R. T. Carline

Spectroscopic ellipsometry characterization of strained and relaxed Si1-xGex epitaxial layers

Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Si1−xGex on Si in the range 0.1<x<0.25. Dielectric functions of relaxed Si0.87Ge0.13 and Si0.8Ge0.2 have been obtained and long‐wavelength absorption coefficient values, required for interference fringe fitting, shown to be higher than measured previously. The dielectric function of strained Si0.78Ge0.22 has been measured for the first time and the effects of strain on the critical points shown to be consistent with deformation potential theory. An interpolation procedure has been developed for the fitting of layer composition and thickness, and excellent agreement with conventional techniques obtained for a series of uncapped single epilayers. The surface roughness of Si1−xGex epilayers has been studied as a function of time and deposition temperature and shown to play an important role in the modeling. The application of the technique to the characterization of buried strained layers is discussed.

Dielectric function spectra of strained and relaxed Si1−xGex alloys (x=0–0.25)

Dielectric function spectra for strained and relaxed Si1−xGex alloys with x∼0.13 and 0.20 are presented in numerical form. The effect of strain is shown to cause a modification of the spectra in the E1 critical point region, resulting in a decrease in refractive index at 1.96 eV, amounting to 0.06 at x=0.22. The spectral dependence of the refractive index is presented for a series of strained layers. An overview is given of spectral databases and the single‐wavelength ellipsometry data available in the literature.

Dielectric functions and critical points of strained InxGa1−xAs on GaAs

Dielectric function spectra of strained InxGa1−xAs (x≤0.25) epilayers on GaAs are presented for the first time, together with spectra of relaxed layers of the same compositions. Critical point energies, obtained by line‐shape fitting to second‐derivative spectroscopic ellipsometry (SE) data, show an increase in the E1, E1+Δ1 splitting with strain, in agreement with theory using GaAs deformation potentials. SE is shown to be capable of determining layer thickness, composition, and strain in this alloy system.

Spectroscopic ellipsometry of Si1−xGex epilayers of arbitrary composition 0≤x≤0.255

Critical point (CP) transition energies have been calculated for strained Si1−xGex (0≤x≤0.255) between 2.5 and 3.5 eV from Lorentzian fits to the second differential of reference dielectric function spectra. E1 and E’0 transition energies are similar to those of the relaxed alloy. Comparison with deformation potential theory shows E1+Δ1 to be coincident with E’0 due to a strain‐induced up shift in the former’s transition energy. The reference spectra and CP transition energies are used in an interpolation procedure to analyze spectroscopic ellipsometry spectra of both uncapped and buried layers of strained Si1−xGex. Compositions and thicknesses are obtained in good agreement with alternative techniques.

In-situ dual-wavelength and ex-situ spectroscopic ellipsometry studies of strained SiGe epitaxial layers and multi-quantum well structures

In-situ dual-wavelength ellipsometry and ex-situ spectroscopic ellipsometry have been used to study strained Si 1-x Ge x /Si multilayers. Reference dielectric function spectra of strained Si 1-x Ge x with 0.06<x<0.29 have been obtained for the first time and an interpolation procedure based on the strain dependence of the dominant critical point energies developed. Good agreement with composition and thickness values from corroborative techniques was obtained when the effects of strain were taken into account

Resonant cavity longwave SiGe-Si photodetector using a buried silicide mirror

We describe a resonant cavity detector which uses epitaxial p-type SiGe-Si quantum wells for absorption which are epitaxially grown above a high reflectance tungsten silicide layer. The device operates in the 8-12 /spl mu/m band in normal incidence and exhibits a /spl times/8 enhancement in its peak photoresponse when compared to a nonresonant control device. The black body responsivity is comparable to current n-GaAs-AlGaAs detectors at 1 V making it suitable for integration in a monolithic Si-based focal plane array. Ways to optimize the device design to achieve improved performance are discussed.

Spectroscopic ellipsometry of epitaxial Si {100} surfaces

The dielectric spectra of Si {111} and Si {100} orientations are shown to be equivalent using ex situ spectroscopic ellipsometry on clean epitaxial surfaces. The peak values for the real and imaginary parts (er, i) of the dielectric function exceed those previously reported, values of ei (at 4.25 eV)≥47 being obtained. Surface features with lateral scales of ≊0.5–2 μm, do not affect the dielectric spectra significantly. The high dielectric function peaks indicate that the nanometer lateral‐scale roughness on these epitaxial surfaces is very small.

Absorption in p‐Si1−xGex quantum well detectors

The normal incidence absorption between 2 and 14 μm in a pseudomorphic p‐Si0.81Ge0.19/Si multiple quantum well sample with doping 5×1012 cm−2 per well is described by a Drude conductivity characteristic of free carriers, with an in‐plane mobility of 32 cm2/V s and a relaxation time of 5.5 fs at 77 K. When the absorption is scaled with dopant concentration these parameters predict quantum efficiencies for quantum well infrared photodetectors in reasonable agreement with experiment.

The surface roughness and optical properties of high quality Si epitaxial layers

Abstract New recently published Si dielectric function data collected from specially prepared epitaxial Si are compared with literature values. Atomic force and optical microscopy studies of the epitaxial surfaces revealed them to be smooth on the fine scales to which ellipsometry is sensitive. The use of these new dielectric function data is demonstrated to lead to significantly improved fitting of ellipsometric data collected from a thermal oxide on Si structure.

Optical properties of bonded silicon silicide on insulator (S2OI): a new substrate for electronic and optical devices

Abstract A new type of silicon on insulator substrate was fabricated using wafer bonding. The inclusion of a highly conducting buried tungsten silicide layer below the silicon device layer but above the oxide film results in many attractive properties for electronic and optical devices such as high performance bipolar transistors, power devices and optoisolators. Commercial products are being developed using this new S 2 OI material. However, to fully exploit this material a detailed understanding of its optical and physical nature is required. To this end a study of the buried silicide film, its interfaces and the overlying silicon was carried out using spectroscopic ellipsometry and atomic force microscopy. It was found that the buried silicide undergoes a structural transformation, due to the thermal bonding anneal, resulting in a rough interface between it and the silicon overlayer.