摘要:

The photoluminescence (PL) and cathodoluminescence (CL) characteristics of lithium gallate and lithium zinc gallate were investigated as a function of composition and firing temperature. As Li/Ga of lithium gallate decreased, the emission peak shifted from about 420 to 390 nm under ultraviolet (UV) excitation. Similar results were obtained under cathode ray (CR) excitation. PL spectra of lithium gallates fired at high temperature were most similar to those of Li-deficient lithium gallate. This result clearly indicates that lithium gallate fired at high temperature is Li deficient. The PL and CL emission spectra of lithium zinc gallate consisted of a single broadband under UV and CR excitation. The emission peak of the composition of(1−x)Li0.5Ga2.5O4–xZnGa2O4shifted from 406 to 440 nm asxincreased under UV excitation and the peak intensity decreased withx.However, the intensity increased withxunder CR excitation. When the composition of lithium zinc gallate was0.4Li0.5Ga2.5O4–0.6ZnGa2O4,the brightest CL was observed.

ISSN:1071-1023    

DOI:10.1116/1.589920

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Additive nanolithography with electron-beam induced deposition is applied to generate a nanostructured integrated field emission electron source. The source is built into a lithographically fabricated pattern of connecting lines on a chip. Current stabilizing resistors are integrated in to the connecting lines with the deposition technique. Field emission microscope investigation of deposited supertips proves that a confined emission is delivered from conducting tips into a beam divergence angle of±7°.The reduced brightness of the deposited supertips is evaluated. A tenfold higher reduced brightness is observed if compared to conventional Schottky field emitters.

ISSN:1071-1023    

DOI:10.1116/1.589921

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

This article investigates the merits of molybdenum (Mo) silicide formation on gated polycrystalline silicon (poly-Si) field emitters. Metal silicides are promising materials for field emission cathode due to their high electrical and thermal conductivity and high-temperature stability. In our experiment, Mo silicide was produced by direct metallurgical reaction, that is, deposition of Mo and subsequent rapid thermal annealing. The surface morphologies and field emission properties of Mo-silicided poly-Si (Mo-polycide) emitters have been examined and compared with those of pure poly-Si emitters. Field emission from these Mo-polycide emitters exhibited significant enhancement compared with pure poly-Si emitters in both total emission current and stability. The reason for this improved electron emission efficiency and stability could be explained by the smaller work function and better surface inertness of Mo-polycide emitters than those of poly-Si emitters.

ISSN:1071-1023    

DOI:10.1116/1.589922

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We observed the emission characteristics and stability of TiN-coated Si field emitter arrays (FEAs) with a TiW gate structure. The TiN layer on Si tips was formed by a two-step rapid thermal nitridation process in anNH3ambient by which a Ti layer was thermally converted to aTiN/ TiSi2bilayer. This process could suppress the formation ofTiO2 on the surface and make the TiN layer thicker than a one-step process. By coating Si tips with TiN, the operating voltage of the TiN-coated Si FEAs was reduced by about 20 V compared with non-coated ones. Also, the TiN-coated Si FEAs showed thermally stable electron emission compared with non-coated ones.

ISSN:1071-1023    

DOI:10.1116/1.590222

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

Selective reduction of work function on a W(100) field emitter was observed due to co-adsorption of Si and Ti, followed by angular confinement of field emission on the top (100) surface. Si was vacuum deposited on the side surface near the apex of the field emitter by an amount, which is enough for spreading by 1 ML. Then it was flash heated to spread the deposited Si over the apex surface. Ti was vacuum deposited over it from the opposite side and heat treated to spread over. The work function, which is determined from the Fowler–Nordheim plot, reduced to 3.3 eV. It is assumed that the work function of the clean tungsten is 4.5 eV. The experimental evidences suggest that there is a certain Ti/Si ratio for giving the minimum value of the work function.

ISSN:1071-1023    

DOI:10.1116/1.589923

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

There is growing interest in high current field emitter arrays (FEAs) capable of delivering high current density and high conductance electron beams, particularly for microwave applications. Large, high packing density molybdenum and silicon FEAs have been placed in ultrahigh vacuum chambers, carefully conditioned, and tested for maximum performance and have yielded total FEA currents of 20–200 mA and beam current densities of5–2000 A/cm2at gate voltages of 80–150 V. However similar Mo and Si FEAs, and GaAs edge arrays, when placed in a prototype 10 GHz klystrode amplifier, have failed at 1–4 mA, even for pulsed operation at a low duty factor. Hence, the current must be increased by 25–50 in order to meet klystrode design objectives. We compare the intrinsic FE stable current limits of various materials: Mo, Si, GaAs, ZrC, and ZrC films on Mo emitters. We conclude that Mo FEAs have a high FE current limit but demand an extremely clean environment, Si or GaAs FEAs are more tolerant of a poorer environment but have a relatively low FE current limit, while ZrC/Mo FEAs have at least as equally high a FE current limit as Mo FEAs but are much more robust and tolerate a much poorer environment. We hypothesize that failures of high density Mo FEAs at relatively low current levels (below 1 μA per tip) in a microwave tube are due to ion bombardment of the FEA creating sharp nanoprotrusions on the sides of the emitters, which emit intense, focused electron beams directed at the gate, leading to a vacuum arc. Binh’s recent study presents strong evidence for the ongoing creation and destruction of nanoprotrusions on Mo FEAs. A ZrC thin film coating protects and passivates the Mo FEA surface, thus minimizing nanoprotrusion formation and allowing more stable operation at higher current levels and/or in more degraded environments. Studies of carbide (ZrC, HfC) film coatings on W, Mo, and Si single tips and on Mo and Si FEAs show that indeed the carbide film reduces the work function and operating voltage (by about 25% and 40%, respectively) and increases stability. Other studies still in progress show that blunt ZrC or ZrC/Mo single tips can operate for reasonable periods(∼1 h)at currents averaging 400 μA in ultrahigh vacuum or 200 μA in10−5 Torrair. More extensive studies are planned to verify and to quantify the advantages of carbide film coatings for producing lower voltage, higher current, environment tolerant, and long life FEAs for various applications.

ISSN:1071-1023    

DOI:10.1116/1.589924

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The transient emission current densities from flat band semiconductors and the stationary emission from graded electron affinity devices are computed by a combined semi-classical transport+transmission coefficient method. A rapid sequence of sharp current overshoots can be obtained in the first case for a wide range of built-up speeds of the external field. Their amplitudes and frequencies are field dependent and can be diminished by previous “heating” of the electronic system. In the second case, low field saturation and temperature assisted emission enhancement were found as expected. Several practical conclusions are drawn.

ISSN:1071-1023    

DOI:10.1116/1.589925

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

We have proposed a cone-shaped metal-insulator-semiconductor cathode (COSMISC) to improve the emission efficiency of the conventional metal-insulator-semiconductor cathode. This cathode is also recognized as the field emitter with prior electron acceleration mechanism. Since the COSMISC emits the electrons with higher energy than those at the Fermi level of the metal electrode, it is expected that the current fluctuation due to the change in work function of the metal electrode is less significant than that of a conventional field emitter. In this article, we analyzed the emission characteristics of the COSMISC in detail by Monte Carlo simulation, especially from the viewpoint of the emission stability against the change in work function of the upper metal electrode. The calculation procedure is as follows: electrons are generated according to their energy distribution at the semiconductor-insulator surface, and the scattering processes in the insulator and in the metal electrode were simulated with random numbers. Emission of electrons into vacuum was judged also according to the transmission probability at the surface barrier of the metal electrode. The obtained results are arranged with respect to the work function and also to the external field at the apex of the metal electrode. It was shown that the fluctuation of the emission current in COSMISC due to the change in work function is lower than that of the conventional field emitter.

ISSN:1071-1023    

DOI:10.1116/1.589926

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

A model to describe internal field emission through the interface between highlyn-doped Si and nitrogen (N)-doped diamond is presented. We describe the roughness on the Si surface as a collection of sharp, spherically pointed Si asperities embedded in the diamond film. These “tips” provide enhancement of the applied electric field, which, in conjunction with the high N doping of diamond, results in the formation of a Schottky barrier which allows for tunneling or internal field emission from the Si into the conduction band of diamond. This enhanced electric field is also sufficient to induce valence band tunneling from the Si into the diamond conduction band. In our model limitations on the field mediated transport of holes from then-doped Si/diamond interface to the cathode base leads to charging of the Si asperities. This charge accumulation results in band bending in Si and a significant reduction in the valence band current. The calculatedJ–Vcharacteristics for the internal field emission lead to nonlinear behavior when plotted in Fowler–Nordheim coordinates. This is a consequence of the limitation of the conduction band current due to density of states effects at high fields in addition to the suppression of the valence band current. The calculated results are in qualitative agreement with recent field emission studies of Okano et al. [K. Okano, S. Koizumi, S. Ravi, P. Silva, and G. A. J. Amaratunga, Nature381, 140 (1996)] for a compositen-Si and N–diamond cold cathode source. A plausible geometric argument suggests that there is also reasonable quantitative agreement.

ISSN:1071-1023    

DOI:10.1116/1.589927

出版商:American Vacuum Society    

年代:1998

数据来源: AIP

摘要:

The field emission current from ann-type GaN is theoretically calculated as a function of carrier concentrationn.The obtained emission current densityjincreases slowly with increasingneven though the band bending has the oppositendependence. In evaluating thendependence of field emission, the internal voltage drop due to field penetration is found to be crucial. The current densityjis also calculated for several electron affinities χ. It seems that at the lowest χ and at high field,F,the calculated emission currents from the bulk states can be close to the measured values. The electric field at the GaN conical tip is found to be very high in the large area and yield such a large emission current as measured in experiment.

ISSN:1071-1023    

DOI:10.1116/1.589928

出版商:American Vacuum Society    

年代:1998

数据来源: AIP