## 2016年9月27日星期二

### Medium-energy ion irradiation of Si and Ge wafers: studies of surface nanopatterning and signature of recrystallization in 100 keV Kr+ bombarded a-Si

We report new and exciting experimental results on ion-induced nanopatterning of a-Si and a-Ge surfaces. The crystalline Si (100) and Ge (100) wafers were amorphized and an a/c interface was developed by pre-irradiation with a 50 keV Ar+ beam at normal incidence with an ion fluence of 5.0 × 1015 ions cm−2. These amorphized surfaces were post-irradiated with Ar+ and Kr+ beams at an angle of 60°. The post irradiation was done with ion fluences of 1.0 × 1017 ions cm−2. For each beam, two energies (50 and 200 keV for Ar+, 100 and 250 keV for Kr+) were chosen to ensure ion stopping in both sides of the a/c interface. Regular nanopatterning (in the form of ripples) is observed on the Ge surface only with the post irradiation of the Kr+ beam. The Si surface showed regular nanopatterning with the irradiation of both beams with two energies. For the ion beams crossing the a/c interface, ripples of higher amplitude and longer wavelength were formed. Further, the irradiation with a heavy beam yielded surface ripples of relatively larger amplitudes. The Raman measurements confirm amorphization of the pre-irradiated surfaces. Surprisingly, the post-irradiated Si surface with the 100 keV Kr+ beam showed evidence of recrystallization. In the paper we discuss the physics at the interface and explain the experimental findings.

Keywords: on-induced nanopatterning;  a-Si and a-Ge surfaces; crystalline Si (100) and Ge (100) wafers;

Source:  Iopscience

## 2016年9月18日星期日

### Wafer-scale layer transfer of GaAs and Ge onto Si wafers using patterned epitaxial lift-off

We have developed a wafer-scale layer-transfer technique for transferring GaAs and Ge onto Si wafers of up to 300 mm in diameter. Lattice-matched GaAs or Ge layers were epitaxially grown on GaAs wafers using an AlAs release layer, which can subsequently be transferred onto a Si handle wafer via direct wafer bonding and patterned epitaxial lift-off (ELO). The crystal properties of the transferred GaAs layers were characterized by X-ray diffraction (XRD), photoluminescence, and the quality of the transferred Ge layers was characterized using Raman spectroscopy. We find that, after bonding and the wet ELO processes, the quality of the transferred GaAs and Ge layers remained the same compared to that of the as-grown epitaxial layers. Furthermore, we realized Ge-on-insulator and GaAs-on-insulator wafers by wafer-scale pattern ELO technique.

Keywords: GaAs wafers ;   epitaxial lift-off (ELO);  X-ray diffraction (XRD);  Ge-on-insulator;     GaAs-on-insulator

Source: iopscience

## 2016年9月11日星期日

### Impact of thermal annealing on Ge-on-Insulator substrate fabricated by wafer bonding

We propose the Ge CMOS photonics platform with Ge-on-Insulator (GOI) substrate on which Ge mid-infrared photonic devices and Ge CMOS transistors can be monolithically integrated. The GOI wafer for the Ge CMOS photonics was fabricated by combining wafer bonding and H ion cut technologies. We studied the effect of thermal annealing on the GOI substrate in terms of crystal quality, surface morphology and electrical property. From Raman spectrum, it was found that the crystal quality of the Ge layer was significantly recovered after a 550 °C annealing in N2 (or O2) ambient for 1 h. Meanwhile, the surface roughness of the GOI substrate remained very low even after the annealing process. As a result, the significant improvements on electrical properties of the GOI substrate were confirmed by Hall measurement results. The carrier density of a GOI Hall device decreases from 2.9×1016 to 8.9×1015 cm−3 and hole mobility increases from 925 to 2295 cm2/V s. These results strongly suggest the necessity of a proper thermal annealing on improving the GOI qualities.

Keywords:  Germanium;  Ge-on-Insulator;  Thermal annealing;  Wafer bonding

Source: Sciencedirect

### Plastically deformed Ge-crystal wafers as elements for neutron focusing monochromator

Plastically deformed Ge-crystal wafers that have the cylindrical shape with a large curvature were characterized by neutron diffraction. The box-type rocking curve of Bragg reflection with the angular width of Γbox ~ 2° in FWHM, which is observable in the monochromatic neutron diffraction, results in an enhancement in the angle-integrated intensity (Iθ). Besides,Iθ efficiently increases by stacking such Ge wafers. In the course of white neutron diffraction, the reflected-beam width near the focus point becomes sharper than the initial beam width. Further, the dependence of the horizontal beam width on the distance between the sample and detector is quantitatively explained by taking account of the large Γbox, the small mosaic spread of η~0.1°, and the thickness of the wafers. On the basis of these characterizations, use of plastically deformed Ge wafers as elements for high-luminance neutron monochromator is proposed.

Keywords:  Plastically deformed Ge wafer;  Neutron monochromator crystal;  Neutron beam focus

Source: Sciencedirect

## Highlights

•A ~100nm CVD Ge film was deposited on Si wafer by two-step chemical vapor deposition.
•A wafer level eutectic bonding was used to bond the CVD Ge/Si and Au/Ti/Si wafers.

•The two-step Ge deposited sample showed uniform film after the eutectic bonding.

•A uniform interface was detected between the bonded wafers using two-step deposition.

•An Au-Ge interlayer formed at the bonded interface, which enhanced bonding quality.

A Ge thin film deposited by chemical vapor deposition (CVD) was used to obtain a uniform bonding between Au and Ge films for applications of wafer level packages (WLPs). This Ge CVD thin film showed selective growth on Au and Cu metals when the substrate has both metal and oxide. A one-step and two-step Ge deposition followed by eutectic bonding method was employed to bond the wafers. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy equipped with an energy dispersive spectroscopy (FESEM-EDS), atomic force microscopy, high resolution Field emission transmission electron microscopy, IR inspection tool and secondary ion mass spectroscopy (SIMS). According to the IR inspection results, the two-step Ge deposited sample showed more uniform film compared to one-step deposition after eutectic bonding. Moreover, an improved bonding quality was obtained from the two-step process. Based on FESEM observations, a uniform and crater-free interface was detected between the bonded 4-inch wafers, in which the presence of Ge beside Au and Si was confirmed by EDS. SIMS profiles proved the formation of a thin Au-Ge interlayer at the bonded interface, which enhanced the bonding conditions.