Boron Doping Level Research Articles

Temperature Sensor On Boron Ion Implanted Diamond

ABSTRACTp-type semiconducting boron doped layers have been fabricated on diamond substrates by ion implantation and subsequent annealing. A number of the related published experimental data and theoretical models on electrical properties of boron doped diamond are analyzed with regard to the temperature coefficient of resistance (TCR) of temperature sensors. The dependencies of the conductivity and activation energy on three parameters: (i) boron doping level NA, (ii) electrical compensation ratio ND/NA- C and (iii) duration of the postimplantation annealing time ta are studied. By variation of NA, C and t, an optimized technological regime for the temperature sensor fabrication can be obtained. One can summarize that: 1) the TCR value is not remarkably reduced with the boron concentration up to NA -1019 cm-3, 2) an increase of the electrical compensation decreases the activation energy and consequently the TCR coefficient,3) 1 h annealing at 1500°C is sufficient to remove the compensating radiation defects, 4) the variation of the ta from 1 min to 1 h changes the TCR value by 20% to 30%. Technological steps of the fabrication of a micro temperature sensor are given.

Silicon on Insulator Structures Obtained by Epitaxial Growth of Silicon over Porous Silicon

Epitaxial silicon films are obtained by low temperature chemical vapor deposition on porous silicon layers (PSL). The PSL are formed on lightly and highly boron doped silicon substrates. In the case of lightly doped substrates, the epitaxial films exhibit a large defect density (1010 cm−2). It is shown that this defect density can be reduced by a 102 to 103 factor through the use of silicon channeled implantation and subsequent thermal annealing. On the other hand, when the epitaxial growth is performed on PSL formed from highly doped boron substrates, the epitaxial quality of the resulting films is equivalent to the homoepitaxy of silicon on bare silicon. On both kinds of samples it is shown that during oxidation of the buried PSL, the back interface of the epitaxial layer is oxidized by rapid diffusion of oxygen through the porous network, and then a dense oxide is formed at the epitaxial layer/porous silicon interface. Furthermore this oxide, whose thickness can be controlled, acts as a barrier towards boron diffusion even at the high densification temperature (1300°C) necessary to obtain a good quality buried oxide. Very low boron doping level is then measured in the epitaxial film.

Hydrogen pile-up at interfaces between differently doped layers of amorphous silicon

Hydrogen profiles for layered a-Si:H structures are presented. Substantial accumulation of hydrogen at the p-i interface is found. Additional incorporation of hydrogen in p-layers is also observed for intermediate boron doping levels compared to intrinsic layers. Hydrogen profiles in single pin and in pinpin amorphous silicon structures enable determination of individual layer thickness.

Optical Studies of Doping-Characteristics in Boron-Doped a-Si:H Films Prepared by the Photo-CVD Technique

We measured subgap optical absorption and photoluminescence spectra in boron-doped a-Si:H films prepared by photochemical vapor deposition (photo-CVD) techniques. We estimated the Urbach energy (E0) and the density of defect states (Ns) from the subgap optical absorption spectra; the value of Ns was estimated from PL spectra. We conclude that Ns is approximately proportional to a square root of the boron doping level (B2H6/SiH4) and that E0 increases linearly with an increase in the doping level. It is found that the doping mechanism proposed by Street applies to the photo-CVD films.

Electron diffraction study of the structure of boron-and phosphorus-doped hydrogenated amorphous silicon

Abstract The effect of gas-phase doping with boron and phosphorus on the structure of glow-discharge amorphous hydrogenated silicon has been studied by means of energy-filtered electron diffraction. The reduced density function was calculated and the network was found to contract upon doping. At levels of less than 20 at.% neither boron nor phosphorus segregated from the network. At high phosphorus doping levels an amorphous chemically ordered structure corresponding to Si2P was formed. At high boron doping levels, evidence for the presence of boron icosahedra was obtained.

Enhanced activation of Ga implanted Si through rapid thermal processing

Metastable activation of Ga implants has been achieved through rapid annealing. Carrier concentrations of ≃2 × 1020cm−3 exceed the Ga solubility limit by a factor of five and are comparable to boron doping levels. Retention of these doping levels severely limits any subsequent thermal processing.

Defect engineering for VLSI epitaxial silicon

The control of dopants, impurities and defects for very large scale integration of silicon integrated circuits requires a complex set of crystal and processing conditions to be satisfied simultaneously. In order to achieve the maximum yield and highest level of electrical performance for a given device design, we have manipulated the lattice constant and boron doping levels in CVD epitaxial silicon layers co-doped with germanium. By adjusting the ratios of germane and diborane in a dichlorosilane/hydrogen CVD reactor we can achieve extrinsic gettering using controlled introduction of interfacial misfit dislocations with Si(Ge), and buried high conducting layers which are strain-free and lattice matched to the Si substrate. A variety of these structures have been characterized using gated-diode leakage, spreading resistance profiling, MOS lifetime, cross-sectional TEM, SEM-EBIC and SIMS depth profiling.

Microstructure of boron-doped silicon layers prepared by low pressure chemical vapour deposition

The microstructures of silicon layers 0.55–0.60 μm thick with boron contents of about 10 17 or 10 20 atoms cm -3, prepared by low pressure chemical vapour deposition at 570 or 620°C on thermally oxidized silicon wafers, were characterized in the as-grown condition and after chemical thinning. The microstructural characteristics obtained from transmission electron microscopy examination on cross-sections, reflection high energy electron diffraction patterns, Raman spectrometry at 488 nm and UV absolute reflectance measurements as well as the optical and mechanical roughness of the sample surfaces were compared. The results showed the following. 1. (i) The layers are polycrystalline throughout their depth, with an external region of columnar character, intense twinning and 〈110〉 texture, and with a near-interface zone 50–100 nm thick of randomly oriented grains of size not greater than 10nm. 2. (ii) The thickness of the interfacial zone decreased as the deposition temperature increased. In the external region the texture became more developed as the level of boron doping and the deposition temperature increased, whereas the twinning, dislocation density, vacancy and/or impurity concentrations (from Raman results) and excess volume fraction (from absolute reflectance results) appear to be enhanced by increases in doping and decreased by increases in temperature. 3. (iii) The surface roughness was also clearly higher for layers with lower boron contents.

Effet hall et diamagnetisme de composes residuels pyrocarbone-bore-halogene

In order to clarify the electronic structure of halogen residue compounds, particularly the amount of charge transfer that occurs between the carbon π band and the intercalated species, bromine and iodine chloride were intercalated into pyrolytic carbons with various levels of boron doping, and the Hall effect and diamagnetic anisotropy of the resulting residue compounds were studied. The positive Hall coefficient is always independent of temperature and yields the concentration of holes in the π band, while the amount of intercalated halogen can be obtained from weight variation measurements. Table 1 shows the Hall coefficients and hole concentrations of the boronated pyrocarbons before intercalation, and Table 2 gives the results of measurements performed on residue compounds between 77 and 300 K. Increasing heat treatments reduce the amounts of halogen (Table 3). From these various data it can be stated that the halogen content of the residue compounds does not depend on the boron doping and the resulting initial position of the Fermi level (see Tables 2 and 3). The charge transfer from carbon to halogen is always found to be quite small: 0.02–0.07 electronic charge per Br 2 or ICl molecule (Fig. 1). The charge transfer also varies if the compounds undergo thermal cycles without loss of halogen. This was shown by in situ measurements of the Hall coefficient and diamagnetic anisotropy during such cycles (Figs. 2–6). Successive intercalations and deintercalations, as suggested by the Marchand-Rouillon model[5,6], are responsible for the hysteresis cycles observed[1–7] with many properties of these compounds.

Defect and Dopant Control During Silicon Epitaxy Using B and Ge

ABSTRACTThe control of dopants, impurities and defects for VLSI of silicon integrated circuits requires a complex set of crystal and processing conditions to be satisfied simultaneously. In order to achieve the maximum yield and highest level of electrical performance for a given device design, we have manipulated the lattice constant and boron doping levels in CVD epitaxial silicon layers co-doped with germanium. By adjusting the ratios of germane and diborane in a dichlorosilane/hydrogen CVD reactor we have obtained buried high conducting layers which are strain-free and lattice matched to the Si substrate. Degenerate boron and boron and germanium codoped epitaxial layers on (100) p-type silicon substrates were investigated. Solubility, electrical activity limits and defect structure of boron in strained and strain-free silicon epitaxial layers were investigated by spreading resistance, SIMS profiling, X-ray and transmission electron microscopy techniques. Bright field and weak-beam dark field imaging of cross-sectional and plan-view specimens were used to confirm the presence or absence of precipitates and threading dislocations. A model has been proposed to describe the mechanism of threading dislocation formation in heavily boron-doped layers. We are now in a position to strategically locate co-doped Si(B, Ge) p++ layers as recombination zones or buried field plates to suit the needs of MOS latchup control, high speed and radiation hard devices, as well as the needs of defect free p++ etch stops for thin membranes and three-dimensional silicon structures.

Time-of-flight measurement of hole transport in lightly boron-doped a-Si:H films

Effects of slight boron-doping on the mobility and the mobility-lifetime ( μτ ) product of holes in glow-discharged hydrogenated amorphous silicon films have been investigated by means of time-of-flight measurement. When a small amount of boron in the range of the flow rate ratio B 2 H 6 /SiH 4 = 17–50 ppm is doped, hole transport at room temperature becomes non-dispersive, in contrast with a dispersive nature in undoped films. The hole mobility and the μτ product at room temperature have large values at these flow rate ratios. However, when the flow rate ratio B 2 H 6 /SiH 4 is further increased, holes show again dispersive transport accompanying a reduction in mobility and μτ product. The activation energy of the hole mobility is nearly 0.4 eV, independent of boron-doping level. These results are tentatively interpreted in terms of an introduction of localized states associated with boron or on the basis of a two-phase model in which a-Si:H films are considered to be composed of an entangled network of paramicrocrystalline zones and highly disordered Si:H alloy regions.

Electron-spin-resonance study of boron-doped amorphousSixGe1−x: H alloys

We report on ESR and Raman spectroscopy in $a\ensuremath{-}{\mathrm{Si}}_{x}{\mathrm{Ge}}_{1\ensuremath{-}x}$: H prepared by glow discharge with a 1-vol% boron-doping level. For most silicon contents $x$, a preferential deposition of germanium into the solid film is found. The Raman spectra show that the samples are amorphous and that no phase separation is present. Four different ESR resonances can be observed over the compositional range investigated ($0<x<0.7$) at 20 K: the known resonances of the Ge dangling bonds and of localized holes in Ge---Ge bonding states, a signal due to carbon impurities, and a new resonance with strong negative $g$-value shift ($g=1.925$) that seems to be related to surface states. A model for the density of states in the amorphous Si-Ge alloys is proposed that can qualitatively account for the experimental results.

Effect of boron compensation on the photovoltaic properties of amorphous silicon solar cells

Intrinsic amorphous silicon films are normally slightly n type. As a result, in n+-i-metal and n+-i-p+ solar cell structures the major potential barrier is at the i-m or i-p+ interfaces. Low levels of boron compensation of the i layer move the Fermi level down to midgap. Further increases in boron render the i layer slightly p type, and move the major barrier to the i-n+ interface. Therefore, it becomes possible to tailor the level of boron doping throughout the i layer so as to achieve high electric fields in all regions of the layer, and thus maximize the short circuit current.