO films by 0.0009 nm when doping Al atoms from 1% to 5% is explained by the shift of the main structural line (002) at small angles (Δθ=0.12°). It has been established that nanocrystallites with lattice parameters аn = 0.5791 nm, belonging to the spatial group Fd3m, self-assemble on the surface areas of ZnO:Al films. the curve due to the presence of a monoenergetic level of fast surface states at the heterojunction.

Анализ вольт-фарадных характеристик МДП-структур с ALD Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- на n- и p-CdHgTe, стабилизированном сверхтонким собственным оксидом

Capacitance−voltage characteristics of metal dielectric semiconductor structures with atomic layer deposition Al2O3 on n- and p-Cd0.22Hg0.78Te (with and without a surface graded-gap layer) preliminary oxidized in oxygen glow discharge plasma (with the resulting oxide thickness of 2 nm) have been studied. The obtained structures reveal the positive fixed charge with a density of ∼ (1−6) · 10^11 cm^(−2). The ratio between a slow surface states density and a surface band gap width is almost independent on graded-gap layer presence, with the value of ∼ (4−8) · 10^11 cm^(−2) · eV^(−1). The proposed passivation approach provides near-ideal low-frequency capacitance-voltages characterized by weak influence of fast surface states. Films of CdHgTe grown without the graded-gap surface layer are proved to be much more sensitive to the process of oxidation in glow discharge plasma.

Исследование структур металл-диэлектрик-полупроводник на основе CdHgTe и HfO-=SUB=-2-=/SUB=-

The interface between Cd0.22Hg0.78Te and HfO2 grown by plasma-enhanced atomic layer deposition at a temperature of 120 ℃ in a specifically optimized deposition mode has been studied. The method used in this work for measuring the admittance of metal-dielectric-semiconductor structures made it possible to establish that their electrophysical parameters are uniform over the sample surface. The spectrum of fast surface states density at the HfO2 - Cd0.22Hg0.78Te interface has been calculated.

Investigation of metal-insulator-semiconductor structure based on CdHgTe and HfO-=SUB=-2-=/SUB=-

The interface between Cd0.22Hg0.78Te and HfO2 grown by plasma-enhanced atomic layer deposition at a temperature of 120oC in a specifically optimized deposition mode has been studied. The method used in this work for measuring the admittance of metal-dielectric-semiconductor structures made it possible to establish that their electrophysical parameters are uniform over the sample surface. The spectrum of fast surface states density at the HfO2-Cd0.22Hg0.78Te interface has been calculated. Keywords: CdHgTe, HfO2, ALD, C-V, passivating coating.

Studying C-V characteristics of MIS structures with ALD Al-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=- on n- and p-CdHgTe stabilized with ultra-thin native oxide

Capacitance--voltage characteristics of metal dielectric semiconductor structures with atomic layer deposition Al2O3 on n- and p-Cd0.22Hg0.78Te (with and without a surface graded-gap layer) preliminary oxidized in oxygen glow discharge plasma (with the resulting oxide thickness of 2 nm) have been studied. The obtained structures reveal the positive fixed charge with a density of ~(1-6)·1011 cm-2. The ratio between a slow surface states density and a surface band gap width is almost independent on graded-gap layer presence, with the value of ~(4-8)·1011 cm-2·eV-1. The proposed passivation approach provides near-ideal low-frequency capacitance-voltages characterized by weak influence of fast surface states. Films of CdHgTe grown without the graded-gap surface layer are proved to be much more sensitive to the process of oxidation in glow discharge plasma. Keywords: mercury cadmium telluride, film, surface states, plasma.

Anodic Passivation of InSb(100) by Sodium Sulfide Solution with Additional Sulfidization Pretreatment

The MIS-structures of InSb with anodically grown dielectric coating in galvanostatic mode in sodium sulfide solution were studied. Fast and slow surface states extracted by using the C–V characteristics method. The extracted values of Dit and NF were 2 × 1011 cm–2 eV–1 and 9.2 × 1010 cm–2, respectively. The hysteresis behavior was investigated. Additional sulfidation pretreatment using (NH4)2S–ethylenglycol solution lower the value of hysteresis and 25% reduce the interface state density. The arithmetic average roughness after anodizing increases from 0.6 to 0.9 nm, but preliminary sulfidation does not significantly affect this parameter. The formed dielectric coating has sufficient film continuity for its use as a passivating coating of InSb based FPA’s.

Effect of Process-Related Impurities on the Electrophysical Parameters of a MOS Transistor

It is established that the electrophysical characteristics of MOS transistors largely depend on the quality of a gate dielectric. The presence of an extra built-in charge in the dielectric and fast surface states at the SiO2/Si interface leads to both an increased threshold voltage and decreased saturation current and voltage, decreased slopes of the characteristics of the MOS transistor in the linear and saturation regions, and a decreased structure conductance in the linear region. The gate leakage currents also increase. It is shown that the view and shape of the capacity–voltage characteristics are determined by the value of an extra positive charge in the bulk of the dielectric and the density of fast surface states at the Si/SiO2 interface. These values are correlated to the profile of the distribution of the surface concentration of the process-related impurities adsorbed at the wafer surface during the manufacturing of the device, which allows us to judge the quality of the materials used, adherence to the production conditions, and, if necessary, correct them opportunely as required.

Effect of annealing on the electrophysical properties of CdTe/HgCdTe passivation interface by the capacitance–voltage characteristics of the metal–insulator–semiconductor structures

The capacitance–voltage characteristics of metal–insulator–semiconductor structures based on Hg1−xCdxTe (x = 0.218) with CdTe passivation are studied before and after the passivation annealing process. We found that after vacuum annealing at 300 °C for 24 h, the micromorphology of the passivation layer was significantly improved, and as the fixed charge density decreased from 1.3 × 1012 cm−2 to 1.0 × 1010 cm−2, the fast surface state density decreased from 2 × 1013 cm−2 eV−1 to 3 × 1012 cm−2 eV−1, with a minimum value of 1.2 × 1011 cm−2 eV−1. From these findings, combined with the secondary ion mass spectroscopy analysis, we conclude that the annealing process propagates an equivalent electrical surface for CdTe/HgCdTe uniformly from the principal physical interface to the inside of the bulk material, effectively improving the characteristics of the CdTe passivation layer.

Investigation of the effect of soft X-ray radiation on the electrophysical characteristics of n-CdxHg1-xTe epitaxial layers

The impact of soft X-ray radiation on the electrophysical characteristics of MIS structures formed on irradiated graded-gap MBE n-Cd0.24Hg0.76Te was investigated. It is established that the electron concentration, the differential resistance of the space-charge region in the strong inversion mode, and the spectra of fast surface states change nonmonotonically with increasing radiation dose. The results can be explained by the mechanism of the decay of electronic excitations.

The effect of fast and slow surface states on photoelectrochemical performance of hematite photoanodes fabricated by electrodeposition and hydrothermal methods

The hematite films prepared by electrodeposition (ED) and hydrothermal (HT) methods have similar nanorods morphology and the same length. However, the hematite prepared by HT method has higher photocurrent density and negative shift of onset potential. The samples are systematically characterized by scanning electron microscopy, UV–Vis spectra, X-ray diffractometry and photoelectrochemical measurements. The results reveal that the enhanced photoelectrochemical (PEC) performance of HT hematite is attributed to the superior surface charge injection efficiency, which is caused by a slower surface recombination rate rather than a more catalytically active hematite surface. And the slower surface recombination rate can be attributed to the absence of the slow surface states CSS2. This work provides an in-depth understanding of the reasons for the different PEC performance of hematite photoanodes fabricated by ED and HT methods, which is of certain significance in guiding the modification of hematite photoanodes prepared by the two typical routes in PEC water splitting system.

On the nature of the effect of adsorbed oxygen on the excitonic photoluminescence of ZnO

The mechanism of the effect of adsorbed oxygen on photoluminescence (PL) of ZnO powders and ZnO/Si ALD films in the UV–VIS regions was studied, simultaneously with the in-situ UV photoelectron spectroscopy (UPS) and mass spectrometry (MS) measurements. We have found a drastic (up to 10 times) increase of the exciton PL along with a slight (by ~ 1.5 times) increase of green PL induced by thermo-reducing of ZnO surface in H2 or CO atmosphere or by a UV–VIS photo-reducing in the vacuum. The reaction products H2O, CO2 and photo-desorbed O2 were registered by the MS. According to UPS (8.43eV), the change in PL is accompanied by a significant change in the surface dipole value δ without shift of the Fermi level EF or of the band bending VS. We believe that the slow surface states interact with the adsorbed oxygen and thus create a surface 2D-quantum well whose internal field destroys the excitons. The internal fast surface states not interacting with the slow ones provide a pinning of the Fermi level and the stability of the band bending value. The adsorbed oxygen also affects the surface defects thus reducing the VIS luminescence of ZnO.

Electrical characterizations of MIS structures based on variable-gap n(p)-HgCdTe grown by MBE on Si(0 1 3) substrates

Metal–insulator–semiconductor (MIS) structures based on n(p)-Hg1-xCdxTe (x = 0.22–0.40) with near-surface variable-gap layers were grown by the molecular-beam epitaxy (MBE) technique on the Si (0 1 3) substrates. Electrical properties of MIS structures were investigated experimentally at various temperatures (9–77 K) and directions of voltage sweep. The “narrow swing” technique was used to determine the spectra of fast surface states with the exception of hysteresis effects. It is established that the density of fast surface states at the MCT/Al2O3 interface at a minimum does not exceed 3 × 1010 eV−1 × cm−2. For MIS structures based on n-MCT/Si(0 1 3), the differential resistance of the space-charge region in strong inversion mode in the temperature range 50–90 K is limited by the Shockley-Read-Hall generation in the space-charge region.

Interface properties of MIS structures based on hetero-epitaxial graded-gap Hg1-xCdxTe with CdTe interlayer created in situ during MBE growth

Heterostructures based on n-Hg1-xCdxTe (x = 0.23–0.40) with near-surface graded-gap layers were grown by molecular beam epitaxy on Si (013) substrates. At 77 K, the admittance of the In/Al2O3/Hg1-xCdxTe metal-insulator-semiconductor (MIS) structures with grown in situ CdTe intermediate layer and without such a layer was investigated. It has been established that MIS structures of In/Al2O3/Hg1-xCdxTe with an interlayer of in situ grown CdTe are characterized by the electrical strength of the dielectric and the qualitative interface. The hysteresis of the capacitive characteristics is practically absent within a small range of variation in the bias voltage. The density of fast surface states at the minimum does not exceed 2.2 × 1010 eV−1 cm−2. MIS structures of In/Al2O3/Hg1-xCdxTe without an intermediate layer of CdTe have significantly higher densities of fast and slow surface states, as well as lower values of the differential resistance of the space-charge region in the regime of strong inversion.

New mechanism of semiconductor polarization at the interface with an organic insulator

A semiconductor—organic-insulator system with spatially distributed charge is created with a uniquely low density of fast surface states (N ss ) at the interface. A system with N ss ≈ 5 × 1010 cm–2 is obtained for the example of n-Ge and the physical characteristics of the interface are measured for this system with liquid and metal field electrodes. For a system with an organic insulator, the range of variation of the surface potential from enrichment of the space-charge region of the semiconductor to the inversion state is first obtained without changing the mechanism of interaction between the adsorbed layer and the semiconductor surface. The effect of enhanced polarization of the space-charge region of the semiconductor occurs due to a change in the spatial structure of mobile charge in the organic dielectric layer. The system developed in the study opens up technological opportunities for the formation of a new generation of electronic devices based on organic film structures and for experimental modeling of the electronic properties of biological membranes.

Capacitance-voltage characteristics of MIS-structures on the basis of graded-band MBE Hg1−xCdxTe at passivation by epitaxially grown in situ CdTe

The electrical properties of the interface between Hg1−xCdxTe (x = 0.22 and x = 0.32–0.36) and CdTe prepared in situ molecular beam epitaxy were estimated at 77 K. The methods of determination of main parameters of interface semiconductor/insulator and insulator from capacitance-voltage characteristics of MIS-structures based on graded-band Hg1−xCdxTe have been developed. The fixed charge states density, fast surface states density, and density of mobile charge are obtained from capacitance-voltage measurements. For improvement in stable and electrical strength of insulator coating for several samples over CdTe additional protective layers SiO2-Si3N4 are formed for x = 0.22 and ZnTe for x = 0.32–0.36.

Capacitance-voltage characteristics of MIS-structures on the basis of graded-band MBE Hg1−xCdxTe at passivation by epitaxially grown in situ CdTe

AbstractThe electrical properties of the interface between Hg1−xCdxTe (x = 0.22 and x = 0.32–0.36) and CdTe prepared in situ molecular beam epitaxy were estimated at 77 K. The methods of determination of main parameters of interface semiconductor/insulator and insulator from capacitance-voltage characteristics of MIS-structures based on graded-band Hg1−xCdxTe have been developed. The fixed charge states density, fast surface states density, and density of mobile charge are obtained from capacitance-voltage measurements. For improvement in stable and electrical strength of insulator coating for several samples over CdTe additional protective layers SiO2-Si3N4 are formed for x = 0.22 and ZnTe for x = 0.32–0.36.

Surface Preparation and Passivation of III-V Substrates for Future Ultra-High Speed, Low Power Logic Applications

III-V compound semiconductors have been recognized among the potential options for continuing transistor power-performance scaling owing to their ultra high charge carrier mobility. In order to realize their potential in high performance and lower-power digital logic applications, there must be strong gate control and a high Ion-Ioff ratio, achieved by integrating a stable, ultra thin high-K dielectric between the semiconductor and the gate [1, 2]. Unlike Si, which has long benefited from its very stable native oxide, III-V materials suffer from their poor native oxides that cause charge traps and Fermi level pinning at the semiconductor-oxide interface. Attempts to deposit high-K directly on III-V often produce MIS structures with fast surface state and CV instability [3].

Determination of Some Kinetic Parameters of Fast Surface States in Silicon Single Crystals by Means of Surface Acoustic Wave Method

The paper presents the acoustic method for determining some parameters of fast surface states in semiconductors. This method uses the interactions of the phonon{electron type for determining both the efiective carrier lifetime ? in∞uenced by the fast surface energetic states and the velocity g of the carrier trapped by the surface states. Some experimental results of the parameters ? and g in near-surface region of real Si(111) samples for their various surface treatments, obtained by the ofiered method, are presented.

Studies on surface processing and passivation of p-Hg1−xCdxTe

A mercury cadmium telluride (MCT) surface subjected to different processing steps of polishing, chemical and electrochemical etching has been examined using x-ray diffraction (XRD). The presence of several oxide phases as well as the elemental tellurium on the substrate surface has been revealed. It is shown that a combination of chemical and in situ electrochemical etching can effectively remove the defective layer containing the oxides as well as the surface tellurium. Cadmium sulfide films grown by a chemical deposition route have been investigated as a passivant for mercury cadmium telluride. The CdS films have been characterized using optical and x-ray diffraction techniques. Frequency-dependent low temperature capacitance measurements of the Au/Hg1−xCdxTe/CdS/Au structure have been used to investigate the electrical properties of the interface. It is shown that the in situ electrochemical etching prior to passivation results in the fabrication of metal–insulator– semiconductor (MIS) devices with low fast and slow surface state density and negligible hysteresis.

Characterization of CMOS sub-65 nm metallic contact by laser scattering: Thermal stability of Ni(Si 1− xGe x)

Very efficient in particles detection, light scattering also offers fast non-invasive full-mapping wafer surface state. This sensitivity was used in the case of germano-silicide process development. As a matter of fact, we report on haze measurement performances, compared to the usual methods used to investigate thermal stability of Ni(Si 1− x Ge x ), such as sheet resistance (SR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). We observed defectivity related to thermal agglomeration and Ge-segregation of Ni(Si 1− x Ge x ) on strain Si 1− x Ge x ( x ⩽ 30%) by haze measurement (like SEM observations) earlier than SR measurement. Moreover, we noticed that a high Ge content affects at lower temperature the stability of Ni(Si 1− x Ge x ) with a segregation phenomena.