Takuzo Ogawa

High current characteristics of asymmetrical p-i-n diodes having low forward voltage drops

A closed form solution for the forward characteristics of a very asymmetrical step-junction p-i-n diode at high current levels is derived and discussed. It is found that the forward voltage decreases significantly when the amount of the impurities per unit area of one of the highly doped regions is reduced. The theory is confirmed by experiment, and the diodes obtained show a low forward loss together with high reverse blocking voltage and fast reverse recovery.

Diode-integrated high speed thyristor

A diode-integrated high speed thyristor formed into one body by using a separation region for preventing interference between a thyristor and a diode.

Surface Charges in a Zinc‐Borosilicate Glass/Silicon System

Surface charges in a zinc‐borosilicate glass/silicon system were studied by measuring capacitance‐voltage curves of metal‐glass‐silicon capacitors at various temperatures. The capacitance‐voltage curves change remarkably with measurement frequency and temperature. The density of positive fixed charge decreases significantly with increasing glass firing temperature and also when nitrogen gas is added to the oxygen firing atmosphere. On the other hand, the density of the surface state is about and insensitive to glass firing conditions. The surface charge is positive for n‐type silicon and negative for p‐type silicon when the Fermi level is near the intrinsic energy level. The surface charges are reversed, however, when the Fermi level is near the bandedge.

Newly Developed Thyristor Chopper Equipment for Electric Railcars

In the chopper control system for electric railcars, it is effective to adopt high operational frequency of the chopper for achievement of the following: 1) decrease of higher harmonic current induced in the trolley wire, 2) reduction of weight for reactors and capacitors in the traction circuit, and 3) improvement of control response. Through development of reverse-conducting thyristors with very short turn-off time and a repulsion type two-phase chopper, we finally realized production of a new standard high-frequency chopper equipment with regenerative braking for 1500-V dc railcars. Technical achievements mentioned previously were completely realized as a result of adoption of high frequency, 660 Hz, in the equipment. The newly developed standard high-frequency chopper equipment for 30 cars were delivered to the Chiyoda Line of Teito Rapid Transit Authority in Tokyo, and they have been operated satisfactorily in revenue service since March 1971. This paper also describes: 1) the chopper circuit using fast-switching reverse-conducting thyristors and series saturable reactors, 2) analysis of commutation circuit and methods of suppressing reapplied forward voltage increasing rate (dv/dt) and shortening commutation period, 3) the composition of the traction circuit including the protection system, such as protection for overvoltage at the regenerative braking, and 4) test results on the Chiyoda Line of Teito Rapid Transit Authority.

In-process monitoring and control of doping gas concentration during vapor phase silicon epitaxial growth by using a flame photometric detector

Abstract An in-process monitoring and control method of the doping gas concentration during epitaxial growth of Si was developed. A flame photometric detector (FPD) can be used as a monitor for the PH 3 and B 2 H 6 dopant concentrations in the injected doping gases. A combination of this dopant monitor with an automatic control system of the silicon source (SiHCl 3 ) gas concentration using an infrared spectrophotometer as a monitor, makes possible an automatic in-process control of the concentrations of dopant and of silicon source gas supplied to the reactor. The present system provides an accurate and reproducible control of impurity concentrations in Si epitaxial layers. Good correlation between the monitored signal (or the doping gas concentration) and the impurity concentration incorporated into the growth layers was confirmed for PH 3 (n-type) and B 2 H 6 (p-type) doping. For the B 2 H 6 doping, a divergence from the linear relationship between the doping gas concentration and the impurity concentration in the layers was observed in the level of acceptor concentration below about 10 15 atoms/cm 3 . The transient response of the present system was measured by growing epitaxial layers with increasing and decreasing step-changes in the dopant gas flow during continuous deposition of the layers. Some interesting, but complicated, transient responses of impurity concentration in the growth layer were observed. The responses are different between the PH 3 doping and the B 2 H 6 doping, and also different between increasing and decreasing steps especially for the B 2 H 6 doping.

Elimination of Stacking Fault in Si Epitaxial Layer by Heat Treatment

Elimination of stacking faults in Si epitaxial layer by heat treatment is investigated by observing repeated etch patterns. Two types of stacking faults are observed. One of them (about 70~90%) is eliminated easily by heat treatment and the other (about 10~30%) is stable and cannot be eliminated. Heat treatment at a temperature higher than 450°C is required to eliminate the faults in either atmosphere of O2, Ar and H2. In the temperature range higher than 600°C, the elimination is completed within a few minutes. Contrary to Mendelsons model, the observations on the initial stage of elimination process show that the elimination proceeds locally from the surface of growth layer to the substrate-growth interface.

“Integrated Photo-coupled Semiconductor Crosspoint Switches”

Integrated photo-coupled crosspoint switches using thyristors are investigated. In comparison with current-coupled crosspoint switches, these offer the advantage of having little electric interference between switches and control circuits. In order to realize both easy mounting and low triggering gate power, an efficient photo-coupling using both an edge emitting LED and a lateral thyristor is developed, and an accurate alignment technique utilizing the surface tension of solder is also developed. A trade-off between triggering gate sensitivity and the allowable dv/dt capability is improved by a new photo-coupled PNPN switch circuit. The developed device has low triggering gate current (15?30 mA for 4 thyristors) and a high dv/dt capability (>1000 V/?s). A switch network fabricated by newly developed devices is seen to have good transmission characteristics.

Application of low-impurity concentration (high-resistivity) Si epitaxial technique to high-voltage power transistors

The results of an application of an epitaxial technique of low-concentration (<1 × 10¹⁴atoms/cm³) impurity doping control to high-voltage power transistors (BV<inf>CB0</inf>= 1200 V, I<inf>c</inf>= 2.5 A) are described. An n-epitaxial layer of about 1 × 10¹⁵atoms/cm³concentration and about 25-µm thickness and ν-epitaxial layer of 5-8 × 10¹³atoms/cm³concentration and 155-165- µm thickness are successively grown on the n⁺-substrates to form the collector region. The p-base and n⁺-emitter regions are formed by diffusion. It is shown that the transistors fabricated have a collector-base breakdown voltage (BV<inf>CB0</inf>) of 1400-2300 V and other reasonable electrical characteristics.