Shinya Kominami

THM Growth and Characterization of 100 mm Diameter CdTe Single Crystals

The THM growth technology for 100 mm diameter CdTe single crystals has been intensively developed. In consequence of the optimization of growth conditions, we have succeeded in controlling growth interface shape and growing 100 mm diameter CdTe single crystals with 300 mm in length. Concerning the behavior of Te inclusions in the grown crystal, their size and density were investigated by IR transmission microscopy. The size distribution of Te inclusions was divided into two groups, and the density of them was less than 1 × 105 cm−3. Charge transport properties of the grown crystal were investigated by using the “μτ-model” spectral fitting method, and were found to be quite uniform all over the wafer. To investigate the homogeneity of radiation detector performances, Ohmic type and Schottky type detectors with 4 mm × 4 mm × 1 mm were fabricated from the left half and the right half of the 100 mm diameter wafer, respectively. Standard deviations of their energy resolutions for the 122 keV line from 57Co were less than 6 %. This excellent uniformity is essential for the room temperature semiconductor detectors in the major application areas, such as medical imaging, non-destructive inspection and homeland security.

Improvement of the Productivity in the THM Growth of CdTe Single Crystal as Nuclear Radiation Detector

The effect of the THM growth rate on the CdTe crystalline quality and the detector performance was intensively investigated. The maximum growth rate for the single crystal growth was found to be approximately 15 mm/day which was 3 times greater than the conventional one. By optimizing other growth conditions, 90% of every ingot volume has become a single crystal. Te inclusions in the CdTe single crystal grown at various growth rates were also investigated by IR transmission microscopy. There was no correlation between the behavior of Te inclusions and the growth rate. The detector performance was also independent of the growth rate. Taking advantage of the large volume CdTe single crystals, about 700 000 Schottky detectors with 4 mm × 7.5 mm × 1 mm were fabricated for the research and development of the new positron emission tomography (PET) system using CdTe detectors. The average FWHM for the 662 keV line from 137Cs and its standard deviation were 2.24% and 0.48%, respectively. This uniformity was essential for the development of the new PET system.

Effects of underlayer roughness on Nb/AlO/sub x//Nb junction characteristics

The effects of underlayer roughness on Nb/AlO/sub x//Nb Josephson junction characteristics are clarified. MoN/sub x/ and SiO films with 0.1-2.7-nm surface roughness are used as underlayers for the junctions. MoN/sub x/ films with varying levels of roughness are prepared by sputter-etching. SiO films retain a smooth surface after sputtering etching. The existence of grain boundaries in the MoN/sub x/ films causes surface roughness. Subgap leakage current of junctions on MoN/sub x/ underlayers is higher than that of junctions on SiO underlayers, and it increases with the roughness of the underlayers. The roughness of the underlayers surface is reflected in the Nb base electrodes surface; however, the roughness of the Nb surface is not directly reflected in the AlO/sub x/ surface. The AlO/sub x/ surface is smoother than the Nb surface. The cause of the leakage increase in the junctions on rough underlayers may be dispersion in the deposited-Al thickness.<<ETX>>

THM growth and characterization of 100 mm diameter CdTe single crystals

The THM growth technology for 100 mm diameter CdTe single crystals has been intensively developed. In consequence of the optimization of growth conditions, we have succeeded in controlling growth interface shape and growing 100 mm diameter CdTe single crystals with 300 mm in length. Concerning the behavior of Te inclusions in the grown crystal, their size and density were investigated by IR transmission microscopy. The size distribution of Te inclusions was divided into two groups, and the density of them was less than 1 times 105 cm-3. Charge transport properties of the grown crystal were investigated by using the ldquomutau-modelrdquo spectral fitting method, and were found to be quite uniform all over the wafer. To investigate the homogeneity of radiation detector performances, Ohmic type and Schottky type detectors with 4 mm times 4 mm times 1 mm were fabricated from the left half and the right half of the 100 mm diameter wafer, respectively. Standard deviations of their energy resolutions for the 122 keV line from 57Co were less than 6%. This excellent uniformity is essential for the room temperature semiconductor detectors in the major application areas, such as medical imaging, non-destructive inspection and homeland security.

Light Detection by Superconducting Weak Link Fabricated with High-Critical-Temperature Oxide-Superconductor Film

The light-induced changes in the current-voltage characteristics are studied for a superconducting weak link fabricated with a polycrystalline YBa2Cu3O7-δ film. The maximum superconducting current decreases by exposure to light at temperatures up to 77 K. The sensitivity of the light detection is enhanced by the use of a photoconductive semiconductor film on the surface of the weak link.

Superconducting packet switch

Very broad band throughputs greater than 1T bit/sec are desired in heavily loaded communication systems. Using the merits of superconducting devices, a superconducting network system is expected to improve the throughputs of such communication bottleneck systems. The paper describes a superconducting packet switch which is indispensable to a proposed superconducting network system. Considering the characteristics of various switch architectures, the space-division Banyan type architecture is adopted for a superconducting packet switch proto-type. The complete design of the proto-type is performed and the total operation is numerically simulated and confirmed. A 2/spl times/2 switching element which controls the paths of two packets is a key component of the proto-type. The basic switching element with one-bit data width is fabricated and the correct operation is completely confirmed.<<ETX>>

Pulsed Bias Voltage Shutdown to Suppress the Polarization Effect for a CdTe Radiation Detector

Pulsed bias shutdown operation, in which the bias voltage supply is periodically shut down for a certain time, is suitable for suppressing the polarization effect in a CdTe radiation detector. The duration of the bias voltage shutdown should be short to decrease the dead time and ensure the continuity of the measurement; however, the polarization effect may not be suppressed if the duration is too short. Therefore, we investigated bias voltage shutdown durations and intervals that stabilize the detector performance. A stacked type detector consisting of four 1-mm-thick CdTe diodes was used. At 35degC, the energy resolution for the 511 keV photopeak of the 22 Na source saturates at around 30 min after the measurement start and then does not change up to 300 min when the bias voltage is shut down for 10 ms every 5 min. Similarly at 60degC, the energy resolution for the 511 keV photopeak is unchanged for 300 min when the bias voltage is shut down for 10 ms every 10 s.

Improvement of the productivity in the growth of CdTe single crystal by THM for the new PET system

The effect of the THM growth rate on the CdTe crystalline quality and the detector performance was intensively investigated. The maximum growth rate for the single crystal growth was found to be approximately 15 mm/day which was 3 times greater than the conventional one. By optimizing other growth conditions, 90% of every ingot volume has become a single crystal. Te inclusions in the CdTe single crystal grown at various growth rates were also investigated by IR transmission microscopy. There was no correlation between the behavior of Te inclusions and the growth rate. The detector performance was also independent of the growth rate. Taking advantage of the large volume CdTe single crystals, about 700,000 Schottky detectors with 4 mm times 7.5 mm times 1 mm were fabricated for the research and development of the new PET system using CdTe detectors. The average FWHM for the 662 keV line from 137Cs and its standard deviation were 2.24% and 0.48%, respectively. This uniformity was essential for the development of the new PET system. For the further improvement of productivity, the growth technology of a 100 mm diameter crystal by THM is in the development and is presented.

Optical input/output interface system for Josephson junction integrated circuits

An optical input/output interface system for a Josephson junction integrated circuit is fabricated and tested. The system consists of a superconducting optical detector, a dc powered Josephson circuit, a dc powered Josephson high voltage circuit, a liquid-He-cooled semiconductor amplifier, and a liquid-He-cooled semiconductor laser. Features of the system are use of an ultrathin NbN film for the optical detector and adoption of the dc powered Josephson circuits for logic operation circuits. Correct optical output signal is detected by a liquid-He-cooled semiconductor photodiode. The optical input/output interface has the advantage of low heat penetration and low crosstalk compared to the interface using conventional coaxial lines. Moreover, dc powered Josephson circuits have an advantage of low crosstalk from power supply lines compared to conventional Josephson circuits, which are driven by ac supply current.<<ETX>>

3.5 GHz operation of a superconducting packet switch element

The paper introduces a prototype model of a superconducting packet switch which is composed of an input buffer, a contention solver, and a distribution network. The input buffer and the contention solver enable contention-free distribution of data packets. The total design of the prototype has been completed and the total operation has been numerically simulated and confirmed. A 2/spl times/2 switching element which controls the paths of two packets is the key component of the prototype. The basic switching element with 1-b data-width is fabricated by a standard Nb trilayer process. Three-junction SQUIDs driven by a three-phase powering clock are used in the switch. The correct operation up to 3.5 GHz, limited by the measurement setup, is confirmed. The margin evaluation shows there remains enough margin at GHz operations.