Xiangjiu Zhang

Solid state reaction of Co,Ti with epitaxially‐grown Si1−xGex film on Si(100) substrate

The solid state reaction of Co,Ti with an epitaxially grown Si1−xGex strained layer is investigated in this article. The reaction was performed in a rapid thermal annealing system. The resulting films were characterized by Rutherford backscattering, Auger electron spectroscopy, x‐ray photoelectron spectroscopy, x‐ray diffractometry, and scanning electron microscopy. The electrical resistivity and Hall effect were measured in the temperature range of 77–300 K. Rapid thermal annealing of Co/Si0.8Ge0.2 at 650 °C results in a Co(Si0.9Ge0.1) film with cubic crystalline structure. At higher temperature CoSi2 is formed with Ge segregation towards the surface. After a multi‐step annealing, a highly oriented CoSi2 layer can be grown. For TiN/Ti/SiGe, the ternary phase of Ti(Si1−yGey)2 is formed, with a smooth surface and with resistivity comparable to the lowest value exhibited by TiSi2. The Co/Ti/SiGe/Si reaction is studied for the first time, demonstrating that the uniformity of Co/SiGe reaction is improved by a...

Si1−xGex/Si asymmetric 2×2 electro‐optical switch of total internal reflection type

Based on plasma dispersion of Si1−xGex, we have fabricated asymmetric 2×2 switches of total internal reflection type, in which Si1−xGex was grown by molecular beam epitaxy. The optimum intersecting angle is 4°, and the crosstalk is less than −10.6 dB at 76 mA injection current. The insertion loss is 2.8 dB, and the switch time is 0.6 μs.

Effect of Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate

Abstract Cross-sectional transmission electron microscopy and Raman spectra are used to investigate the effect of monolayer Sb as a surfactant on the inner diffusion of epilayer Ge atoms into Si substrate. Without Sb, inner diffusion of the epilayer Ge atoms into the Si substrate occurs, resulting in a severe intermixing of atoms at the Ge–Si interface. With the presence of Sb as a surfactant, the inner diffusion of epitaxial Ge atoms into the Si substrate is greatly suppressed. This result is explained in terms of the strain relief in the Si substrate by the Sb surfactant.

Boron-mediated growth of Ge quantum dots on Si(100) substrate

Abstract The influence of boron atoms on the growth of self-organized Ge quantum dots (QDs) on Si(100) substrate is studied by atomic force microscopy (AFM). The boron coverage varied from 0 monolayers (ML) to 0.3 ML. AFM observation shows that the boron atoms have a great influence on the size, uniformity and the density of Ge QDs. In the presence of 0.2 ML of boron atoms, the growth of quite uniform Ge QDs is achieved with a mean base diameter of 60 nm and areal density of 6×10 9 cm −2 . The mechanism of B atom influence on the growth of Ge QDs is discussed.

Strong surface segregation of Sb atoms at low temperatures during Si molecular beam epitaxy

Surface segregation of Sb atoms at low temperatures below 400°C during Si molecular beam epitaxy (MBE) growth is studied by ex situ X-ray reflectivity measurements and secondary ion mass spectroscopy (SIMS). One monolayer of Sb atoms was first deposited at the temperature of 300°C, followed by a 23-nm thick Si overlayer grown at different temperatures of 250, 300, 350, and 400°C. The decay lengths of dopant Sb distribution profiles are obtained to be 0.45, 0.95, 3.5, and >20 nm by simulations of their X-ray reflectivity curves, respectively. A strong surface segregation of Sb atoms is observed at temperatures of 350 and 400°C, which is also confirmed by the SIMS profiles. Surface structure change caused by a high coverage of Sb is suggested to explain such a strong segregation.

SiGe/Si Mach–Zehnder interferometer modulator based on the plasma dispersion effect

A SiGe Mach–Zehnder interferometer modulator based on the plasma dispersion effect has been fabricated. A maximum modulation depth of 86% and a switching current of 40 mA with a π-phase-shift voltage of 0.9 V have been achieved at 1.3 μm wavelength. The device has a measured insertion loss of 2.5 dB and a response time of 238 ns.

Heteroepitaxial growth of Ge films on Si substrates by molecular beam epitaxy

A new approach of growing thick Ge layers on Si substrates by molecular beam epitaxy is presented. A 30–80 A thick Ge overlayer is first deposited on the Si(100) substrate at room temperature. By thermally annealing the sample to 300 or 500 °C for 10 min, the Ge atoms cluster into randomly distributed islands which would play a role in releasing the mismatch stress at the interface. The Ge film of 10 000 A thickness epitaxially grown on this surface at 550 °C shows a better crystalline quality than that grown by a conventional method. A full width at half maximum of 262 s for the Ge (400) x‐ray diffraction peak has been achieved.

Surfactant influence on the Ge heteroepilayer on Si(0 0 1) studied by X-ray diffraction and atomic force microscopy

X-ray diffraction and atomic force microscope were used to investigate the effect of Sb atoms as a surfactant on the morphology and strain relaxation of 6 nm-thick Ge epilayers grown on Si(0 0 1). Without Sb atoms, Ge atoms accumulate and form fully relaxed islands. With the presence of Sb atoms, the Ge epilayer is smooth with a roughness of 0.28 nm and partially relaxed.

SiGe quantum dot molecules grown on patterned Si (001) substrates

SiGe quantum dot molecules (QDMs) grown on patterned Si (001) substrates by molecular beam epitaxy were studied. Experimental results showed that the density, the dimension, and the dimension distribution of the SiGe QDMs grown in the windows were dependent on the window size. When the thickness of the Si0.8Ge0.2 film was 40 nm, QDMs only appeared in the unpatterned areas of the Si substrate and none could be found inside the windows of 6×6 μm2 on the same substrate. However, when the thickness of Si0.8Ge0.2 film was increased to 80 nm, QDMs appeared both inside the windows and in the unpatterned areas, and the density of QDMs was reduced with the decrease in the window size. We attribute these results to the different strain relaxations in different size windows, which are caused by the edge effect of the epitaxial film in the window. Based on these experimental results we discuss the formation and the size stability of the QDMs and conclude that the formation of the SiGe QDM originates from an intrinsic...

Crystalline quality of Si epilayers influenced by Sb doping

Reflection high energy electron diffraction and Raman scattering show that the crystalline quality of Sb-doped epilayers is strongly dependent on the doping conditions. Surface roughening, which is induced by surface segregation of the dopants during growth, degrades the quality of the film grown and develops with growth. Surface roughening could be explained by a two-state-exchange model of Sb segregation.