摘要:

Insitureflection high‐energy electron diffraction and cross‐sectional and plan‐view transmission electron microscopy have been used to investigate the initial stages of InSb growth on GaAs(001), by molecular‐beam epitaxy. Growth of the InSb commences with the formation of rectangular‐based islands, having flat tops and sloping sides, with facets on certain planes of types {111} and {113}. The islands show near normal lattice spacings, with no significant straining. As deposition proceeds, islands coalesce and, after the equivalent of 40 monolayers of deposition, form a connected network. Complete coverage of the GaAs substrate is achieved after &bartil;300 monolayers of deposition. This places a lower limit on the thickness of InSb layers, which may be considered in the design of optoelectronic devices.

ISSN:0021-8979    

DOI:10.1063/1.345735

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial Si‐Ge/Si heterostructures have been formed from amorphous Si0.86Ge0.14, Si0.7Ge0.3, and Si0.56Ge0.44films which were deposited at a vacuum of 10−7Torr, followed by a wet oxidation process. The presence of an initial native oxide precluded solid phase epitaxy under standard annealing conditions, but epitaxy could be achieved by the use of wet oxidation. The samples were oxidized for various times at 900 °C and examined in reflected electron diffraction, ellipsometry, and cross‐sectional and plan‐view transmission electron diffraction. The formation of the epitaxial layer has been examined, and an epitaxial growth model is suggested.

ISSN:0021-8979    

DOI:10.1063/1.345736

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A series of amorphous hydrogenated silicon‐germanium films has been produced by the glow‐discharge dissociation of a GeH4+SiH4+H2gas mixture. The subgap optical absorption has been measured with the photothermal deflection spectroscopy (PDS) technique, and the results are discussed and referred to a model density of states. The density of defects has been found meaningfully correlated to the bulk material, despite a number of possible complications intrinsic of the PDS technique and/or of the material itself, which can potentially prevent the correct determination of the density of defects from the subgap optical absorption. Namely, the defect density ranges from 1016cm−3ina‐Si:H to 5×1017cm−3in a Ge:H, whereas the Urbach tail width is only slightly increased from 50 to 70 meV. The amount of disorder and the defect density of the material are compared to the predictions of an available thermodynamical model: the increasing number of defects brought about by germanium results in being an intrinsic feature of the material. Furthermore, the impact of the variable concentration of silicon and germanium dangling‐bond states on the position of the Fermi level has been studied by means of the same model density of states: a noticeable correlation was found between the activation energy of the steady‐state dark conductivity (EA) and the volume density of silicon and germanium dangling bonds (Nd). In other words, the three‐step trend ofEAvsxcan be considered to be a fingerprint of the separate dangling‐bond densities in germanium and silicon. These can be deconvolved, provided that the dangling‐bond states in the forbidden energy gap are known as a function of the alloy composition.

ISSN:0021-8979    

DOI:10.1063/1.345737

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polycrystalline HgTe samples have been prepared by taking Hg and Te in stochiometeric compositions. The effect of annealing in mercury has also been studied. The effect of temperature on the electronic conduction mechanism and grain‐boundary states has been observed through the measurement of Hall coefficientRHresistivity (&rgr;) and Hall mobility &mgr;H=(RH/&rgr;) on the polycrystalline HgTe in the temperature range ∼77–350 K. It is found that in electronic conduction in the low‐temperature range, the conduction is dominated by the thermionic emission of electrons over the grain boundaries. At a critical temperatureTcwhere the barrier height &Fgr;band, hence the width of the space‐charge region near the grain boundaries tends to zero, a crossover from the barrier limited to the mobility limited resistivity occurs.RHis found to be thermally activated over the temperature range where the conduction mechanism is governed by the grain‐boundary barrier. The experimental results are explained on the basis of a grain‐boundary trapping model combined with two‐phase model. It is found that the mobility and the grain size increased with annealing time. We achieved the carrier mobility of polycrystalline HgTe at 270 K to as much as 11 000 cm2/V s.

ISSN:0021-8979    

DOI:10.1063/1.345738

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A convectively cooled, recirculating thermoelectric generator based on &bgr;‘alumina has been designed and operated over the temperature range of 400–600 °C. The design employs a stainless‐steel wick and flame sprayed molybdenum electrodes and the unit can be assembled and operated with ease. A full treatment of all thermal and electrical flows is given and theoretical efficiencies of 10%–15% are predicted. Critical parameters are the internal resistance and radiation coefficients for thermal losses, while it is also shown that the flow of sodium within the electrode and the geometry of the evaporating and condensing surfaces is of importance in limiting the measured efficiency to 1%–3%. Units have been operated for up to 3000 h.

ISSN:0021-8979    

DOI:10.1063/1.345739

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Biaxially stretched poly (p‐phenylene sulfide) (PPS) film showed high photosensitivity after being annealed in oxygen for 6 h at a temperature between 270 and 285 °C. The spectral dependence of xerographic photosensitivity of the film had a peak at around 365 nm, and xerographic gain under 365‐nm UV irradiation was 0.1 or above. The micro‐Vickers hardness of PPS reached 60 kg/mm2after annealing at 280 °C for 6 h. The spectral photosensitivity was greatly improved by depositing a thin amorphous selenium‐tellurium alloy on the annealed PPS film. The half‐decay exposure of the annealed PPS with Se‐Te alloy film was 2.3 lx s under white illumination. These experimental results demonstrate that the annealing of PPS film under an oxygen environment gives this film excellent photosensitivity and mechanical durability and hence, renders this material attractive for a xerographic application.

ISSN:0021-8979    

DOI:10.1063/1.345740

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Thermally stimulated current (TSC) of nominally undoped bismuth silicon oxide crystals was measured after UV excitation at liquid nitrogen temperature. The results were compared with the data in the literature, and the origins of some discrepancy discussed. The TSC measurement was very sensitive to the crystal lot; that is probably to the structural defects.

ISSN:0021-8979    

DOI:10.1063/1.345741

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Electrical and optical measurements are reported for samples from two undoped semi‐insulating GaAs crystals grown by a vertical molten zone method. The electrical data, taken over the range 290–420 K, included results for samples from both crystals that were so close to intrinsic as to require an ambipolar correction in determining the electron concentration. The compensation balance in this material is controlled by the EL2 midgap defect, of which the fraction ionized depends on trace presence of CAsshallow acceptors, and of shallow donors, probably including SiGa. An increase of the latter towards the tail (top) end of one crystal led to a reduction of the EL2 ionized fraction, and a lowered resistivity—but one still within the conventional semi‐insulating range. Carbon was measured from the strength of its local vibrational mode absorption, while near‐infrared measurements showed that EL2 was present in a concentration ∼1016cm−3, with relatively small variation across a wafer.

ISSN:0021-8979    

DOI:10.1063/1.345742

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The galvanomagnetic transport in (111)B HgCdTep‐type layers, grown by molecular beam epitaxy, was studied as a function of temperature and magnetic field strength. Experimental data on the Hall coefficient and conductivity tensor versus magnetic field have been analyzed with the assumption of three charge carriers involved in the conduction mechanism: one carrier coming from the conduction band and the other two from the complex nature of the valence band. Indeed, two kinds of positive charge carriers with completely different mobilities in the extrinsic region are seen. The extracted parameters are in very good agreement with the intrinsic concentration over a wide temperature range.

ISSN:0021-8979    

DOI:10.1063/1.345743

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The paper presents low‐frequency (flicker) noise measurements onn‐channel metal‐oxide‐semiconductor transistors with TCE (trichoroethylene), dry, thermally nitrided, or reoxidized nitrided oxides as gate dielectrics. Results show that the noise level is lowest for conventional silicon oxide with TCE treatment and highest for thermally nitrided oxide. The frequency index (&ggr;), which characterize a least‐square fit of the noise spectrum in the frequency range of 10 Hz–5 kHz to the spectrum (∝f−&ggr;), is not a constant, but fluctuates between 0.8 and 1.4 with the gate bias. In addition a trend is found that the higher the interface‐state density at the midgap of silicon, the higher the noise level. But these two quantities are not in direct proportion to each other especially for the nitrided oxide device. All these observations lead to a unique implication: in addition to interface states, the oxide traps also contribute to the flicker noise generation. Our new observations also lend support to the past speculation that the carrier number fluctuation in the conduction channel is responsible for the noise generation. However, not all the noise parameters in the present study agree well with the general predictions of the existing flicker noise models.

ISSN:0021-8979    

DOI:10.1063/1.345744

出版商:AIP    

年代:1990

数据来源: AIP