摘要:

X‐ray diffraction in thin layers containing small randomly placed defects is described by means of the kinematical diffraction theory and optical coherence formalism. The method enables us to calculate both the diffracted intensity and its angular distribution, so that it can be used for simulating double crystal and triple crystal x‐ray diffractometry experiments. The theory has been applied to experimental data obtained from diffractometry measurements of an epitaxial ZnTe layer with mosaic structure after several steps of chemical thinning. A good agreement of the theory with experiments has been achieved.  

ISSN:0021-8979    

DOI:10.1063/1.354828

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Metal adhesion to polymers depends on the chemical structure at the interface. In the present work, we study the evaporation of Cr, Ti, and Au onto Teflon PFA (perfluoromethyl‐vinyl‐ether) substrates, and we modify the interface by post‐deposition x‐ray irradiation.Insitux‐ray photoelectron spectroscopy shows that deposition of reactive metals such as Cr and Ti leads immediately to crosslinking and to the formation of carbide and fluoride species. Less reactive metals, such as Au, cause only small loss of fluorine without formation of any new species. The metal/PFA interface is strongly affected by x‐ray irradiation in the case of Cr and Ti: remarkably enhanced crosslinking has been observed, which further increases with the metal coverage, while the carbides and fluorides remain basically unaffected. On the other hand, crosslinking increases only very slightly for pure PFA and for the Au/PFA interface, regardless of the Au thickness. These results suggest that radical recombination reactions are responsible for crosslinking at the interface between PFA and reactive metals.

ISSN:0021-8979    

DOI:10.1063/1.354803

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Semiconducting &bgr;‐FeSi2is drawing much current research interest because of hoped‐for silicon‐based optoelectronics applications. The study of heteroepitaxial film growth on silicon depends heavily upon several transmission and reflection electron‐diffraction techniques. Because of the complicated crystal structure of this material, the possibility of competing heteroepitaxial relationships, the propensity for formation of epitaxial variants by rotation twinning, and the uncertainty in the crystalline surface nets, the analysis of experimental diffraction patterns is complicated. A theoretical reference for a number of fundamental electron‐diffraction patterns is provided and they are illustrated with a broad range of experimentally obtained patterns from the surfaces of epitaxial films.Insitutransmission reflection high‐energy electron diffraction (RHEED) (transmission electron diffraction with conventional RHEED instrumentation), from rough but epitaxial films, is of great utility and quite feasible with epitaxial systems such as this one, which exhibit a tendency toward islanding. The possibilities for experimentally distinguishing, with this technique, the competing epitaxial relationships on Si(111) are clarified; it is found that the &bgr;‐FeSi2(110) matching face is certainly present in these samples and the (101) may be also. An experimental determination of the two‐dimensional space groups of the (100), (110), and (101) faces is also presented—in the first and third cases the surface unit meshes are different from the simple projections of the bulk crystalline unit cell.  

ISSN:0021-8979    

DOI:10.1063/1.354804

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A time‐dependent model for focused‐ion‐beam‐induced deposition is presented which explicitly takes the scanning strategy of the beam during deposition into account. The model differentiates between the contribution of the beam center and that of the beam wings, and contains all major experimental variables such as current density, focus size, scan speed, and frame time. The deposition rate has been measured for tungsten as a function of the major experimental variables. The model has been fitted to these data and is found to describe the various dependences very well. By use of the model inclusive of the parameters obtained from the fit, we can predict optimum deposition conditions. Furthermore, the model clarifies effects observed during deposition on the structured surface of an integrated circuit, such as redeposition of sputtered material and poor step coverage due to an impeded gas flow.

ISSN:0021-8979    

DOI:10.1063/1.354805

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The segregation and interdiffusion of In atoms in the GaAs/InAs/GaAs heterostructures were investigated by secondary‐ion mass spectroscopy. When the 1‐ML‐thick InAs layer was grown in a layer‐by‐layer growth mode with no dislocations, the segregation of In atoms became marked with the increase of the growth temperature. However, the segregation was observed even at a relatively low growth temperature of 400 °C in molecular beam epitaxy. It was found that the segregation was markedly enhanced by dislocations near the heterointerface when thick InAs layers were grown in a three‐dimensional island growth mode. The interdiffusion of In atoms toward the growth direction occurred after thermal annealing, which could be assisted by vacancies propagating from the film surface into the epilayer. It became apparent that the interdiffusion was effectively suppressed by a thin AlAs layer inserted in the GaAs cap layer.

ISSN:0021-8979    

DOI:10.1063/1.354806

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A method for parameter identification in grazing incidence x‐ray reflectometry is presented. It is based on a nonlinear least‐squares approach with on‐line low‐pass filtering and fits the measured reflectivity curve as a function of the incidence angle to a simulation model. The filter is applied in the (angular) frequency domain; it introduces, even for strong filtering, no bias and renders the result independent of the angular stepsize of the data. Automatic restarting helps to determine the global solution. The commonly used roughness model is generalized to non‐normal distributions in order to assess data with large scattering vectors. The method is demonstrated for data from single and double film samples. Thickness and roughness can be determined with an accuracy of about 0.2 nm. However, only in special cases it is possible to determine accurately materials constants such as compositional fractions or densities. Absorption cannot be neglected, but the corresponding parameters are difficult to determine separately.

ISSN:0021-8979    

DOI:10.1063/1.354807

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

p‐nGa0.65In0.35P homostructure light‐emitting diodes grown on GaAs0.7P0.3substrates have been fabricated by low‐pressure metalorganic vapor‐phase epitaxy. The growth and characterization of undoped, Si‐, and Zn‐doped layers are described in detail. The optimum growth condition to grow the high‐quality Ga0.65In0.35P epitaxial layers is at the growth temperatures of 700–740 °C and V/III ratios of 100–200. The strongest photoluminescence peak intensity occurs at 2×1018and 7×1017cm−3for electron and hole concentrations, respectively. Diodes fabricated from thep‐nhomostructure are characterized by current‐voltage measurement, electroluminescence, and external quantum efficiency. A forward‐bias turn‐on voltage of 1.68 V with an ideality factor of 2.5 and a breakdown voltage of 9 V are obtained from the current‐voltage measurements. The emission peak wavelength and full width at half‐maximum of electroluminescence are around 610 nm and 79 meV at 20 mA. The external quantum efficiency of the uncoated diode is about 0.015%.

ISSN:0021-8979    

DOI:10.1063/1.354781

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Polycrystalline‐silicon (poly‐Si) thin film transistors (TFTs) have been assessed using deep level transient spectroscopy (DLTS) based on the measurement of current transients due to the thermal emission of carriers trapped at deep levels in the poly‐Si. Measurements were made on fully hydrogenated TFTs and the DLTS signal was found to vary continuously between 77 K and room temperature, without showing the characteristic peaks normally associated with point defects in single crystal Si. This demonstrates the existence of a continuous distribution of states through the band gap rather than discrete monoenergetic states. Analysis of the DLTS signal suggests the density of states increases rapidly toward the conduction band edge indicating the presence of a relatively high density of tail states. After annealing the TFTs at 450 °C the current DLTS signal was found to increase due to an increase in trap state density, which occurs because Si–H bonds are thermally unstable at this temperature. The increase in signal was over the whole temperature range of the measurement showing that hydrogen passivates states up to at least 0.1 eV below the conduction band as well as states nearer mid‐gap. The effects of varying the fill voltage on the measurement and the time dependence of the current transient were also investigated and added weight to arguments that the current transient was due to the thermal emission of carriers trapped at deep levels.  

ISSN:0021-8979    

DOI:10.1063/1.354782

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Results of Shubnikov–de Haas (SdH), cyclotron resonance (CR), and Hall‐effect measurements on &dgr;‐doped InSb:Si films grown by molecular‐beam epitaxy on insulating InP substrates are reported. The investigation covers samples with sheet densities of Si dopant atoms ranging from 1×1011to 1×1013cm−2, temperatures from 4.2 to 300 K, and fields from 0 to 7 T. The SdH oscillations show that the samples contain electrons of two‐dimensional nature, occupying multiple subbands. The effective masses obtained from the CR data correspond well to the subband occupation densities. The Hall measurements as well as the CR experiments also give evidence for the presence of additional electrons, with the conduction‐band‐edge massm*=0.014m0of bulk InSb, which exist presumably in the bulk of the films.

ISSN:0021-8979    

DOI:10.1063/1.354783

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The optical absorption coefficient &agr; of doped and undoped hydrogenated amorphous silicon (a‐Si:H) has been measured for photon energies from 2.2 to 1.0 eV using photo‐pyroelectric spectroscopy (PPES). A simplified experimental setup and analysis for extracting &agr; from the PPES data are described. In PPES the temperature rise induced in thea‐Si:H thin film due to weakly absorbed light is detected via a pyroelectric polymer in thermal contact with the sample. This technique presently has a sensitivity of &agr;d≳10−3, wheredis the sample thickness.

ISSN:0021-8979    

DOI:10.1063/1.354784

出版商:AIP    

年代:1993

数据来源: AIP