Generation of 1180 Å period gratings with a Xe ion laser

Holographic lithography with the 2315 Å line of a xenon ion laser is used to produce gratings in polymethylmethacrylate. An 1180 Å period grating is made and examined with a scanning electron microscope (SEM). This grating period is appropriate for use as a first-order grating with a GaAs distributed feedback laser     

InGaAsP-InP ridge-waveguide DBR lasers with first-order surfacegratings fabricated using CAIBE

The design and operation of InGaAsP-InP ridge-waveguide (RW) distributed Bragg reflector (DBR) multiple quantum-well lasers with first-order surface gratings are presented. The RW DBR lasers are fabricated using only a single growth step without growth on a corrugated surface. Uncoated devices with grating etch depths of 0.6 and 0.5-μm exhibit pulsed threshold currents of 32 and 43 mA with slope efficiencies of 0.34 and 0.24 W/A, respectively. The device with a grating etch depth of 0.5-μm operates on a single longitudinal mode with about 40 dB side-mode suppression. All these results are from devices with Bragg condition wavelengths which are red-shifted from the peak spontaneous emission wavelength by over 400 Å     

Two-dimensional effects in titanium silicidation

New experimental results are reported on the two-dimensional (2-D) effects associated with titanium silicidation on small and nonuniform structures. Based on a unique set of test structures, new insight into the silicidation process is obtained. Small geometry by itself does not seem to be restraining silicide formation. Thick silicide is demonstrated to form on the vertical surface of silicon posts of 1000 Å radius and on top of 1200 Å wide silicon lines. Also discussed are the possible roles of mechanical stress and the Si-SiO₂ interface in the 2-D silicidation and diffusion processes. The original data presented here will be useful in further analysis and simulation of 2-D silicidation process     

The fabrication of thin-film bulk acoustic wave resonatorsemploying a ZnO/Si composite diaphragm structure using porous siliconlayer etching

Thin-film bulk acoustic wave resonators (FBARs) are used in monolithic microwave integrated circuits (MMICs) for semiconductor devices. FBARs are more attractive than surface acoustic wave resonators since they have the advantages of small size, low cost, and mass-production ability. In this letter, an FBAR with an air gap is fabricated by a surface micromachining technique which utilizes porous silicon layer (PSL) etching. This FBAR has a forward reflection coefficient of -18.912 dB when the thickness of the ZnO thin film measures 1 μm. The FBAR is composed of a piezoelectric zinc oxide (ZnO) thin film and top and bottom electrode thin films of Au(1000 Å)/Ni-Cr(50 Å). The ZnO thin film is deposited by RF magnetron sputtering. This fabrication process is compatible with conventional IC processes, thereby enabling the development of monolithic-integrated FBAR's on Si or GaAs substrates     

Frequency selective Bragg filters based on (Mg,Zn) (S,Se)waveguides for the visible spectral range

Bragg grating transmission filters were fabricated on ZnMgSSe-ZnSSe-ZnMgSSe planar optical waveguide structures using a high resolution electron-beam lithographic process. Varying the grating geometry, the filter characteristics like resonance wavelength, modulation contrast, and stopband width can be adjusted. For example, for a L=600-μm-long grating with a period of Λ=120 nm, we achieve 16% residual transmission and a spectral width of 4 Å for the designed resonance wavelength of 603 mm. The experimental data can be explained quantitatively with a transfer matrix calculation assuming a coupling coefficient of 40 cm^-1     

An 8-channel digitally tunable transmitter with electroabsorptionmodulated output by selective-area epitaxy

We demonstrate an 8-frequency digitally tunable laser based on a waveguide grating router with an electroabsorption modulated output. The laser wavelengths range from 1.567 to 1.580 μm with channel spacings of 200 GHz (1.6 nm). The modulator extinction is -10 dB/VN with a -5-V bias. A unique output coupler design delivers an ASE noise suppression of -55 dB/Å     

Gain-coupled DFB lasers with a titanium surface Bragg grating

The improved performance of gain-coupled DFB lasers incorporating a titanium surface Bragg grating and a strained layer multiquantum well active region for operation at 1.55 μm is presented. Besides the essentially simplified fabrication process, the incorporation of the metallic, absorptive grating yields stable singlemode operation with a high sidemode suppression     

A WDM receiver photonic integrated circuit with net on-chip gain

We demonstrate a photonic circuit with an optical preamplifier, a WDM filter and a fast photodetector integrated on the same chip. The passive integrated filter is formed by an aspheric waveguide lens and a planar Bragg grating. This arrangements yields narrow filter response (8 Å width at -3 dB is demonstrated) and high rejection ratio of 24 dB. The optical preamplifier consisting of strained multi-quantum well layers provides sufficient amplification to overcome the passive losses. Response curves demonstrate net on-chip gain with low ripple     

MOSFET transistors fabricated with high permitivity TiO2dielectrics

Layers of polycrystalline anatase TiO₂ have been deposited through the thermal decomposition of titanium tetrakisisopropoxide (TTIP). 500 Å films deposited and annealed in oxygen at 750°C had average roughnesses (R_a) of about 30 Å. Capacitors made from 190 Å layers of TiO₂ displayed a voltage dependent accumulation capacitance. This was postulated to be caused by finite width effects in the accumulation layer which we have dubbed the quantum capacitance effect. N-channel transistors made with these films showed near ideal behavior, but mobilities were significantly lower than those of thermal oxide MOSFETs. This mobility reduction was believed to be caused by interface states, which fell below 10¹¹ cm^-2 eV^-1 at midgap, but rose sharply on either side, unlike the “U” shaped behavior in thermal oxide MOSFET's     

Comparative physical and electrical metrology of ultrathin oxidesin the 6 to 1.5 nm regime

In this work, five methods for measuring the thickness of ultra-thin gate oxide layers in MOS structures were compared experimentally on n⁺ poly-SiO₂-p-Si structures. Three methods are based on electrical capacitance-voltage (C-V) and current-voltage (I-V) data and the other two methods are HRTEM and optical measurement. MOS capacitors with oxide thickness in the range 17-55 Å have been used in this study. We found that thickness extracted using QM C-V and HRTEM agree within 1.0 Å over the whole thickness range when a dielectric constant of 3.9 was used. Comparison between thickness extracted using quantum interference (QI) I-V technique and optical measurement were also within 1.0 Å for thickness 31-47 Å. However, optical oxide thickness was consistently lower than the TEM thickness by about 2 Å over the thickness range under consideration. Both optical measurement and QM C-V modeling yield the same thickness as the nominal oxide thickness increases (>50 Å)     

Thickness dependent gate oxide quality of thin thermal oxide grownon high temperature formed SiGe

For thin oxides grown on high temperature formed Si_0.3Ge_0.7, the gate oxide quality is strongly dependent on oxide thickness and improves as thickness reduces from 50 to 30 Å. The thinner 30 Å oxide has excellent quality as evidenced by the comparable leakage current, breakdown voltage, interface-trap density and charge-to-breakdown with conventional thermal oxide grown on Si. The achieved good oxide quality is due to the high temperature formed Si_0.3Ge_0.7 that is strain relaxed and stable during oxidation. The possible reason for strong thickness dependence may be due to the lower GeO₂ content formed in thinner 30 Å oxide rather than strain relaxation related rough surface or defects     

Temperature insensitive arrayed waveguide gratings on InPsubstrates

A temperature insensitive arrayed waveguide grating (TI-AWG) with an InGaAsP-InP material system is proposed. Less than 0.1 Å/°C temperature dependence for all eight channels was achieved for the first time even though we used the InGaAsP-InP material system. This novel characteristic is in good agreement with the design principle of the TI-AWG     

Analysis of a λ/4-phase-shifted doublephase-shift-controlled distributed feedback wavelength tunable opticalfilter

We have proposed a new λ/4-phase-shifted double phase-shift-controlled distributed feedback wavelength tunable optical filter structure. Theoretical analysis based on the transfer matrix method reveals that this filter can achieved a wavelength tuning range of 28.3 and 34.3 Å for the grating coupling coefficients of 6 and 10 mm, respectively. The filter has almost constant peak transmissivity (gain) of more than 30 dB within its tuning range, and its side-mode suppression ratio (SMSR) ranges from 15 to 34.7 dB     

Planarization of emitter-base structure of heterojunction bipolartransistors by doping selective base contact and nonalloyed emittercontact

The authors report an n-p-n heterojunction bipolar transistor (HBT) with a planar (and thus passivated) emitter-base structure fabricated using a simple, low-temperature technique. They use a nonalloyed emitter contact facilitated by δ-doping grown at the surface of the sample, so that the cap layer is only 75 Å thick. The base is contacted by depositing Au-Zn or Au-Be on the surface and alloying at 420°C for 10 s, resulting in an ohmic contact with the base and rectifying contact with the emitter. The authors present large-emitter area (50-μm diameter) HBTs with homogeneous-doped bases (gain of 170) and δ-doped bases (10¹⁴ cm^-2, gain of 20). Upon reducing the emitter size of the latter to 3×8 μm the gain increased to 30, demonstrating excellent surface passivation     

2-D simulation of interface properties of a polysilicon-contactedBJT: is there a residual potential barrier after the oxide is broken?

Two dimensional simulations were performed on a poly-contacted bipolar, studying the effects of changing the size of broken sections of the “oxide” on the base current. Previous simulations (Egley et al. 1991) used sections which were ~250 Å in length, while the simulations presented here use ~50 Å sections, closer to what was observed from TEM by Wolstenholme et al. (1987). The smaller gaps provide a substantially more rapid increase in base current with percentage oxide broken than found with the 250 Å sections. This extremely rapid rise in base current with the percentage oxide broken is not observed experimentally. It is proposed that a residual barrier remains after a section of the oxide is removed. This potential energy barrier would arise from the grain boundary itself and from the possible presence of electrically active As there     

The leakage current improvement in an ultrashallow junction NMOSwith Co silicided source and drain

The leakage current characteristics of the cobalt silicided NMOS transistors with a junction depth of 800 Å have been studied. In order to minimize the junction leakage current, the thickness of the CoSi₂ layer should he controlled under 300 Å and the Si surface damage induced by the gate spacer etch should be minimized. The post furnace annealing after the second silicidation by the rapid thermal annealing (RTA) process also affected the leakage current characteristics. The gate induced drain leakage (GIDL) current was not affected by the lateral encroachment of CoSi₂ layer into the channel direction when the gate spacer length was larger than 400 Å     

Cascade self-induced holography: a new grating fabricationtechnology for DFB/DBR lasers and WDM laser arrays

A method of fabricating submicron gratings for optoelectronic devices from a glass mask was proposed and demonstrated. The glass mask has gratings on both sides with a period of at least four times the final feature size. By introducing an offset to the grating periods on the mask, one can achieve multiple-period gratings with a very fine period spacing for advanced wavelength-division multiplexing (WDM) devices. In this paper, we demonstrated 0.5-μm second-order gratings for 1.55-μm DFB lasers and gratings with a 6-Å period difference for a four-channel WDM laser array using only optical sources. The Moire pattern caused by the spatial frequency beating was also observed and discussed. The Moire pattern could serve as an effective tool to measuring wavelength channel spacing between devices with an unprecedented (0.1 Å) resolution     

Determination of Si/SiO2 interface roughness using weaklocalization

The interface roughness of intentionally textured Si/SiO₂ interfaces was measured using the quantum weak localization (WL) correction to the electrical conductivity at low temperatures. The deduced roughness was confirmed by observation of the Si surface replicas by atomic force microscopy (AFM). Quantitative agreement between the two methods was found (Δ=1.2 to 1.4 Å from WL and 1.35 Å from AFM). For a surface with artificially induced texture, it is found that WL can easily distinguish a significant increase in roughness relative to the smooth surfaces. AFM confirms this qualitative conclusion     

Wide-bandgap epitaxial heterojunction windows for silicon solarcells

It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a=5.43 Å), nearly lattice-matched wide-bandgap materials are ZnS (a=5.41 Å) and GaP (a=5.45 Å). Isotype n-n heterojunctions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched ((111) faceted) surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length     

Thin oxide thickness extrapolation from capacitance-voltagemeasurements

Five oxide-thickness extrapolation algorithms, all based on the same model (metal gate, negligible interface traps, no quantum effects), are compared to determine their accuracy. Three sets of parameters are used: (acceptor impurity concentration, oxide thickness, and temperature): (10¹⁶ cm^-3, 250 Å, 300 K), (5×10¹⁷ Cm^-3, 250 Å, 300 K), and (5×10¹⁷ cm^-3, 50 Å, 150 K). Demonstration examples show that a new extrapolation method, which includes Fermi-Dirac statistics, gives the most accurate results, while the widely-used C_o≃C_g (measured at the power supply voltage) is the least accurate. The effect of polycrystalline silicon gate is also illustrated