Analysis of inherent potential nonuniformities at the extrinsic-semiconductor surface

The concept of an inherent dimensional effect in depleted semiconductor layers (comparability of the characteristic scale of a depleted layer to an average distance between electrically active defects) is introduced. Inherent nonuniformities of an electric field and the potential at the semiconductor surface are determined for intrinsic and impurity surface states. The dependence of these nonuniformities on surface and bulk parameters is considered.     

On the impedance spectroscopy of structures with a potential barrier

A detailed analysis of the spectral dependences of the real and imaginary components of the measured impedance of a simulated silicon p-n junction is carried out within the framework of a conventional equivalent circuit (parallel R _d C _b chain and series resistance R _s). A simple technique was proposed for determining the true value of the barrier capacitance of structures with a potential barrier (without surface electrically active states) on the basis of analysis of the spectral dependence for the imaginary part of the measured impedance.     

Interface states under LOCOS bird's beak region

A method has been developed which allows the extraction of the density of electrically active defects in the bird's beak region of LOCOS isolation of a MOS structure. The measurements were performed on a special structure with enhanced edge effects using quasi-static techniques. The experimental results are compared with simulations using a model which allows for the inclusion of surface states in the bird's beak region. It is found that the best fit is obtained for a uniform energy distribution with N_ss = 1E12 cm⁻² eV⁻¹, while the states are situated in the bird's beak region up to 1800 Å from the gate oxide edge.     

Tunable Dielectric Function in Electric‐Responsive Glass with Tree‐Like Percolating Pathways of Chargeable Conductive Nanoparticles

The design of nanostructured materials with specific physical properties is generally pursued by tuning nanoparticle size, concentration, or surface passivation. An important step forward is to realize “active” systems where nanoparticles are vehicles for controlling, in situ, some specific, tuneable features of a responsive functional material. In this perspective, this work focuses on the rational design of a nanostructured glass with electrically tuneable dielectric function obtained by injection and accumulation of charge on embedded conductive nanocrystals. This enables electrically controlled switching of semiconducting nanophases to charged polarisable states to be achieved, which could lead to smart, field‐enhancement applications in nanophotonics and plasmonics. Here, it is shown that such response switching can be obtained if a percolating charge‐transport mechanism is activated through a disordered tree‐like network, as is demonstrated to be possible in SiO₂ films where suitable dispersions of SnO₂ nanocrystals, with conductive interfaces, are obtained as a result of a new synthesis strategy.     

A study of grown-in impurities in silicon by deep-level transient spectroscopy

Deep levels due to various impurities incorporated into Czochralski silicon ingots during crystal growth have been delineated. The largest impurity-induced deep-level concentration, defined as the electrically active impurity concentration, is found to be a fraction of the metallurgical impurity content of the crystals. This fraction for a specific impurity depends on the thermal history of the sample and the ability of the impurity to diffuse. POCl₃ gettering of Ti and V produces a decreasing electrically active impurity concentration toward the surface of a silicon wafer, while there is no observable effect of this heat treatment on the Mo concentration. In the case of Cr, which diffuses much more rapidly than Mo, Ti, or V in silicon, a very significant reduction in the electrically active concentration is observed after heat treatment. Similarly, in metal-doped polysilicon wafers the electrically active Mo concentration appears unaffected by grain boundaries, but the electrically active Cr concentration at or near some grain boundaries is reduced by more than an order of magnitude compared to that at grain centers.     

Hopping ε2 conductivity of boron-doped a-Si:H films annealed in hydrogen at high temperature

It is shown that the high-temperature annealing in hydrogen flow results in substantial modification of the temperature dependence of the conductivity of boron-doped and undoped a-Si:H films. For doped films subjected to annealing, the ε₂ conductivity related to hopping between localized states near the valence-band edge appears in the intermediate temperature range, along with the contributions of the band conductivity and the variable-range hopping conductivity. The ε₂ conductivity becomes possible due to an increase in the concentration of electrically active boron atoms and to the appreciable shift of the Fermi level after high-temperature annealing of doped films in hydrogen atmosphere. The experimentally measured parameters of the ε₂ conductivity make it possible to determine the width of the energy region, in which the density of localized states near the valence band falls off nonexponentially.     

A novel technique for in-line monitoring of micro-contamination andprocess induced damage

The use of a simple, rapid and nondestructive technique for inline monitoring of electrically active impurities introduced during wafer fabrication is reported. This AC surface photovoltage-based technique can determine the substrate doping type, doping concentration, oxide charge, and energy distribution of interface traps on both bare and oxidized silicon wafers without the formation of gate electrodes and substrate contacts. The technique is shown to have good reproducibility and resolution for quantifying the electrically active impurities, on the order of 1×10¹⁰ q/cm². Detection of contaminants and static charges by this technique is shown to correlate well with the electrical performance of thin dielectrics. The use of this technique for inline monitoring of very low levels of plasma-induced damage in the SiO₂/Si system is also discussed as is the potential for this tool in reducing furnace downtimes and in prompt identification of the source of contamination     

Processing and reconstruction effects on Al-GaAs(100) barrier heights

We have used low-energy electron diffraction, soft x-ray photoemission, and cathodoluminescence (CLS) spectroscopies to investigate the effects of the GaAs(100) surface geometry and composition on the formation of electrically active interface states at Al-GaAs(100) contacts. Clean GaAs(100) surfaces in the 350 to 620°C annealing temperature range undergo large compositional, structural, and electronic changes with temperature. Aluminum thin film deposition induces new discrete deep level CLS features between ∼0.80 and 1.20 eV photon energy, whose properties depend sensitively and systematically on surface annealing temperature and/or reconstruction. Fermi level (E_F) stabilization energies at these interfaces span the range from 0.58 eV above the valence band maximum (E_v) for an arsenic-rich starting surface to 0.46 eV above E_v for a gallium-rich starting surface. Correlation between the aluminum-induced deep level energies and the interface E_F position suggests an important role of localized bandgap states in determining the interface barrier height. The sensitivity of these states to starting surface composition and reconstruction may open new possibilities for tailoring Schottky barrier properties.     

Electrical properties of anisotype heterojunctions n-CdZnO/p-CdTe

Anisotype surface-barrier n-Cd_0.5Zn_0.5O/p-CdTe heterojunctions are fabricated by the high-frequency sputtering of a Cd_0.5Zn_0.5O alloy film onto a freshly cleaved single-crystal CdTe surface. The main electrical properties of the heterojunctions are studied and the dominant mechanisms of charge transport are established, namely, the multistage tunnel-recombination mechanism under forward bias, Frenkel-Pool emission, and tunneling under forward bias. The influence of the surface electrically active states at the heterojunction interface is analyzed and their surface concentration is evaluated: N _ss ?? 10¹⁴ cm^?2.     

Analysis of frequency dependences of conductance of MIS structures with the fluctuation-and tunneling-based theoretical models taken into account

A method for analyzing the frequency dependences of normalized conductance of MIS structures taking into account the effects of the surface-potential fluctuations and penetration of electrically active states deeper into the insulator is suggested. The parameters for estimating the broadening of the dependences are chosen. Analytic expressions for these parameters are derived. A method for separating the effects of the tunneling-and fluctuation-based mechanisms of broadening on the form of the conductance’s frequency dependence is suggested.     

Photoinduced relaxation of metastable states in (<Emphasis Type="Italic">a</Emphasis>-Si:H):B

The kinetics of thermal relaxation of an ensemble of photoinduced metastable electrically active B atoms in (a-Si:H):B films is studied after partial relaxation of the ensemble in the dark and under illumination of various intensities and duration. The parameters of a stretched exponential function that describes the ensemble kinetics are determined. It is found that photoinduced relaxation of metastable states manifests itself under conditions in which its rate exceeds the rate of the states’ photoinduced generation. It is shown that the variations in the relaxation-time distribution function of metastable states caused by thermal and photoinduced relaxation are similar.     

Electrical properties of ZnSe crystals doped with transition elements

The conductivity and photoconductivity of ZnSe crystals doped with transition elements are studied. It is shown that the doping of ZnSe crystals with 3d impurity elements is not accompanied by the appearance of electrically active levels of these impurities. At the same time, the introduction of these impurities into the cation sublattice brings about the formation of electrically active intrinsic defects. It is established that ZnSe crystals doped with Ti, V, Cr, Fe, Co, or Ni exhibit high-temperature impurity photoconductivity. Photoconductivity mechanisms in the crystals are proposed. From the position of the first ionization photoconductivity band, the energies of ground states of 3d ²⁺ ions in ZnSe crystals are determined.     

Surface passivation of HgCdTe by CdZnTe and its characteristics

In this paper, we report the results of capacitance-voltage measurements conducted on several metal-insulator semiconductor (MIS) capacitors in which HgCdTe surfaces are treated with various surface etching and oxidation processes. CdZnTe passivation layers were deposited on HgCdTe surfaces by thermal evaporation after the surfaces were etched with 0.5?2.0% bromine in methanol solution, or thin oxide layers (t_ox ～ few ten Å) were grown on the surfaces, in order to investigate effects of the surface treatments on the electrical properties of the surfaces, as determined from capacitance-voltage (C-V) measurements at 80K and 1 MHz. A negative flat band voltage has been observed for MIS capacitors fabricated after etching of HgCdTe surfaces with bromine in methanol solutions, which is reported to make the surface Te-rich. It is inferred that residual Te on the surface is a positive charge, Te⁴⁺. C-V characteristics for MIS capacitors fabricated on oxide surfaces grown by air-exposure and electrolytic process have shown large hysteresis effects, from which it is inferred that imperfect and electrically active oxide compounds and HgTe particles near the surface become slow interface states.     

Nonradiative recombination at shallow bound states in quantum-confined systems in an electric field

The one-phonon recombination of carriers at shallow impurity states in parabolic quantum wells in a longitudinal electric field is investigated. It is shown that one-phonon recombination processes are more active in quantum-confined systems than in the bulk material. The possibility of electrically induced one-phonon transfer in a confined system is discussed. Fiz. Tekh. Poluprovodn. 33, 97–100 (January 1999)     

Temperature dependence of turn-on voltage of gold-doped MOSFETs

The temperature dependence of the turn-on voltage of gold-doped and control n- and p-channel MOSFETs has been measured. To account for the large positive shift of turn-on voltage, VT Au, of gold treated n- and p-channel devices, it has been proposed that the gold eliminates the fast interface traps of continuous energy distribution, and that additional acceptor states very close to the valence band can cause additional charge QA Au, which can dominate the effect of acceptor and donor levels of gold ions in the silicon surface space charge region, and can also over-compensate the surface state charge, Qss. To fit the theoretical VT Auversus T curve to experimental curves, an accumulation of electrically active gold within the surface space charge region has been considered in n-channel devices and depletion in p-channel devices.     

High-temperature spreading-resistance profiling for the characterization of impurity distributions in n-type silicon

We have developed the technique of high-temperature spreading-resistance profiling (HT-SRP) for the characterization of electrically active impurities or defects in semiconductors. As a major feature, HT-SRP together with the well-established SRP method at room temperature combines the accurate resolution of an impurity profile with a determination of the defect states that control the electronic properties of the semiconductor. Some basic aspects of this technique are demonstrated on Si samples diffused with sulfur or selenium.     

Mechanism of drain current droop in GaAs MESFETs

The mechanisms responsible for the drain current droop in GaAs MESFETs are discussed and their relative contributions evaluated. Contrary to a common belief that the cause is mainly self-heating, it is shown on the example of a power MESFET that deep level effects (surface states and bulk traps) have a higher contribution     

Scanning Kelvin Probe Microscopy on Bulk Heterojunction Polymer Blends

Here, correlated AFM and scanning Kelvin probe microscopy measurements with sub‐100 nm resolution on the phase‐separated active layer of polymer‐fullerene (MDMO‐PPV:PCBM) bulk heterojunction solar cells in the dark and under illumination are described. Using numerical modeling a fully quantitative explanation for the contrast and shifts of the surface potential in dark and light is provided. Under illumination an excess of photogenerated electrons is present in both the donor and acceptor phases. From the time evolution of the surface potential after switching off the light the contributions of free and trapped electrons can be identified. Based on these measurements the relative 3D energy level shifts of the sample are calculated. Moreover, by comparing devices with fine and coarse phase separation, it is found that the inferior performance of the latter devices is, at least partially, due to poor electron transport.     

Analytical threshold voltage model for cylindrical surrounding-gate MOSFET with electrically induced source/drain extensions

Physics-based analytical threshold voltage model for cylindrical surrounding-gate MOSFET with electrically induced source/drain extensions is presented. The effect of inversion carriers on the channel’s potential is considered in presented model. Using this analytical model, the characteristics of EJ-CSG are investigated in terms of surface potential and electric field distribution, threshold voltage roll-off, and DIBL. Results show that the application of electrically induced S/D extensions to the cylindrical surrounding-gate MOSFET will successfully suppress the hot-carrier effects, threshold voltage roll-off, and DIBL. It is also revealed that a moderate side-gate bias voltage, a small gate oxide thickness, and a small silicon channel radius are needed to improve device characteristics. The derived analytical model is verified by its good agreement with the three-dimensional numerical device simulator ISE.     

Scanning the Issue: 3-D Integration Technologies

This issue responds to the observation that only the surface of an integrated circuit is electrically active; it explores three-dimensional techniques to extend Moore's Law by a variety of approaches including the thinning and stacking of chips.