Barrier heights in metal-semiconductor contacts may be modified by interlayers. The effects of atomic interlayers are due to interface dipoles. With the restriction to nearest-neighbor interactions and monovalent interlayer atoms, they may be described as interface molecules which consist of an interlayer and a substrate atom. If the interlayers are thicker than a few atomic layers their two interfaces with the metal and with the semiconductor will be non-interacting. Both types of interfaces are described by the model that interface-induced gap states determine the alignment of the bands and the electronegativity difference describes the charge transfer across the interface. The present paper discusses and analyzes experimental data for H-modified diamond and silicon, Al/Si/GalnP, and metal/ Si3N4/Si Schottky contacts.

W/n-GaAs/In Schottky contacts of area 1.75 mm2 were fabricated by deposition of W on (100) n-GaAs by rf Sputtering using rf power values in the range 200–400 Watt. The I-V and high frequency C-V measurements at 300 K, in the 200 Watt W/n-GaAs Schottky contact indicated that W formed a good rectifying contact to n-GaAs, with a rectification ratio (r) of 270, ideality factor (n) of 1.39, reverse saturation current (Io) of 1.2×10−6 A and the C-V barrier height (φbo) of 1.6 V. However, n and Io increased, whereas r and φbo decreased for the W/n-GaAs Schottky contacts prepared using higher rf power. For the 300 Watt W/n-GaAs contact, the values of 70, 1.70, 6.3}10−6 A, and 1.2V for r, n, Io and φbo, respectively, were estimated. The low frequency forward bias capacitance (or surface defect density) was an order of magnitude higher in the 300 Watt contact than in the 200 Watt contact. This fact suggested that the degradation in the quality of W/n-GaAs Schottky contacts fabricated by using high rf power was caused by high density surface defects created during sputter deposition of W on n-GaAs.

Al/n-GaAs Schottky barrier type diode was fabricated by thermal deposition of Al on chemically etched polished surface of (100) n-GaAs at a pressure of 4×10−6 Torr. Back ohmic contact to n-GaAs was prepared by thermal deposition of In, followed by a 90 min. anneal in Ar atmosphere at 390° C. The C−2 vs V characteristics were quite linear for reverse bias voltages in the range 0-4 V. Over the temperature range 300–360 K, the values of the barrier height and the net carrier density (Nd-Na), obtained from the C−2-V data, were in the range 1.33–1.26 V and 4.3×l0−16-5.0×l0−16 cm−3, respectively. The forward I-V data over the temperature range 300–400 K, indicated that the electrical current across the Al/n-GaAs Schottky junction was transported by the mechanisms of generation-combination (GR) in the space charge, thermionic emission (TE) and ohmic leak current. A value of (1.20±0.04) V for the zero bias barrier height was deduced from the temperature dependence of the TE reverse saturation current. The barrier height deduced from the I-V data was practically independent of temperature. The 20% change in Nd-Na with temperature, obtained from the C-V data, and important contributions of the GR and leak currents to the total forward current, suggested the presence of defect levels in the surface space charge layer in n-GaAs, which may be responsible for the discrepancy in the values of the barrier height obtained from the I-V and C-V data.

We have examined the temperature dependence of the barrier height of Au, Ag, Ni, and Al, metal-semiconductor contacts on n-type 6H-SiC, and Al metal-semiconductor contacts on p-type 6H-SiC. The barrier height was determined from the (1/C2) vs VR characteristics of the contacts at temperatures ranging from 300K to 670K. The measurements were made at 1 MHz. These measurements were compared to I-V measurements at various temperatures, and to the behavior predicted by standard models.

Gold and platinum metal contacts have been deposited on the cleaved and etched surfaces of ZnCdTe single crystals by “electroless” method from AuCl3, PtCl2 and PtCl4 aqueous solutions with different concentrations and deposition times. Atomic Force Microscopy (AFM) has been employed to reveal the surface morphology of metal contacts and it was found that for AuCl3 and PtCl2 solutions, the surface morphology and grain size are similar, and uniformly distributed. The surface morphology on contact made from PtCl4 shows a larger grain size, higher roughness and non-uniformity. The effect of different heat treatments to the surface morphology will be discussed.

An important issue in semiconductor device operation is the rate at which current or voltage stress creates defects that degrade eventually device operation. Based on recent results on nitrided gate dielectrics, we have concluded that bonded-H at the Si-SiO2 interface plays a role in the formation of metastable defects that can be activated, and subsequently neutralized, by sequential trapping of injected holes and electrons. In this paper, differences in defect behavior for Si-SiO2 interfaces that have exposed to nitrogen (N-) atoms or N-H groups are discussed. Based on these results, a microscopic model for interfacial defects is proposed.

Electrical characterization of MOS structures and device modeling require accurate information about dopant concentration, particularly at the poly-Si/SiO2 interface. We compare four experimental techniques (secondary ion mass spectrometry SIMS, resonant ion mass spectrometry RIMS, differential Hall effect profiling, and spreading resistance analysis) to measure boron and free carrier concentrations in poly-Si, SiO2 and crystalline Si. We find that no single technique completely characterizes the entire MOS structure, and that spreading resistance analysis in particular substantially underestimates the free carrier concentration at the poly-Si/SiO2 interface. We conclude that in most cases of technological interest the magnitude of the poly depletion effect scales with the average carrier concentration at some distance away from the interface and that the interfacial effects, such as dopant segregation, are of only secondary importance. These findings are supported by theoretical modeling of capacitance-voltage behavior of boron-doped MOS capacitors.

The so-called Direct Wafer Bonding (DWB) technique opens new possibilities for the electronic industry but still suffers from the poor knowledge we have of the microstructure of these interfaces and hence of their electrical activity. In this work, we have extensively used Transmission Electron Microscopy techniques in plan-view and cross-section to identify the structure of the interfaces found between two bonded silicon wafers. The general structure of these interfaces is that of a perfect grain boundary and evidently depends on the misorientation between the two bonded wafers. A twist component in the range 0>θ>13˚ creates a square network of pure screw dislocation whereas an unavoidable tilt component (<0.5˚) is compensated by a periodic array of 60˚ dislocation lines perpendicular to the tilt direction. Therefore, the regularity of these networks can be disrupted by the presence of steps (of up to several nanometers) in the interface plane. Silicon oxide precipitates are seen heterogeneously distributed on the interface with preferential nucleation sites on the dislocations.

This paper presents the comparison of the structural and electrical characteristics of Si/Si bonded interfaces depending on whether the surface layers were rendered amorphous by high dose ion implantation prior to annealing or not. While the general structure of the interfaces is the same when the wafers are preamorphized more precipitates are seen in the interface along with a few extended defects propagating into the volume. The most striking difference between both procedures is that the Spreading Resistance profile is more complicated in shape and difficult to master in the case of preamorphized wafers. Careful TEM analysis shows that only in this case the interfacial region is stressed in contrast with the fully relaxed structure obtained by direct bonding of crystalline wafers.

For these reasons, there is little chance that the preamorphization technique will benefit to the bonding procedure of direct Si wafers.

During organometallic vapor phase epitaxy of GaAs, the Fermi energy is found to be pinned ≈200 meV below the intrinsic Fermi energy on a (lOO)-oriented surface. This was determined by making the first comparison of Zn concentration, Nzn. obtained from growth with that obtained at equilibrium, all under the same nominal ambient conditions. Donor solubility has been found to be virtually unchanged during growth of n- or p-type GaAs, and this is strong evidence that the Fermi level remains pinned at essentially the same energy during growth of n- or p-type GaAs. Consistent with Fermi level pinning, we find (1) the NZn is supersaturated in the epilayer for the ambient growth conditions used, (2) a large excess concentration of positively charged Ga interstitials can be grown into n-type GaAs and which diffuses into nearby p-type layers, causing (3) the Zn diffusivity, DZn ∼10−13 cm2/s, out of buried npn layers to be essentially independent of the ambient conditions. Annealing of a heavily Zn-doped layer at the surface can lead to 10−16<DZn<10−13 cm2/s at T=800°C simply by varying the Zn partial pressure over its commonly used range. Use of In-doped spikes in n- and p-type GaAs suggest that interstitial point defects have a strong effect on the group III diffusion.

The radiative recombination processes of the two-dimensional hole gas formed in SiGe quantum wells (QWs) due to modulation doping are studied in details by photoluminescence (PL) spectroscopy. Boron-modulation-doped Si/Sil−xGex/Si heterostructures grown by molecular beam epitaxy (MBE) are studied. It is shown that charge transfer of holes from the doped Si layers causes the filling of the SiGe QWs leading to an appearance of a broad asymmetric PL band with a characteristic sharp high energy cut-off and enhanced recombination near the Fermi edge. A reduction of this PL enhancement is observed with an increase of measuring temperature. The PL bandwidth and the high energy cut-off are found to vary with either the doping level or the spatial separation between the delta-doped layers and the QWs. This PL band is argued to arise from the recombination of the holes in the QWs and electrons confined near the QWs as a result of the band bending induced by the delta-doping. The shape of the PL band with enhanced intensity near the Fermi edge are discussed in terms of the phase space filling and many-body effects.

Radiative isoelectronic impurity complexes consisting of pairs of Be atoms that bind excitons can be formed in both Si and SiGe/Si superlattices during growth by molecular beam epitaxy. We describe the conditions under which these radiative complexes can be formed and show that they can be localized in the alloy layers of a superlattice. Experimental results from samples with grown-in Be are compared to previous results from ion implanted samples. Superlattices of varying well widths are examined and a narrowing of the no-phonon linewidth is observed.

The structural and luminescence properties of (001) p-type porous silicon samples (p∼0.1-0.2 Ω•cm) fabricated electrochemically under various conditions were investigated using high resolution double and triple axis diffraction and photoluminescence spectroscopy. We show the sensitivity of the structure of the porous silicon to the current density in the range of 10-50 mA/cm2, HF acid concentration in the range of 15% - 30%, and the evolution of the structure with time. We have found a systematic dependence of the amount of strain in the porous silicon layer (PSL) on the current density. The effect of the HF concentration is such that at 25% and 30% HF, PSLs are formed which are crystalline and strained, but at a lower HF concentration (15%), strained layers are not formed. The perpendicular strain in the layer increases linearly with storage time but the in-plane lattice constant of the porous silicon remains matched to the substrate. Further, we utilized x-ray reciprocal space maps to observe that, with storage time, there is an increase in the diffuse scattering from the PSL due to an increase in the range of tilts in the layer. Room temperature photoluminescence emission was observed for all 15% and 25% HF samples, but not for all 30% HF samples. Higher peak luminescence energy was obtained with lower HF concentration. Finally, we note the relationship between the strain in the PSL and the luminescence properties.

Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the luminescence spectra and scanning tunneling microscopy (STM). Both the effective area and the luminescence intensity are found to increase with anodization time, reaching maximum values for the same anodization time (1–2 minutes). In most cases, they decrease monotonically with further anodization. The surface state density, on the other hand, decreases with anodization time from the initial value of ∼1012 cm−2 for the virgin surface, down to ∼1011 cm−2 at the common anodization time for which both the effective area and the luminescence intensity are peaked. The surface-state density increases upon further anodization, reaching a value of at least 1013 cm−2 after ∼10 minutes of anodization. Apart from its intensity, the luminescence spectrum is essentially independent of anodization time. The common peak of the spectra is at about 700 nm. The STM measurements reveal a pronounced surface roughness. Preliminary results indicate that for 1 - 2 minute anodization (maximum effective area), the roughness scale is of the order of 1 -2 nm. After 10-minutes anodization, on the other hand, the roughness microstructure becomes finer (roughness scale of only 0.5 - 0.7 nm). These findings indicate that the various characteristics studied are closely interrelated. Such information may help in understanding the luminescence mechanism, but further work is required in order to interpret more fully the results presented.

We have investigated the light-induced change of photoluminescence(PL) and its recovery in porous silicon. The exposure of the porous silicon to continuous laser light in vacuum results in the quenching of the PL intensity, which is almost fully recovered by simply keeping the samples in vacuum or in air at room temperature for a few days. When the light exposure is done in air, the PL spectra of the samples with initial PL peak at 800 nm are blue-shifted to the peak position at 740 nm and the samples with the initial PL spectrum peaked at 740 nm shows only a rise of PL intensity without any change of its peak position. Fourier transform infrared(FTIR) studies suggest that the light-induced change of PL in air is a irreversible process and occurs as a result of optically induced replacement of some of the Si-H bonds with O-Si-H bonds or adsorption of oxygen with hydrogen loss.

The chemistry of the interactions between point defects and impurities is discussed by considering first the general thermodynamic and kinetic aspects of these reactions, deserving major attention to the identity of of the stable chemical species eventually formed and to the boundary conditions for diffusion controlled and reaction controlled interaction processes.

The second part of the paper is instead dedicated to the analysis of the chemistry of carbon, oxygen, hydrogen and point defects in silicon, which is a system of major technological interest.

We postulate that at low enough temperatures, when homogeneous nucleation processes are slow, spinodal decomposition assists oxygen aggregation phenomena. We postulate, also, on the basis of the existing knowledge, that carbon and hydrogen favour alternative reaction paths for oxygen in the due of clustering processes and discuss the hydrogen-enhanced oxygen diffusivity in the frame of a conventional trapping model.

The DX center in AlGaAs alloy is reviewed as an example of bistability of defects in semiconductors. Also presented is some technological importance of the defect bistability.

The interaction between EL5 and EL6 in the n-type bulk GaAs have been observed by using isothermal constant-capacitance voltage transient spectroscopy (CCVTS). Each CCVTS spectrum of EL5 and EL6 was broader than a theoretical one expected for a single level, and was found to be consistently interpreted by two main trap components. With the increase of the filling pulse duration in a wide range, one component of EL6 decreased to about 50 % of its initial value, while one component of EL5 increased and saturated. This variation in peak heights could be reversed by controlling electron occupation fractions of EL5 and EL6 by application of two adjacent filling pulses. Such interaction between both levels was commonly observed in n-type bulk GaAs independent of carrier density.

The kinetics of multiple DX related emission centers are studied using the isothermal Time Analyzed Transient Spectroscopy (TATS) of constant capacitance voltage transients. Four distinct emitting centers have been obtained using higher order TATS in the same silicon doped Al0.33As0.67As sample without use of hydrostatic pressure. Accurate identification of the multiple DX states has allowed a better understanding of the charge redistribution process during capture. Improved resolution due to increase in order of spectroscopy has enabled quantitative fitting of spectral lineshape and thus accounting for degree of nonexponentiality associated with each of the four discrete centers. The capture kinetics of these centers are studied over six orders in magnitude of filling time. The resulting quality of kinetic data makes possible detailed quantitative comparison with kinetics predicted by positive U and negative U models of DX centers. We show that our data is in agreement with positive U model of DX center.

Up to the recent times it was believed that observation of the DX-centers is restricted to the rather wide-bandgap III-V and II-VI semiconductors. However it becomes obvious now that some of the narrow-gap IV-VI semiconductors doped with the group III elements reveal the features of DX-centers. A range of features, such as negative-U behavior, large lattice relaxation, metastability of the local excited states, narrow bandgap - make the effects resulting from the DX-like behavior much more complicated than in the “classical” materials with the DX-centers. We review the most unusual recent results obtained in the field that originate from the specifics of the DX-like centers in IV-VI.