Kokuya Iwamura

Influence of fast neutrons on electrical properties in neutron transmutation doped GaAs: New annealing stage

In neutron transmutation doping (NTD) to the undoped semi‐insulating GaAs, a new annealing stage related to the tunneling assisted hopping conduction was found around 400 °C for fast neutron fluences of ≥7.0×1017 n/cm2. It is suggested that this stage is based on the enhancement in the hopping conduction by the activated dopant in the NTD process. The stage was not observed for the irradiation with a small amount of fast neutrons. The activation energy for the annihilation of As antisite defects (AsGa) was found to be 0.9 eV. The annealing temperature to achieve the desired carried concentration increased with the fast neutron fluence.

Annealing effects on electrical properties of thermal neutron transmutation doped Ge

A neutron transmutation doping technique was applied to the high purity n‐type germanium with 50 Ω cm (n=5.9×1013/cm3). For a neutron flux density of 5×1011/cm2 s and an irradiation time of 60 min, the doped Ge was converted into p type with 7 Ω cm ( p=3.5×1014/cm3). By neutron irradiation it has been possible to introduce the shallow acceptors resulting from the damage in addition to gallium atoms as acceptors. The recovery of radiation damage was evaluated by the improvements of some electrical properties for various annealing stages. By annealing at 600 °C, a room temperature hole mobility of 2200 cm2/Vs has been achieved at p=6.2×1013/cm3 and ρ=45 Ω cm. And, also, we found that higher mobility holes in p‐type Ge play an important role for the weak magnetic field as the lattice atoms recover from the radiation damage. Finally, the direct observation of the recovery of damage was performed by the measurement of channeling effects using a helium ion beam.

Recovery of refractive-index profiles of planar graded-index waveguides from measured mode indices : an iteration method

An iteration method for calculating refractive-index profiles of graded-index waveguides from measured effective indices is presented. The refractive-index profiles recovered from the effective indices for the exponential function indicate that the accuracy of this method is better than ±10−4. We apply this method to Ti in-diffused Fe2O3–LiNbO3 and two-step ion-exchanged glass waveguides and obtain a good agreement between the theoretical and the experimental values.

Quantitative analysis of phosphorus in amorphous silicon using PIXE with a crystal spectrometer and PIPC

Abstract A PIXE (particle induced X-ray emission) method for analyzing impurities in solid materials was developed using a crystal spectrometer combined with a position sensitive proportional counter (PSPC). Numerical expressions for quantitative analysis of impurities by this method are established. This technique was applied to the nondestructive measurement of P in a-Si matrix. The concentration of P obtained in this method is 0.717%, which is consistent with the value of 0.68% deduced from the Auger electron spectroscopy.

Doping of phosphorus in hydrogenated amorphous silicon by a neutron transmutation doping technique

Doping of phosphorus in hydrogenated amorphous silicon (a‐Si:H) produced by rf glow discharge has been achieved by a neutron transmutation doping technique. Electrical and electron spin resonance measurements showed that the neutron irradiation damages have been recovered by the thermal annealing near the growth temperature of a‐Si:H films. After thermal annealing at 220 °C, the activation energies of 0.57 and 0.50 eV were obtained for transmuted phosphorus concentrations of 3.1×1012 and 1.6×1013/cm3, corresponding to neutron doses of 1.8×1016 and 9.0×1016 n/cm2, respectively.

Ion channeling study of damage in neutron irradiated GaAs

Abstract The lattice disorder in GaAs produced by fast neutrons with a fluence of 7 × 10 17 n cm −2 has been investigated with 1.5-MeV 4 He + channeling and electron spin resonance (ESR) measurements. The slight change in the 〈100〉-aligned yield for irradiated crystals indicates that each primary knock-on (PKO) produces approximately 10 3 displaced atoms. Detailed angular scans suggest a spread distribution of randomly-located defects imbedded in the lattice structure. On the other hand, As Ga 4 antisite defects per PKO estimated from ESR measurements are ~ 100. It is suggested that neighboring atoms of As Ga 4+ antisite defects are slightly distorted after the PKO event.

Studies of thin films of Li-B alloys

Abstract Thin films of Li-B alloys have been prepared on a glass substrate in a vacuum of 10 -6 Torr making use of the reaction of lithium and boron by the Sandwich-Type Evaporation Method. In this method Li-B films are deposited using LiBH 4 and lithium metal by cycling in the order of Li-B from a Ta boat first, Li-B and Li from another Ta boat secondly, and Li-B last continuously to make a sandwich-type structure. As a result, it is found from the electron diffraction method that Li-B films of 1 μm thick deposited at 450°C have interplanar spacings ( d =3.57, 2.06 A) which correspond to those of the Li 7 B 6 compound. On the other hand, LiAl x B 1− x films have been prepared evaporating Al and (Li-B+Li) at 350°C by the Sandwich-Type Evaporation Method. For LiAl x B 1− x films, the electron diffraction patterns are in agreement with the ASTM data for the NaTl-type LiAl compound. The (220), (311), (400), (311) and (422) planes are observed.

Field emission from LiIn single crystals

Field emission from single crystals of LiIn, which behave as either narrow‐gap semiconductors or semimetals, have been studied using a field emission microscope. A linear Fowler‐Nordheim relationship was found. The specimen surfaces were believed to be contaminated.

The electrical and optical properties of LiAlxB1−x thin films

The electrical and optical properties of LiAlxB1−x thin films deposited at 350°C by the Sandwich-Type Evaporation Method are measured. These films are metallic with a resistivity of (1–4) × 105 ohm cm at room temperature. In addition, we have developed a unique method. named the Brewster Angle Method (BAM), for obtaining the optical constants of thin films for LiAlxB1−x. In this method reflection coefficients are measured on the surface of thin films at any angle of incidence using a HeNe laser beam. The optical constants are calculated from the Brewster angle, φB, at the minimum value of reflection coefficient |RB|min. For a typical LiAlxB1−x film the optical constants are n = 1.42 − j0.31 and the complex dielectric constants are ϵ = 1.94 − j0.87.

A study of NaTi-type NaIn films prepared by the sandwich-type evaporation method

Abstract The sandwich-type evaporation method has been developed as a technique for the preparation of films of NaTl-type compounds including one containing an active material, namely lithium. In the investigation reported here the method was applied to the preparation of NaIn films with the NaTl-type lattice structure, in which each component has a diamond-type sublattice. The method consists in the evaporation of firstly indium (99.99% pure), then sodium (99.999% pure) and indium together and finally indium. The evaporation process is continuous to prevent oxidation of the sodium. Thus, the film of codeposited sodium and indium is formed between indium films. The films were deposited onto a glass substrate by evaporating the sodium and indium from a tantalum boat and were annealed in a conventional vacuum system that employed an oil diffusion pump which maintained a vacuum of about 6×10−6 Torr. The degree of crystallization of the films deposited at various substrate temperatures was investigated by electron diffraction and measurements of the electrical resistance during annealing. The interplanar spacings in the NaIn layers were calculated from the radii of the Debye rings on the original plates of the electron diffraction patterns of the films. From the results obtained for substrate temperatures of 120 and 150°C, there was no evidence of free indium in any of the films and the (111), (220), (311), (400), (331), (422), (440), (531) and (620) planes of NaIn were detected, in agreement with ASTM data within experimental error. For a typical NaIn films resistivity is about 8.13×10−5 Ohms cm at room temperature and the temperature coefficient of the resistivity is about 0.48×10−6 Ohms cm K−1, which is very similar to that for an NaTl film.