Kiichi Komatsubara

Phase Transition in SnTe with Low Carrier Concentration

The phase transition in SnTe was investigated on a single crystal with low carrier concentration (0.88×10 20 cm -3 ) by the neutron diffraction method. A second-order phase transition takes place a...

Compositional and structural properties of amorphous SixC1−x : H alloys prepared by reactive sputtering

Amorphous SixC1−x : H alloys are prepared by simultaneous rf reactive sputtering of silicon and graphite in a H2‐Ar gas mixture. Silicon, carbon, and hydrogen contents are measured for the entire range of x by electron spectroscopy for chemical analysis (ESCA), Rutherford‐backscattering method, and thermal evolution of hydrogen. Evolution temperature dependence of the number of evolved hydrogen atoms is measured. The hydrogen‐evolution behavior and the optical gap are x dependent. These phenomena are discussed in the light of chemical‐bonding states.

Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation

The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD−3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the impla...

Optical studies of deep‐center luminescence in CdS

Red luminescence in CdS has been studied in as‐grown and ion‐implanted crystals. An IR band consisting of two emission bands, IR1 and IR2, is produced by ion implantation. The higher‐energy band, IR1, has the same origin as the R band observed in some as‐grown crystals. A comparison of the R and IR1 bands in CdS with self‐activated (SA) luminescence in ZnS and GaAs shows that they are SA luminescence at 1.7 eV at low temperatures in CdS. The temperature variations in peak energy, half‐width, and intensity of luminescence are discussed, and the behavior is explained in terms of a configurational coordinate model. A vibrational energy of 0.025 eV, which is about 70% of the LO phonon energy in CdS, is calculated for the excited state of the center. The study of the excitation dependence of the center shows that the luminescence is due to an electronic transition within a localized center and not due to a donor‐acceptor pair recombination. The center has an excitation band about 0.22 eV below the band gap. Th...

Resistance anomaly due to displacive phase transition in SnTe

Abstract The effect of displacive phase transition on electrical transport properties is investigated in a p -type single crystal of SnTe with carrier concentration of 1.2 × 10 20 /cm 3 at 77 K. The resistivity vs temperature curve shows an anomalous increase in the vicinity of the transition temperature. An attempt is made to interpret the temperature dependence of the resistivity increment on the basis of the carrier-soft TO-phonon interaction.

Molecular beam and solid-phase epitaxies of silicon under ultra-high vacuum

Abstract Low temperature growth of silicon epitaxial layers has been performed by two methods: by molecular beam epitaxy and by solid-phase crystallization of amorphous films deposited onto crystalline substrates under ultra-high vacuum.

Ion Implantation of Nitrogen into Cadmium Sulfide

Ion implantation of nitrogen into n‐type cadmium sulfide has been investigated with energy up to 200 keV at dose levels 1015–1017 cm−2. The measurements of I‐V, C‐V characteristics, and photoelectric properties of diodes made on implanted CdS have given evidence for p‐type layer formation. EPR studies have clarified the nitrogen center and lattice‐defect centers produced by the ion implantation. Current of the implanted diodes can be expressed by I=I0[exp(eV/nkT) −1] and the parameter n was remarkably reduced from 10 to 2.7 by a 10‐min anneal at 400°C. Overannealing degraded the diode characteristics. The peculiar C‐V characteristics and the negative photovoltage were observed for the implanted diode, which can be understood only by presuming a series structure of the p‐n junction formed by nitrogen implantation and a Schottky barrier on a p‐type surface. The relative spectral response of photovoltage of the diode had a peak at 800 mμ, i.e., at 0.85 eV below the band edge after annealing below 400°C. The ...

Amorphous GaP produced by ion implantation

Two types of non-crystalline states (“disordered” and “amorphous”) of GaP were produced by using ion implantation and post annealing. A structural-phase-transition-like annealing behaviour from the “disordered” state to the “amorphous” state was observed. The ion dose dependence and the annealing behaviour of the atomic structure of GaP implanted with 200 keV − N+ ions were studied by using electron diffraction, backscattering and volume change measurements. The electronic structure was also investigated by measuring optical absorption and electrical conductivity. The implanted layer gradually loses the crystalline order with the increase of the nitrogen dose. The optical absorption coefficient α and electric conductivity σ of GaP crystals implanted with 200 keV−N+ ions of 1 × 1016 cm−2 were expressed as αhν = C(hν − E0)n and log σ = A − BT-14, respectively. Moreover, the volume of the implanted layer increased about three percent and the electron diffraction pattern was diffused halo whose intensity monotonically decreases along the radial direction. These results indicate that the as-implanted layer has neither a long range order nor a short range order (“disordered state”). In the sample implanted at 1 × 1016 cm−2, a structural phase-transition-like annealing stage was observed at around 400°C. That is, the optical absorption coefficient α abruptly fell off from 6 × 104 to 7 × 103 cm−1 and the volume of the implanted layer decreased about 2% within an increase of less than 10 degrees in the anneal temperature. Moreover, the short range order of the lattice structure appeared in the electron diffraction pattern. According to the backscattering experiment, the heavily implanted GaP was still in the non-crystalline state even after annealing. These facts lead us to believe that heavily implanted GaP, followed by annealing at around 400°C, is in the “amorphous” state, although as-implanted Gap is not in the “amorphous” state but in the “disordered” state.

Studies of Dielectric Properties and Band Parameters of N-Pb1-xSnxTe by Magnetoplasma Waves

From magnetoplasma experiments at 50 GHz for n -Pb 1- x Sn x Te (0≤ x < 0.3), a static dielectric constant e s is determined as a function of x . For x =0, 0.063, 0.091, 0.152 and 0.293, e s is found to be 1410, 1770, 2840, 4610 and 10800 at 1.6 K, respectively. e s seems to depend on band gap as well as on carrier density. It is suggested that free carriers tend to stabilize the lattice instability and that the transition to the ferroelectric phase would be possible at around x =0.2 if the carrier density would be very small. It is further found that the band structure of alloys is essentially the same as that of PbTe at least up to x =0.3.

Transport properties of conduction electrons in n-type inversion layers in (100) surfaces of silicon

Abstract The conductivities of n -type inversion layers in (100) surfaces of p -type silicon were measured extensively as functions of electron density in the inversion layer, the ambient temperature and the applied magnetic field. Measurements were made on the carefully fabricated four “classes” of MOS field-effect transistors whose maximum mobilities at 4·2K were 14,000, 8000, 6800 and 1500 cm 2 /V·sec, respectively. From the temperature dependence of the mobility, dominant momentum scattering was reasonably ascribed to surfon at 100 ∼ 300 K. and degenerate or non-degenerate coulomb scattering at lower temperatures as treated by Stern and Howard. From the curves of conductivity vs temperature at low temperatures and low electron concentration for specimens with high mobilities, an activation energy of 1·2 meV, relating to the shallow bound states associated with the lowest electrin sub-band, was observed. The conductivity σ xx of the inversion layer in a strong transverse magnetic field showed behaviors like those of completely free electrons without effects belonging to its material in its oscillation pattern. That is, the peak value of σ xx as a function of the gate voltage V R dependend only on the Landau index. The σ xx as a function of the magnetic field H at a constant V R showed a similar Shubnikov-de Haas (SdH) type oscillation to that of three dimensional one. The SdH oscillation gave an “apparent” g -value g * which ranges from 2 to 5 depending on the surface carrier density n s , due to the change in the ratios of the widths of the Landau levels to the level separation. The “reasonable” g -value of the conduction electrons in the inversion layer has been determined using a modified tilted magnetic field method. The g -value at the fixed magnetic field was independent of surface carrier density n s and tended to 2 in the extreme strong magnetic field. Discussion is made of the g -value relating to the Landau level width and the energy gaps in the density of states under strong magnetic field.