Silicon Doping Level Research Articles

Electrical phenomena in a metal/nanooxide/p +-silicon structure during its transformation to a resonant-tunneling diode

To investigate and develop novel silicon-based electronic components, the electro-physical effects in a metal-insulator-semiconductor (MIS) structure with nanometer size parameters, gained by enhancement of the silicon doping level up to NA ∼ 1019 cm−3 and reduction of the oxide thickness down to 0.4–4.0 nm, have been studied. As a result of such changes, the MIS nanostructure satisfies necessary and sufficient conditions for the electron resonant tunneling that can be observed at relatively low (some volts) reverse biases. Thereby a MIS capacitor can be transformed into a resonant-tunneling diode with substantial extension of its properties and functions.

Evaluation on residual stresses of silicon-doped CVD diamond films using X-ray diffraction and Raman spectroscopy

The effect of silicon doping on the residual stress of CVD diamond films is examined using both X-ray diffraction (XRD) analysis and Raman spectroscopy measurements. The examined Si-doped diamond films are deposited on WC–Co substrates in a home-made bias-enhanced HFCVD apparatus. Ethyl silicate (Si(OC2H5)4) is dissolved in acetone to obtain various Si/C mole ratio ranging from 0.1% to 1.4% in the reaction gas. Characterizations with SEM and XRD indicate increasing silicon concentration may result in grain size decreasing and diamond [110] texture becoming dominant. The residual stress values of as-deposited Si-doped diamond films are evaluated by both sin2ψ method, which measures the (220) diamond Bragg diffraction peaks using XRD, with ψ-values ranging from 0° to 45°, and Raman spectroscopy, which detects the diamond Raman peak shift from the natural diamond line at 1332 cm−1. The residual stress evolution on the silicon doping level estimated from the above two methods presents rather good agreements, exhibiting that all deposited Si-doped diamond films present compressive stress and the sample with Si/C mole ratio of 0.1% possesses the largest residual stress of ∼1.75 GPa (Raman) or ∼2.3 GPa (XRD). As the silicon doping level is up further, the residual stress reduces to a relative stable value around 1.3 GPa.

EFFECT OF THE STRUCURE OF SILICON P-N JUNCTIONS ON THEIR CHARACTERISTICS AS GAS SENSORS

Effect of the doping level of silicon p-n junctions was studied on their characteristics as ammonia vapors sensors. Numerical 2-D calculations of the non-equilibrium surface processes in p-n junctions, due to the adsorption of donor gas molecules, were performed. It is established that the mechanism of the sensitivity of sensors is changed with the increase in the impurities concentrations. Under a low doping level the sensitivity is due to the forming of a surface channel with electron conductivity. In highly doped structures the electron tunneling into the surface channel playsa significant role in the reverse surface current forming. The increase in the doping level results in a lowering of the background forward current of sensors and to a significant sensitivity decrease under low ammonia vapors concentrations.

Effect of the silicon doping level and features of nanostructural arrangement on decrease in external quantum efficiency in InGaN/GaN light-emitting diodes with increasing current

A comprehensive study of blue lightemitting diodes based on quantumwell InGaN/GaN struc� tures with external quantum efficiencies η of up to 40% has been carried out. It is shown that, in the general case, the manner in which the efficiency depends on the current density j is determined by the competition of contributions to the radiative recombination of localized and delocalized carriers. The contribution of the latter grows with worsening structural organization of the nanomaterial, increasing temperature and drive current, and decreasing width of the depleted layer in the active region (under zero bias). The steepest effi� ciency droop relative to the maximum value (by up to a factor of 2 at j ≈ 50 A cm -2 ) is observed in the case of heavy doping of the n + �region (to 10 19 cm -3 ) and upon appearance of compensated layers in the active or p + �region. At j > 50 A cm -2 , the contribution of delocalized carriers is predominant and the current dependences of efficiency are of uniform type, approximated with η(j) ∝ j -b , where 0.2 < b < 0.3.

Investigation of current‐voltage characteristics of p‐type silicon during electrochemical anodization and application to doping profiling

AbstractThe analysis of anodic current‐potential I‐V characteristics of p‐type silicon in concentrated hydrofluoric acid solution shows that the mechanism at the origin of porous silicon PS formation is determined by the charge exchange at the silicon surface over a Schottky barrier formed at the interface through a thermionic emission process. In addition, a negative potential shift in the I‐V characteristics is observed with increasing doping concentration which can explain the selective formation of PS towards the doping level of silicon. In fact, when a silicon wafer of different regions of doping concentration is anodized at a fixed current or potential, the dissolution current will be more important in regions of higher doping level and PS formation can only take place there. The property of selectivity is used in this work in order to determine the p‐type doping impurity profiles. During anodization under galvanostatic conditions of a specific test sample presenting dopant concentration variations, it is shown that the measured anodization potential varies according to silicon doping concentration. Consequently, by converting potential values to dopant concentration, and the electrolysis time to a depth scale, a doping impurity profile can be extracted. The profile using this technique appears to be in a good agreement with the secondary ion mass spectrometry (SIMS) analysis. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Local anodization of silicon as a step for electrical isolation process

The selective formation property of porous silicon PS is presented which is a basis step for the local electrical isolation process. In fact, when a silicon wafer of different doping concentration regions is anodized at a fixed potential, the dissolution current will be more important in the higher doping level regions where PS formation can only take place. The analysis of anodic current-voltage I-V characteristics of p-type silicon in the conditions corresponding to porous silicon formation shows a potential shift in the I-V characteristics with the silicon doping concentration which can explain the selectivity of PS formation towards the doping level of silicon. In addition, it is noticed that the mechanism at the origin of PS formation on p-type silicon in concentrated hydrofluoric acid solution is determined by the charge exchange at the silicon surface over a Schottky barrier which is formed at the interface through a thermionic emission process.

The effect of the internal capacitance of InGaN-light emitting diode on the electrostatic discharge properties

The electrostatic discharge (ESD) properties of the InGaN-light emitting diode (LED) were investigated in terms of the internal capacitance of the InGaN-LED. The LEDs with higher internal capacitance were found to be more resistant to external ESD impulses. The internal capacitance of the InGaN-LED was controlled by the silicon doping level of the n-GaN layer bordering the active layer. The human body model ESD yield at −500 V was increased from 27% to 94% by increasing the internal capacitance. Moreover, the high ESD pass yield was maintained up to −7000 V.

Nanorelief formation under ion irradiation of germanium and silicon surfaces

The surface topography of silicon and germanium single crystals formed under 10-keV Ar+ and Ne+ irradiation was studied experimentally. A relief with typical nanometer-scale dimensions is detected using atomic-force microscopy. It is established that the average height of the nanorelief formed depends on the silicon doping levels. It is also shown that the average height is determined by the parameters of ion irradiation.

Impact of substrate temperature on the incorporation of carbon-related defects and mechanism for semi-insulating behavior in GaN grown by molecular beam epitaxy

The electrical conductivity and deep level spectrum of GaN grown by molecular beam epitaxy and codoped with carbon and silicon were investigated for substrate temperatures Ts of 650 and 720°C as a function relative carbon and silicon doping levels. With sufficiently high carbon doping, semi-insulating behavior was observed for films grown at both temperatures, and growth at Ts=720°C enhanced the carbon compensation ratio. Similar carbon-related band gap states were observed via deep level optical spectroscopy for films grown at both substrate temperatures. Due to the semi-insulating nature of the films, a lighted capacitance-voltage technique was required to determine individual deep level concentrations. Carbon-related band gap states underwent substantial redistribution between deep level and shallow acceptor configurations with change in Ts. In light of a Ts dependence for the preferential site of carbon incorporation, a model of semi-insulating behavior in terms of carbon impurity state incorporation mediated by substrate temperature is proposed.

Influence of Pyridine Molecule Adsorption on Concentrations of Free Carriers and Paramagnetic Centers in Porous Silicon Layers

The influence of adsorption of donor pyridine (C5H5N) molecules on free-hole and defect concentrations in porous silicon layers differing in the morphology of composing nanocrystals and pores, as well as in the boron doping concentration, was studied using infrared and electron spin resonance spectroscopy. It was shown that the dependence of the hole concentration on the pyridine vapor pressure is controlled by the initial boron doping level of porous silicon, while the number of defects, i.e., dangling silicon bonds, is almost unchanged during adsorption for all sample types. For samples on substrates with a boron concentration of ∼1020 cm−3, a decrease in the number of holes at low pyridine pressures is observed and is attributed to hole capture by surface states of adsorbed C5H5N molecules. At pyridine pressures close to the saturated vapor pressure, the hole concentration in porous silicon layers increases, which is associated with hole “trap” depopulation due to an increase in the permittivity of the silicon nanocrystal neighborhood under conditions of C5H5N vapor condensations in sample pores.

Electrochemical Micromachining of p-Type Silicon

Electrochemical micromachining (ECM) of p-type Si substrates is accomplished in HF-based solutions by applying nanosecond potential pulses between the substrate and a tungsten tool electrode. With sufficiently high potential pulses, the silicon potential locally reaches the electropolishing regime and microstructures may be machined. ECM precision is investigated as a function of pulse height, pulse duration, solution composition, and silicon doping level. Results show that micrometer precision may be obtained with highly doped substrates and that experimental data can be explained within a simple model, taking the charging time of the interface capacitance into account. In highly doped p-Si, well-defined microstructures can be realized without application of a mask on the surface. In addition, the isotropy of the process allows fabrication of structures not constrained by the crystal direction. In the case of low-doped material, ECM is only possible for very short pulses (<3 ns).

LOW-NOISE SILICON-ON-INSULATOR HALL DEVICES

Hall sensors are used in a very wide range of applications. A very demanding one is electrical current measurement for metering purposes. In addition to high precision and stability, a sufficiently low noise level is required. Cost reduction through sensor integration with low-voltage/low-power electronics is also desirable. The purpose of this work is to investigate the possible use of SOI (Silicon On Insulator) technology for this integration. We have fabricated SOI Hall devices exploring the useful range of silicon layer thickness and doping level. We show that noise is influenced by the presence of LOCOS and p-n depletion zones near the edges of the active zones of the devices. A proper choice of SOI technological parameters and process flow leads to up to 18 dB reduction in Hall sensor noise level. This result can be extended to many categories of devices fabricated using SOI technology.

Intersubband Transitions in InxGa1-xAs/AlGaAs Multiple Quantum Wells for Long Wavelength Infrared Detection

ABSTRACTWe report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.

The role of impact ionization in the formation of reverse current-voltage characteristics of Al-SiO2-n-Si tunnel structures

Physical processes responsible for the reverse current-voltage (I-V) characteristics of Al-SiO2-n-Si structures with 1.2–3.2-nm-thick SiO2 and a silicon doping level of 1014-1018 cm−3 were analyzed. A new model describing the evolution of the hot-electron energy in structures of this kind is suggested. The roles played by Auger ionization and impact ionization are differentiated. The turn-on voltages of a tunnel MOS structure are studied both theoretically and experimentally. The turn-on voltage is shown to decrease with increasing oxide layer thickness.

Mechanisms of transport and injection of carriers into a porous silicon: Electroluminescence in electrolytes

A model describing the transport and injection of carriers into a heterophase system (silicon substrate)/(silicon nanocrystals)/(electrolyte) under excitation of electroluminescence is proposed. The main fraction of current passes from the electrolyte directly into a substrate by-passing the nanocrystals. Electromechanical processes at the electrolyte-substrate interface produce the electroactive particles, which inject one or both types of carriers in macro-and nanocrystals, respectively. For the bipolar injection, the nanocrystals play the role of catalyst in the exothermal reaction of charge exchange between the electroactive particles, which possess the opposite charges. In this case, the particles transfer the energy to nanocrystals, which they accumulated in the process of their formation. A fraction of this energy is released by the radiative recombination. The resulting efficient visible electroluminescence is weakly dependent on the doping level and conduction type of the initial silicon.

Transition metal defect behavior and Si density of states in the processing temperature regime

In order to make predictive models of transition metal gettering during semiconductor processing, a complete understanding of the process variables in high temperature ranges is essential. These variables are the internal gettering site density and capture radius, the intrinsic metal solubility, silicon doping level, the band gap, the effective density of states of the conduction and valence bands, and the transition metal defect level position in the gap. The least understood of these parameters is the temperature dependence of the transition metal defect level position. The work of Gilles et al. and McHugo et al. demonstrates that the doping enhancement of the solubility of Fe in p-type silicon vanishes at temperatures above 1000°C. They model this behavior by proposing movement at high temperature of the defect level for interstitial Fe from within the energy gap into the valence band. We explore the available models for Si effective density of states as a function of temperature and generate a third density of states model based on 0 K ab initio band structure calculations with the temperature-appropriate carrier occupations given by Fermi–Dirac statistics. We also consider uncertainty in EG in the processing temperature regime. We show that uncertainties in the Si intrinsic properties database in the processing temperature regime can account for the available dopant-enhanced solubility data by assuming that ET remain at a constant fraction of EG. To quantitatively model gettering processes at high temperatures, more reliable estimates are needed for the densities of states of the conduction and valence bands, EG and the behavior of defect levels as temperature rises.

Wafer level backside emission microscopy: dynamics and effects

Abstract Emission microscopes have been widely adopted as an important tool for analyzing failures in integrated circuits from the front surface. More recently, the development of multilevel metallization, flip chip and lead-on-chip package design has eliminated or greatly restricted this avenue of inspection. Inspection from the backside of semiconductors is an obvious alternative. However, this inspection is complicated by a ‘silicon filter effect’ strongly tied to the silicon doping level. To address this effect, a wafer thinning and polishing technique is used, as a companion paper describes. This paper first explores the relation of optical absorption characteristics of silicon to its carrier concentration and the remaining thickness. It will be shown that the wafer needs to be thinned to below 150 μm for heavily doped substrate. Next, the deflection and bending stress on the thinned wafer induced by the application of microprobing are calculated. The maximum number of probe pins allowed under different thinning conditions is quantified, leading to the conclusion that the traditional tungsten probe pins are to be replaced by those that produce lower probing force. A beryllium–copper, wire-based, Ultra-Low Force (ULF) probe card providing an acceptable alternative is shown.

Porous silicon for microelectronics and optoelectronics

Porous silicon is a material which is obtained by anodic dissolution of monocrystalline silicon in concentrated hydrofluoric acid solutions. Its structure consists of a network of interconnected pores of very small radii (in the range 1.5–20 nm) corresponding to porosities which can be varied up to 90% according to the formation parameters: silicon doping level, electrolyte composition and anodic current density. The formation mechanisms of porous silicon are briefly presented, and the main properties of the material are reviewed. It is shown that they are at the origin of different applications in the field of thin films for microelectronics and for microsensor technology. The interest in porous silicon has been renewed recently by the discovery of a bright emission of visible light at room temperature from high porosity porous silicon films. The main characteristics of this new property, which opens up possibilities for silicon based optoelectronics, are described and discussed in relation to the mechanisms proposed for the light emission. Recent results on the visible electroluminescence which is obtained either from electrolytic cells or from solid devices are also presented.

Porous silicon for microelectronics and optoelectronics

Porous silicon is a material which is obtained by anodic dissolution of monocrystalline silicon in concentrated hydrofluoric acid solutions. Its structure consists of a network of interconnected pores of very small radii (in the range 1.5–20 nm) corresponding to porosities which can be varied up to 90% according to the formation parameters: silicon doping level, electrolyte composition and anodic current density. The formation mechanisms of porous silicon are briefly presented, and the main properties of the material are reviewed. It is shown that they are at the origin of different applications in the field of thin films for microelectronics and for microsensor technology. The interest in porous silicon has been renewed recently by the discovery of a bright emission of visible light at room temperature from high porosity porous silicon films. The main characteristics of this new property, which opens up possibilities for silicon based optoelectronics, are described and discussed in relation to the mechanisms proposed for the light emission. Recent results on the visible electroluminescence which is obtained either from electrolytic cells or from solid devices are also presented.

Two-dimensional simulation of total dose effects on NMOSFET with lateral parasitic transistor

The trapped charge density in the LOCOS bird's beak resulting from irradiating a conventional NMOSFET has been analysed using a 2D finite element simulation. This paper shows a maximum of trapped charge density in the bird's beak region. The resulting voltage shift of the lateral parasitic transistor in the bird's beak region induces a high leakage current, and prevents any normal circuit operation. The silicon doping level, the supply voltage and the bird's beak shape are key parameters for device hardening of rad-tolerant technologies.