No abstract

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.

An investigation of the ternary phase diagram Cr‐Si‐C has been completed in the region normalCr‐Cr3C2‐Cr5Si3 . Phase boundaries have been established to an accuracy of ±2 a/o (atomic per cent). The extent of a ternary single‐phase region of approximate stoichiometry Cr5Si3Cx is established. Lattice parameter measurements of this phase show that all or nearly all C enters the D88‐Mn5Si3 structure at interstitial sites, rather than substitutionally as previously reported. Finally, the possibility of normalSiC crystal growth from solutions of transition metal silicides is discussed.

Platinum silicide Schottky barrier infrared diodes have been formed on p-type silicon substrates having both 〈100〉 and 〈111〉 orientations. The potential barrier to optically generated hot carriers has been measured and found to be 0.219 eV for 〈100〉 substrates and 0.313 eV for 〈111〉. Platinum-layer thickness was varied from 1 to 10 nm. The nearly 0.1 eV difference in Schottky barrier potential appears to depend only on the orientation of the silicon substrates.

Ge x Si 1−x / Si heterojunction internal photoemission (HIP) detectors with thresholds in the medium-wave infrared and long-wave infrared (LWIR) regions were fabricated and characterized. Measurements of the photoresponse are fit well by a theory which takes into account the scattering of excited carriers. The probability of escape of an excited hole is calculated and compared with that observed in another detector, the multiple quantum well structure. It is shown that HIP detectors can achieve background-limited performance in the LWIR region when operated at 40 K.