摘要:

In GaAs doping superlattices the conductivity parallel to the constituent layers is tunable over wide ranges by injection or extraction of free carriers via selective electrodes. The transport simultaneously involves electrons in thenlayers and holes in theplayers. The tunability of bipolar conductivity depending on temperature in the range 10 to 300 K and on the design parameters of the superlattice configuration is analyzed in detail. The carrier concentrations and mobilities as a function of biasUnpare determined independently from Hall effect measurements. The observed tunability of carrier concentration is in good agreement with calculations based on a simplified semiclassical approach. The carrier mobility is found to be strongly influenced by the carrier concentration and correspondingly by the effective thickness of the constituent superlattice layers. This behavior is analyzed in terms of the classical size effect. Only a minor influence of the temperature on the carrier mobility is detected. The temperature dependence of the carrier concentration is solely determined by the temperature dependence of the threshold voltage. The present detailed investigation is of importance for application of GaAs doping superlattices in bulk multijunction field effect transistors.

ISSN:1071-1023    

DOI:10.1116/1.582907

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

High purity, single‐phase TiSi2thin films were prepared by deposition of titanium onto polycrystalline silicon layers followed by furnace annealing. Measurements of the temperature dependence of resistivity show that the material behaves as a classical metallic conductor, with an intrinsic resistivity proportional to temperature and having a room temperature value of ∼11μΩ cm. Geometrical magnetoresistance measurements on Corbino disk samples give a ‘‘representative’’mobility value (∼60 cm2/V‐s at room temperature) that mirrors the temperature dependence of resistivity. The very small Hall effect, taken together with a sizeable physical magnetoresistance, indicates the material is predominantly an electron conductor with a spectrum of mobility values for carriers on the Fermi surface because an isotropic, two‐band model cannot quantitatively account for the data.

ISSN:1071-1023    

DOI:10.1116/1.582905

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

A variational calculation of hydrogenic impurity binding energies in quantum well wires has been performed. The binding of the hydrogenic impurity has been calculated as a function of the transverse dimensions of the wire. It is found that the binding energy of the hydrogenic impurity increases as the ratio of the Bohr radius of the impurity in a bulk semiconductor to the transverse dimension of the wire increases. To test the sensitivity of the binding energies to the trial wave function we have used in our calculations, we use a wave function of the same type to calculate the binding energy of hydrogenic impurities confined in a quasi‐two‐dimensional quantum well as a function of well width and compare our results for the binding energies to the results obtained by Bastard [Phys. Rev. B24, 4714 (1981)].

ISSN:1071-1023    

DOI:10.1116/1.582906

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Nickel was deposited on Si substrates and the feasibility of studying the formation process of Ni silicides with the atom‐probe mass spectrometer was examined by atomic layer‐by‐layer mass analysis of the specimen from the deposited layer to the substrate through the interface. The epitaxially grown silicide with a well ordered cubic structure was observed when the specimen was heated above 800 K. The main part of the Ni–Si mixed layer formed at room temperature was Ni‐rich Ni2Si regardless of substrate materials, Ni or Si. At high temperatures the Ni concentration in the mixed layer depends on the substrate materials. The result indicates that the silicide composition is regulated by the diffusivity of Ni into Si at low temperatures and by the relative quantities of Ni and Si at high temperatures. A clear interface between the silicide and the Si substrate was formed at around 800 K.

ISSN:1071-1023    

DOI:10.1116/1.582908

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

This paper reports the use of a modulated ion beam system to probe the reaction dynamics occurring in an ion/surface interaction which results in the removal of material from a solid. A modulated ion gun (15 μs rise time) was used to provide pulses of incident ions (primarily CF+3) at a Si surface. The resulting products were detected by a mass spectrometer and signals have been observed at mass 28 (Si), mass 47 (SiF), mass 66 (SiF2), and mass 85 (SiF3, principal cracking fraction of SiF4). A comparison of the amount of signal with the measured cracking pattern of SiF4indicated that a substantial fraction of the Si left the surface with fewer than four fluorine atoms. By performing the experiments in two different sample positions, we have confirmed that complications due to collisions between the product molecules and the vacuum system walls have been eliminated. The time evolution of these product signals following the start of the ion beam pulse has been measured with signal averaging. The results are consistent with a model where mass 47 (SiF) and mass 66 (SiF2) are produced with ∼1 eV energy in a fast process. Roughly 70% of the Si is removed in this manner. In contrast, mass 28 (Si) and mass 85 (SiF3and SiF4cracking fraction) have an appreciably slower time dependence and a model which partially fits this observation assumes that these species are produced at the same time as SiF and SiF2but have thermal (0.02 eV) energies and thus take longer to reach the mass spectrometer. The observed time dependence is even slower than this model predicts, however, which indicates the possibility of a surface residence time delay due to the formation of a surface complex prior to the desorption of the products.

ISSN:1071-1023    

DOI:10.1116/1.582910

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Oxygen ion beam etching for resist materials has been studied. Etch rates of resists depend on oxygen pressure and on acceleration ion energy. The oxygen pressure dependence of etch rates is attributed to the effect of ion assisted neutral oxygen molecules. The neutral oxygen contribution leads to high etch selectivity for resist materials over metals; a selectivity more than 50 is obtained for AZ1350J over Au at 100 eV acceleration energy condition. The oxygen ion beam etching is applied to the pattern transfer for the multilevel resist technique. Hard baked AZ1350J, titanium, and PMMA are applied for a bottom layer, a middle layer, and a top imaging resist layer material, respectively. Under low acceleration energy conditions, an undercut profile is observed in the transferred patterns due to large ion beam divergence. At 500 eV, patterns having square cross sections are obtained. However, with the increase in gap aspect ratio (etch depth over gap width), a slight widening of etched channels at their midpoint (barrel shaped channel) is observed.

ISSN:1071-1023    

DOI:10.1116/1.582911

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

This paper reports on etch yield measurements on Au films by ion beams generated from Ar, Ne, O2, N2, CF4, and C2F6in a Kaufman‐type ion gun for ion energies between 0.2 and 1.4 keV. Ions and neutral species emanating from the gun are characterized by mass spectrometry. For CF4and C2F6the ion composition is a strong function of the magnetic field in the gun, CF+3being the major ion only for CF4at low magnetic field. The physical etch yield of CF+3is found to be close to that of Ne+, not Ar+. The results on the dependence of the etch yields on ion mass, ion energy, and incident angle can be correlated quantitatively by assuming complete dissociation of molecular ions upon impact on the substrate. The same model is also shown to explain the data by Tachietal. on etching Si by mass‐selected ions of the form CF+xand BF+x. The implications of these results for plasma and reactive ion etching are discussed.

ISSN:1071-1023    

DOI:10.1116/1.582912

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

A reactive‐ion‐etching technique for direct transfer of resist grating patterns onto InP surfaces was developed. A mixture of CCl4and O2at a pressure of 1–5×10−3Torr enabled a high etching rate of about 850 Å/min for InP. The etch rate ratio of InP to AZ‐1350 resist was 3.5‐1. Fine grating patterns with periodicity of 4700 Å were successfully transferred to InP and a corrugation depth of about 2000 Å was obtained.

ISSN:1071-1023    

DOI:10.1116/1.582913

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

Chronic problems have been experienced in integrated circuit fabrication lines in the formation of Ohmic contacts between Al–Si interconnect metallization and device (bulk or epi) silicon. One of the reasons for such problems has been the absence of a simple and reliable method for predicting, immediately after metal deposition, whether or not the contact resistances in the finished circuits will be satisfactory. This paper describes and demonstrates such a method for (Al–1% Si)/(phosphorus‐implanted)n+Si contacts.

ISSN:1071-1023    

DOI:10.1116/1.582915

出版商:American Vacuum Society    

年代:1984

数据来源: AIP

摘要:

The effects associated with implanting high power ion beams into photoresist masked silicon wafers have been investigated. Outgassing from the photoresist mask can result in significant dose control errors when Faradays with conventional electrostatic suppression schemes are used. Sheet resistivity measurements show that these errors can be reduced by a factor of 3 when a magnetic suppression technique is employed. With magnetic suppression of secondary charged particles from target impact with an arsenic primary ion beam dose control accuracy is better than 2%, even under severe outgassing conditions. A semiempirical model confirms the sheet resistivity results.

ISSN:1071-1023    

DOI:10.1116/1.582916

出版商:American Vacuum Society    

年代:1984

数据来源: AIP