High-temperature diffusion doping of porous silicon carbide

The results of experiments on high-temperature (2000–2200°C) diffusion doping of porous silicon carbide (PSC) by vanadium and erbium are reported. It is established that the specific features of diffusion processes in PSC at these temperatures are determined by modification of the porous structure due to the transport of vacancies. Based on a comparison of these results to available data on the low-temperature (900–1000°C) diffusion, it is concluded that the mechanisms of diffusion in PSC at low and high temperatures are different and that SiC with a porous structure is an effective medium particularly for low-temperature diffusion.     

The bending of silicon wafers by thin polycrystalline silicon film deposition and by film doping using boron diffusion

The existence of stress at the interface between a monocrystalline silicon substrate and a thin (under 1 μm) polycrystalline silicon film was demonstrated using X-ray topography. The wafer-bending direction was studied for a polycrystalline film doped by boron prediffusion and by prediffusion followed by drive-in diffusion. Wafer bending in the presence of SiO₂ thermal growth between the monocrystalline substrate and the polycrystalline film was also investigated. The causes of the wafer bending and its change during polycrystalline film doping are discussed.     

Solid-state diffusion as an efficient doping method for silicon nanowires and nanowire field effect transistors

In this work we investigate doping by solid-state diffusion from a doped oxide layer, obtained by plasma-enhanced chemical vapor deposition (PECVD), as a means for selectively doping silicon nanowires (NWs). We demonstrate both n-type (phosphorous) and p-type (boron) doping up to concentrations of 10(20) cm(-3), and find that this doping mechanism is more efficient for NWs as opposed to planar substrates. We observe no diameter dependence in the range of 25 to 80 nm, which signifies that the NWs are uniformly doped. The drive-in temperature (800-950?°C) can be used to adjust the actual doping concentration in the range 2 × 10(18) to 10(20) cm(-3). Furthermore, we have fabricated NMOS and PMOS devices to show the versatility of this approach and the possibility of achieving segmented doping of NWs. The devices show high I(on)/I(off) ratios of around 10(7) and, especially for the PMOS, good saturation behavior and low hysteresis.     

Ion beam doping of silicon nanowires

We demonstrate n- and p-type field-effect transistors based on Si nanowires (SiNWs) implanted with P and B at fluences as high as 10(15) cm (-2). Contrary to what would happen in bulk Si for similar fluences, in SiNWs this only induces a limited amount of amorphization and structural disorder, as shown by electrical transport and Raman measurements. We demonstrate that a fully crystalline structure can be recovered by thermal annealing at 800 degrees C. For not-annealed, as-implanted NWs, we correlate the onset of amorphization with an increase of phonon confinement in the NW core. This is ion-dependent and detectable for P-implantation only. Hysteresis is observed following both P and B implantation.     

Zigzag structures obtained by anisotropic etching of macroporous silicon

High-aspect-ratio structures with thin corrugated walls have been obtained by processing of macroporous silicon with a trigonal lattice in anisotropic etchants. For this purpose, a pattern of seeding etch pits with a certain orientation relative to crystallographic axes is created prior to electrochemical etching and a solution of definite composition for treating macropores is used after anodizing. The possibility of using zigzag structures as anodes in lithium-ion batteries is discussed.     

Cobalt diffusion during doping of ZnSe single crystals

Cobalt diffusion into single crystals of the compound semiconductor ZnSe has been studied under the conditions of the S _ZnSe-S _CoSe-L _Zn-V phase equilibrium at temperatures from 700 to 970°C, and the diffusion coefficients of cobalt in (100)-and (111)-oriented single-crystal samples of zinc selenide have been determined as functions of temperature. The diffusion rate of cobalt along the [111] direction is shown to exceed that along [100].     

Size limits on doping phosphorus into silicon nanocrystals

We studied the electronic properties of phosphorus-doped silicon nanocrystals using the real-space first-principles pseudopotential method. We simulated nanocrystals with a diameter of up to 6 nm and made a direct comparison with experimental measurement for the first time for these systems. Our calculated size dependence of hyperfine splitting was in excellent agreement with experimental data. We also found a critical nanocrystal size below which we predicted that the dopant will be ejected to the surface.     

Method of selective doping of silicon by segregating impurities

An original method for the controlled doping of silicon by segregating donor impurities is proposed. The approach is based on a rapid variation of the growth temperature during the molecular beam epitaxy between the regimes of kinetically limited segregation and maximum segregation of the dopant. By example of antimony, it is demonstrated that the proposed method can be used to obtain several-nanometer-thick selectively Sb-doped Si epilayers, in which a tenfold change in the volume concentration of the dopant is achieved on a 2–3 nm scale.     

Boron doping of silicon rich carbides: Electrical properties

Boron doped multilayers based on silicon carbide/silicon rich carbide, aimed at the formation of silicon nanodots for photovoltaic applications, are studied. X-ray diffraction confirms the formation of crystallized Si and 3C-SiC nanodomains. Fourier Transform Infrared spectroscopy indicates the occurrence of remarkable interdiffusion between adjacent layers. However, the investigated material retains memory of the initial dopant distribution. Electrical measurements suggest the presence of an unintentional dopant impurity in the intrinsic SiC matrix. The overall volume concentration of nanodots is determined by optical simulation and is shown not to contribute to lateral conduction. Remarkable higher room temperature dark conductivity is obtained in the multilayer that includes a boron doped well, rather than boron doped barrier, indicating efficient doping in the former case. Room temperature lateral dark conductivity up to 10^?3 S/cm is measured on the multilayer with boron doped barrier and well. The result compares favorably with silicon dioxide and makes SiC encouraging for application in photovoltaic devices.     

Label-free quantitative detection of protein using macroporous silicon photonic bandgap biosensors

A label-free biosensor was demonstrated using macroporous silicon (pore size >100 nm) one-dimensional photonic band gap structures that are very sensitive to refractive index changes. In this study, we employed Tir-IBD (translocated Intimin receptor-Intimin binding domain) and Intimin-ECD (extracellular domain of Intimin) as the probe and target, respectively. These two recombinant proteins comprise the extracellular domains of two key proteins responsible for the pathogenicity of enteropathogenic Escherichia coli (EPEC). The optical response of the sensor was characterized so that the capture of Intimin-ECD could be quantitatively determined. Our result shows that the concentration sensitivity limit of the sensor is currently 4 microM of Intimin-ECD. This corresponds to a detection limit of approximately 130 fmol of Intimin-ECD. We have also investigated the dependence of the sensor performance on the Tir-IBD probe molecule concentration and the effect of immobilization on the Tir-IBD/Intimin-ECD equilibrium dissociation constant. A calibration curve generated from purified Intimin-ECD solutions was used to quantify the concentration of Intimin-ECD in an E. coli BL21 bacterial cell lysate, and results were validated using gel electrophoresis. This work demonstrates for the first time that a macroporous silicon microcavity sensor can be used to selectively and quantitatively detect a specific target protein with micromolar dissociation constant (Kd) in a milieu of bacterial proteins with minimal sample preparation.     

Recrystallization behavior of zinc selenide during chromium diffusion doping

We have studied the effect of high-temperature diffusion doping with chromium (Cr²⁺) ions on the microstructure of polycrystalline zinc selenide (ZnSe). We have determined energy and kinetic characteristics of solid-state recrystallization in ZnSe and assessed the effect of chromium concentration on the rate of grain growth during the doping process.     

Background doping of films in molecular beam epitaxy of silicon

Unique results obtained as a result of the development of epitaxial silicon layers with an extremely low concentration of background impurities for infrared photodetectors with blocked impurity photoconduction are analyzed and generalized. Changes in the type and concentration of electrically active background impurities in films grown by molecular beam epitaxy were investigated at all stages in the operation of the system, from initial startup to the fabrication of films having an extremely low level of background impurities <4×10¹³ cm⁻³. The laws governing the changes in the type and level of background doping during operation of the system and the mechanism responsible for these changes are established. Pis’ma Zh. Tekh. Fiz. 24, 24–29 (February 12, 1998)     

Pore formation in aluminum films on macroporous silicon during high-temperature annealing

The surface of an aluminum metallization coating applied on a macroporous silicon layer and annealed for 10–60 min at 550°C has been studied by atomic-force and electron microscopy techniques. It is established that the annealing results in the formation of through (open) macropores with lateral dimensions within 400–1300 nm in the aluminum film and in the growth of large hillocks with heights of up to 1.2μ m on the surface, which are located at the edges of these macropores. The geometric parameters of large hillocks are independent of the duration of annealing.     

Investigation of Sb diffusion in amorphous silicon

Amorphous silicon materials and its alloys became extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry. Amorphous Si/Si_1−xSb_x/Si tri-layer samples with 5 at% antimony concentration were prepared by direct current magnetron sputtering onto Si substrate at room temperature. Annealing of the samples was performed at different temperatures in vacuum (p<10⁻⁷ mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent of diffusion, the evaluated diffusion coefficients are in the range of ∼10⁻²¹ m²s⁻¹ at 550 °C.     

Laser induced diffusion of indium in silicon

In this work, a 300 s pulsed Nd:YAG laser was employed to induce indium diffusion in silicon wafer. Electrical properties were studied for a range of laser pulse energies (0.225–0.369 J) and substrate temperature (300–398°k). The four point probe measurements showed that a minimum sheet resistance (54 /) was resulted at the melting threshold energy and room temperature. The sheet resistance was a decreasing function of the temperature rise of the substrate. The (I-V) and (C-V) measurements expressed improvement in the characteristics of the fabricated diodes when substrate temperature rises and irradiating pulse energy increases up to melting threshold value after which these characteristics starts to deteriorate.     

Modeling of silicon diffusion in gallium arsenide

A model is developed and a study is performed for amphoteric diffusion of silicon in gallium arsenide. A comparison of predictions with experimental data indicated adequacy of the devised model and high efficiency of the numerical method for solving the diffusion equation.Belorussian State University, Minsk. Minsk Radio Engineering Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 65, No. 5, pp. 567–572, November, 1993.     

Low-temperature diffusion of implanted sodium in silicon

Technical Physics Letters - We have studied the low-temperature diffusion of sodium atoms implanted (at primary ion energy E = 300 keV to total doses within Φ = 5 × 1014–3 ×...     

Novel aspects of oxygen diffusion in silicon

Normal diffusion of interstitial oxygen atoms (O_i ) accounts for the rate of oxygen aggregation in silicon for T > 500C. There is evidence for the dissociation of SiO₂ precipitates (Ostwald ripening) and the formation of self-interstitials (I-atoms) to accommodate the local increase in volume. For T < 500 C, measurements of the loss of oxygen atoms from solution indicate that O₂ dimer formation is the rate-limiting process, but dissociation of dimers must be taken into account when modelling this process. Large clusters of up to 10–20 O_i atoms, usually assigned to thermal donor (TD) defects cannot form unless dimer diffusion is much greater (by a factor of 10⁴ to 10⁷ ) than diffusion of O_i atoms and unless there is dissociation of clusters with the emission of dimers. Hydrogen impurities enhance O_i diffusion by a catalytic process and speed up donor formation. Infrared absorption measurements reveal H-O_i complexes and there is also partial passivation of TD defects to produce shallow thermal donors (STDs).     

Neutron transmutation doping of silicon 30Si monoisotope with phosphorus

Phosphorus-doped silicon ³⁰Si monoisotope samples with a highly homogeneous impurity distribution at a concentration of 5 × 10¹⁶ cm^?3 were obtained for the first time by means of neutron transmutation doping.