摘要:

We report the quantum efficiency of various metals irradiated by 266‐nm, 4.66‐eV laser pulses of 10‐ps duration. The highest quantum efficiency obtained is 7.25×10−4with samarium photocathodes. Current densities exceeding 66 and 21 kA/cm2have been obtained from an area of 0.05 and 7 mm2, respectively. The maximum currents and current densities obtainable in these experiments are limited by the space charge. For surface fields exceeding 5×107V/m on gold, the efficiency increases linearly with the field for the values investigated. Based on the quantum efficiency and optical damage threshold measurements, current densities exceeding 100 kA/cm2seem feasible without damaging the photocathode.

ISSN:0021-8979    

DOI:10.1063/1.348550

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The growth rates of GaP and InP deposited by metalorganic molecular beam epitaxy using triethylgallium, trimethylindium, and precracked phosphine have been studied by reflection high energy electron diffraction and related to composition variations of the ternary alloy GaxIn1−xP. The influence of the substrate temperature and phosphine flow rate have been investigated for each material. The GaP growth rate dependence with temperature exhibits qualitatively the same behavior as already reported for the growth of GaAs by metalorganic molecular beam epitaxy. In the case of InP, a constant growth rate is observed in the temperature range of 450–500 °C. At higher temperatures, a strong decrease of the growth rate, attributed to the desorption of dimethylindium species, is measured. Meanwhile, the GaxIn1−xP composition is found to become Ga rich while increasing temperature. Furthermore, it is found to significantly depend on the phosphine flow rate at a fixed temperature. In the low phosphine flow regime, the composition is associated with the preferential formation of GaP bonds, and in the high phosphine flow regime, the composition is closely correlated with the sharp decrease observed for the binary InP growth rate.

ISSN:0021-8979    

DOI:10.1063/1.348551

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present the results from the photoreflectance (PR) analysis of a set of molecular‐beam epitaxially grown silicon on sapphire films whose thicknesses ranged from 6 to 4000 nm. The strain undergone by the silicon films due to lattice mismatch at the silicon sapphire interface and to the difference in the thermal expansion coefficient of the two materials was investigated. To this purpose the position of the 3.4‐eV PR structure was monitored with bulk silicon as a standard. A shift of this structure toward lower energies was observed in the thinnest films. A drastic increase in elasticity is observed as the film thickness varies from 550 to 700 nm. This fact can be correlated with transmission electron microscope observations of the predominant defects in the films. Special attention was also devoted to the effects of native oxide on the films, that appeared to cause a shift of the 3.4 eV structure toward higher energies. This shift suggests that the native oxide layer is exerting a compressive strain on the silicon films.

ISSN:0021-8979    

DOI:10.1063/1.348552

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Reactive ion‐beam deposition of zirconia films is carried out to demonstrate the characteristic difference between the sputtered species from a metallic zirconium target and a compound zirconia target, and their effects on the structural properties of deposited films. Films deposited from the compound target have compositions much closer to the ideal stoichiometry of zirconia, and have higher stresses and are mechanically harder, due to the ionic nature of the sputtered species and their inherently low mobility on the substrate surface. In contrast, adatoms sputtered from the metal target are chemically less active but have a higher mobility which facilitates the relief of film stress by low‐energy Ar+bombardment during deposition. This stress modification process requires a much greater dosage of Ar+flux when a compound target is used. X‐ray diffraction analysis indicates that all of the zirconia films deposited from the metal target are amorphous, whereas the monoclinic phase is observed in the films from the compound target at sputtering energies of 500 and 1000 eV. However, the monoclinic crystallites diminish as additional energy is imparted to the growing film from either a higher sputtering energy or a greater flux of Ar+bombardment. The polymorphic transformation of zirconia films is examined by isochronal annealing of the films in a temperature range from 150 to 600 °C. The phase transformation of the zirconia films shows that the monoclinic zirconia persists after annealing while the amorphous matrix transforms into a cubic structure in the temperature regime from 300 to 450 °C.

ISSN:0021-8979    

DOI:10.1063/1.348553

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thermal decomposition mechanisms have been inferred for a series of organoarsine chemical vapor deposition precursors, and this data has been correlated with the quality of GaAs films grown from these reagents. Tri‐, di‐, and mono‐ethylarsine, as well as a mixture of triethylarsenic and arsine, were pyrolyzed under pseudogrowth conditions, and their decomposition mechanisms were inferred from a qualitative and quantitative analysis of the reaction mixture components. The primary decomposition step for the ethylarsines appears to be a thermally induced, arsenic‐carbon bond homolysis to produce both an ethyl radical and an alkyl and/or hydride substituted arsenic radical species. For a mixture consisting of arsine and triethylarsenic, it appears that the triethylarsenic reagent undergoes arsenic‐carbon bond homolysis, and the radicals thus produced enhance the decomposition of the arsine coreagent. The more highly substituted ethylarsine reagents were found to generate the greatest number of alkyl‐substituted arsenic radicals upon decomposition, and also produced the least pure GaAs films. Since alkylarsenic radicals can react with a growing GaAs epilayer to cause severe carbon contamination, this decomposition data is consistent with the observed growth results. In the coreagent mixture, the free‐radical activation of arsine results in a large production of dihydridoarsenic radicals, which is consistent with the high‐purity, low‐carbon films produced from this reagent mixture. These results indicate that any viable organoarsenic precursor must decompose preferentially to produce hydrido‐arsenic radical intermediates, in order to produce high‐purity GaAs epilayers.

ISSN:0021-8979    

DOI:10.1063/1.348554

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Field effect transistors (FETs) have been fabricated with metal phthalocyanines and rare earth diphthalocyanines. The influence of the metallic ion in mono‐ and diphthalocyanines and the conditions of FET fabrication on electrical characteristics has been determined for devices tested in ambient atmosphere. Aging under various conditions has identified the role of oxygen on the device behavior. Unlike conventional inorganic FETs, these diphthalocyanine based devices work through the modulation of an accumulation layer formed by majority carriers.

ISSN:0021-8979    

DOI:10.1063/1.348555

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The base current densityJBis an important parameter in determining the common‐emitter current gain &bgr; of heterojunction bipolar transistors (HBTs). To develop an analytical &bgr; model with which a circuit designer can quickly estimate the current gain in a HBT, it is also important to identify the dominant component ofJBso that minimum computations are required. Based on heterojunction device physics, the three components ofJBhave been calculated, namely, the recombination current density in the baseJRB, the recombination current density in the space‐charge regionJSCR, and the injection current density from the base to the emitterJRE, and have determined their relative importance toJBfor abrupt AlGaAs/GaAs and InAlAs/InGaAs HBTs under normal bias conditions. It is found that relative importance of the three current densities depends strongly on the bias condition, strongly on the density of statesNtIat the emitter‐base heterointerface, but weakly on the density of trapping statesNtBin the bulk of the emitter‐base space‐charge region. Also,JBis relatively insensitive to device makeup such as doping concentration and layer thickness. Depending onNtIand on the bias condition, eitherJSCRorJREis the dominant component for AlGaAs/GaAs HBTs and eitherJSCRorJRBis the dominant component for InAlAs/InGaAs HBTs. Effects of base and heterojunction grading on the present findings are also addressed.

ISSN:0021-8979    

DOI:10.1063/1.348556

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Acoustic charge transport devices in GaAs are charge‐coupled devices that typically transport charge at the velocity of sound. However, charge transport can be temporarily inhibited by electrical barriers in the transport channel, a process known as charge storage. In this paper the fundamental properties of two methods of charge storage, single‐packet and double‐packet, are investigated and compared using theory and experiments. A 1‐D storage model is developed which provides insight into the dynamics of the charge storage process. The impact of charge storage on device frequency response is analyzed. Storage capacity is experimentally characterized as a function of storage voltage. The key factors that limit storage capacity are found to be intercell diffusion, surface charge extraction, barrier transition times, and delay‐line charge capacity. Furthermore, double‐packet storage has been found to provide higher storage capacity with less storage voltage than single‐packet storage.

ISSN:0021-8979    

DOI:10.1063/1.348562

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A coherent transport model is described which accommodates bandstructure nonparabolicity by using a ‘‘local energy parabolic band approximation.’’ The model and a knowledge of its limitations is used to design resonant tunneling diodes in the GaAs/AlAs material system with measured peak current densities of 2.5(2.8)×105A cm−2concurrent with peak‐to‐valley ratios as high as 1.8 (3.1) at room temperature (77 K).

ISSN:0021-8979    

DOI:10.1063/1.348563

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The Schottky‐barrier heights of several silicides on bothn‐ andp‐Si(100) have been measured in the temperature range 77–295 K. The results deviate significantly from the predictions of a recent model based on the assumption of barrier height inhomogeneities at such interfaces. For all these interfaces, the sum of the barrier heights ton‐ andp‐Si(100) is always equal, within the experimental accuracy, to the indirect band gap of Si. Furthermore, the temperature dependence of the barrier height suggests that the Fermi level at these interfaces is pinned relative to the Si valence‐band edge.

ISSN:0021-8979    

DOI:10.1063/1.348564

出版商:AIP    

年代:1991

数据来源: AIP