Seung-Chang Lee

Solid phase crystallization of amorphous Si1−xGex films deposited on SiO2 by molecular beam epitaxy

We have investigated solid phase crystallization behavior of the molecular beam epitaxy grown amorphous Si1−xGex (x=0 to 0.53) alloy layers using x‐ray diffractometry and transmission electron microscopy (TEM). Our results show that the thermal budget for the full crystallization of the film is significantly reduced as the Ge concentration in the film is increased. In addition, we find that a pure amorphous Si film crystallizes with a strong (111) texture while that of the Si1−xGex alloy film crystallizes with a (311) texture suggesting that the solid phase crystallization mechanism is changed by the incorporation of Ge. TEM analysis of the crystallized film shows that the grain morphology of the pure Si is an elliptical and/or a dendrite shape with a high density of microtwins in the grains while that of the Si0.47Ge0.53 alloy is more or less equiaxed shape with a much lower density of defects. From these results, we conclude that the crystallization mechanism changes from a twin‐assisted growth mode to ...

Study of Interaction between Incident Silicon and Germanium Fluxes and SiO2 Layer Using Solid-Source Molecular Beam Epitaxy

The dependence on the substrate temperature and the flux rates of the behavior of impinging elemental Si and Ge fluxes on a SiO2 surface, including SiO2 etching and the deposition of polycrystalline Si and SiGe films, was investigated by using the solid source molecular beam epitaxy (MBE). Flux rates of the source beams and a substrate temperature were in the range of 1 to 5×1013 atoms/cm2 s and 710–810 °C, respectively. Under these experimental conditions, the Ge flux was not individually effective to etch the SiO2, but contributed to etching the oxide layer with an accompanying Si flux. The critical flux of Si for SiO2 etching at 740 °C was determined to be about 1×1013 atoms/cm2 s.

Phase transformation of crystallinity of Si1−xGex layers grown on Si(001) by low temperature molecular beam epitaxy

The phase transformation of crystallinity of Si 1-x Ge x layers (0≤x≤0.67) on Si(001) grown at low temperature (150-430°C) is investigated. During the growth of a Si 1-x Ge x layer, its crystallinity changes from single crystalline to amorphous or polycrystalline phase. As the Ge mole fraction r increases, the thickness of the single crystalline phase, the so-called limiting thickness h L , increases exponentially and the crystallinity beyond h L changes from amorphous to polycrystalline phase. Moreover, the decrease of growth temperature at which the polycrystalline phase begins to appear beyond h L and the randomization of polycrystalline texture are also observed as increasing r. These alloy characteristics of the crystallinity transformation depending on r can be explained by lower melting point of Ge than of Si, since the increase of r can lower the thermal processing temperature of Si 1-x Ge x alloy to get a physical phenomenon equivalent to that of pure Si

Effect of a vacuum ion gauge on the contamination of a hydrogen‐passivated silicon surface

The effect of operating a vacuum ion gauge on carbonaceous (C) contamination of a hydrogen (H)‐passivated Si surface before epitaxial growth was investigated. The dependence of C contamination on the residence time in the loading chamber, tlc, was determined with or without operating a vacuum ion gauge. The results showed that C contamination of a H‐passivated surface was greatly increased by use of the ion gauge. With ion gauge operation in a vacuum of 1×10−6–1×10−7 Torr in the loading chamber, the configuration of the ion gauge and upside down‐stacked wafers is shown to be a dominant factor of C contamination of the Si surface. The presence of C contaminants could be determined by observing SiC diffraction patterns using in situ reflection high energy electron diffraction (RHEED), since the C contaminants reacted with Si to produce single crystalline SiC at a temperature as high as 850 °C. The RHEED patterns demonstrated that the single crystalline SiC had a zinc‐blende structure. Single crystalline SiC...

Effect of Si+ and Ge+ ions on the growth of Si1−xGex films on Si(001) using potential‐enhanced molecular‐beam epitaxy

The effect of Si+ and Ge+ source ions on surface morphology and strain relaxation of Si1−xGex (0.25≤x≤1.0) film on Si (001) substrate was investigated using potential‐enhanced molecular beam epitaxy. The growth temperature ranged from 450 to 710 °C. The applied potential to the substrate was varied between −2.0 and 1.5 kV. The acceleration of a small fraction of source ions toward the substrate suppressed three‐dimensional nucleation mode, and dramatically improved the surface morphology. Contrary to the negative potential, the application of a positive potential did not contribute to improving the surface smoothness of Ge on Si. For the growth of Si0.5Ge0.5 film, the surface morphology was degraded further by applying a positive potential of 1.5 kV. Si0.75Ge0.25 films grown with a negative potential of −1.6 kV relieved the strain at the much earlier stage of heteroepitaxial growth than that of conventional molecular‐beam epitaxy.

The effect of in situ boron doping on the strain relaxation of Si0.8Ge0.2 : B/Si heterostructure grown by molecular beam epitaxy

Abstract The effect of in situ elemental boron doping (boron concentration N B = 1 × 10 19 to 3 × 10 20 cm −3 on the strain relaxation of a Si 0.8 Ge 0.2 : B/Si(001) heterostructure grown at 680°C is investigated. Although boron gives rise to lattice contraction in bulk Si, it does not compensate the lattice mismatch between the Si 0.8 Ge 0.2 layer and Si substrate. On the contrary, it stimulates the strain relaxation. The strain relaxation of the Si 1 - xGe x : B/Si(001) heterostructure mainly gives way to dislocation half-loops generated not in the Si 0.8 Ge 0.2 layer, but in the Si buffer layer just below it. This means that heterointerfacial quality may be one of the major control factors of strain relaxation. The strain relaxation induced by boron doping is observed even at N B ∞ 10 19 cm −3 , which is in the doping range typically used in Si 1 - xGe x / Si heterojunction bipolar transistors (HBTs). Therefore, as well as Ge mole fraction and growth temperature, N B should also be considered in determining critical thickness of a Si 1 - xGe x layer grown on a Si substrate.

Study of Quasi-Two-Dimensional Hole Gas in Si/SixGe1-x/Si Quantum Wells.

Quasi-two-dimensional hole gas in strained Si/SixGe1-x/Si quantum well structure is investigated both theoretically and experimentally. The hole effective mass and the charge distribution in the structure are obtained from the self-consistent solution of the Schr\ddotodinger-Poisson equations. The calculation results show the dependence of the averaged mass on the measurement temperature and the averaged mass of 0.20 m0 at T = 4 K. High quality Si/Si0.8Ge0.2/Si p-type modulation-doped quantum well is grown by molecular beam epitaxy and the electrical properties measured. Hall mobility as high as ~10,400 cm2/Vs with a sheet carrier concentration of ~1.1 ×1012 cm-2 and an effective mass of ~0.30 m0 is obtained at T = 4 K.

Strain relaxation mechanism of 250 °C grown Si0.33Ge0.67/Si(001) heterostructure

The strain relaxation mechanism of a 500‐nm‐thick Si0.33Ge0.67 layer grown on Si(001) at 250 °C by molecular beam epitaxy has been investigated. During growth, the strain relaxation occurs without misfit dislocations. Moreover, a strained region coexists with a relaxed one in a single Si0.33Ge0.67 layer. In the relaxed region of Si0.33Ge0.67 layer, stacking faults, instead of misfit dislocations, are the major relief source of strain energy. These anomalous behaviors which are different from conventional relaxation mechanism have been interpreted by the characteristics of the stacking fault.

LDSS research activities in Korea

Abstract It has been only about ten years since Korea was recognized as an emerging country in the field of memory devices in the semiconductor industry. When the first GaAs MBE reactor in Korea was installed in 1983, it gave a very special meaning to the physicists, material scientists, and electronics engineers of Korea. The purchase of such a sophisticated machine could be regarded as the starting point of research on low dimensional semiconductor structures (LDSS) in Korea.