Search

Si0.5Ge0.5/Si multiquantum-well structures are grown using a production-compatible ultrahigh vacuum chemical vapor deposition system. The structures are designed in order to obtain dislocation-free undulating strained layers used as the absorbing layers in photodetector structures. The Si/SiGe/Si stack on a silicon-on-insulator wafer is used as the waveguiding layer. Transmission electron microscopy and photoluminescence are used to characterize the undulating layers. A photoluminescence emission corresponding to the band edge “no phonon” transition is measured at a wavelength beyond 1.55 μm. Preliminary data from metal–semiconductor–metal photodetectors fabricated with this material show a responsivity of approximately 0.1 A/W at the telecommunication wavelength of λ=1.55 μm.

Heterostructure Si/Ge/Si p-metal–oxide–semiconductor field effect transistors (MOSFETs) with 1-nm-thick pure Ge channels grown pseudomorphically on Si substrates have been fabricated and characterized. Simultaneous solution of Schrodinger and Poisson’s equations reveals that the 1-nm-thick Ge region can effectively confine holes in a subsurface channel. This result is confirmed through the fabrication of test MOS capacitors and MOSFETs using a process with plasma enhanced chemical vapor deposition gate oxide and a peak thermal budget of just 5 s at 600 °C. (Raman spectroscopy shows that this thermal treatment does not significantly relax the strain in the Ge layer). However, transconductance measurements on the MOSFETs indicate that the mobility of holes in the buried channel is substantially less than at the Si surface. It is speculated that this poor mobility may result from hole scattering at the abrupt Si/Ge interface.

The effect of power on the electrical and interface properties of silicon dioxide films produced by direct plasma‐enhanced chemical‐vapor deposition, using nitrous oxide and silane with high helium dilution, has been investigated. Auger depth profiling measurements indicate that while the bulk of the films have no measurable impurities, the interface region contains about 1.6×1015 atoms/cm2 of nitrogen. In contrast to thermal oxides, there is no thick interface layer with a large intrinsic compressive stress. The interface‐state densities of the films obtained from capacitance‐voltage measurements on metal‐oxide‐semiconductor diodes increase with increasing plasma power, but these can be removed to some extent by high‐temperature annealing at temperatures in the range 800–950 °C. The flatband voltage is relatively insensitive to plasma power. Thermal oxide samples have been subjected to the plasma processes and these also show evidence of plasma damage. A thin layer produced at the interface by a separate...

We have grown Si-Si1-xGex undulating layer superlattices with x=0.39 and 0.45 by molecular-beam epitaxy on top of epitaxial implanted CoSi2 layers and fabricated vertical metal-semiconductor-metal detectors. The detectors show a quantum efficiency of 5% for the wavelength of 1320 nm and 0.9% for 1550 nm. We performed temporal response measurements, using a Ti:sapphire laser and an optical parametric oscillator which generates ultrafast pulses at infrared wavelengths. An electrical response time of 16 ps full width at half maximum was obtained at a wavelength of 1300 nm. (C) 2002 American Institute of Physics.

To understand the nature of resonant tunneling in triple‐barrier/double‐quantum‐well structures, we have investigated the properties of transmission probability TT of such structures with use of the transfer‐matrix method. The transfer matrix of the middle barrier is calculated to analyze the amplitude decay, the phase shift, and the coupling effects that are induced between the two quantum wells. The dependencies of TT and the splitting of the resonant peaks on the middle‐barrier thickness, the well width, and the symmetry of the structures are calculated. The origin of the transmission resonance and the resonant condition for symmetric (equal well widths) and asymmetric structures are discussed. The variations of TT with the applied voltage are also analyzed. The calculation results lead to some suggestions on how to design triple‐barrier structures with improved performance.

A new approach to analyze the transport characteristics of resonant tunneling structures has been developed. It is shown that the Fermi‐level Ef position per se, the temperature variations of the Fermi‐level, the effective mass, and the mobility, have important influences on the resonant tunneling transport properties. Both calculations and experiments have shown very different features for heavy‐hole and light‐hole resonant tunneling in SiGe/Si resonant tunneling structures. These different features can for the first time be explained coherently. The calculated subband energy at current resonance can be much higher or lower than the Fermi level and the peak current can decrease or increase with temperature, depending on the device structure, the carrier type, and the working conditions. The calculations have predicted an interesting result that, in the low‐temperature region, the valley current for the first heavy‐hole resonance decreases with temperature, and that is confirmed by our experiments. The ca...

We report a Ni and Si L3,2-edge x-ray absorption near edge structures (XANES) study of nickel–silicon interaction in submicron (0.15 and 0.2 μm) lines on a n-Si(100) wafer as well as a series of well characterized Ni–Si blanket films. XANES measurements recorded in both total electron yield and soft x-ray fluorescence yield indicate that under the selected silicidation conditions, the more desirable low resistivity phase, NiSi, is indeed the dominant phase in the subhalf-micron lines although the formation of this phase is less complete as the line becomes narrower and this is accompanied by a Ni rich surface.

Electrical and structural properties of platinum monosilicide (PtSi) in deep submicron lines are reported. The sheet resistance of the silicide films was found to be rather independent of the linewidth down to dimensions as small as 0.15 µm. Plan-view and cross-sectional transmission electron microscopy was performed to study the structural properties of these films, including their gain structures and lateral growth. The insensitive nature of the electrical properties of the silicide films to the linewidths is correlated with their structural properties.

In Si/SiGe/Si heterojunction bipolar transistor structures, very shallow arsenic implant on the emitter has been found to cause anomalous boron diffusion in the base. This phenomenon imposes stringent constraints on the device fabrication processes. We discovered that by using platinum silicide, which also served as a self‐aligned low resistance contact material to the emitter and base, the anomalous diffusion in the base was significantly reduced. In this letter, we report the experiment results, and propose possible explanations.

We have investigated the resonant tunneling feature variations with temperature in molecular beam epitaxy grown strained Si0.78Ge0.22/Si double‐barrier structures with different well width w and spacer thickness LS. Both w and LS have strong effects on the temperature characteristics of the peak current JP, the valley current JV, and the current peak‐to‐valley ratio (PVR). When w is reduced, both JP and JV are greatly increased. The resonant tunneling devices (RTDs) also have better temperature stability and PVR decreases slower. The RTD with larger LS has higher peak current. Beside w and LS, the quasi‐Fermi level position has a very important influence on the resonant tunneling feature variations, which is stressed in the present work.

Temperature effects on current transport and the negative differential resistance for SiGe/Si and GaAlAs/GaAs resonant tunneling structures (RTS) have been studied, and the maximum working temperature Tm has been estimated. The calculations show that decreases in the carrier effective mass, well width and barrier thicknesses, lead to better temperature characteristics, implying higher peak current and larger peak‐to‐valley ratio (PVR) at higher temperature. These results are consistent with our experiment on SiGe/Si RTSs and other published experiments. The crucial role of nonresonant tunneling current Jnon in temperature effects for current transport is emphasized. Suggestions for optimizing RTS design to increase its Tm and PVR are discussed.

Optically-pumped long-wavelength vertical-cavity surface-emitting lasers (VCSELs) have been fabricated exhibiting more than 2mW over 20–70°C, and 1.25mW at 85°C. Small-signal modulation measurements on the VCSEL at 20°C indicate a 3dB bandwidth of 14.8GHz at an output power of 2mW. The VCSELs have a narrow spectral width suitable for data transmission over single-mode fiber. The good temperature performance of the VCSEL is maintained in a suspended configuration that would allow monolithic integration.

The measurement and analysis of I‐V characteristics from molecular beam epitaxially grown Si0.9Ge0.1/Si p‐n diodes are presented. When a diode is forward biased the current transport is mainly injection diffusion of the holes and defect recombination within the depletion region of the n side. At reverse bias, the current comes from tunneling of holes from the top of the p‐type valence band to the n‐type conduction band, and also to the interface states followed by multistep recombination tunneling via defect states in the depletion region of the n side. The forward voltage drop was found to be much lower than that of Si diodes. Electron irradiation damages have opposite effects on the forward‐biased I‐V characteristics of Si0.9Ge0.1/Si diodes as compared to the effects observed for Si diodes.

Two different structures of n‐Si/p‐Si1−xGex/n‐Si double‐heterojunction bipolar transistors have been fabricated by molecular beam epitaxy. A common emitter current gain β of about 15 was demonstrated in one kind of structure and the β‐IC curve has been investigated. In the other structure, a novel multistep collector current IC vs collector‐emitter voltage VCE characteristic together with a strong negative resistance behavior was observed at room temperature. In this letter the basic experiments are described; a comparison and a discussion of the two kinds of devices are presented.