Kazuhisa Taketoshi

Excess Noise in Amorphous Selenium Avalanche Photodiodes

Excess noise in amorphous Selenium avalanche photodiodes (a-Se APD) has been measured in a frequency range from 3 kHz to 30 kHz. The deduced excess noise factors, including dependences on photocurrent, frequency, applied electric field and the a-Se layers thickness, agreed with McIntyres theoretical values.

Novel Digital Photosensor Cell in GaAs IC Using Conversion of Light Intensity to Pulse Frequency

A photoelectric GaAs integrated circuit that converts light intensity to digital signal frequency has been fabricated using the GaAs MES-FET process. The circuit includes a metal-semiconductor-metal photodiode (MSM-PD), a preamplifier (PA), a Schmitt trigger (ST), a flip-flop (FF) (1-bit digital counter) and a reset (Rst) FET. This sensor cell has a wide dynamic range of over 5 decades of incident light power and a ? characteristic suitable for an image pickup device.

Development of a novel image intensifier of an amplified metal-oxide semiconductor imager overlaid with electron-bombarded amorphous silicon

We developed a novel image intensifier (II) of an amplified metal-oxide-semiconductor (MOS) imager (AMI) overlaid with electron-bombarded (EB) amorphous silicon (a-Si). The electron bombardment gain (EB gain) was 1500 at an accelerating voltage of 10 kV. Since the multiplication process was free from a phosphorescent screen and a coupling fiber plate as in the conventional II, the resolution was high and the picture quality was good and free from granularity noises, white spots, lag and sticking. As for fatigue of X-ray irradiation, the contrasts of a vertical stripe (Smear) are not detectable and damaged areas in AMI are weak whereas both of those in charge-coupled devices (CCDs) are strong.

Structural Analyses of the β and γ Alloys of Al-Mg

The atomic positions of the β and γ phases of Al-Mg alloys are determined, and the kinds of atoms corresponding to them are assigned by taking account of the difference of atomic radii between Al and Mg. The structure of the β phase is cubic with a unit cell containing 108 atoms. The space group, the lattice parameter and the average coordination numbers are Pm3m, 12.419 A and 12 respectively. The structure is a superstructure of fundamental f.c.c. arrangement. The observed satellite spots are essentially explained by the displacement of atoms from average positions. The structure of the γ phase is cubic with a unit cell containing 54 atoms. The space group is Im3m, and the lattice parameter is 10.437 A. The structure is a superstructure of fundamental b.c.c. arrangement.

Analyses of Noise in a Highly Sensitive Image Device

A dipole charge-discharge (i.e., DCD) model was proposed to explain the excess noise factor (i.e., θ) of an amorphous selenium APD target below unity beyond the theoretical limit of shot noise. If the dipole distribution between stored holes and electrons is proper, the electric field in the target is formed between storage periods without interfering with the reading-writing mechanism for the signal, and can control the number of stored carriers so that θ becomes smaller than unity. The theoretical relationship between the signal (i.e., Is) and was obtained and could explain the experimental value well. The theoretical photoelectric conversion characteristics were obtained, and agreed with the experimental values obtained at a high illumination intensity. The magnitude of the negative lag was calculated and was in good agreement with the experimental value.

Structural Study on Amorphous Tellurium Using Reverse Monte Carlo Simulation

We calculated the best fitting model of 6002 tellurium atomic random chains using the reverse Monte Carlo (RMC) simulation. The coincidence between the experimental and calculated structure factors is within 4.5%. In this analysis, we adopted a novel convergence since the normal convergence yielded a false homometric structure without triangular molecules. The mean dihedral angle is 95.78?, the mean bond angle of triangular molecules is 98.12?, and the mean bond length of triangular molecules is 2.84 ?. The obtained structure consists of 1320 (21.99%) parallel bonds, and 690 (11.9%) chainlike and ringlike bonds are 690 in number (11.49%), the ratio of which is 2.73/1. Three-fold coordinated atoms make up 50%. Positional errors for convergent parameters ras below 0.125 were less than 0.03%. The obtained model gave the same structural parameters as the above convergence.

Studies of multiplication process of a novel image intensifier of an amplified metal-oxide-semiconductor imager overlaid with electron-bombarded amorphous silicon

We studied the multiplication process of a novel image intensifier (II) of an amplified metal-oxide-semiconductor (MOS) imager (AMI) overlaid with electron-bombarded amorphous silicon (a-Si), by Monte Carlo (MC) simulation. The electron bombardment gains (EB-gains) of MC simulation for acceleration voltages between 2 and 10 kV coincide well with the measured values. The threshold voltage of 2 kV is well explained in terms of Bethes electron beam energy losses of the Al and Si/sub x/N/sub 1-x/ layers. The penetration depth of an electron beam of 10 kV is 0.83 /spl mu/m and supports an experimentally safe optimal target thickness (1.2-1.3 /spl mu/m). The standard deviation of lateral spread is 2198 /spl Aring/. The theoretical excess noise coefficient is 1.2 between 7 and 1.3 kV, which coincides exactly with the measured value.

The noise reduction effect of the amplified metal oxide semiconductor imager

It is predicted that the amplified metal oxide semiconductor imager (AMI) exhibits carrier movements between adjacent pixels. Consequently, it is considered that a spurious resolution reduction effect or a random noise reduction effect occurs. The authors have clarified these phenomena theoretically and have measured the sensitivity characteristic between pixels and the random noise using devices. As a result, carrier movements below 5% between adjacent pixels were clearly observed, and it was confirmed that 0.89-times random noise reduction already occurred at an intensity of incidence of 1/1000 of saturation, and 0.79-times reduction at intensity of 1/100 of saturation.

Analysis of the correlative characteristics between adjacent pixels of amplified metal oxide semiconductor imager by a new-type least squares method

The magnitude and distribution of spurious response of the pattern of a circular zone plate of the amplified metal oxide semiconductor (MOS) imager are different from those for charge-coupled devices (CCD). When using the trial-and-error or the least squares method, these features could not be explained by any special shape of the sensing aperture or the sensing distribution, but were explained only by the correlation of accumulated charges between adjacent pixels. This correlation causes less spurious resolution and improves the characteristics of the S/N. (1) The shape of the aperture can be shown by a Gaussian distribution in which the standard deviations in the horizontal and vertical directions are 0.266, and 0.231, respectively. (2) The correlative coefficients in the longitudinal, lateral and diagonal directions each stood at 0.0175. The reliability factor R is 0.6%. (3) The measured signal leakage in adjacent pixels by the microoptical spot is 0.02, which fits the calculated value well. (4) The calculated coefficient of noise reduction is 0.65, which agrees with the obtained value of 0.621.