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application/pdf, We have performed electron spin resonance (ESR) measurements on Er-doped GaAs grown with oxygen codoping by metal organic chemical vapor deposition. An isotropic line (an effective g value, g = 5.95) which had been already reported was observed in samples without oxygen codoping. On the other hand, for samples with oxygen codoping other strong anisotropic ESR lines originated from four kinds of Er3 + (4f11) centers (A, B, C, and D) were newly observed in addition to the weaker isotropic line. The anisotropic g tensors obtained by analyzing the angular dependence of the ESR lines indicate that B and C centers are of orthorhombic C2v symmetry, A center has lower symmetry than orthorhombic symmetry, and D center is of trigonal C3i symmetry. The ESR intensities of A, B, and C centers were approximately two orders of magnitude higher than that of the isotropic line with g = 5.95. The ESR intensity of D center was one order of magnitude lower than those of A, B, and C. The Er concentration dependence of the relative ESR intensities of these centers was investigated, which indicates (i) the ESR intensities of A and D increase with increasing Er concentration, and (ii) those of B and C are saturated above the Er concentration [Er] >= 1018 cm – 3. The ESR measurement under light illumination, as well as the Er concentration dependence, suggests that the B center with C2v symmetry corresponds to the dominant Er luminescent center under host photoexcitation.

application/pdf, We have performed electron spin resonance (ESR) measurements on Yb-doped n-type and p-type InP layers epitaxially grown by metalorganic chemical vapor deposition. ESR spectra of Yb3 + (4f13) were observed in both n-type and p-type samples. However, the ESR intensity of Yb3 + (4f13) for n-type samples was found to be much lower than that for p-type samples. This suggests that most Yb ions in Yb-doped n-type InP are in the Yb2 + (4f14) state rather than in the Yb3 + (4f13) state. Thus an electron captured by the trap level formed by Yb in the band gap of InP is not located outside the Yb 4f shell as reported previously, but accommodated in the Yb 4f shell.

application/pdf, We have investigated phosphorus ion (P+) implantation in Si nanocrystals (SiNCs) embedded in SiO2, in order to clarify the P donor doping effects for photoluminescence (PL) of SiNCs in wide P concentrations ranging in three orders. Some types of defects such as Pb centers were found to remain significantly at the interfaces between SiNCs and the surrounding SiO2 even by high-temperature (1000 °C) annealing of all the samples. Hydrogen atom treatment (HAT) method can efficiently passivate remaining interface defects, leading to significant increase in the intensity of PL arising from the recombination of electron-hole pairs confined in SiNCs, in addition to significant decrease in interface defects with dangling bonds detected by electron spin resonance. From both the results of the P dose dependence before and after HAT, it is found that the amount of remaining defects is higher for samples with SiNCs damaged by implantation with relatively lower P+ doses and then annealed, and that through HAT the observed PL intensity increases surely as the P concentration increases up to a critical concentration. Then it begins to decrease due to Auger nonradiative recombination above the critical concentration which depends on the size of SiNCs. These results suggest an effect of relatively low concentration of P atoms for the enhancement of PL intensity of SiNCs and we present an unconventional idea for explaining it.

application/pdf, The formation of Si nanocrystallites (nc-Si) in erbium (Er)-dispersed SiOx (x

application/pdf, The formation of hydrogen (H)-related complexes and H effects on boron (B) and phosphorus (P) dopants was investigated in B- or P-doped silicon (Si) crystal treated with high concentration of H. The reactivation process of dopant carriers by annealing after hydrogenation was significantly different between the p-type and n-type specimens. The difference is likely to be attributable to the formation of H-related defects based on the stable sites of the H atoms, i.e., complicated H multiple trapping centers are formed by bond breaking due to H atoms in only p-type B-doped Si.

application/pdf, The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.

The Hg content of anodic sulfide films on Hg1−xCdxTe (MCT) were investigated for as‐grown and heat‐treated films by using 30–40‐MeV O5+ ion backscattering. Heat treatments were performed in a vacuum for 60 min at various temperatures up to 300 °C for the samples with x=0.20 and up to 350 °C for the samples with x=0.30 and 0.35. A significant Hg content of about 15 at. % of Cd was found in the as‐grown anodic sulfide film on MCT samples with x=0.20, 0.30, and 0.35. After heat treatment above 260 °C for x=0.30 and 0.35 and above 210–240 °C for x=0.20, the Hg atoms were removed from the films, and Hg deficient layers were formed near the interface region of the MCT crystal. This suggests that the residual Hg in the anodic sulfide films introduced during the sulfidization process plays an important role toward the degradation of the passivation properties of the sulfide film on MCT.

We report the first time‐resolved x‐ray absorption measurements on pulsed laser irradiated Si in the photon energy range from 90 to 300 eV, at irradiation energy densities up to 4 J/cm2, and at several delay times between irradiation pulse and x‐ray probe pulse. The absorption spectra recorded at a delay time of 12 ns can be classified in three categories. Below ≊0.17 J/cm2 only thermal damping of extended x‐ray absorption fine‐structure (EXAFS) oscillations is observed. Between ≊0.17 J/cm2 and ≊1 J/cm2 annealing takes place. Several changes are observed, among which a ≊7‐eV LII,III edge shifts towards higher energy, while the LI edge remains approximately at the same position. This edge shift behavior is explained by a largely reduced 3s density of states of the conduction band. This supports the idea that pulsed laser molten Si has a metalliclike structure. Thermal damping in this region is so strong that EXAFS oscillations are no longer visible. This is consistent with a lattice temperature above or eq...

Dissociation and evaporation of Hg from the near‐surface region of Hg1−xCdxTe crystals was investigated, up to several microns, by means of 40‐MeV O5+ backscattering. Samples with x=0.18 and 0.32 were heat treated in a vacuum for 60 min at various temperatures up to 320 and 340 °C, respectively. The change of the backscattering spectra with the temperature of heat treatment indicated that the Hg atoms outdiffused partly from the near‐surface region of the crystals at higher temperatures than 280 and 320 °C for x=0.18 and 0.32, respectively. This behavior of outdiffusion is in contrast to the case of HgTe crystal.

application/pdf, Charge states of substitutional N impurities (Ns) in Si are found to be controllable by doping with P, B, and O impurities in N-ion implanted and subsequently pulsed-laser annealed Si (Si:N system). Electron-spin resonance measurements of the Si:N system doped with P, B, or O impurities show that the spin density of neutral Ns (N0s) decreases because of doping with these impurities. Compensation by multiple doping with equal amounts of P and B impurities leaves the density of N0s essentially unchanged. These results yield evidence for charge-state changes of Ns due to the Fermi level shift. Oxygen doping is found to introduce donors. Three charge states, i.e., positive (N + s) , neutral (N0s) , and negative (N - s) are assigned to off-center substitutional N in Si.

We present x‐ray absorption measurements on silicon clusters and silicon plasmas produced by pulsed laser irradiation of bulk silicon. The results are compared with earlier time‐resolved x‐ray absorption measurements on amorphous silicon foils under pulsed laser irradiation. Clusters are formed at an irradiance as low as 3.0 J/cm2. At an irradiance of 14 J/cm2 ionized species up to Si4+ are formed. We find a removed Si layer thickness of 80 A at an irradiance of ≊6 J/cm2, at 15 ns pulse duration.