Masashi Suezawa

Nitrogen-Oxygen Complexes as Shallow Donors in Silicon Crystals

Optical absorption of silicon crystals involving nitrogen and oxygen is investigated at low temperature. New absorption lines are found and attributed to seven defect levels that act as shallow donors. The characteristics of the absorption lines are well described by the effective mass approximation. Five among these seven levels are related to complexes of nitrogen and oxygen atoms.

Hydrogen–oxygen interaction in silicon at around 50 °C

Formation kinetics of oxygen–hydrogen (O–H) complexes which give rise to an infrared absorption line at 1075.1 cm−1 have been studied in Czochralski-grown silicon crystals in the temperature range of 30–150 °C. Hydrogen was incorporated into the crystals by high temperature (1200 °C) in diffusion from H2 gas. It was found that the observed kinetics can be explained as being due to an interaction of mobile neutral hydrogen-related species with bond-centered oxygen atoms. The binding energy of the O–H complex was determined to be 0.28±0.02 eV. An activation energy for migration of hydrogen-related species responsible for the formation of the O–H complexes was found to be 0.78±0.05 eV. It was shown that atomic hydrogen and H2*, a complex containing two hydrogen atoms, one at bond-centered site and another one at antibonding site, cannot account for the hydrogen–oxygen interaction considered. Hydrogen molecules (H2) located at tetrahedral interstitial site are suggested to be the species which interact with i...

The Nature of Nitrogen-Oxygen Complexes in Silicon

The nature of nitrogen-oxygen complexes acting as shallow donors in silicon was investigated by measuring the optical adsorptions due to the electronic transitions associated with donor electrons. The complexes were eliminated by heat treatment at temperatures higher than 1100°C. The generation processes of nitrogen-oxygen complexes of several kinds were traced by means of both isochronal and isothermal annealings. An analysis of the result led to a picture in which the complexes of the dominant type consist (each) of one oxygen atom and two or three pairs of nitrogen atoms.

Resonant excitation of visible photoluminescence from an erbium-oxide overlayer on Si

A thin Er2O3 layer grown on a Si surface by vapor doping of Er exhibits intense photoluminescence in the green and red regions excited by laser beams in the 800 nm and 450–490 nm ranges. These intense light emissions take place via resonant two or one step photoexcitations of the 4f levels in Er3+ ions. Our sample fabrication procedure is integrated circuit compatible and produces Er2O3 layers of excellent homogeneity and quality as demonstrated in the optical measurements.

Optical studies of heat‐treated Si‐doped GaAs bulk crystals

The effect of heat treatments on optical properties of Si‐doped GaAs was investigated. Special care was taken to avoid the evaporation of As during heat treatment. Several kinds of photoluminescence peaks were found to be developed, depending on the Si concentration of the crystal and the temperature of the heat treatment. In crystals of high concentrations of Si a broad photoluminescence peak centered at about 1040 nm in wavelength was observed. The intensity and position of the peak were found to depend on the temperature of the heat treatment for a crystal in which the Si concentration was higher than 3.8×1018 atoms/cm3. The change in the peak position was accompanied by the changes in the optical absorptions related to SiGa‐SiAs and SiAs‐VGa pairs and also by the change in the concentration of free electrons. The characteristics of the observations were well interpreted with the idea that the photoluminescence peak was related to clusters of Si atoms and that clustering of Si atoms took place during h...

Radiation‐induced shallow donors in Czochralski‐grown silicon crystals saturated with hydrogen

Far‐infrared absorption has been investigated in n‐type Czochralski‐grown silicon saturated with hydrogen and then irradiated with fast electrons. Two series of absorption bands in the range 200–330 cm−1 are observed upon postirradiation annealing of the crystals at 300–550 °C. These bands are associated with ground–to–excited‐state electronic transitions in two kinds of shallow donors with ionization energies of 37.0 and 42.6 meV, which are described well with the effective‐mass approximation. These donors are related to defects observed earlier in electrical measurements.

Vacancy Formation Energy of Silicon Determined by a New Quenching Method.

By applying a new quenching method, we determined the formation energy of vacancies in high-purity silicon. Specimens were heated in H2 gas at high temperatures for 1 h followed by quenching in water. By this method, vacancies are quenched in the form of complexes with hydrogen and the vacancy formation energy can be determined from the quenching temperature dependence of the intensity of the optical absorption peak due to the complexes. The vacancy formation energy of silicon was determined to be about 4.0 eV. This value is in good agreement with results of recent theoretical calculation.

ESR Observation of the Motion of Optically Induced Paramagnetic Dimers in [Pt(en)2][Pt(en)2Cl2](ClO4)4 (en=ethylenediamine)

On the basis of the temperature dependence of the ESR spectrum, the optically induced unpaired spins in [Pt(en) 2 ][Pt(en) 2 Cl 2 ](ClO 4 ) 4 , where en is ethylenediamine, are verified to form dimeric states of Pt ions which are mobile but transport no electric charge. The dimer hops along the ···-Pt-Cl-Pt-Cl-··· chain in a manner of random walk. The hopping rate is given by ν c =ν 0 exp (-Δ/ k T ) with ν 0 =1.3×10 9 sec -1 and Δ=13±1 meV over a wide temperature range from liquid He to the ambient. This state is most likely the neutral soliton.

Deep Defect Levels in Plastically Deformed GaAs

Defect states in plastically deformed GaAs are investigated by means of the Hall effect, photo-ESR and photoluminescence. A high concentration of acceptors is generated in GaAs as a result of plastic deformation. ESR-active centers giving rise to a signal consisting of four isotropic absorption lines are introduced by both plastic deformation and electron-irradiation. The energy of photo-activation of unpaired electrons from such centers to the conduction band is about 0.8 eV. Defects related to such centers induced by deformation or electron-irradiation are different from grown-in ESR-active centers and are concluded to be As atoms on tetrahedral interstitial sites each surrounded by four Ga atoms. A broad photoluminescence line is developed at 1.13 eV in plastically deformed GaAs but not in electron-irradiated GaAs. This line is thought to be related to the radiative recombination occurring at β dislocations.

Radiative Recombination on Dislocations in Silicon Crystals

Photoluminescence spectra in plastically deformed silicon crystals have been measured to investigate the dislocation-induced energy state of electrons in the band gap. Plastic deformation gives rise to four luminescence lines irrespective of the type of conduction of the crystal. The luminescent lights are strongly polarized in the direction parallel to the dislocation line. A phenomenological expression which relates the luminescent intensity with parameters characterizing the dislocations is deduced on the basis of the experimental results.