Myeong-cheol Kim

Ternary SiGeC alloys: growth and properties of a new semiconducting material

Abstract The growth and properties of Si1−yCy and Si1−x−yGexCy alloys pseudomorphically strained on Si(001) will be critically reviewed. Although the bulk solubility of carbon in silicon is small, epitaxial layers with more than 1 at.% C can be fabricated by molecular beam epitaxy and different chemical vapour deposition techniques. One of the most crucial questions is the relation between substitutional and interstitial carbon incorporation, which has a large impact on the electrical and optical properties of these layers. We will show that the interstitial to substitutional carbon ratio is strongly influenced by the chosen growth conditions, like growth temperature and Si growth rate. In addition, angle-resolved X-ray photoelectron spectroscopy measurements indicate a surface segregation of interstitial carbon-containing complexes (more significant for higher growth temperature). Substitutionally incorporated C atoms allow strain manipulation, including the growth of an inversely strained Si1−x−yGexCy layer. Local ordering effects due to atomic size differences and the growth on reconstructed surfaces, the mechanical and structural properties, and the influence of C atoms on band structure of Si and SiGe layers will be discussed.

Infrared spectroscopy of strained Si1−yCy alloys (0≤y≤0.015) grown on silicon

Abstract We have performed infrared absorption spectroscopy and X-ray diffraction measurements on strained Si 1− y C y layers grown by molecular beam epitaxy on Si substrates. Our experiments show that the formation of substitutional carbon and the appearance of β -SiC precipitates depend on growth rate and growth temperature. Post-growth annealing experiments at temperatures higher than 850 °C cause the formation of β -SiC precipitates accompanied by a decrease of substitutional carbon. The simulation of the X-ray data shows that substitutional carbon is lost mainly near the surface. Infrared absorption studies reveal that the loss is accompanied by the formation of β -SiC precipitates in the near-surface region. Post growth moderate annealing experiments below 800 °C lead to a smaller linewidth for the carbon vibrational mode, indicating improved crystal quality.

Structural and optical properties of undoped and doped ZnSe/GaAs strained heterostructures

Abstract Double-crystal X-ray rocking curve (DCRC), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), photoluminescence (PL), and Raman scattering measurements on undoped and doped ZnSe epitaxial films grown on GaAs (100) substrates by molecular beam epitaxy were performed to investigate the structural and optical properties of the ZnSe films. From the DCRC analyses, the grown layer was found to be a ZnSe epitaxial film with high quality. The results of TEM measurements showed that the misfit dislocations of the nitrogen-doped ZnSe thin films was reduced in comparison with those of the undoped ZnSe films. The PL spectra of the nitrogen-doped ZnSe epilayer was dominated by donor–acceptor pair recombination and by a sequence of its longitudinal optical phonon replicas. Raman spectroscopy measurements showed that there was a lattice mismatch between the ZnSe epitaxial layer and the GaAs substrate and that a plasma–phonon coupling mode existed together with its characteristic longitudinal optical phonons. These results indicate that the ZnSe epitaxial films grown on GaAs hold promise for applications as buffer layers for the growth of Zn 1− x Mg x S y Se 1− y .

Effect of thermal annealing on the structural and optical properties of CdTe (111)/GaAs (100) heterostructures

Abstract Reflection high-energy electron diffraction (RHEED), double-crystal X-ray rocking curve (DCRC), and photoluminescence (PL) measurements were performed to investigate the effect of thermal annealing on the structural and the optical properties of CdTe (111) epilayers grown on GaAs (100) substrates by molecular beam epitaxy (MBE) at low temperature. The results of the RHEED patterns showed that the oxidized layer on the GaAs substrate was removed in a Te atmosphere, and that the 20-A CdTe layer was grown by three-dimensional process. When the rapid thermal annealing (RTA) was performed at 500°C for 14 s, the FWHM of the DCRC for the CdTe layer had the smallest value. After the RTA process, the luminescence intensity of the exciton remarkably increased, and the peak at 1.476 eV was dominant. As the RTA temperature increased, the luminescence intensity of the exciton peak related to neutral acceptors (A°, X) increased. The temperature dependence of the spectra showed that the (A°, X) peak originated from the recombination of the excitons bound in high-density defects. The excitation power intensity dependence of the PL spectra showed that the peaks of the transitions due to donor-acceptor pairs shifted to larger energies. These results indicate that the structural and the optical properties of the CdTe epilayers grown on GaAs (100) are improved by RTA, and that the RTA process is very useful for the growth of HgxCd1−xTe on CdTe/GaAs heterostructures.

Comparison of double patterning technologies in NAND flash memory with sub-30nm node

Fine patterning technologies - E-beam lithography, SPT (Spacer Patterning Technology) and SaDPT (Self aligned Double Patterning Technology)-have been introduced to develop a single unit of nano-scale MOSFET. However, in order to achieve manufacturable high density NAND Flash memories, the merits and demerits of each technology should be considered in three points of view: device characteristics, process controllability and mass production. In this paper, we suggest the appropriate technology for particular cell types, CTF(Charge Trap Flash) cell, floating poly-Si gate cell, and for process steps such as active, gate and bit-line.

Determination of defect types of ZnSe-based epilayers by etch-pit configurations

Abstract Determination of defect types by etch-pit configurations was studied. A NaOH (30 mol%) etchant was found useful for etch-pit development on ZnSe-based epilayers grown on (001) GaAs. After etch-pit formation on the surface, Transmission Electron Microscopy (TEM) experiments were conducted. The etch-pits have been formed in three different configurations; regularly paired etch-pits in the horizontal direction, regularly paired etch-pits in the vertical direction and an array of single etch-pits in the 〈110〉 and 〈100〉 directions which result from Frank-type stacking faults, Shockley-type stacking faults and threading dislocation segments, respectively.