McDonald Robinson

Infrared waveguiding in Si 1−x−y GexCy upon silicon

Polarization-independent waveguiding at 1.32 and 1.54 microm was observed in single-crystal S(1-x-y)Ge(x)C(y) grown nearly lattice matched upon Si(100) by chemical vapor deposition. Losses were <5 dB/cm at 1.54 microm. Experiments indicate that the band gap of three SiGeC alloy waveguides was in the 0.93-0.99-eV range, in agreement with theory.

Schottky and ohmic contacts to doped Si1−x−yGexCy layers

Abstract We report on titanium contacts to n-type and p-type Si 1− x − y Ge x C y strained heteroepitaxial layers on (100)Si and material and electrical characterization of n-type and p-type platinum–silicide–germanide contacts to Si 1− x − y Ge x C y strained heteroepitaxial layers on (100)Si. Ti contacts to n-type Si 1− x − y Ge x C y show rectifying behavior at low doping levels but become ohmic as layers reach 10 18 cm −3 . Ti contacts to p-type Si 1− x − y Ge x C y /Si are ohmic at doping levels as low as 10 15 cm −3 . Contact resistances for Ti/Si 1− x − y Ge x C y contacts had values ranging from 10 −1 to 10 −2 Ω cm 2 . X-ray diffraction (XRD) studies of rapid thermal anneal (RTA) silicidation of Pt on SiGeC indicate the reaction proceeds from elemental Pt to Pt 2 (SiGeC) and ends in the Pt(SiGeC) phase, analogous to Pt/Si silicides. However, the Pt–silicide–germanide reaction with SiGeC requires higher temperatures than the counterpart Pt reaction with Si. Pt(SiGeC) contacts to n-type SiGeC layers show rectifying behavior with nonideality factors ( n ) of 1.02 to 1.05 and constant barrier heights of 0.67 eV independent of composition, indicating that Fermi level pinning relative to the SiGeC conduction band is occurring. For contact doping levels of 10 18 cm −3 and above, Pt(SiGeC) contacts to n-type SiGeC layers are ohmic with constant contact resistance values of 10 −2 Ω cm 2 . Pt(SiGeC) contacts to p-type Si 1− x − y Ge x C y /Si were ohmic over the entire doping range studied, with resistances from the 1 Ω cm 2 range at intrinsic alloy doping levels, to the 10 −2 Ω cm 2 range for doping levels of 10 18 cm −3 . Using Pt(SiGeC) ohmic contacts to p-type SiGeC, current–voltage measurements of Si 1− x − y Ge x C y to (100)Si heterojunctions are also presented. Heterojunction barrier heights track the variation of the SiGeC energy bandgap to a factor of 0.84×. The Si 1− x − y Ge x C y /Si heterojunction valence band discontinuity, Δ E v , decreases 15 meV per %C incorporated into the strained alloy layer for 0 y E v by 2.8 meV per %Ge for 0 x

Cryogenic field effect transistors using strained silicon quantum wells in Si :SiGe heterostructures grown by APCVD

Abstract High mobility strained silicon quantum wells in modulation doped SiGe heterostructures, grown epitaxially on silicon substrates, offer exciting opportunities for devices compatible with silicon CMOS processing, having significantly improved performance over their single crystal silicon counterparts. We present results from a collaborative academic/industrial program to develop field effect transistors suitable for cryogenic circuit applications. This work reports on the fabrication and characterization of heterostructure material grown using atmospheric pressure CVD, low temperature characterization of the electronic properties of the material, FET device fabrication and FET performance at 0.3–4.2 K.

Mobility characterization of p-type and n-type strained si l - x - y Ge x cy/Si Epilayer hall devices

Mobilities in Si 1 - x - y Ge x C y layers were measured using mesa etched Van der Pauw structures for alloy layers with 0 15 18 cm -3 . Mobilities in Si 1 - x - y Ge x C y layers with x = 0.27 were found to approach Si mobilities for both μn and μp.While electron mobilities in phosphorous-doped SiGeC decrease with doping concentration, hole mobilities in boron-doped SiGeC increase with doping level, indicating ionized impurity scattering is not dominant for μp over the temperature range studied.