Measurement of the conduction band offsets in Si/Si1−x−yGexCy and Si/Si1−yCy heterostructures using metal-oxide-semiconductor capacitors

Abstract

Metal-oxide-semiconductor (MOS) capacitors fabricated on in situ doped n-type Si/Si1−x−yGexCy and Si/Si1−yCy epitaxial layers were used to study the conduction band offsets in these heterojunctions. The heterostructures were grown epitaxially in a rapid thermal chemical vapor deposition reactor. Si/Si1−x−yGexCy samples with a nominal Ge concentration of 20 at. % and carbon fractions up to 1.3 at. % were studied. Carbon fractions up to 1.6 at. % were studied for the Si/Si1−yCy samples. Gate oxides were formed by thermal oxidation of the Si cap at 750 °C. X-ray diffraction measurements confirm that the processing did not affect the strain in the layers. Devices exhibit well-behaved high frequency and quasistatic capacitance–voltage (C–V) characteristics indicating the high electronic quality of the material. Capacitance–voltage measurements performed over a range of temperatures were used to extract the band offsets. Confinement of electrons at the heterointerface is apparent in the C–V curves of the Si/Si1−yCy MOS capacitors. Comparison of the measured C–V data to one-dimensional device simulations yields a conduction band edge lowering of ∼65 meV per at. % C in the Si1−yCy samples. The Si1−x−yGexCy samples, on the other hand show no evidence of electron confinement. Based on a sensitivity analysis of this technique, it is estimated that the conduction band offset in these samples is less than 30 meV. The smaller offsets in Si/Si1−x−yGexCy compared to Si/Si1−yCy can be explained by the competition between strain compensation and the intrinsic chemical effect of carbon in Si1−x−yGexCy.

Theory of valence and conduction band offsets in Si/Si 1−yCy heterostructures

“…Some of the results of equation (6) are compared with MOS C-V measurements [1] in Table 3. The tensile strain caused by the growth of Si 1−y C y layers on silicon leads to a decrease of the bandgap for low carbon concentrations [11][12][13].…”

“…Sing et al [1] studied the conduction band offsets in Si/Si 1−y C y heterojunctions using metal-oxidesemiconductor capacitors. Carbon concentrations up to y = 0.016 were studied.…”

Schottky Barrier Height of Nickel Silicide Contacts Formed on $\hbox{Si}_{1 - x}\hbox{C}_{x}$ Epitaxial Layers

“…It was shown that the electron barrier height was reduced by 27 meV as a result of carbon incorporation in the underlying Si layer. Sinha et al attributed the barrier-height reduction entirely to the smaller bandgap of strained Si 1−x C x , which was previously demonstrated by other groups [8], [9]. In doing so, the authors implicitly assumed that the NiSi Fermi level was pinned to a fixed energy level relative to the valence band.…”

Effect of substitutional carbon concentration on Schottky-barrier height of nickel silicide formed on epitaxial silicon-carbon films

“…16 The sum of the effective electron Schottky barrier height ⌽ B N and effective hole Schottky barrier height ⌽ B P is assumed to be equal to the band gap of Si 1−y C y . 17,18 The extracted effective electron Schottky barrier heights ⌽ B N obtained from subtracting the extracted effective hole barrier height from the band gap of Si 1−y C y are found to be 0.68, 0.60, and 0.51 eV for C sub of 0.5%, 1.1%, and 1.5%, respectively, and the built-in voltage obtained from C-V measurement is 0.411 V.…”