Semiconductor Cathode Research Articles

Coherent and sequential tunneling mechanisms for field electron emission through layers of wide band gap materials

A sequential two-step tunneling model was developed for the electron field emission from semiconductor cathodes covered with dielectric layers. The results are compared with a previous coherent (one-step) approach and remarkable differences are obtained. Electron heating effects are predicted in not-too-thick dielectric layers. Multiple peaks in the emitted electron energy distribution, which appear in some experiments, may be explained by the sequential field emission model.

Analysis of prebreakdown current in a gas discharge system with a semiconducting cathode

Results are presented of an analysis of the prebreakdown current of a Townsend discharge in a planar gas discharge system with a GaAs semiconductor cathode for a gap thickness of 45 µm and gas pressures of 6.9, 8.9, 34.2 and 36.9 kPa. IR radiation excites the cathode in the system, thus controlling the current density in the gas discharge layer. It is shown that the prebreakdown current is caused by electron emission from the semiconductor surface. The present experimental investigations show that the prebreakdown current decreases anomalously with increase of the feeding voltage and that it also decreases under the illumination of a semiconductor cathode. Both these anomalies depend on gas pressure. The current density change through the cross-section of the discharge gap, i.e. the appearance of the spatio-temporal self-organization of non-linear dissipative systems, causes these observed effects. These characteristics of the system can be applied for fast IR imaging and a high speed UV light source.

Microcapillary plate as a built-in intensifier for semiconductor gas discharge image converters

Using a microcapillary discharge plate (MCDP) integrated with the discharge gap of a semiconductor gas discharge infrared image converter has been tested as a basis for building gas discharge image converters with internal image intensification. A Townsend-type discharge with current density controlled by infrared illumination of the semiconductor cathode is produced in a 100 μm gap in Ar gas under pressures of 50 – 200 hPa. Electrons generated in the discharge gap are multiplied by a non-self-sustained discharge in the MCDP of 100 μm thickness, which has just a single channel 200 μm in diameter. The authors have observed a significant increase of the discharge brightness in the MCDP channel compared to that of the main discharge gap.

Current instability in a planar gas discharge system with a large-diameter semiconductor cathode

The current instability in a planar gas discharge system is studied experimentally in a wide range of the gas pressure, p (44–550 Torr), interelectrode distance, d (45–330 µm), and diameter, D (5, 9, 12, 18, 22 mm), of the electrode areas of the semiconductor cathodes. While being driven with a stationary voltage, it generates current instabilities with different amplitudes of the oscillation. Through spatially uniform irradiation of the semiconductor cathode, non-stationary states which are non-homogeneous can be generated in a system. It is shown that under the experimental conditions the discharge gap played only a passive role and was not responsible for the appearance of the current instability. At the same time, for different diameters, D, of the electrode an expanded range of current oscillations is observed. The pronounced N-type negative differential resistance is observed in the current–voltage characteristic of a planar gas discharge system with a large-diameter semiconductor cathode.

A Large Emitting Area UV Light Source With Semiconductor Cathode

Light emission in the ultraviolet (UV) and visible (blue) range (330-440 nm) generated by a planar gas discharge system and the possibility of locally increasing the discharge light emission for a given photosensitivity of a planar GaAs semiconductor cathode has been studied. The use of metallic patched concentrators with an area of S=5/spl times/10/sup -4/ cm/sup 2/ and a density of 400 cm/sup -2/ leads to a fivefold increase in the gas light density. In a system with metallic patched concentrators, the local density of gas discharge light exceeds the density of uniform gas discharge light in the ionization system as many times as the working area of the semiconductor cathode exceeds the total area of the current concentrators. By using the infrared light to excite the semiconductor cathode of the system, we have shown that the uniform discharge light emission of the device with N/sub 2/ in the gap can serve as a source of UV radiation with a large emitting area of GaAs cathode if gas pressure and electric field are sufficiently high. Moreover, the use of metallic patched concentrators prolongs the working time of the cathode. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap, which changed the discharge from the Townsend to the glow type.

Behaviour of current in a planar gas discharge system with a large-diameter semiconductor cathode

Gas breakdown in air in a planar gas discharge system was studied experimentally at various distances L between the electrodes and different diameters R of the electrode areas of the semiconductor cathodes. The cathode was irradiated on the back-side with light in a particular wavelength range that was used to control the photoconductivity of the material. The current–voltage characteristics of the gas discharge system with a large-diameter GaAs semiconductor cathode were studied in a wide range of the gas pressure p (28–550 Torr), interelectrode distances L (45–330 μm), and conductivities of the cathode. We show that for all experimental conditions the current density increases over the entire range of voltages U>Udc as the diameters R of the electrode areas increase. It is shown that, for arbitrary geometric dimensions of the semiconductor cathode (in the range of L/R under investigation), the ratio of the breakdown electric field to the gas pressure holds constant (Edc/p)min≈const. at the breakdown curve minimum. The breakdown voltage Udc is a function of both the product of the gas pressure p by the distance L and the ratio L/R (Udc = f(pL,L/R).

Electronic behaviour and field emission of metal–semiconductor–insulator–metal (MSIM) heterostructures based on a-C:H films

In this paper, we report on electronic and field emission properties of metal–semiconductor–insulator–metal (MSIM) heterostructures employing semiconducting and insulating hydrogenated amorphous carbon (a-C:H) films. The a-C:H layers were deposited from plasma polymerisation of methane in a 20 kHz discharge. The current as a function of voltage ( I– V) characteristic is consistent with Fowler–Nordheim (F–N) type tunnelling of carriers from semiconductor cathode into polymer-like a-C:H. The onset field for emission is about ∼6 V/μm. The transition barrier is found to be ∼0.05 eV, which is close to that obtained with a-C:H:N/Si heterojunctions. capacitance–voltage ( C– V) measurements show negligible hysteresis and zero flat band voltage, and the interface states density, estimated from capacitance–frequency plot, is very low ( N SS∼4×10 10 cm −2). Heterostructures based on amorphous carbon films are perspective for the development of field emission displays (FEDs).

Multioscillatory patterns in a hybrid semiconductor gas-discharge system.

A planar pattern forming semiconductor gas-discharge device is examined. While being driven with a stationary voltage, it generates patterns that contain domains oscillating with different frequencies. The multioscillatory pattern is formed in a sequence of bifurcations from the homogeneous stationary state. A nonlinear interaction between different parts of the pattern can be detected. It is suggested that the observed behavior is due to the coupling of processes in two nonlinear components, the gas-discharge gap and the semiconductor cathode fabricated from high resistance gallium arsenide.

Emission characteristics of semiconductor cathodes

AbstractThis paper describes emission characteristics of MOS (metal–oxide–semiconductor) electron tunneling cathodes and Si field emitters, and shows that their characteristics reflect the energy band structures of the semiconductor and the electron transport in an incorporated semiconductor device. In addition, it proposes hybrid electronics combining solid‐state device and vacuum device technologies, and shows that this approach provides highly efficient high‐frequency devices with coverage from the microwave to the optical wave regions. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(5): 1–9, 2001

Nonlinear interaction of homogeneously oscillating domains in a planar gas discharge system

A planar dc gas discharge system with a high Ohmic semiconductor cathode is investigated with respect to temporal destabilization of the stationary homogeneous state. A subcritical Hopf bifurcation is observed, leading to a spatial homogeneous oscillation. The dependence of the oscillator's properties on control parameters is investigated. By applying spatial nonuniform optical control of the semiconductor cathode, several domains that may oscillate on different frequencies can be created. These spatially homogeneous domains can interact with each other through common boundaries. By adjusting the strength of coupling of the domains, their interaction can be controlled. In this interaction, regularities have been found that are, in some aspects, similar to those observed in externally driven nonlinear oscillators.

The concentration of currents on the artificial surface inhomogeneities of semiconducting cathodes in ionization cells

The possibility of locally increasing the gas-discharge light emission for a given photosensitivity of a planar GaAs semiconductor cathode has been studied. The maximum emittance of gas-discharge light for given values of the residual pressure, the feeding voltage and the intensity of external illumination is determined by the photosensitivity of the semiconductor cathode. In a system with inserted metallic current concentrators the local density of gas-discharge light exceeds the density of uniform gas-discharge light in the ionization system as many times as the working area of the semiconductor cathode exceeds the total area of the current concentrators. The filamentation was primarily due to the formation of a space charge of positive ions in the discharge gap which changed the discharge from the Townsend to the glow type. The assessment of the image formation is then based on analysis of the discharge light emission, visualized by taking a photograph through the transparent anode plate. Means of locally increasing the light emission and improving the working characteristics are proposed.

Behaviour of current in gas discharge system between parallel-plane electrodes

The current-voltage characteristics of a gas discharge system in parallel-plane geometry are studied. The gas discharge system with a photosensitive semiconductor cathode have been studied in a wide range of the gas pressures p (21.3-1013 hPa), inter-electrode distances d (10 μm-5 mm), and conductivities of the semiconductor. Gallium arsenide (10 7 -10 8 Ω cm) has been used as the semiconducting cathode. The cathode was irradiated on the back-side with light in a particular wavelength range that was used to control the photoconductivity of the material. The semiconductor material was found to stabilize' the discharge. When the current is increased above the stable limit, breakdown or small current oscillations begin. The filamentation was primary due to the formation of a space charge of positive ions in the discharge gap which changed the discharge from the Townsend to the glow type.

Metal–insulator–semiconductor emitter with an epitaxial CaF2 layer as the insulator

An 8-nm-thick epitaxial CaF2 layer grown on an n+-Si substrate was used as the insulator in a metal–insulator–semiconductor cathode with a 10 μm2 emitter region. The fabricated cathodes exhibited two different types of I–V characteristics. The first type showed conventional tunnel emission current of 22 pA at an emitter current of 2.4 mA and an emitter voltage of 7 V. The emitter with the other type of characteristics showed an emission current of 5.6 nA at an emitter current of 2.2 mA and an emitter voltage of 4.5 V but it showed current instability.

真空と電子源 半導体電子源の電界電子放射特性

A metal-oxide-semiconductor (MOS) electron tunneling cathode using n-and heavily doped p-type Si substrates were fabricated and their characteristics were measured. Two energy peaks in the energy distributions of emitted electrons from the n-type and the p-type cathodes were observed. The paper discuses the experimental results to clear an emission mechanism from a semiconductor cathode and shows that a part of electrons are emitted into vacuum from the valence band of Si substrate by tunneling through the oxide barrier. In addition, the paper discusses a functional cathode with high emission efficiency and low energy dispersion based on a concept of energy band engineering of semiconductor.

Cone-shaped metal–insulator–semiconductor cathode for vacuum microelectronics

A cone-shaped metal–insulator–semiconductor (MIS) cathode, in which a field emitter is combined with a MIS structure, has been proposed in order to achieve a low-voltage operation and stable cathode for vacuum microelectronics. The cathode can supply the electrons with higher energies than those at the Fermi level of the metal surface of the emission area, by which the emission voltage and stability of a field emitter will be improved. We made a theoretical investigation on the influence of the electron energy to the electron transmission coefficient. It was found that the transmission coefficient increased drastically with the electron energy. The cone-shaped MIS cathodes were fabricated and their characteristics were investigated in a high vacuum condition. The emission efficiency reached 8% without applying an external electric field. We also confirmed the reduction of the emission voltage by 5 V with the external field. Fundamental characteristics of the cone-shaped MIS cathode have been demonstrated.

Temperature dependence of the Fowler–Nordheim current in metal-oxide-degenerate semiconductor structures

A comprehensive study of the temperature dependence of the Fowler–Nordheim (F–N) tunnel emission in a metal-oxide-semiconductor structure is conducted both theoretically and experimentally. The theoretical variations with temperature of the F–N emission is analyzed both for metallic and degenerate semiconductor cathode materials. The influence of the electron concentration of a degenerate semiconductor on the amplitude of the F–N current is demonstrated. A new analytical formula for the F–N current temperature dependence is derived from the exact expressions using the Sommerfeld expansion. This new analytical approximation proves to be much more efficient than the previous analytical formula developed by Good and Müller [Field Emission, Handbuch der Physik, Vol. 21 (Springer, Berlin, 1956)] and may be very useful for F–N current computer-aided-design-oriented numerical simulation. The experimental study of the F–N current in MOS capacitors clearly demonstrates the strong impact of temperature on the F–N emission above 250 °C. It is also shown that the pre-exponential and the exponential F–N coefficients can still be determined as a function of temperature. The relative variation with temperature of the experimental F–N current data can be well interpreted by the exact F–N emission formula provided that the temperature dependence of the semiconductor (metal) -oxide barrier height Φb is well accounted for by a quasilinear function of temperature. The absolute amplitude of the F–N current can also be satisfactorily predicted by the exact F–N theory while adjusting the semiconductor electron concentration.

An effective infrared-visible conversion technique for remote quantitative measurements of thermal fields

In this paper we study the applicability of a semiconductor gas discharge (SGD-) structure with a cryogenic discharge in neon for measuring spatially extended temperature distributions of heated bodies. The IR radiation from a heated body excites the photosensitive semiconductor cathode of the device thus controlling the current density and the visible light emission from the gas discharge layer. The infrared radiation distribution emitted by the heated body can be found from the visible discharge glow in the gas layer. Present experimental investigations show that the lower temperature limit of this technique is about 400 K while the spatial resolution is in the order of 50 to 100 μm.

Energy distribution of tunneling emission from Si-gate metal–oxide–semiconductor cathode

An Si-gate metal–oxide–semiconductor (MOS) electron tunneling cathode was fabricated and its emission characteristics were examined. The emission occurred at a gate voltage higher than the work function of the Si gate by electron tunneling through the potential barrier in the MOS cathode and was stable in the Si-gate cathode. The energy distribution of emitted electrons was measured and was confirmed to be mainly determined by the scattering process of hot electrons in the oxide. The emission current from the Si-gate MOS cathode was nearly independent of pressure.

Reactive Ion Etching Techniques for Silicon Sidewall Angle Control in Microengineering

This paper describes reactive ion etching (RIE) techniques with silicon substrates for initial processing of semiconductor field emitter array cathodes for vacuum microelectronics. A secondary focus is process research for optical reflecting gratings for opto‐ and micromechanical devices. These applications each require control of the sidewall angle and apex radius. In this paper, we describe micromachining control of trenches with remainder sidewall angles varying from 15–60° and resulting apex ridge radii of as small as 40 nm. A fluorine‐based chemistry with oblique angles for the incident beam (tilted substrates) and overetching is used. The use of both deep UV‐hardened photoresist and aluminum as RIE shadowmasks is compared. Unannealed aluminum as a shadowmask for RIE micromachining has the advantage of lower etch/sputtering rates and higher process temperature tolerance compared to photoresist in the RIE system. Etch environments in the pressure range 30–80 mTorr with flow rates of 20/2 seem, RF power 100–200 W, and etch duration 30 min are described. Both tilted and untilted substrates mountings were studied. Under these conditions, the surface erosion is primarily a combination of ion milling and chemical etch mechanisms. Both P‐type and N‐type substrates of 100 nm diam wafers were used. Relatively sharp single‐ and double‐ridged silicon structures were obtained using the photoresist shadowmask on untilted substrates. The photoresist shadowmask provides an advantage over Al only for the sidewall orientation where we were able to specify a condition for obtaining a smooth optically reflective surface. The more vertical sidewall angles obtainable with the unannealed Al shadowmask should permit fabrication of field emitter cone or ridge cathodes on pedestals with higher height‐to‐width ratios. A field cathode pedestal with a more vertical sidewall results in a higher electric field at the electron emission tip or ridge.

The Analysis of Growth Kinetics in Liquid Phase Electroepitaxy (LPEE) of binary systems

AbstractGrowth kinetics of binary systems in liquid phase electroepitaxy (LPEE) is analysed in terms of one‐dimensional forced diffusion with initial and boundary conditions reflecting the features of various modifications of LPEE. Electromigration of a solute in the melt and the Peltier effect at the interface between liquid and solid phases induced by electric current are taken into account.Three LPEE modifications are considered here. The first modification is when liquid phase is constantly riched due to dissolution of the semiconductor cathode. The second one‐when liquid phase is constantly riched from vapour phase by controlled vapour pressure. The third one‐when any source of the melt enrichment is absent.This consideration is limited by the assumption that the deviation of the solution heighs or convection doesn' affect the steady‐state temperature at the interfaces between solid and liquid phases. The obtained expressions for growth rate show that quantitative results of the epitaxial growth are closely connected with a concrete method of LPEE realization.