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Epitaxial Mo/NbN and W/NbN superlattices with modulation wavelengths Λ ranging from 1.3 to 120 nm were grown on MgO (001) substrates by dc reactive magnetron sputtering in Ar/N2 mixtures. The superlattices were shown to be epitaxial with nearly planar layers using high- and low-angle x-ray diffraction and transmission electron microscopy. Computer simulation fits of the x-ray data indicated that interface widths were ⩽0.3 nm. The epitaxial relationship between the layers was (001)metal∥(001)NbN and [110]metal∥[100]NbN. The nanoindenter microhardness values from W/NbN and Mo/NbN superlattices with 50 vol % metal were nearly identical. The largest hardnesses were 30 GPa, observed at superlattice periods Λ=2–3 nm, compared to rule-of-mixtures values of 10 GPa. The hardness decreased with increasing Λ above ≈3 nm, following the dependences H=10.3+26.70Λ−0.38 GPa for Mo/NbN and H=12.88+22.1Λ−0.3 GPa for W/NbN. Hardness versus metal volume fraction with Λ≈5 nm showed a flat-topped dependence. Brillouin scatteri...

We have investigated steady-state and transient electrical properties of undoped polycrystalline diamond thin films deposited using hot filament chemical vapor deposition on (100)-oriented n-type and p-type silicon substrates. The capacitance-voltage characteristics are strongly influenced by slow traps located close to the interface between the diamond layer and the silicon substrate. When interpreting data one has to consider that the traps are not in thermal equilibrium during measurements. The steady-state current through the diamond film has the same behavior for films deposited on both n-Si and p-Si. Its temperature and field dependency can be interpreted in terms of Poole–Frenkel transport involving ionized sites with overlapping potentials in the diamond film. Electrically excited current transients decay with time according to a power law. The kinetics depend only weakly on temperature. Further, the transients contain very long time scales and show much similarity to earlier reported optically ex...

Phosphorus diffusion gettering of gold in silicon is a reversible process with strong temperature and phosphorus concentration dependence. We show explicitly that gold diffuses back and forth between the highly doped phosphorus layer and the bulk of the material when the annealing temperature is varied. This was investigated using secondary‐ion mass spectroscopy to study the gold within the gettering layer and using deep level transient spectroscopy to estimate the gold content in the bulk. We observed no internal gettering or outdiffusion of gold as long as the gold concentration is below the solubility limit. The concentration profile of gold after successful gettering follows the phosphorus profile but virtually all the gold atoms are found in the region where the phosphorus concentration exceeds ∼3×1019 cm−3. This is related to a large solubility enhancement of gold when the phosphorus concentration is above 3×1019 cm−3. The simplest explanation for the observed gettering mechanism is formation of gol...

Observations of discrete conductance fluctuations are reported at voltages well below the breakdown voltage in selected reverse‐biased p+‐n++ base‐emitter junctions originating from gate turn‐off thyristors. The occurrence of the phenomenon is attributed to the presence of defect clusters at the p‐n junctions. The defect clusters introduce field confinements which activate tunneling processes that would not otherwise be present in these nonabrupt p‐n junctions. The fluctuating reverse current was only observed in voltage and temperature regions where the total reverse current was influenced by tunneling‐related conduction mechanisms. The experimental observations concerning the voltage and temperature dependences of the fluctuation amplitude and rate deviate from earlier reports on decisive points. Both the amplitude and the switching rate of the observed fluctuations were unstable in time and influenced by the measurement procedure itself. This instability is attributed to small structural changes of the...

The electrical and optical properties of wafer bonded unipolar silicon‐silicon junctions were investigated. The interfaces, both n‐n type and p‐p type, were prepared using wafers with hydrophilic surfaces. The current versus voltage characteristics, the current transients following stepwise changes in the applied bias, and the capacitance versus voltage characteristics as well as the temperature dependence of the current and capacitance were experimentally obtained and theoretically modeled. The proposed model assumes two distributions of interface states, one of acceptors and one of donors, causing a potential barrier at the bonded interface. It is argued that the origins of the interface states are impurities and crystallographic defects in the interfacial region. The capacitance of the bonded structures includes contributions from the depletion regions as well as from minority carriers. When bonded n‐n type samples were illuminated with light of photon energies larger than the silicon band gap the curr...

A negative charging effect is studied in small, ultrathin metal‐oxide‐silicon diodes biased at constant voltage. The charging is seen as a gradual decrease in the magnitude of the tunnel current over time. Along with the charging, the current noise power decreases. Results are described from measurements of the temperature and voltage dependence of the current transients. A physical model is presented in which filling and emptying of electron traps in the as‐grown oxide cause the noise, and the conductance decrease is caused by the transformation of these traps into fixed negative charge storage centers. From fits of the model to measured data, we obtain a thermal activation energy of 0.3 eV for the charging process. A low‐temperature annealing treatment at 200 °C restores the conductance of a previously charged device to its initial value. On the other hand, the charging effect can be eliminated by a 350 °C anneal in nitrogen. Together, these experiments suggest that the traps are water‐ or hydrogen‐related defects.

This article gives a quantitative analysis of electron photoemission yield from N+-type and P+-type substrates of MOS structures. Based on this analysis, a method is presented to estimate both the scattering length, l, of electrons in the image force potential well and of photoelectron escape depth, x(esc), from the semiconductor substrate. This method was used to estimate the scattering length and the escape depth from the substrates of Al-SiO2-Si (N+-type and P+-type) structures. It was found that for N+-type substrate structures the scattering in the image force potential well has a dominating influence on the photoemission yield while for P+-type substrate structures both the scattering in the image force potential well and the photoemission from the subsurface regions of the photoemitter play important roles. It was found that the scattering length in the image force potential well was equal to l = 6.7-6.9 nm for structures on both N+ and P+ substrates, produced in the same processing conditions. For structures on P+ substrates, the escape depth was found to be equal to x(esc) = 8-9 nm. The scattering length, l, determined in this study is considerably larger than the one reported previously (l = 3.4 nm) for similar MOS structures. The escape depth x(esc) determined in this study is also considerably larger than the escape depth determined previously (x(esc) = 1.2-2.5 nm) for the external photoemission from uncovered silicon surfaces into vacuum.

Admittance spectroscopy is extended for measuring capacitance and conductance on metal-oxide-semiconductor (MOS) structures as a function of gate voltage, frequency, and temperature. An automatic setup has been designed for collecting data along these dimensions in one measurement cycle. The theory for admittance spectroscopy has been developed by starting from basic charge carrier statistics. Using numerical integration of energy dependent parameters instead of the commonly used analytical solution, conductance dispersion curves are obtained which do not need to be adjusted by assuming lateral surface potential variations at the oxide-semiconductor interface. Also, we find that interface state densities extracted by using traditional methods are four times lower than those obtained by using our theory. Experimental data presented in three-dimensional plots are compared with theoretical calculations, revealing the possibilities and limitations of the conductance method.

Emission rates for electron tunneling from InAs quantum dots to GaAs substrate (vol 96, pg 6477, 2004)

A hard x‐ray waveguide capable of reducing a 13 keV monochromatic beam in one direction from 30 to only 0.1 μm has been characterized with synchrotron radiation. The guiding structure consisted of a carbon layer sandwiched between two Ni layers sputter‐deposited onto float glass. A beam exiting at the end of the guide in guiding direction was observed when a resonance effect due to the formation of x‐ray standing waves in the total reflection region takes place. The measured beam divergence (1.3 mrad) agrees with expectations. The total efficiency (exiting photon flux/incident photon flux) can ideally exceed 10−2 but is only 10−4 for this first prototype.

The thermal emission rates of electrons and holes at gold−acceptor levels in silicon have been measured in P+N junctions as a function of temperature using the dark−current transient method. From these measurements the linearly extrapolated absolute zero thermal activation energies of electrons (553 meV) and holes (641 meV) have been determined taking the temperature dependence of the hole capture rate into account. The latter has been determined by measuring the diffusion length at different temperatures. Using earlier optical results which showed that the energy distance of the gold−acceptor center from the conduction band is independent of temperature, the thermal activation energies of electrons and holes are calculated as a function of temperature. These results are to within a few meV in agreement with previously published optical data. Using the principle of detailed balance in thermal equilibrium, values of ctp=1×10−7 cm3/s, ctn=2×10−3 cm3/s, and gA?3.2 are estimated for the capture rates and the ...

A general statistical language developed for impurities and defects in semiconductors has been applied to the interpretation of experimental results from different methods of investigations of insulator–semiconductor interface traps. Interface state energy distributions obtained from traditional capacitance–voltage methods or ‘‘Scanned Light Pulse Technique’’ are interpreted in a Gibbs free energy scale. On the other hand, distributions obtained from Deep Level Transient Spectroscopy (DLTS) are put on an enthalpy scale. The difference between the two parameters depends on the entropy properties of the trap centers. Carrier capture data taken from DLTS are demonstrated to be influenced by the ‘‘entropy factor’’ of the interface trap resulting in discrepancies of capture cross sections of up to two orders of magnitude. It is further pointed out that the energy resolution of experimental energy state distributions is fairly rough for different methods ranging up to 0.1 eV for CV technique at room temperature.

A new measurement method, scanned light pulse technique, for the investigation of the interface properties of metal–insulator–semiconductor (MIS) structures is introduced. The measured signal is the charge contents of current transients induced by light pulses applied to the investigated sample. This signal depends on surface potential, interface state density and voltage applied to the MIS structure. By analyzing the results of such measurements it is quantitatively demonstrated how insulator charge and interface state distribution influence the voltage dependence. By scanning a light spot across the surface of an MIS structure with transparent metal electrode it is further shown that pictures of the spatial variation of the surface potential and the interface state density can be obtained.

Photocurrent measurements in sulfur‐doped silicon p‐n junctions have been used to determine optical threshold energies and spectral distributions of the photoionization cross sections associated with two deep sulfur centers in silicon. In addition, absolute values of three of the cross sections have been determined. It is shown that the optical cross‐section spectra for the excitation of electrons from the sulfur centers to the conduction band cannot be described by the Lucovsky model. On the other hand, they are not in contradiction with the Pantelides‐Sah correction of KL‐EMT. The temperature dependence of the energy position of the sulfur centers is discussed.