摘要:

Photoreflectance (PR) and reflectance have been applied to characterize undoped and modulation‐doped heterostructures of AlGaAs/GaAs grown by metal‐organic chemical vapor deposition. The PR spectra were taken on these samples after sequential etching steps in a phosphoric acid etch to study the effects of the surface electric field, the heterointerface, and the two‐dimensional electron gas. PR spectra were also taken with an external electric field applied through a transparent gate electrode. The results show that the oscillations appearing near the bandgap energy of GaAs are Franz–Keldysh oscillations originating from the large surface electric field. The surface electric field of the heterostructures can be modified through the application of an external electric field or by etching. The oscillation period is observed to increase with increasing reverse bias or with etching of the GaAs cap layer and the PR features disappear at a forward bias of 0.45 V. The very sharp features associated with the GaAs bandgap energy after etching have also been verified to be Franz–Keldysh oscillations and the presence of a two‐dimensional electron gas cannot be confirmed with PR.

ISSN:0021-8979    

DOI:10.1063/1.346544

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Raman spectroscopy has been used to monitor the changes induced in glassy carbon as a result of irradiation with H, He, C, N, Si, and Xe ions. The Raman spectrum of unirradiated glassy carbon consists of an intrinsic graphite peak at 1590 cm−1(the a peak) and a disorder‐inducedDpeak at 1350 cm−1. TheGpeak position and FWHM and the ratio of theDpeak intensity to that of theGpeak [I(D)/I(G)] are plotted as functions of the calculated damage density induced by the ion beam. The results show that at very low damage levels [ < 0.008 displacements per atom (DPA)], considerable disorder is being introduced into the system, and the average crystallite size has been reduced from 35 A˚ for the unirradiated material to about 25 A˚. At damage levels of ∼0.21 DPA, the material starts to undergo an ion‐beam‐induced modification which saturates at about 5 DPA. The Raman spectra for these heavily irradiated samples are very similar to those obtained from amorphous carbons. At yet higher doses there is some evidence suggesting that ion‐beam‐induced partial graphitization of the irradiated glassy carbon has occurred. The results are discussed in the context of previously reported Raman studies of amorphous carbons and highly oriented pyrolytic graphite.

ISSN:0021-8979    

DOI:10.1063/1.346547

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A systematic study of the photoluminescence (PL) of Se‐dopedn‐type GaAs grown by metalorganic chemical vapor deposition is reported. A new method is presented to determine the electron effective mass ofn+‐direct‐gap semiconductors from the PL spectrum. GaAs samples with electron densities from 1015to 8×1018cm−3were investigated over the temperature range of 13 to 353 K. The PL spectra ofn+‐GaAs are analyzed using a physical model which for the first time explains in a consistent manner both the energy of the peak and the full width at half‐maximum, and accounts for the electron density. An accurate fit of the PL spectra is obtained by invoking band‐to‐band transitions withoutkselection. The electron exchange and correlation interactions account for all the observed band shrinkage, which reaches 48 meV forn=8.0×1018cm−3. No significant density of band‐tail states is observed. The Fermi energy is obtained directly from the PL fitting and is used with the measured Hall electron densitynto determine the energy‐dependent effective massm*. An increase inm* beyond the value expected from the nonparabolicity of the conduction band in pure GaAs is observed. The mass at the minimum of the conduction bandm@B|0increases from 0.0636mefor pure GaAs to 0.073meforn=8.0×1018cm−3, wheremeis the free electron mass. The increase inm*0is given empirically asm@B|0/me=0.0635+2.06×10−22n+1.16×10−40n2. The change inm* is interpreted as a distortion of the conduction band produced by the impurities. The small dilation of the lattice, 0.0035% atn=8.0×1018cm−3, indicates that this distortion is not mechanical, but electrical in nature. Also, the PL linewidth is abnormally small for samples in which inhomogeneities are believed to exist.

ISSN:0021-8979    

DOI:10.1063/1.346520

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A study of the mobility &mgr; of Se‐dopedn+‐GaAs grown by metalorganic chemical vapor deposition is presented. A significant decrease in &mgr; is observed forn>1×1018cm−3, which is a general characteristic ofn+‐GaAs. Previous explanations that the low values of &mgr; are the result of autocompensation by the dopant are unsatisfactory in view of the universality of the decline in &mgr;. A new formula is derived for the ionized impurity mobility &mgr;Ifor degenerately doped material which accurately predicts the experimental &mgr; using no compensation and no adjustable parameters. The formula takes into account the increase of the effective massm* due to nonparabolicity of the conduction band and due to distortion of the band by the donor atoms. For degenerate material, &mgr;Iis inversely proportional to the square ofm* at the Fermi energyEF. For uncompensated GaAs withn=1×1019cm−3,m* atEFis 2.4 timesm* for pure GaAs, and &mgr; is only 1000 cm2/V s. Previous theories, which use the smaller optical effective massm@B|optin place ofm*, predict higher mobilities and temperature variations of &mgr; forn+‐GaAs. The new formula correctly predicts that &mgr; does not change with temperature whenn>2×1018cm−3.

ISSN:0021-8979    

DOI:10.1063/1.346495

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A semi‐empirical sputtering model is demonstrated to provide a good description of electron‐induced secondary electron emission. A simple formula for the yield of secondary electrons as a function of primary energy, incident angle, and material parameters is obtained. In comparison to the most commonly employed semi‐empirical model, the present model provides a superior fit to the universal energy dependence curve, a better description of energy and mass effects at off‐normal incidence, and additional insights into factors affecting the magnitude of the yield. The bulk and surface contributions to the yield magnitude are separately deduced from experimental data in the literature. Trends in these contributions are assessed for metals and insulators.

ISSN:0021-8979    

DOI:10.1063/1.346496

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Damage in GaAs induced by Ga+focused‐ion‐beam‐assisted Cl2etching is studied by photoluminescence (PL) intensity measurements as functions of ion energy, ion dose, and substrate temperature. By decreasing the ion energy from 10 to 1 keV, the damage depth decrease to 1/5, where damage depth is taken as the thickness at which the PL intensity recovers by wet etching. The damage depth is shallower when the etching yield is larger with the same ion energy. By increasing the ion dose, the normalized PL intensity decreases, but damage depth is nearly constant. Over 1015ion dose, the normalized PL intensity shows a constant value. By increasing the sample temperature, the damage depth becomes shallower. At 150  °C with ion energy of 1 keV, the damage depth is less than 0.5 &mgr;m, which is the detection limit of the PL measurement in GaAs substrate.

ISSN:0021-8979    

DOI:10.1063/1.346497

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Chlorine reactive ion etching of silicon requires the initial removal of the native oxide prior to rapid etching of silicon. The threshold energy for sputter removal of the native oxide on silicon was measured from the apparent oxide thickness on the silicon surface as determined by x‐ray photoemission spectroscopy of the Si 2pcore level. Using model computations, the threshold energy to sputter the modified native oxide was determined to be 72±5 eV. The surface film chemistry during etching is different above and below the sputter threshold energy. Above the threshold, the silicon surface is contaminated with 1–2 monolayers of SiClx(x=1,2,3) and residual SiClOy. Below the threshold, the oxide is not etched and SiClOyforms on the native oxide surface. The film thickness is observed to increase with ion energy to the threshold energy indicating that ion induced chemisorption phenomena control the film thickness.

ISSN:0021-8979    

DOI:10.1063/1.346498

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High concentrations of recombination‐promoting impurities in the near‐surface region of a semiconductor can produce virtually complete suppression of carrier‐driven photochemical etching processes. In‐diffusion of Zn to levels appropriate for ohmic contact formation on GaAs (mid‐1020/cm3) has been employed to reduce etching to an undetectable level inn‐GaAs withn=1.0×1017and 1.3×1018/cm3and to produce a greater than ten‐fold reduction in etching of semi‐insulating GaAs. Raman spectroscopy of the altered near‐surface region shows enhanced electronic scattering, which indicates the presence of a sufficient impurity concentration to suppress etching. Transmission electron microscopy shows the near‐surface region to be crystalline without significant numbers of defects following Zn diffusion. Possible applications of this process include self‐aligned etching of transistor and laser structures.

ISSN:0021-8979    

DOI:10.1063/1.346499

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Epitaxial ruthenium silicides have been successfully grown on silicon for the first time. Chemical electroless plating of a Ru thin film on silicon with subsequent annealing is a new approach and also the first demonstration of epitaxial growth of these silicides. Transmission electron microscopy was applied to characterize phases of silicides, microstructure, and orientation relationships. Three different epitaxial phases were found and identified to be Ru2Si3, RuSi, and Ru2Si. RuSi and Ru2Si are two new phases discovered in comparison with those previously reported in thin film reactions. Furthermore, Ru2Si3was found to be a stable phase at elevated temperatures since it can be transformed from Ru2Si and RuSi by sufficiently long annealing. Various diffraction patterns were analyzed and orientation relationships were determined. Moire’s fringes of RuSi and interfacial dislocations of Ru2Si3and Ru2Si were found. The average spacings were measured to be from 1000 to 4000 A˚ for Ru2Si3/Si. The composition of the silicides was measured by scanning Auger electron spectroscopy and 2% phosphorus was found.

ISSN:0021-8979    

DOI:10.1063/1.346500

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

As part of a general effort to understand the etching of metals in both plasma and chemical systems the etching of platinum foils in an oxygen plasma generated in a flow‐type microwave system was studied. It was found that very rapid etching (∼ 6 A˚/s) took place even at low power inputs (200 W). The principal plasma parameters, including oxygen atom concentration, ion concentration, and electron temperature, were measured as a function of distance below the microwave coupler. These were correlated to the rate of foil etching, which decreased with increasing distance from the coupler. On the basis of these correlations a simple mechanistic model was formulated. Etching of platinum in an oxygen plasma jet results from the concomitant action of oxygen atoms and high energy electrons.

ISSN:0021-8979    

DOI:10.1063/1.346501

出版商:AIP    

年代:1990

数据来源: AIP