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Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (kvector ≈0). The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory. [ABSTRACT FROM AUTHOR]

The directional, density-of-states, and carrier-concentration effective masses of light, heavy, and split-off holes have been calculated for strained Si1-xCx alloys on Si (001) substrate. The results for the directional effective mass show that the effect of strain makes the constant energy surface of light holes near the band edge more symmetric than that in pure silicon. The effect of strain on the heavy and split-off hole bands is rather regular; up to 7% of carbon concentration the strain effect monotonically reduces the density-of-states effective mass for the two bands at energy values within energy interval of 0.4 eV below the valence band edge. This reduction is obtained for the carrier-concentration effective mass at temperatures from 0 to 600 K. The strain effect on the light hole band is less trivial; at nonzero carbon concentrations the strain effect influences the density-of-states and the carrier-concentration effective mass in a similar way as it does to the heavy and split-off bands but irregular behavior shows up in the energy interval of 0.02 eV below the valence band edge and at the temperature range from 0 to 140 K. At 7% of carbon doping the total density-of-states effective mass for holes at 77 and 300 K are almost the same, namely, the values are 0.39 and 0.40 in units of free electron mass, respectively. [ABSTRACT FROM AUTHOR]

We report the energy band structures of strained Si[sub 1-x]C[sub x] alloys on Si (001) substrates. All calculations are based on a 20×20 Hamiltonian matrix constructed from the linear combination of atomic orbital approximation with spin-orbit interaction, strain effect, and lattice disorder effect taken into account. The lattice disorder parameter is obtained from fittings with the experimental band gap of strained Si[sub 1-x]C[sub x] alloy with small carbon concentration and reflects the initial reduction of band gap of relaxed Si[sub 1-x]C[sub x] alloy, while simple virtual crystal approximation does not. The effect of strain on band structure is incorporated in terms of the interatomic interaction parameters, which are functions of bond length and bond angle. The strained Si[sub 1-x]C[sub x] alloy becomes metallic when x = 28%. All the directional effective masses are affected by the strain. Overall agreements are found between our theoretical calculations and recent experimental results. [ABSTRACT FROM AUTHOR]

Characteristics of electroluminescence from indium tin oxide (ITO)/SiO[sub 2]/Si metal-oxide-semiconductor (MOS) structures fabricated on both p-type and n-type Si wafers were investigated. The ITO/SiO[sub 2]/Si MOS on p-type Si could have both the visible and band edge electroluminescence, while the ITO/SiO[sub 2]/Si MOS on n-type Si has only band edge emission. The reason for the difference is attributed to the impact ionization that only occurs for ITO/SiO[sub 2]/Si(p) MOS. The study indicates that the band edge emission and visible luminescence are competing processes. The electroluminescence from ITO/SiO[sub 2]/Si(n) is also discovered to be less than that from the Al/SiO[sub 2]/Si(n). The reason is possibly due to the damage of the oxide bonding and the SiO[sub 2]/Si interface during the ITO sputtering. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The correlation between microstructures and magnetic properties of Pr-Fe-B thin films with thickness in the range of 25-150 nm sputtered on Ta underlayer buffered glass substrates was investigated. The films with thickness of 50-125 nm showed Pr2Fe14B phase with (004) preferred orientation. Perpendicular magnetic properties, including perpendicular magnetic anisotropy, coercivity ((Hc˔)2T), remanence ratio ((Mr/M2T)˔), and energy product [(BH)max˔]2T were improved with increment of magnetic layer thickness to 150 nm. Higher (Hc˔)2T of 10.3 kOe and energy product [(BH)max˔]2T of 19.8 MGOe were attained in the film with the thicker thickness, in turn resulted from fine microstructure and impeded domain wall motion due to nonmagnetic Pr-rich grain boundary phase as a pinning site. [ABSTRACT FROM AUTHOR]

The strain effect on the hole mobility is investigated by bulk Si field-effect transistor, substrate-strained Si devices, and these devices under biaxial tensile mechanical strain. The hole mobility along <110> direction on (001) Si substrate degrades at small biaxial tensile strain (<∼0.3%) but enhances at the biaxial tensile strain larger than ∼0.3%. This abnormal behavior can be understood in terms of the effective hole conductive mass which is the population average of heavy-hole and light-hole masses. The effective mass is more heavy-hole-like at small strain, since the heavy-hole band has a larger density of state than light-hole band. As the biaxial tensile strain increases, the hole population in the light-hole band increases due to the upshift and crossover of the light-hole band above the heavy-hole band. Therefore, the effective mass with larger biaxial tensile strain decreases significantly due to the small mass of light hole. The effective hole mass, which increases at small strain, then decreases at large strain, is responsible to the abnormal hole mobility behavior. [ABSTRACT FROM AUTHOR]