Controllable p-n junction formation in monolayer graphene using electrostatic substrate engineering

We investigate electric transport in graphene on SiO2 in the high field limit and report on the formation of p-n junctions. Previously, doping of graphene has been achieved by using multiple electrostatic gates, or charge transfer from adsorbants. Here we demonstrate a novel approach to create p-n junctions by changing the local electrostatic potential in the vicinity of one of the contacts without the use of extra gates. The approach is based on the electronic modification not of the graphene but of the substrate and produces a well-behaved, sharp junction whose position and height can be controlled.     

Current rectification in a single silicon nanowire p-n junction

Diodes within individual silicon nanowires were fabricated by doping them during growth to produce p-n junctions. Electron beam lithography was then employed to contact p- and n-doped ends of these nanowires. The current-voltage (I-V) measurements showed diode-like characteristics with a typical threshold voltage (Vt) of about 1 V and an ideality factor (n) of about 3.6 in the quasi-neutral region. The reverse bias I-V measurement showed an exponential behavior, indicating tunneling as the current leakage mechanism.     

Realization of a linear germanium nanowire p-n junction

Germanium nanowires grown by chemical vapor deposition exhibit a peculiar dopant incorporation mechanism. The dopant atoms, such as boron and phosphorus, get incorporated through the wire surface, a mechanism which limits the doping modulation along the wire length, and therefore the fabrication of more elaborate structures that combine both n- and p-type doping. Using a novel device design that circumvents these constraints, we demonstrate here a linear Ge nanowire p-n junction.     

Charging capacity of a sharp p-n junction in a variband semiconductor

The barrier capacitance of a sharp p-n junction in a variband semiconductor with coordinate-independent bandgap gradient and electron affinity was calculated. It is shown that the square inverse barrier capacitance is a linear function of the applied voltage and that the cutoff voltage may significantly exceed the contact potential difference.     

Influence of an auxiliary planar short-circuited p-n junction positioned near a main junction

A possible method of reducing the reverse currents and increasing the forward currents in smallscale planar diodes is discussed and demonstrated experimentally. This method involves using an auxiliary short-circuited planar p-n junction positioned within the diffusion length of minority carriers from the planar boundaries of the diodes. Pis’ma Zh. Tekh. Fiz. 24, 72–76 (March 26, 1998)     

GaN nanorod Schottky and p-n junction diodes

Conductive atomic force microscopy has been used to characterize single GaN nanorod Schottky and p-n junction diodes. The ideality factor, reverse breakdown voltage, and the Schottky barrier height of individual nanorod diodes were compared to those from conventional thin-film diodes. Large-area contacts, enabling diodes with arrays of GaN nanorods in parallel, were also fabricated and their electrical characteristics investigated. The defect-free nature of the GaN nanorods and enhanced tunneling effects due to nanoscale contacts have been invoked to explain the electrical behavior of the nanorod diodes.     

A highly linear single p-n junction temperature sensor

A temperature sensor based on the use of two forward-biased p-n junctions is known to exhibit good linearity. An alternative sensor configuration, based on the same principle, but employing only one p-n junction is presented in this paper. The forward current through the p-n junction is switched alternately between two fixed values, and the difference between the corresponding voltages is shown to vary linearly with temperature. This scheme eliminates the problems associated with close matching required for the two p-n junction sensors. Experimental results obtained with the proposed scheme are presented. A configuration to exploit the temperature dependence of the p-n junction incremental resistance is also presented     

Nonstationary local reorientation of a nematic liquid crystal in a cell with a silicon p-n junction

We report the first observation of the phenomenon of nonstationary local reorientation of a nematic liquid crystal (NLC), which is initiated by a reverse biased p-n junction in a cell with silicon substrate. The velocity of reorientation and the distance traveled by a reoriented nematic band (which is tenfold greater than the cell thickness) are determined by the p-n junction bias voltage. The band profile depends on the distribution of the surface conductivity, which has been set in this work either by irradiation with 30-keV Ga ions or by light-induced generation of nonequilibriun carriers in silicon. The local reorientation of NLC and the depletion of the silicon surface are explained by the influence of ion space charge in the liquid crystal.     

Amplifier using p-n junction field-effect transistors with 1/f-type noise

Conclusions The KPS104A field-effect transistor, which produces practically no 1/f-type noise down to frequencies f2 Hz, may be used to advantage as the active element of a high-sensitivity amplifier at subsonic frequencies.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 38–39, March, 1979.     

Comments on “A highly linear single p-n junction temperaturesensor”

The concept of using switched currents through a single p-n junction for a linear temperature measurement as proposed by Freire et al. (Apr. 1994) has been previously described by J. Williams (1991). Williams uses asynchronous set of switches (LTC 1043) to switch separate currents through a diode-connected transistor, and also to switch capacitors synchronously with the currents. This action creates an output that is proportional to the peak-to-peak voltage of the sensor. The circuit uses relatively few components. There are, however, some design errors in the the current generator that he uses. It was pointed out to Williams that trimming is necessary due to component tolerances, and a simpler and more accurate means of generating the two selected currents was proposed (May 1991)     

Preparation and activity evaluation of p-n junction photocatalyst NiO/TiO2

p–n Junction photocatalyst NiO/TiO₂ was prepared by sol–gel method using Ni(NO₃)₂·6H₂O and tetrabutyl titanate [Ti(OC₄H₉)₄] as the raw materials. The p–n junction photocatalyst NiO/TiO₂ was characterized by UV–vis diffuse reflection spectrum, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the photocatalyst was evaluated by photocatalytic reduction of Cr₂O₇²⁻ and photocatalytic oxidation of rhodamine B. The results show that, for photocatalytic reduction of Cr₂O₇²⁻, the optimum percentage of doped-NiO is 0.5% (mole ratio of Ni/Ti). The photocatalytic activity of the p–n junction NiO/TiO₂ is much higher than that of TiO₂ on the photocatalytic reduction of Cr₂O₇²⁻. However, the photocatalytic activity of the p–n junction photocatalyst NiO/TiO₂ is much lower than that of TiO₂ on the photocatalytic oxidation of rhodamine B. Namely, the p–n junction photocatalyst NiO/TiO₂ has higher photocatalytic reduction activity, but lower photocatalytic oxidation activity. Effects of heat treatment on the photocatalytic activity of p–n junction photocatalyst NiO/TiO₂ were investigated. The mechanisms of influence on the photocatalytic activity were also discussed by the p–n junction principle.     

具有边缘缺陷石墨烯纳米结的自旋输运特性(英文)

利用第一性原理研究了两种具有边缘缺陷石墨烯纳米结的自旋输运,即边界氢原子饱和和未被饱和两种情况。结果表明:边缘缺陷改变了电子的输运行为。对于完整的石墨烯纳米带,两种自旋的电子在费米能级附近是完全简并的;对于含有边缘缺陷的石墨烯纳米结,两种自旋的电子在费米能级附近的很大能量范围内表现出自旋分离。电子局域态密度可进一步说明这种输运行为。这些纳米结可产生与自旋相关的极化电流。特别对于未饱和的缺陷结,在任何偏压下都有较高的自旋滤波效率。     

Characterization of a β-FeSi2 p-n junction formed by the PECS method

We have fabricated semiconducting β-FeSi₂ bulks without doping and with Mn and Co doping by using a pulse electric current sintering (PECS) method, and explored the possibility of a direct bonding of n-type and p-type β-FeSi₂ bulks to form a p-n junction structure. P-type Mn-doped and n-type Co-doped β-FeSi₂ bulks were obtained by an annealing process at 800-850 °C for 100 h. The PECS was applied to bond the n-type and p-type bulks together for forming a p-n junction structure. We confirmed that the bonding was processed without any change in the β-FeSi₂ phase and was strongly joined with each other. Although we could not obtain the electrical characteristics of the p-n junction, Seebeck coefficients for n-type and p-type β-FeSi₂ in the bonded sample were determined to be −356 and 778 μV/K, respectively. We propose that these results should lead to an expanded use of the sintered β-FeSi₂ bulks in thermoelectric devices.     

Kinked p-n junction nanowire probes for high spatial resolution sensing and intracellular recording

Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p-n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p-n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p-n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p-n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p-n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p-n junction. High spatial resolution sensing using these p-n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p-n devices. In addition, kinked p-n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p-n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.     

Ultra-high vacuum direct bonding of a p-n junction GaAs wafer using low-energy hydrogen ion beam surface cleaning

Low-energy hydrogen ion bombardment is used to clean GaAs surfaces. The hydrogen ions produce contamination-free surfaces without changes in surface composition (stoichiometry) and surface roughness. The wafers were brought into contact at room temperature after cleaning under ultra-high vacuum (UHV), and bonded over the whole area (2 inches) without application of external mechanical pressure. After bonding, the p-GaAs/n-GaAs wafer pair was annealed at 200 °C for 30 min under UHV conditions (<5×10⁻¹⁰ mbar) to improve the interface bonding strength and to achieve a full-area wafer bonding.Infrared (IR) imaging of the as-bonded wafers directly reveal the real bonding behaviour. High-resolution transmission electron microscopy images reveal that the wafers have been directly bonded without damage of the crystal lattice or intermediate layer and the interface is smooth. Current-voltage characterization shows near-ideal forward characteristics and the recombination in p-n junction space charge region.