P-doped Silicon Research Articles

Low temperature mechanical dissipation measurements of silicon and silicon carbide as candidate material for DUAL detector

We present the results of measurements of mechanical dissipations in silicon and silicon carbide samples within the 2-300 K range of temperature. These materials are possible candidates for the sensitive mass of DUAL detector. We have investigated sintered and infiltrated Silicon Carbide (SiC) and P-doped Silicon (Si) in flat plates and cantilevers. Moreover the dissipation of bonded P-doped silicon wafers is scheduled for measurement in the 2-300 K range for the next cryogenic run. We tested a nodal suspension with sapphire and inox steel spheres for flat plates within the same temperature range. We developed two different kinds of capacitive readout: electrostatic comb one for semiconductor silicon and plane capacitor-like for conductor silicon carbide. Moreover an optical lever readout was employed to measure loss angle on SiC cantilevers and silicon disks.

Silicon nanowire-based solar cells

The fabrication of silicon nanowire-based solar cells on silicon wafers and on multicrystallinesilicon thin films on glass is described. The nanowires show a strong broadbandoptical absorption, which makes them an interesting candidate to serve as anabsorber in solar cells. The operation of a solar cell is demonstrated with n-dopednanowires grown on a p-doped silicon wafer. From a partially illuminated area of0.6 cm2 open-circuit voltages in the range of 230–280 mV and a short-circuit current density of2 mA cm−2 were obtained.

Resistivity and surface states density of n- and p-type silicon nanowires

The resistivity and the density of surface states of semiconductor nanowires are not measurable using classic electrical measurements such as capacitance-voltage techniques, because of too low capacitance associated with a single nanowire. To overcome this problem, the authors measured the resistance of a set of n- and p-doped silicon nanowires versus their length and width. Thus, the authors deduce both the resistivity and density of surface states of the nanowires. This approach could be extended to any nanowire, once its shape is known.

Fabrication of nanostructures with high electrical conductivity on silicon surfaces using a laser-assisted scanning tunneling microscope

Nanostructures with high electrical conductivity were fabricated on silicon surfaces using a laser-assisted scanning tunneling microscope (LA-STM). The nanostructures, dots and lines, were fabricated on H-passivated p-doped silicon (110) surfaces. By precisely controlling the experimental conditions such as pulse energy and tip-surface gap distance, feature sizes (dot diameters and line widths) and heights of the fabricated nanostructures could be controlled. For instance, a dot with a diameter of 30nm and a line with a width of 30nm were obtained. In addition, scanning tunneling microscopy investigation of the structures revealed that their band gaps were changed during the LA-STM process. As a consequence, the local conductivity (more precisely the tunneling probability) was enhanced. Numerical simulations based upon the finite-difference-time-domain algorithm provide detailed insight into the spatial distribution of the enhanced optical field underneath the STM tip and associated physical phenomena. Potential applications of the developed nanostructuring process are anticipated in various nanotechnology fields, particularly in the field of nanoelectronics.

Influence of the front contact barrier height on the Indium Tin Oxide/hydrogenated p-doped amorphous silicon heterojunction solar cells

The band bending at the transparent conductive oxides/hydrogenated p-doped amorphous silicon (p-a-Si:H) interface is one of the most important factors limiting the performances of HIT (Heterojunctions with Intrinsic Thin layers) solar cells. In order to study this effect, a solar cell (Indium Tin Oxide (ITO)/p-a-Si:H/i-polymorphous Si:H/n-doped crystalline silicon (n-c-Si)) simulation, focused on the front contact barrier height, has been performed. The results show that a reduction of the surface potential barrier at the interface ITO/p-layer leads to an increase of the built-in potential, and hence an increase of open circuit voltage and fill factor. We have also observed that the performance of HIT solar cells remains constant above 12nm thickness of the p-layer.

Polycrystalline silicon with large disk-shaped grains by Ni-mediated crystallization of doped amorphous silicon

Silicide mediated crystallization (SMC) of p-doped amorphous silicon (a-Si) has been studied. There are the different grain-shapes of crystallization of doped and non-doped a-Si. Non-doped a-Si is crystallized with needle-shaped grains, while it is observed the disk-shaped grains are formed in crystallized doped a-Si. The crystallization of slightly doped a-Si exhibits larger grain size compared with non-doped and heavily doped films. The p-dopant in a-Si suppresses the formation of the NiSi2 precipitate which act as a crystallization nucleus, causing continuous grain growth and the formation of disk-shaped grains.

Ohmic conduction of sub-10nm P-doped silicon nanowires at cryogenic temperatures

We investigate the conduction properties of an embedded, highly phosphorus-doped nanowire with a width of 8nm lithographically defined by scanning tunneling microscope based patterning of a hydrogen-terminated Si(100):H surface. Four terminal I-V measurements show that ohmic conduction is maintained within the investigated temperature range from 35K down to 1.3K. A prominent resistance increase is observed below ∼4K which is attributed to a crossover into the strong localization regime. The low temperature conductance follows a one-dimensional variable range hopping model accompanied by positive magnetoresistance which dominates over weak localization effects at low temperature.

Persistent Photocurrent in InP Nanowires Heteroepitaxially Bridged Between Single Crystal Si Surfaces

ABSTRACTRoom temperature photoelectrical characterization with 325-nm ultraviolet and 633-nm visible laser excitations is performed on lateral p-type InP nanowires bridged between vertically oriented heavily p-doped single crystal silicon electrodes. Experimental results under 5 V bias demonstrate persistent photoconductivity through a slow decay of excess photocurrent with relaxation times ∼110 s and ∼50 s for the UV and visible laser illuminations, respectively. Persistent photocurrent originates from the long recombination time due to carrier trapping in vacancies, defect centers, and surface states in the InP nanowires. The study opens a new understanding of trap physics of nanowire heterostructures, a critical investigation for applications of these materials in photonic devices.

Epitaxial growth of Si nanowires by a modified VLS method using molten Ga as growth assistant

ABSTRACTIn this paper the deposition and morphological characterization of gallium island structures on silicon and first results of silicon wire growth assisted by the created gallium droplets is presented. The islands and wires were grown on (111)-oriented single crystalline p-doped silicon substrates by microwave plasma enhanced chemical vapor deposition (MW PECVD) using trimethylgallium (TMGa) and silane (SiH4) as precursors for island and wire growth, respectively. The samples were investigated by SEM, EDS, XPS, and AFM.

Servo scanning 3D micro-EDM based on macro/micro-dual-feed spindle

Using the end discharge of micro-rod-shaped electrode to scan layer by layer, micro-electrical discharge machining (EDM) can fabricate complex 3D micro-structures. During the machining process, the discharge state is broken frequently due to the wear of the tool electrode and the relative scanning motion. To keep a favorable discharge gap, the feed spindle of the tool electrode needs the characteristics of high-frequency response and high resolution. In this study, an experimental system with a macro/micro-dual-feed spindle was designed to improve the machining performance of servo scanning 3D micro-EDM (3D SSMEDM), which integrates an ultrasonic linear motor as the macro-drive and a piezoelectric (PZT) actuator as micro-feeding mechanism. Based on LabVIEW and Visual C++ software platform, a real-time control system was developed to control coordinately the dual-feed spindle to drive the tool electrode. The micro-feed motor controls the tool electrode to keep the favorable discharge gap, and the macro-drive motor realizes long working range by a macro/micro-feed conversion. The emphasis is paid on the process control of the 3D SSMEDM based on macro/micro-dual-feed spindle for higher machining accuracy and efficiency. A number of experiments were carried out to study the machining performance. According to the numerical control (NC) code, several typical 3D micro-structures have been machined on the P-doped silicon chips. Our study results show that the machining process is stable and the regular discharge ratio is higher. Based on our fundamental machining experiments, some better-machined effects have been gained as follows. By machining a micro-rectangle cavity (960 μm×660 μm), the machined depth error can be controlled within 2%, the XY dimensional error is within 1%, the surface roughness R a reaches 0.37 μm, and the material removal rate is about 1.58×10 4 μm 3/s by using a tool electrode of Φ=100 μm in diameter. By machining multi-micro-triangle cavities (side length 700 μm), it is known that the machining repeatability error is <0.7%.

Density functional study on electronic properties of P-doped spinel silicon carbon nitride

We performed density functional calculations on the electronic properties of P-doped spinel silicon carbon nitride. When Si is replaced by C at the tetrahedral sites of P-doped c-Si 3N 4, the band gap can be adjusted, and an insulator-to-metal transition is predicted to occur at the C-to-Si ratio of 0.27. Finally, some possible examinations and potential applications for the large band-gap reduction are discussed.

The influence of Fermi energy on structural and electrical properties of laser crystallized P-doped amorphous silicon

A series of phosphorous-doped hydrogenated amorphous silicon films (a-Si:H) were crystallized using step-by-step laser crystallization process. The structural changes during the sequential crystallization process were detected by Raman measurements. The dehydrogenation was monitored by measuring the Si–H local vibrational modes using Raman spectroscopy and hydrogen effusion measurements. Interestingly, hydrogen bonding is affected by doping of the amorphous material. The influence of doping concentrations, thus the Fermi energy on electronic properties has been investigated employing secondary ion mass spectroscopy (SIMS), dark-conductivity- and Hall-effect measurements. The results from hydrogen effusion are consistent with the results obtained from Raman spectroscopy, Hall-effect- and dark-conductivity measurements.

Memory and Coulomb blockade effects in germanium nanocrystals embedded in amorphous silicon on silicon dioxide

Germanium nanocrystals embedded in amorphous silicon and self-organized on a tunnel silicon dioxide layer thermally grown on (100) p-doped silicon substrate have been electrically studied at different temperatures by using current-voltage and capacitance-voltage measurements. Results showed a carrier exchange between the gate and isolated germanium nanocrystals via amorphous silicon. Hysteresis loops observed in the capacitance-voltage curves were attributed to electron injection∕emission process in germanium nanocrystals, which indicated a memory effect behavior. Resonant tunneling effect through germanium nanocrystals with large voltage gaps was observed at room temperature in these ultradense Ge nanocrystals of ∼3.5nm mean size. It appeared for increasingly low voltages when the temperature decreases. All these results are consistent with a Coulomb blockade effect in ultrasmall Ge nanocrystals in which an effective number of electrons transported by each tunneling step varied between 1.8 and 3.81.

Novel optoelectronic properties of simultaneously n- and p-doped silicon nanostructures

Doping control at the nanoscale can be used to modify optical and electronic properties thus inducing interesting effects that cannot be observed in pure systems. For instance, it has been shown that luminescence energies in silicon nanocrystals can be tuned by properly controlling the impurities, for example by boron (B) and phosphorus (P) codoping. Starting from hydrogen-terminated silicon nanoclusters, we have previously calculated from first-principles that codoping results are always energetically favored with respect to single B- or P-doping and that the two impurities tend to occupy nearest neighbor sites near the surface. The codoped Si nanoclusters present band-edge states localized on the impurities which are responsible for the red-shift of the absorption thresholds with respect to that of pure undoped Si nanoclusters. Here we investigate how the properties of the codoped nanoclusters are influenced by adding one or two more impurities. Moreover we study also the effect of B- and P-codoping on the electronic and optical properties of Si nanowires, thus investigating the role of dimensionality, 0- versus 1-dimensionality, of the systems.

Hydrogen passivation of P donors and defects in P-doped silicon nanowires synthesized by laser ablation

Hydrogen passivation of phosphorus (P) donors and defects in P-doped silicon nanowires (SiNWs) were investigated by electron spin resonance (ESR) at 4.2 K. P doping was performed during the synthesis of SiNWs by laser ablation. Phosphorus doping into substitutional sites of crystalline Si in SiNWs was demonstrated by detection of an ESR signal with a g-value of 1.998, which corresponds to conduction electrons in crystalline Si. ESR signals related to defects in surface oxide layer and at interface between surface oxide and crystalline Si core were observed. These P donors and the defects were partially passivated by hydrogen and oxygen atoms as seen in bulk Si.

Dopant dependence on passivation and reactivation of carrier after hydrogenation

The formation of hydrogen (H)-related complexes and H effects on boron (B) and phosphorus (P) dopants was investigated in B- or P-doped silicon (Si) crystal treated with high concentration of H. The reactivation process of dopant carriers by annealing after hydrogenation was significantly different between the p-type and n-type specimens. The difference is likely to be attributable to the formation of H-related defects based on the stable sites of the H atoms, i.e., complicated H multiple trapping centers are formed by bond breaking due to H atoms in only p-type B-doped Si.

Piezoresistive Cantilever Beam for Force Sensingin Two Dimensions

A novel two-dimensional piezoresistive nano-Newton resolution force sensing cantilever is presented. The silicon cantilever is fabricated using bulk micromachining. Two 500-nm-thick p-doped epitaxial silicon piezoresistive sensors are located on both sides of the cantilever. This structure detects both the lateral and vertical applied forces by electronic switching between two configurations of a Wheatstone bridge. A force sensitivity is measured up to 100 and 540 V/N for lateral and vertical configurations, respectively. The corresponding force resolution is estimated at 21 and 4 nN, respectively. This force-sensing cantilever can be used for measuring the contact force between manipulating tools and small objects in, e.g., living cell handling, minimally invasive surgery, and microassembly

Enhanced Tunneling through sub 30 Angstroms Thick Gallium Nitride Cap Layers on Silicon Carbide for Low Contact Resistance

AbstractWe present numerical calculations of tunneling through ultra thin wurtzite Gallium Nitride cap layers on p-doped wurtzite silicon carbide . We demonstrate the predominance of tunneling of the split-off holes to the total carrier flux, with the contribution of the heavy and the light holes damped by the large potential barrier. We calculate the contributions of spontaneous and piezoelectric polarizations to the tunneling profile seen by the holes. Two orders of magnitude enhancement is seen in the transmission probabilities for a 10 angstroms thick Gallium Nitride cap layer for holes very close to the valence band edge, compared to a barrier without any gallium nitride cap. The contact resistances are also calculated for the Gallium Nitride tunneling caps and more than two orders of magnitude lowering is seen with the ultra-thin caps. Larger cap widths induce hole accumulation layers, but the advantages of hole accumulation are offset by the higher effective tunneling width. Our calculations are relevant to nanostructures and nanodevices involving heterojunctions between gallium nitride and silicon carbide and provide the basis for low contact resistances with as-deposited metals. While our calculations focus on the regime of very high barriers to the metal of the order of 1.5 - 2 electron volts, where the method of ultra-thin caps is most useful, similar conclusions also hold for lower barrier heights.

Charge Patterns as Templates for the Assembly of Layered Biomolecular Structures

Electric fields are used to guide the assembly of biomolecules in predefined geometric patterns on solid substrates. Local surface charges serve as templates to selectively position proteins on thin-film polymeric electret layers, thereby creating a basis for site-directed layered assembly of biomolecular structures. Charge patterns are created using the lithographic capabilities of an atomic force microscope, namely by applying voltage pulses between a conductive tip and the sample. Samples consist of a poly(methyl methacrylate) layer on a p-doped silicon support. Subsequently, the sample is developed in a water-in-oil emulsion, consisting of a dispersed aqueous phase containing biotin-modified immunoglobulinG molecules, and a continuous nonpolar, insulating oil phase. The electrostatic fields cause a net force of (di)electrophoretic nature on the droplet, thereby guiding the proteins to the predefined locations. Due to the functionalization of the immunoglobulinG molecules with biotin-groups, these patterns can now be used to initiate the localized layer-by-layer assembly of biomolecules based on the avidin-biotin mechanism. By binding 40 nm sized biotin-labelled beads to the predefined locations via a streptavidin linker, we verify the functionality of the previously deposited immunoglobulinG-biotin. All assembly steps following the initial deposition of the immunoglobulinG from emulsion can conveniently be conducted in aqueous solutions. Results show that pattern definition is maintained after immersion into aqueous solution.

Ti O 2 and HfO2 in electrolyte-oxide-silicon configuration for applications in bioelectronics

We study the electrical properties of thin TiO2 films made by atomic layer deposition (ALD) on p-doped silicon in an electrolyte-oxide-silicon (EOS) configuration. The electrolyte contact of the TiO2∕Si heterostructure allows measurements of the differential capacitance for a wide range of bias voltages as they cannot be performed in a metal-oxide-silicon structure because of extensive leakage currents. In the accumulation region of p-silicon, we find a saturation of capacitance that decreases with oxide thickness, indicating an insulator with a dielectric constant of 34. In the inversion region of p-silicon, the capacitance increases in two steps far beyond the saturation capacitance. We assign this effect to the presence of electrons in TiO2 which is controlled by the bias voltage and by immobile positive charges at the TiO2∕Si interface: When the Fermi energy in p-silicon is raised to the level of the low lying conduction band of TiO2, electrons accumulate in two layers near the TiO2∕Si interface and at the electrolyte/TiO2 interface with a concomitantly enhanced differential capacitance. As a control, we study HfO2 films also made by ALD. We obtain a dielectric constant of 15 from the capacitance in the accumulation region of p-silicon. For HfO2 with a high lying conduction band, the capacitance decreases as expected in the inversion region for the high-frequency limit of silicon. The electrical characterization of TiO2 and HfO2 in EOS junctions opens future applications of high-κ materials in bioelectronics for efficient capacitive interaction of silicon chips and living cells.