摘要:

A novel micromachined test structure has been used to measure the work of adhesion between polycrystalline silicon surfaces. The effects of several surface treatments, including a hydrogen- and an ammonium-fluoride-induced hydrogen termination and a hydrogen peroxide chemical oxidation, have been investigated with these test structures. A reduction in the average apparent work of adhesion by a factor of 2000 has been observed on theNH4F-treated surface compared to the oxide-coated surface. By using x-ray photoelectron spectroscopy and atomic force microscopy, the observed reduction is traced to the combined effect of the surface chemistry and topography. This work demonstrates that a hydrophobic, rough surface provides a significant reduction of the apparent work of adhesion in polysilicon micromachined devices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365045

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A detailed experimental study of the optical properties of separation by implanted oxygen (SIMOX) substrates is performed using photoluminescence techniques. The photoluminescence properties of SIMOX substrates are compared with those of Si substrates. The silicon-on-insulator (SOI) layer is found to be free of any strain. High-quality SiGe quantum wells are grown on SOI using gas source molecular beam epitaxy. It is found that the photoluminescence properties of these quantum wells on SOI differ significantly from those of the SiGe quantum wells grown on a Si substrate under identical growth conditions. Intense photoluminescence and higher operation temperature are obtained for quantum wells grown on SOI substrates. It is shown that growth of a few hundred Å Si buffer layer on SOI is essential in order to achieve a high quality SiGe epitaxy on SOI. Finally, aSiO2/Si/SiO2optical cavity is proposed on SIMOX substrates, and it is employed to further enhance the photoluminescence intensity of SiGe quantum wells on SOI. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365046

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have deposited epitaxial diamond films with very low angular spread on epitaxial &bgr;-phase silicon carbide layers on silicon (001) substrates. From x-ray rocking curve measurements, half-widths of the angular spread of the crystal orientation as low as 0.6° have been determined, which is the smallest value ever reported in heteroepitaxial diamond films and appears to be smaller than those of the &bgr;-phase silicon carbide underlayers. The film surface exhibits a roughness of about 100 nm with very few discernible boundaries due to misorientation. The optimization of the bias-enhanced nucleation process and the control of selective growth are the main factors for the improvement of the crystallinity. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365047

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Step bunching in chemical vapor deposition of 6H– and 4H–SiC on off-oriented {0001} faces is investigated with cross-sectional transmission electron microscopy. On an off-oriented (0001)Si face, three Si–C bilayer-height steps are the most dominant on 6H–SiC and four bilayer-height steps on 4H–SiC. In contrast, single bilayer-height steps show the highest probability on a (0001¯)C face for both 6H– and 4H–SiC epilayers grown with a C/Si ratio of 2.0. The increase of C/Si ratio up to 5.0 induces the formation of multiple-height steps even on a C face. The bunched step height corresponds to the unit cell or the half unit cell of SiC. The mechanism of step bunching is discussed with consideration of surface formation processes. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365048

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The various mechanisms responsible for the strain relaxation of strain-compensated GaInP/InAsP multilayers grown on InP(001) using low-pressure organometallic vapor-phase epitaxy (LP-OMVPE) were investigated using a combination of transmission electron microscopy (TEM), high-resolution x-ray diffraction (HRXRD), and reciprocal lattice mapping. We examined separately the effect of the misfit strainfas well as the total strain energy&egr;T on the strain relaxation mechanisms. We also investigated the effect of the growth temperatureTson roughening. For the structures composed of a small number of superlattice periods, N=10, TEM and HRXRD indicate that strain relaxation occurs essentially through non-homogeneities at the interfaces for increasing misfit strainfvalues (at least up to |f|=1&percent;, the largest strain used in these experiments). In comparison, when the magnitude of the misfit strain is kept constant, increasing the number of periods eventually leads to a massive generation of dislocations in the multilayer. For |f|=0.75&percent;, coherency breakdown was observed around the 14th–15th period in a 50-period sample. However, the strain-compensated multilayer structures can be in a metastable state since all layers are perfectly flat and no dislocations are visible in a 20-period sample with the same misfit strains in the layers. Finally, we observed that the growth temperatureTshad a drastic effect on the morphology of the layers: increasingTsfrom 620 to 680 °C while keeping all other growth parameters constant introduced large periodic lateral thickness modulations as well as dislocation clusters in the structures. Diffraction contrast analysis in plan-view TEM indicates significant anisotropy with the features elongated in the [11¯0] direction. These results could be used as guidelines for the design of highly perfect and reliable device structures grown by LP-OMVPE. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365049

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this work undoped semi-insulating (SI) GaAs grown by vertical gradient freeze and liquid encapsulated Czochralski methods was studied by near-infrared absorption (NIRA), thermally stimulated current (TSC) and positron annihilation techniques. The positron experiments reveal both gallium and arsenic vacancies, as well as gallium and arsenic antisites, in the samples. By comparing the results from the TSC and positron measurements, the following relations are found in the defect concentrations: trapT2correlates with the arsenic antisite and trapT5with the arsenic vacancy. The ionized fraction of the arsenic-antisite-relatedEL2defect is obtained from NIRA measurements. The positive charge of these ionizedEL2defects correlates with the net negative charge,3[VGa3−]+2[GaAs2−]−[VAs+],related to the gallium vacancies and antisites and arsenic vacancies detected in positron measurements. The intrinsic defects may thus contribute significantly to the electrical compensation in SI GaAs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364705

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Results of carrier lifetime studies in low-doped epitaxial4HSiC layers are reported. The free carrier absorption (FCA) technique was applied to extract carrier lifetime parameters and their spatial distribution in a wide photoexcitation range. The FCA magnitude is shown to scale linearly with the photoinjected carrier concentration, while the absorption cross section increases according to a&lgr;4.4law for near infrared wavelengths. High spatial resolution carrier lifetime mapping of large4HSiC areas revealed features related to structural imperfections of epilayers. Finally, a density dependent fast lifetime component was observed at high injection levels and attributed to band-to-band Auger recombination. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365050

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A variety of undoped (nonintrinsic) hydrogenated amorphous silicon(a-Si:H)thin films was studied in greater detail using steady-state photoconductivity,&sgr;ph,subband-gap absorption,&agr;(h&ngr;), steady-state photocarrier grating (SSPG), and electron-spin-resonance (ESR) techniques both in the annealed and stabilized light soaked states. The experimental results were self-consistently modeled using a detailed numerical analysis. It was found that large differences in the optoelectronic properties of device qualitya-Si:Hthin films can only be explained using a gap state distribution which consists of positively chargedD+defect states above the Fermi level, the neutralD0defect states, and the negatively chargedD−defect states below the Fermi level. There are large differences both in the densities of neutral and charged defect states andRratios in differenta-Si:Hfilms in the annealed state. The densities of both neutral and charged defect states increased, however,Rratios decreased in the stabilized light soaked state. Very good agreement was obtained between the densities of neutral defect states measured by ESR and those derived from the numerical analysis in the stabilized light soaked state. The kinetics of the Staebler–Wronski effect was also investigated. There was no direct correlation between the decrease of steady-state photoconductivity and increase of subband-gap absorption. The self-consistent fits to wide range of experimental results obtained with the three Gaussian distributions of charged defect states imply that this model is much better representation of the bulk defect states in undoped hydrogenated amorphous silicon thin films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365000

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The formation of a Schottky barrier between an eutectic (Ga,In) alloy and a highly doped thiophene oligomer is followed as a function of time using current density–voltage and capacitance–voltage measurements. Within 1 h, the diode characteristics change from almost nonrectifying, leaky behavior into a rectification ratio of104with a considerably reduced leakage current. Measurements and energy band diagram calculations show that the depletion width increases with time due to a decrease in the ionizable acceptor density of the semiconductor at the Schottky interface. This is probably caused by a chemical reaction between the in-diffusing metals and the doped oligomer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364990

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the metal-insulator transition ofLa0.5Sr0.5CoO3thin films deposited by pulsed laser ablation onLaAlO3substrates. The films were cooled in oxygen partial pressures between 760 and10−5Torr and electrical resistivity of the films was measured as a function of cooling oxygen pressure.La0.5Sr0.5CoO3films changed from metallic to insulating behavior depending on their oxygen content. A defect model has been proposed to explain this transition and the change in conductivity is related to the change in the oxidation state of the cobalt ions. The model explains the relationship between oxygen partial pressure and electrical conductivity inLa0.5Sr0.5CoO3, which describes the experimental dependence reasonably well. Positron annihilation studies were also done on the same set of samples and the S parameter was seen to increase by 8&percent; from a fully oxygenated sample to a sample cooled in10−5Torr. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364991

出版商:AIP    

年代:1997

数据来源: AIP