Ting-Wei Liao

Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si-Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm(-2), the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm(-1) at 300.7 cm(-1), which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

Applying low-energy multipulse excimer laser annealing to improve charge retention of Au nanocrystals embedded MOS capacitors

The low-energy multipulse excimer laser annealing (LEM-ELA) is proposed to anneal the nanostructure of nanocrystal (NC) embedded in a SiO2 thin film without causing atomic diffusion and damaging the NCs, since the LEM-ELA combining the advantages of laser annealing and UV curing features rapid heating and increasing oxide network connectivity. A Fourier transform infrared spectroscopy (FTIR) characterization of SiO2 thin films annealed using LEM-ELA indicated that the quality was improved through the removal of water-related impurities and the reconstruction of the network Si?O?Si bonds. Then, LEM-ELA was applied to a SiO2 thin film embedded with Au NCs, which were fabricated as MOS capacitors. The charge retention was greatly improved and the percentage of retained charges was about 10% after 3?????108?s. To investigate and differentiate the effects of LEM-ELA on charges stored in both oxide traps and in the Au NCs, a double-mechanism charge relaxation analysis was performed. The results indicated that the oxide traps were removed and the confinement ability of Au NCs was enhanced. The separated memory windows contributed from the charges in Au NCs and those in oxide traps were obtained and further confirmed that the LEM-ELA removed oxide traps without damaging the Au NCs.

Using rapid developing and developing speed model to decrease line width in electron beam lithography

In this paper, we have established a developing speed model for electron beam lithography. By applying this model and a rapid developing method, we successfully decrease the line width by 51%. Furthermore, we can easily narrow down the line width without adding complex processes on the substrate. Some researches has used many ways to supress the scatterings of electron intensity distribution and control the beam profiles by simulations. In the other hand, we limit the level of developed patterns. This method is easier to perform, however, has not been studied formerly. Aiming for Nano structural devices, this model is valuable and worth studying.

Utilizing Ge interlayer and patterned substrate to improve the contact resistance of n-GaN

This paper is demonstrated the effect of Ge interlayer and patterned substrate to form low resistance Ohmic contact of n-GaN. The Ge interlayer is acted as heavily n-type dopant atoms at the interface of metal and n-GaN to enhance carrier tunneling. The patterned substrate is designed to increase the annealing temperature at the interface of the metal and n-GaN. Contact resistances were derived from the plot of the measured resistance versus gap spacing by TLM (Transmission Line Model). After annealing at 400 °C for 5mins, It is shown that, Al (300nm)/Ti (30nm)/Ge (10nm)/ pit-patterned n-GaN substrate scheme exhibit ohmic contact behavior with a resistivity of 3.49×10-5 Ω-cm2. The low contact resistance is formed by Al (300nm)/Ti (30nm)/Ge (10nm)/pit-patterned n-GaN substrate scheme, and it is compare with Al (300nm)/Ti (30nm)/n-GaN substrate. Therefore, this results show that utilizing Ge interlayer and patterned substrate could serve as an important processing tool for forming low-resistance Ohmic contacts of n-GaN.

Fast fabricated the high quality Ge nanodot arrays on Si substrate

The evaporated amorphous germanium (a-Ge) nanodot arrays transforms into high quality crystal-Ge (c-Ge) nanodot arrays are investigated to fabricate on the lattice mismatched Silicon (Si) substrate. Utilizing the laser annealing to improving the quality of a-Ge nanodot arrays on the Si substrate, and using the local stress of hole structure to affects the treated the Ge nanodot. Therefore, the a-Ge nanodot can be easier and faster crystallized and transforms into c-Ge nanodot. In addition, selective deposition of the Ge material is developed to obtain excellent regular Ge nanodot arrays. The quality of Ge nanodot arrays are significantly depend on laser energy, hole depth of the Si hole substrate, surface cleanliness of the Ge nanodot arrays. To evaluate the crystal quality of the Ge nanodot arrays were investigated by Raman signal measurement. Finally, the Raman spectrums are well fitted, whose narrow FWHM of the Ge nanodot arrays are 4.14 cm and peak position at 300 cm is approach the Ge bulk (FWHM is 3.86 cmand peak position at 300 cm). Those results show that the processed Ge nanodot arrays are crystalline Ge. The Ge nanodot arrays may be promising for use in nonvolatile memories (NVM).

Fast crystallization of Ge nanodot array on Si substrate by local pressure method

The poly-crystalline germanium (poly-Ge) nanodots (~60 nm) have potential for easier and faster to fabricate on Si substrate. Utilizing the laser annealing to improve the quality of evaporated germanium (Ge) nanodot array on Si substrate, and a method of using local pressure for sandwich structure is developed to affects the treated Ge nanodot. Therefore, the amorphous Ge can be faster crystallized and tranforms into poly-crystalline Ge nanodot. In addition, selective deposition of Ge material is developed to obtain regular dot arrays. To evaluate the crystal quality of the Ge nanodot array was investigated by Raman signal measurement. Finally, the Raman spectrums are well fitted, whose narrow FWHM of the Ge nanodot array is 5.29 cm and peak position at 302.745 cm is approach the Ge bulk. Those results show that the processed Ge nanodot is poly-crysalline. The Ge nanodot arrays may be promising for use in nonvolatile memories (NVM).

Improving the quality of the evaporated Ge nanodot arrays by laser annealing

To improve the quality of deposited amorphous germanium (a-Ge) on the Si substrate, a re-crystallization method of a-Ge by laser annealing is demonstrated. Laser annealing has two important advantages: high energy density E (700, mJ/cm2) is melting the a-Ge and a lot of laser spot quantity (20 spots) is alteration the a-Ge quality. These two factors were carefully designed to fabricate the high quality crystalline Ge(c-Ge). High laser energy density E and a lot of laser spot quantity would transform the a-Ge nanorod into c-Ge nanodot due to Ges high cohesion. In addition, the size and distribution of Ge-nanodot arrays can be defined with the electron beam (E-Beam) lithography. The quality of re-crystallized Ge-nanodot arrays as characterized with Micro-Raman. To characterize the crystallinity, the Raman spectrum is fitted with the Lorentz distribution. The result shows that the narrow FWHM is 3.5278 cm−1 and peak position at 303.889 cm−1, which is close to that of single crystal Ge. It implies that the quality of there crystallized Ge-nanodot arrays are almost the same as that of single crystal Ge and the strain is fully relaxed. In summary, the high quality of crystalline germanium (c-Ge) nanodot arrays on Si substrate can be achieved by laser annealing.

Excimer laser crystallization of a-Ge nanowires on Si substrate

The poly-crystalline germanium (poly-Ge) nanowires (100nm) have potential for easier and faster to fabricated on Si substrate. Excimer laser were used to crystallization of amorphous germanium (a-Ge) nanowire array on Si substrate were investigated. The two-step method, consist of higher energy annealing (680 mJ/cm) to decrease defects and laser annealing many times (10 times/mins) to faster melt the a-Ge. Structural properties of the nanowire array were characterized by Raman spectrum. To characterize the phenomenon, the spectrum is fitted with the Lorentz distribution. Finally, the Raman spectrum are well fitted, whose narrow FWHM of the sample is 5.07 cm and peak position is approach 300 cm. Those results show that the processed Ge nanowire array is poly-crystalline.

Growing high crystallinity Ge NCs on patterned Si substrate by post thermal annealing

The melting point of a Ge thin film can be controlled by a hole-array pattern on the host Si substrate due to the variations in the stress distribution and the surface morphology induced by the pattern. A simple annealing process is developed from this effect to produce Ge NCs with a single-domain-crystal size over 20 nm, confirmed by transmission electron microscopy, from an electron-gun evaporated Ge thin film on the patterned Si substrate. Photoluminescence observed around 1157 nm shows the possibility of improving the infrared emission capability by this proposed method. A non-destructive testing method based on near field scanning optical microscopy with a 1.55-μm wavelength infrared laser source, is introduced to examine the samples. At this wavelength, Si and SiO2 are transparent, but Ge NCs are opaque. The scanning transmission image reveals the distribution of Ge buried in the samples directly. The size of Ge clusters is about 1 μm, much larger than the size of a single-crystal domain.

Growing evaporated Ge dots with high crystallinity on patterned Si substrate by post thermal annealing

To obtain the evaporated Ge dots with high crystallinity on Si substrate, a method of using nano-structure and post thermal annealing is demonstrated. The Si substrate is patterned with nano-hole array. After evaporating the Ge thin film layer, SiO2 is capped on it and then thermally annealed. With well-designed hole-array pitch, the distribution of oxygen and quality of Ge QDs can be optimized. The processed Ge QDs size is over 20 nm which is estimated with the phonon confinement model of Raman scattering and confirmed by TEM image.