L. E. Erickson

Material aspects of nickel silicide for ULSI applications

Nickel silicide is being considered as a candidate for applications in deep sub-micron integrated circuits. In this paper, some pertinent electrical and material properties are studied systematically. The effects of substrate doping on the silicide sheet resistance are examined for both single crystal and poly-silicon substrates. The thermal stability of the silicide films and the effects of dopants are discussed. Particular attention is paid to these properties as the silicide feature size is reduced towards the 0.1 μm range. The influence of feature size on the morphology and topography of the silicide is also presented.

Formation of visible light emitting porous GaAs micropatterns

Pore growth on n-type GaAs (100) can be initiated in 1 M HCl solution by electrochemical polarization of the material anodic to a critical potential value—the pore formation potential (PFP). At surface defects, however, the PFP is significantly lower (shifted cathodically). Focused ion beam, implantation of Si++ was used to create defined patterns in the substrate. At these implant sites, the growth of porous GaAs was selectively achieved by polarization below the overall PFP. From the porous GaAs patterns visible photoluminescence at green-yellow wavelengths can be observed. This technique, thus, allows the production of light emitting porous GaAs micropatterns of arbitrary shape by a direct writing process.

Effects of Saturable Absorber Lifetime on the Performance of Giant‐Pulse Lasers

An earlier paper on the theory of saturable absorber giant‐pulse lasers is extended by considering the effects of a finite absorber lifetime ts on the pulse parameters. Digital‐computer studies show that for typical systems the giant‐pulse energy and peak power are practically unchanged from the case for which ts → ∞. A new result is that the initial cavity photon density or, alternately, the pump power, must exceed a threshold value to proceed from the region of initial normal lasing to giant pulsing. The role of the pump in the pulse buildup from noise is examined, in particular the transition region between the low‐level behavior described by Sooy and the onset of absorber saturation. The ratio of photon density in the transition region to the peak density is shown to provide a measure of the product of the ratio of absorber‐to‐laser cross section times the absorber lifetime. Some possible mechanisms which lead either to mode selection or mode locking in passive Q‐switched lasers are discussed.

Predefined initiation of porous GaAs using focused ion beam surface sensitization

Pore formation on n-type GaAs(100) under anodic polarization in I M HCI has been studied. Focused ion beam implantation of Si 2+ into GaAs was used to write defined surface damage/implant patterns into the substrate. These implant sites represent initiation sites for pore growth and show pore formation at potentials significantly cathodic to the intact surface. Hence, pore growth within the patterns can be achieved selectively if anodic polarization is kept below the pore formation potential of the unimplanted surface. The results show that both the polarization potential and the implantation dose strongly influence the morphology and the photoluminescence behavior of the porous structures. Monte Carlo simulations of the implantation process revealed that the morphology of the etch process and its kinetics are both strongly connected to the implant/damage profile. Furthermore, it is demonstrated that green-light-emitting porous GaAs lift-off layers can be produced.

Electrical and structural properties of PtSi films in deep submicron lines

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.

Behavior of Saturable‐Absorber Giant‐Pulse Lasers in the Limit of Large Absorber Cross Section

Using a rate‐equation model, it is shown that the behavior of the saturable‐absorber giant‐pulse (SAGP) laser can be adequately described in terms of two parameters for values of the ratio of absorber to laser absorption cross section σ>200: nai′ the normalized initial inversion and στs, where τs is the normalized absorber relaxation time. In the general case, specification of nai′, σ, and τs is required. Theoretical curves of the giant‐pulse output power, energy, and rise‐ and falltimes are presented. The results are applicable in particular to SAGP lasers employing organic‐dye absorbers.

Polarization compensation in silicon-on-insulator arrayed waveguide grating devices

As the AWG size is reduced our experimental and theoretical work demonstrates that it becomes increasingly difficult to suppress higher order modes and birefringence using ridge dimension alone. In part, it simply becomes difficult to meet the required fabrication tolerances when the ridge dimension approaches the order of a micron. We show that a novel polarization compensator scheme similar to that previously reported for a grating based demultiplexer in InP and consisting of simple shallow etched regions in the combiner sections of an SOI AWG, can eliminate the polarization sensitivity of the device by reducing the initial polarization dispersion of 2.22 nm to 0.04 nm. By combining the polarization compensator with mode filtering using appropriate array waveguide curvature, the shape of the array waveguides is no longer constrained. This allows the size of an AWG device to be scaled down to very small dimensions (e.g. less than a millimeter) and also permits the use of simple fabrication techniques such as wet etching. Our results were obtained on AWG devices based on 1.5 micrometers thick Si-on-insulator waveguides with a typical waveguide array area of a few square millimeters.

Direct micropatterning of Si and GaAs using electrochemical development of focused ion beam implants

Focused ion beam implantation of Si++ was used to write defined surface damage/implant patterns into n-type GaAs (100) and Si (100) substrates. These implant sites represent initiation sites for dissolution processes when electrochemically polarized in HCl or HF electrolytes, respectively. Selective dissolution within the patterns is achieved if anodic polarization of the n-type material is carried out in the dark at potentials below (cathodic to) the onset of dissolution potential of the unimplanted surface. Uniform etching within the implanted region takes place, when local electropolishing conditions are established. Thus, highly defined etch patterns, e.g., lines, gratings, or pits, can be produced in the submicron range. The depth of the etched patterns corresponds to the implant/damage profile created in the implantation process and etch stop occurs at less reactive crystal planes.

Surface topology of GaAs(100) after focused ion beam implantation of Si

GaAs(100) was implanted with Si++ doses ranging from 3×1013 to 3×1016 cm−2 using a focused ion beam. The surface topology and roughness of implanted lines and squares was studied by atomic force microscopy. Above a threshold dose, protrusions of the ion beam treated areas in the range of 1–15 nm in heights and an increase in surface roughness were found. The height of the protrusions and surface roughness increase with increasing implantation dose up to a saturation level. Both the onset of substrate bulging and saturation of the effect are both dependent on the linewidth of the implant. Different causes for the protrusions are discussed. From Monte Carlo simulations, it is deduced that the volume expansion is most likely due to the creation of vacancies during implantation.

On anti-stokes luminescence from Rhodamine 6G in ethanol solutions

Abstract Anti-Stokes luminescence form Rhodamine 6G ethanol solutions excited by a He-Ne laser is observed to be strongly temperature dependent. A theoretical model is proposed for the absorption line shape on the long wavelength side of the pure electronic transition which fits the absorption and luminescence data. Vavilovs law is found to hold even when the absorption coefficient is 10-6 times the peak absorption coefficient for the Rhodamine 6G dye solution. Another luminescence peak at 6650 A is observed which is attributed to impurity fluorescence. It could not be related to photochemical products.