摘要:

It has been observed by several authors that metal‐oxide‐semiconductor devices with polycrystalline Si (poly‐Si) gates behave differently depending on the doping species in poly‐Si: the work‐function difference between the silicon substrate and the gate (&fgr;PS) is higher when the gates are doped with arsenic than when they are doped with phosphorus. As a function of the doping devel, this difference becomes first noticeable at ∼1019cm−3, and then it increases for heavier doped materials, reaching 120 meV near the dopant solubility limit. We believe that the different behavior of &fgr;PScan be explained by different grain textures at the poly‐Si/SiO2interface. Our transmission electron microscopy of the films indicates that while P‐doped material consists of large (≊3000 A˚) grains, As‐doped poly‐Si preserves its as‐deposited columnar structure, even after a high‐temperature anneal. Moreover, at the interface with the gate oxide an as‐deposited microstructure with very small (≊100 A˚) ‘‘embrionic’’ grains is preserved. On the basis of these observations, we suggest a model for the different behavior of &fgr;PS. The model is based on a quantum size effect which becomes important for such small grain dimensions at the interface in As‐doped poly‐Si. This effect drastically reduces the number of states available in the conduction band at low energies and thus forces a more complete filling of the impurity band. The resulting shift of the Fermi level provides a qualitative explanation for the observed puzzling difference between the work functions of As‐ and P‐doped poly‐Si.

ISSN:0003-6951    

DOI:10.1063/1.98482

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A double‐crystal x‐ray topograph was used to determine local strain in metal‐oxide‐semiconductor (MOS) transistor test chips. The double‐crystal machine could sense strains as small as 10−6, with a spatial resolution of a few micrometers. Results indicate that two types of strain are present: local surface strain as well as the more familiar strain due to bulk deformation of the crystal. Both types of strain have been correlated with surface mobility changes inn‐channel metal‐oxide‐semiconductor (nMOS) transistors.

ISSN:0003-6951    

DOI:10.1063/1.98483

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Ga‐As‐In‐As superalloy has been grown by atomic epitaxy on InP substrates. This has been achieved by sequential exposure of the substrate to trimethylgallium, arsine, triethylindium, and arsine. The thickness of the deposited film is in excellent agreement with the predicted value based on the number of exposure cycles. These results demonstrate that atomic layer epitaxy offers the ultimate control for depositing thin films. The superalloy films have been characterized by transmission electron microscopy and photoluminescence.

ISSN:0003-6951    

DOI:10.1063/1.98484

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We report the use ofinsitu, near‐threshold photoemission to study the dynamics of GaAs surfaces during epitaxial crystal growth and, in particular, the observation of oscillations in the photoemitted current. These oscillations are found to depend upon the growth rate in the same manner as do reflecting high‐energy electron diffraction intensity oscillations, occurring at the monolayer accumulation rate. We believe that they depend upon a cyclical variation in the step edge density on the growing surface and discuss the mechanism through which the oscillatory current may result from surface states or surface dipoles.

ISSN:0003-6951    

DOI:10.1063/1.98485

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

By surface passivation using anodic sulfidization, we demonstrated that the inverted surface effect which gives rise to negative Hall coefficients commonly measured inp‐type HgCdTe at low temperatures can be eliminated. Our results of Hall measurements as a function of magnetic field at 77 K and computer simulations allow us to distinguish two different existing models (with shunting or nonshuntingn‐type inversion layer) of the inverted surface effect. Bulk and surface transport parameters such as hole concentration, hole mobility, surface electron concentration, and surface electron mobility have been derived from computer best fits of experimental Hall coefficient curves.

ISSN:0003-6951    

DOI:10.1063/1.98486

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The recombination lifetimes for the radial and angular quantum number conserved 1S–1Sand 1P–1Ptransitions from three‐dimensionally confined electrons in CdSxSe1−xwere measured by time‐resolved photoluminescence (PL). The assignment of the observed transitions was supported by calculations of eigen energy levels and squared matrix element ratio for these transitions as well as well‐resolved PL peaks arising from 1S–1Sand 1P–1Ptransitions.

ISSN:0003-6951    

DOI:10.1063/1.98487

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A technique is described for preparing superconducting cuprate thin films using wet chemical precursors. This new method is simple and inexpensive, and allows facile manipulation of film stoichiometry. A solution of metal acetates in aqueous acetic acid is spun on a substrate, pyrolyzed, and heat treated. A 1600‐A˚ film of Ba2YCu3O7prepared by this method had a room‐temperature resistivity of 500 &mgr;&OHgr; cm,Tc(onset)of 90 K, andR=0 at 58 K. It showed preferential orientation with the orthorhombiccaxis perpendicular to the film, and random azimuthal orientation. The preparation and electrical and microstructural characterization of these films are discussed.

ISSN:0003-6951    

DOI:10.1063/1.98488

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have prepared thin films of Y‐Ba‐Cu‐O superconductors using a pulsed laser evaporation technique. Thin films were formed on (100) Si, (100) MgO, (1¯102) sapphire, (100) SrTiO3, and amorphous SiO2substrates using a XeCl excimer laser (&lgr;=0.308 &mgr;m, &tgr;=45×10−9s). The depositions were done in an ultrahigh vacuum chamber with pressure of about 10−6Torr during thin‐film formation. The deposition by pulsed nanosecond laser irradiation results in stoichiometry close to that of the target. The thickness of the film was controlled by varying the pulse energy density and the number of pulses. The substrate temperature was kept at 470 °C during deposition. Subsequent annealing treatments were carried out at 900 and 650 °C in oxygen atmosphere to recover the superconducting properties of these thin films. The resistance of these films was measured as a function of temperature using the four‐point probe method. These thin films were analyzed using cross‐section transmission electron microscopy, Rutherford backscattering spectrometry, and channeling techniques. The variation in the oxygen content and the interdiffusion of species into the substrate during subsequent annealing treatments are discussed.

ISSN:0003-6951    

DOI:10.1063/1.98489

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Single crystals of Ba2YCu3O7−&dgr;were prepared from melts of a BaO‐Y2O3‐CuO mixture and characterized by the x‐ray microprobe analyzer and x‐ray diffraction. Electrical resistivity was measured by the standard four‐terminal method. Some crystals have the critical temperature above 77 K. After annealing in oxygen, the crystals behave like a semiconductor.

ISSN:0003-6951    

DOI:10.1063/1.98490

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The structure and composition of the superconducting oxide YBa2Cu3O7−xhave been examined in atomic detail by field ion microscopy and imaging atom‐probe mass spectroscopy. The field ion samples were prepared from hot‐pressed disks of the oxide powders. Atomic resolution images were obtained with either argon or hydrogen as the imaging gas. Individual layers of atoms were observed which could be field evaporated in a uniform, layer‐by‐layer manner. Imaging atom‐probe analysis of the field ion tips indicated a metal composition which varied noticeably from sample to sample and an oxygen concentration which was consistently much too low.

ISSN:0003-6951    

DOI:10.1063/1.98491

出版商:AIP    

年代:1987

数据来源: AIP