摘要:

Plasma‐enhanced chemical‐vapor deposition (PECVD) with the surface irradiated by a 193 nm, 50 Hz pulsating laser was performed to synthesize boron films from B2H6+He at a pressure of 200 Pa, where the plasma was employed to generate precursor radicals for the growth while the irradiation was intended for photochemical enhancement of the surface processes such as migration and growth reactions. In addition to the PECVD, PECVD without the irradiation as well as pyrolytic CVD with and without the irradiation were done so as to clarify the effects of the plasma and the laser in the CVD. Micromorphological boron columns were found to grow toward the laser light, and this indicated directly that the surface growth reactions were enhanced photochemically at the laser energy density of 170 mJ/cm2per pulse. Heating of the surface by the irradiation at this energy density was estimated to be negligible. In the pyrolytic CVD, where the surface migration of the precursor radicals was considered to be relatively hindered according to measured activation energies, a morphological change was found to indicate irradiation‐enhanced migration at the laser energy density of 3 mJ/cm2per pulse. Semiempirical molecular orbital calculations predicted that borane molecules (BH3) should be the dominant precursor in the pyrolytic CVD while the counterpart could be BH2radicals in the PECVD: This prediction supports a hypothetical photoinduced growth reaction such as BH*2+nh&ngr; = B(s) + H2(n=1,2, ...) where BH*2signifies a BH2radical chemisorbed to a site for growth reaction and B(s) does a boron atom incorporated into the solid structure. This prediction was also consistent with the experimental result that crystalline boron films have grown only in the PECVD while the pyrolytic CVD yielded only amorphous growth at substrate temperatures between 690 and 890 °C. The predicted precursor BH3for the pyrolytic CVD suggested its photoinduced migration mechanism similar to the photolysis of diborane.

ISSN:0021-8979    

DOI:10.1063/1.350499

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very‐high‐frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50 °C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional frequency of 13.56 MHz considerable differences concerning the electronic and structural properties are observed as the substrate temperature is decreased from 280 to 50 °C. Down to a substrate temperature of 150 °C the electronic film properties change only a little and the total hydrogen contentcHand the degree of microstructure that can be directly correlated tocHincrease only moderately. Below 150 °C the electronic properties deteriorate in the usual manner but still the total hydrogen content does not exceed 21 at. % even at a substrate temperature of 50 °C. It is argued that the influence of the higher excitation frequency on the plasma and on the growth kinetics plays a key role in this context by allowing a highly effective dissociation of the process gas with the maximum ion energies remaining at low levels. It is concluded that deposition processes at higher excitation frequencies can have important technological implications by allowing a decrease of the deposition temperature without losses in the material quality.

ISSN:0021-8979    

DOI:10.1063/1.350500

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Carbon thin films have been prepared by 248 nm excimer laser vaporization of graphite targets. The effect of a variety of process parameters on the film properties is investigated. Deposition at or below room temperature yields diamond‐like films with low hydrogen content, high optical transmission, and high resistivity. Electron energy loss spectra indicatesp3bond fractions of 70–85%. Detailed analyses of the pseudodielectric functions, measured using spectroscopic ellipsometry, show the films to have normal dispersion and an index of refraction of 2.5 in the visible wavelength region. The effects of a low pressure hydrogen background and the use of auxiliary pulsed and dc plasma enhancements are also examined.

ISSN:0021-8979    

DOI:10.1063/1.350501

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

An analytical study of a waveguide with two parabolic cylindrical surfaces separating the guiding region of refractive indexn1from two cladding regions of common refractive indexn2withn1≳n2is presented. The cutoff conditions for modes are derived as equations containing trigonometric functions. The modes show a bunching tendency instead of well‐defined discreteness, and several mode bunches occur because the distance of separation between the two interfaces does not remain constant but continues to increase as one moves away from the region near the vertices of the parabolas. Unlike the planar waveguide, a nonzero cutoff is deduced which may be attributed to the curvature of the boundaries, and the flare.

ISSN:0021-8979    

DOI:10.1063/1.350502

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper describes a vectorial finite element method for the analysis of electromagnetic waves propagating in helical systems. The present method can be as easily used as the methods for guided electromagnetic waves in systems with translational and axial symmetries. The functional for the vector Helmholtz equation is minimized using twisted coordinates in which the problem becomes two‐dimensional. The spurious solutions, which do not satisfy the divergence‐free condition, are removed on the basis of the penalty method. Two finite element equations for the covariant and contravariant components of electromagnetic fields are derived and boundary conditions for both formulations are described. The present method is applied to the analysis of a twisted waveguide with a rectangular cross section and the numerical solutions are shown to be in good agreement with the perturbed solutions for a small helical pitch.

ISSN:0021-8979    

DOI:10.1063/1.350503

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The interactions, in GaAlAs/GaAs heterojunction bipolar transistor structures, between implanted Mg atoms and differentp‐type base dopants (Be in layers grown by molecular beam epitaxy, Zn or C in layers grown by organometallic chemical vapor deposition) have been investigated. Different diffusion behaviors have been observed, according to the base dopant, either for the implanted Mg or for the base dopant itself. The resultant hole concentration profile obtained with aC–Velectrochemical profiler has also been studied as a function of the basep‐type dopant.

ISSN:0021-8979    

DOI:10.1063/1.351355

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Low leakage currentp+/nstep junctions with mechanically stable ohmic contacts top+layer are fabricated onn‐InP wafers simultaneously by a simple procedure consisting of vacuum evaporation of Ni, Zn, and Au followed by a short heat treatment at 340 °C. Current‐voltage and capacitance‐voltage measurements, secondary ion mass spectroscopy, and deep level transient spectroscopy are employed to characterize the diodes fabricated and to understand their structure.

ISSN:0021-8979    

DOI:10.1063/1.351356

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present Fourier transform infrared photoluminescence (PL) and absorption studies on GaAs:Fe to analyze the origin of the Fe‐related emission at 3057 cm−1. Temperature‐dependent PL spectra show additional hot lines and a characteristic phonon sideband linked to this Fe‐related peak. Time‐resolved studies, using the 1.06 &mgr;m line of a Nd:YAG laser for excitation, reveal a decay time of 1.9±0.3 ms. The long lifetime and the fine‐structure splitting fit a model where the transitions take place between the4T1excited state and the6A1ground state of Fe3+(3d5) in tetrahedral environment.

ISSN:0021-8979    

DOI:10.1063/1.350504

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A method is presented for the Auger generation suppression in narrow‐gap semiconductors using the magnetoconcentration effect for the case when all the generation‐recombination mechanisms (Auger, radiative, and Shockley–Read) are taken into account. A numerical solution is given for the kinetic equation determining carrier concentration distribution in a thin semiconductor slab placed in an electric and a magnetic field. The results of the numerical calculation show that the Auger generation suppression becomes very efficient when the concentration of Shockley–Read recombination centers is small enough.

ISSN:0021-8979    

DOI:10.1063/1.350505

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present a novel application of the Fresnel zone plate geometry in which the Mo¨ssbauer effect is used to focus nuclear‐resonant x‐ray photons and thereby to monochromatize synchrotron radiation. The calculated efficiency and energy bandpass of the Mo¨ssbauer–Fresnel zone plate monochromator compare well with those of other Mo¨ssbauer‐effect monochromators currently in use. The unique capability of focusing Mo¨ssbauer radiation into a small (few &mgr;m) spot may have applications in spatially resolved and high‐pressure Mo¨ssbauer‐effect studies.

ISSN:0021-8979    

DOI:10.1063/1.350506

出版商:AIP    

年代:1992

数据来源: AIP