We have fabricated p-type PtSi/SiGe/Si Schottky diodes with barrier heights (from photoresponse) that are lowered (relative to PtSi/Si) and highly dependent on the applied bias. The variability in the barrier height is obtained by using the SiGe/Si valence band offset as an additional barrier. When placed in close proximity to the PtSi/SiGe Schottky barrier, the total effective barrier can be altered dramatically by adjusting the applied reverse bias. The voltage sensitivity of the total barrier height can be controlled by the SiGe layer thickness. The voltage-variable barrier heights range, for example, from 0.30 eV at zero bias to 0.12 eV at 2.4 V reverse bias for a 20%, 450 Å thick SiGe layer. This lowest barrier height corresponds to a cutoff wavelength of 10 μm, extending the detection range of PtSi infrared detectors to the long-wavelength range. The quantum efficiency coefficients C1 are normal at this long-wavelength end, but reduced over the rest of the tunable range, because hot carriers have to traverse the entire SiGe thickness in order to be detected. The hot carriers’ energy losses from quasielastic scattering in the SiGe are taken into account in a theoretical model that gives good agreement with data.

In this work, the solid-phase crystallization kinetics of amorphous SiGe films deposited by low-pressure chemical-vapor deposition on oxidized Si wafers has been studied by x-ray diffraction, Raman spectroscopy, and ultraviolet reflectance. The microstructure of the fully crystallized films has also been analyzed using these techniques in combination with transmission electron microscopy. The Ge fraction of the films (x) was in the 0–0.38 interval. The samples were crystallized at temperatures ranging from 525 to 600 °C. The crystallization monitored by all techniques was found to follow the Avrami model. Different crystallization behaviors are distinguished depending on the Ge content of the films and the crystallization temperature. The results are discussed in terms of the identification of the nucleation site location and the dimensionality of the grain growth, taking into account the probe depth of the different techniques and the values of the Avrami exponent derived from the crystallization curves. The preferred orientations of the grains, the grain morphology, the lateral grain size, the presence of inter- and intragrain defects, the surface roughness, and the overall crystallinity of the fully crystallized films have also been studied and related to the observations concerning the crystallization process.

Lowered-barrier-height silicide Schottky diodes are desirable for obtaining longer cutoff-wavelength Si-based infrared detectors. Silicide Schottky diodes have been fabricated by the reaction of evaporated Pt and Ir films on p-Si,-.Ge, alloys with a thin Si capping layer. The onset of metal-SiGe reactions was controlled by the deposited metal thickness. Internal photoemission measurements were made and the barrier heights were obtained from these. Pt-SiGe and Ir-SiGe reacted diodes have barrier heights of-0.27 and-0.31 eV, respectively, higher than typical values of 0.22 and 0.12 eV for the corresponding silicidelp-Si diodes. Their emission constants are also lower and more voltage dependent than silicide/Si diodes. PtSiiSQSiGe diodes, on the other hand, have lower barrier heights (-0.15 sV) than the PtSi/Si barrier height. The barrier height shifts in such silicide/Si/SiGe diodes are interpreted by accounting for tunneling through the unconsumed Si layer. This is done analytically using a simple model based on the Cohen, Vilms, and Archer (unpublished) modification to the Fowler equation, and leads to an extracted barrier height, that is! the Si barrier height reduced by the Si/SiGe band offset.

We have measured the optical properties of epitaxial CoSi2 films on Si from 0.062 to 2.76 eV by ellipsometry and spectrophotometry. The energy dependencies of the dielectric constants show Drude behavior at energies lower than ∼0.2 eV with Drude parameters ℏωp=(5.8±0.2) eV and ℏ/τ=(0.09±0.02) eV. Using the measured optical constants, the CoSi2 film is shown to have maximum absorptance at a thickness of ∼20 nm for λ≳1.4 μm. Finally, we have calculated the absorptance of a composite film of CoSi2 particles embedded in Si and found that the absorptance peak due to a surface plasmon resonance in the CoSi2 particles shifts to higher energy as the ellipsoidal particles become more elongated, in agreement with recent observations by Fathauer et al. [Phys. Rev. B 44, 1345 (1991)].