A low temperature thermal cleaning method for Si molecular beam epitaxy (MBE) is proposed. This method consists of wet chemical treatment to eliminate carbon contaminants on Si substrates, thin oxide film formation to protect the clean Si surface from contamination during processing before MBE growth, and desorption of the thin oxide film under UHV. The passivative oxide can be removed at temperatures below 800~ It is confirmed that Si epitaxial growth can take place on substrates cleaned by this method and that high quality Si layers with dislocations of fewer than 100/cm ~ and high mobility comparable to good bulk materials are formed. Surface cleanliness, the nature of thin passivative oxide films, and cleaning processes are also studied by using such surface analytic methods as Auger elec tron spectroscopy, reflection high energy electron diffraction, and x-ray photoelectron spectroscopy.Si molecular beam epitaxy (Si-MBE) has been shown to produce device quality epitaxial Si films. This can, however, be obtained only when a clean silicon substrate surface is prepared before epitaxial growth. That is, contaminants on the substrate, such as oxide and carbide, prevent layer growth and become the main causes of crystal defects in the epitaxial layers. In order to provide clean surfaces and eliminate defect origins at interfaces, high temperature thermal etching at about 1200~ prior to epitaxial growth has been commonly used in an ultrahigh vacuum (UHV) (1-5). However, this technique causes undesirable impurity diffusion and changes the designed impurity concentration profile within th.e Si substrate. Furthermore, crystal defects, such as dislocations and stacking faults, tend to increase and slip lines are often generated across the Si substrate during high temperature treatment. Thus, it is important to find a low temperature surface cleaning method in which the temperature can be lowered to below 900~ Several studies have reported low temperature surface cleaning techniques. The methods used include ion sputtering (6, 7), laser annealing (8, 9), "galliation," in which the substrate is exposed to a gallium vapor beam at about 800~ substrate temperature in UHV (10), and exposure to a Si beam (11). Ion sputtering, however, produces undesirable radiation damage at the surface and point defects often remain even after annealing. Galliation is effective in removing silicon oxide, but complete removal of Ga atoms from the Si surface and no Ga diffusion into the Si substrate have not yet been fully confirmed. Also, for the ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 54.245.13.81

Surface segregation of In atoms during molecular beam epitaxy (MBE) and its influence on the energy levels in InGaAs/GaAs quantum wells (QWs) were systematically studied using secondary-ion mass spectroscopy (SIMS) and photoluminescence (PL). Strong dependence of In surface segregation on the growth conditions was found; when the growth temperature was raised from 370 to 520 °C, the segregation length was observed to increase from 0.8 up to 2.9 nm, accompanied by an appreciable peak energy shift in the PL spectra of the InGaAs/GaAs QWs. The correlation between In surface segregation and the energy levels in InGaAs/GaAs QWs was clarified for the first time.

We present a photoluminescence (PL) study on the growth mode changeover during growth of Ge on Si(100) substrates. Intense PL signals originating from both the flat Ge layer and the three-dimensional (3D) Ge islands are observed from Si/Ge/Si quantum wells with various Ge coverage. The onset of the 3D island formation is determined to be 3.7 monolayers (ML). It is also found that the 3D islands grow with only 3.0 ML of the flat Ge layer retained. This implies that only the 3.0 ML Ge is thermodynamically stable on Si(100) and hence corresponds to the ‘‘equilibrium’’ critical thickness.

Phononless radiative recombination is observed in luminescence spectra of Ge quantum wells decorated by self-organized Stranski–Krastanow (S–K) dots grown on Si (100). External uniaxial tensile stress along [011] allows the discrimination of phonon-missing optical transitions. The phononless recombination is attributed to a dipole-allowed k diagonal Δ1-Γ25′ interband transition involving the hole in the Ge wetting layer and the electron in a Si quantum dot encompassed by large S–K dots. The weak oscillator strength of the phononless recombination is evidenced by its slow decay kinetics. The results indicate that low-lying broad band features due to S–K dots are also of phononless origins.

Self-limitation in the surface segregation of Ge atoms in the Si epitaxial overlayers arising from the surface bond geometry on Si(100) during molecular beam epitaxy has been investigated theoretically. It was found that Ge surface segregation is strongly limiting when the Ge concentration exceeds 0.01 monolayer. As a result of this self-limitation, segregation profiles of Ge in Si overlayers are found to decay nonexponentially in the growth direction with a kink in the profile around 3×1020 cm−3, which is in close agreement with the experimental observation. The kinetic barrier of the Ge surface segregation is estimated to be 1.63±0.1 eV.

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Photoluminescence (PL) measurements were performed on cubic GaN films grown on GaAs(100) substrates by metalorganic vapor phase epitaxy. The cubic GaN films show a high optical quality that enables us to study the PL spectra in detail. From temperature and excitation intensity dependence, the emission lines at 3.274 and at 3.178 eV were assigned to the excitonic transition and the donor–acceptor pair transition, respectively. We also observed two additional emission lines at 3.088 and 3.056 eV. An excitonic emission at 3.216 eV with full width half maximum value as small as 73 meV was observed at 300 K.