A. St. Amour

Defect‐free band‐edge photoluminescence and band gap measurement of pseudomorphic Si1−x−yGexCy alloy layers on Si (100)

Pseudomorphic Si1−x−yGexCy alloy layers on Si (100) with band‐edge photoluminescence and without defect‐related luminescence have been achieved. The photoluminescence was measured from 2 to 77 K and was used to make a direct measurement of the band gap shift as a function of strain reduction as C was added. Compared to the effect of just reducing Ge content, results show that as C is added, strain is reduced more efficiently than the band gap is increased. Furthermore, results imply that a fully strain‐compensated Si1−x−yGexCy layer on Si (100) would have a band gap much less than that of Si, and suggest that initial C incorporation reduces the band gap of relaxed, unstrained Si1−x−yGexCy alloys.

Co silicide formation on SiGeC/Si and SiGe/Si layers

The reaction of Co with epitaxial SiGeC/Si layers is investigated and compared to the reaction of Co with SiGe/Si layers. The sequence of phase formation is the same as the reaction of Co with monocrystalline Si, however, cobalt disilicide is formed at much higher temperatures. The presence of C further delays the disilicide formation, as a result of C accumulation at the silicide/substrate interface during the reaction, which blocks the Co diffusion paths. The CoSi2 layers thus formed exhibit a preferential (h00) orientation. The slow supply of Co atoms to the silicide/Si interface, due to the blocking of Co diffusion paths by Ge and C, is believed to be the reason for this epitaxial alignment.

Si/Si/sub 1-x-y/Ge x C y /Si heterojunction bipolar transistors

We report the first Si/Si/sub 1-x-y/Ge/sub x/C/sub y//Si n-p-n heterojunction bipolar transistors and the first electrical bandgap measurements of strained Si/sub 1-x-y/Ge/sub x/C/sub y/ on Si (100) substrates. The carbon compositions were measured by the shift between the Si/sub 1-x-y/Ge/sub x/C/sub y/ and Si/sub 1-x/Ge/sub x/ X-ray diffraction peaks. The temperature dependence of the HBT collector current demonstrates that carbon causes a shift in bandgap of +26 meV/%C for germanium fractions of x=0.2 and x=0.25. These results show that carbon reduces the strain in Si/sub 1-x/Ge/sub x/ at a faster rate than it increases the bandgap (compared to reducing x in Si/sub 1-x/Ge/sub x/), so that a Si/sub 1-x-y/Ge/sub x/C/sub y/ film will have less strain than a Si/sub 1-x/Ge/sub x/ film with the same bandgap.

Growth and photoluminescence of high quality SiGeC random alloys on silicon substrates

We report chemical vapor deposition growth of SiGeC layers on 〈100〉 Si substrates. At the growth temperature of 550 °C, the C concentration as high as 2% can be incorporated into SiGe (Ge content ∼ 25%) to form single crystalline random alloys by using low flow of methylsilane (0.25 sccm) as a C precursor added in a dichlorosilane and germane mixture. For intermediate methylsilane flow (0.5 sccm – 1.5 sccm), the Fourier transform infrared spectroscopy (FTIR) absorption spectra indicate the growth of amorphous layers. For the layers with high flow of methylsilane (12 sccm), there are silicon‐carbide‐like peaks in the FTIR spectra, indicating silicon carbide precipitation. The films were also characterized by x‐ray diffraction, high resolution transmission electron microscopy, secondary ion mass spectroscopy, and Rutherford backscattering spectroscopy to confirm crystallinity and constituent fractions. The defect‐free band‐edge photoluminescence at both 30 K and 77 K was observed in Si/SiGeC/Si quantum well...

The effect of carbon on the valence band offset of compressively strained Si1−x−yGexCy/(100) Si heterojunctions

Capacitance–voltage measurements have been used to study the effect of carbon on the valence band offset of compressively strained Si1−x−yGexCy/(100) Si heterojunctions grown by rapid thermal chemical vapor deposition with substitutional C levels from 0% to 2.5%. The valence band offset between Si1−x−yGexCy and unstrained (100) Si decreases at a rate of 20–26 meV per % C. Our work indicates that the change in the bandgap of Si1−x−yGexCy as carbon is added is entirely accommmodated in the valence band.

DEEP PHOTOLUMINESCENCE IN SI/SI1-XGEX/SI QUANTUM WELLS CREATED BY ION IMPLANTATION AND ANNEALING

Strong broad photoluminescence similar to that observed in some materials grown by molecular beam epitaxy (MBE) has been observed in Si/Si1−xGex/Si quantum wells grown by chemical vapor deposition. As grown, the samples exhibited SiGe band‐edge phonon‐resolved bound‐exciton luminescence, but after being self‐implanted with silicon and annealed at 600 °C, a deep broad luminescence band 80–100 meV below the excitonic gap was observed. This strong luminescence disappeared with an 800 °C anneal and had a pump power and temperature dependence similar to that observed in MBE samples. This is the first time that such luminescence has been observed in material other than that grown by MBE.

Enhancement of high‐temperature photoluminescence in strained Si1−xGex/Si heterostructures by surface passivation

The photoluminescence from strained Si1−xGex alloy quantum wells on Si(100) has been measured from 6 to 300 K. It is shown that the high‐temperature photoluminescence of Si1−xGex quantum wells can be increased by over an order of magnitude by passivation of the top silicon surface. Through experiments and a model, it is clearly demonstrated that the decay of the Si1−xGex photoluminescence at high temperature is controlled by surface recombination, not by an intrinsic property of Si1−xGex. By applying proper conditions, nearly constant Si1−xGex photoluminescence can be achieved from 77 to 250 K.

Effect of carbon on the valence band offset of Si/sub 1-x-y/Ge/sub x/C/sub y//Si heterojunctions

We have grown pseudomorphic single crystal Si/sub 1-x-y/Ge/sub x/C/sub y/ layers on Si (100) substrates by Rapid Thermal Chemical Vapor Deposition with up to 2.5% substitutional carbon. Capacitance-voltage as well as admittance spectroscopy measurements have been used to study the effect of carbon on the valence band offset of compressively strained Si/sub 1-x-y/Ge/sub x/C/sub y//(100) Si heterojunctions. The valence band offset of Si/sub 1-x-y/Ge/sub x/C/sub y//Si decreased by 25-30 meV as 1% carbon was added. Previous studies showed that 1% carbon increased the bandgap of strained Si/sub 1-x/Ge/sub x/ alloys by 21-26 meV, indicating that all the change in bandgap of Si/sub 1-x/Ge/sub x/ as carbon was added is accommodated in the valence band.

Growth and Electrical Performance of Heterojunction P+ Si1−x−yGexCy/p+ Si Diodes

We have fabricated heterojunction p + Si 1−x−y Ge x C y / p + Si diodes. The SiGeC layers were grown epitaxially on Si (100) substrates by the rapid thermal chemical vapor deposition (RTCVD) technique using methysilane gas as a carbon precursor. The germanium concentration is 20% in these SiGeC alloys and the carbon concentrations are in the range of 0% to 1%. By studying the current-voltage characteristics of these diodes as a function of temperature the valence band discontinuities between SiGeC and Si layers were obtained as a function of carbon concentrations. We have found that the valence band discontinuity of the SiGe/Si heterostructure decreases by II meV when 1% of carbon is incorporated. Photoluminescence (PL) results show that 1% carbon increases the bandgap of strained p + SiGe alloys by 25 meV. This would imply that the conduction band discontinuity of SiGe/Si will decrease by 14 meV when 1% carbon is incorporated.

Deposition of Monolayer-Scale Germanium/Silicon Heterostructures by Rapid Thermal Chemical Vapor Deposition

Deposition of monolayer scale Ge/Si heterostructures by Rapid Thermal Chemical Vapor Deposition has been achieved for the first time. All previous work in this area was by Molecular Beam Epitaxy. We have observed the change in Ge growth rate at 500°C as the Si substrate was covered by the first monolayer of Ge. Auger Electron Spectroscopy and Raman scattering experiments determined that the CVD growth mode for Ge on Si (100) at 550°C is Stranski-Krastanov, with the transition to islanding occurring after three monolayers.