JPH029460B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Application of the Invention) The present invention relates to an optical thyristor, and in particular to an optical thyristor that can improve the optical ignition sensitivity without reducing the dv/dt tolerance. be.

(Background of the Invention) FIG. 1 shows a cross-sectional structure of a short-circuited emitter type optical ignition type semiconductor controlled rectifier which is a conventional optical thyristor.

In FIG. 1, a semiconductor substrate 1 includes, for example, p
A first emitter layer p _E 11 of type conductivity, a first base layer n _B 12 of n type conductivity, a second base layer p type conductivity
p _B 13, and a second emitter layer of n-type conductivity n _E 1
4 is formed.

The layers are laminated in the order p _E , n _B , p _B , n _E from one main surface to the other main surface, and there is a gap between each layer.
PN junctions J ₁ to J ₃ are formed. In addition, the second
A part of the emitter layer n _E 14 is a light irradiation area 14L.

On one main surface (lower side of the example shown), p _E layer 1
1 is in low resistance contact with the anode electrode 21. On the other main surface (upper surface), n _E layers 14, 14L
, the p _B layer 13 is exposed, and the cathode electrode 22,
23 and the light-receiving part cathode electrode with low resistance,
This short-circuits Pn junction _J3 .

Such an optical thyristor includes, for example, a first region which is a light receiving thyristor that is first ignited by light 31 from an optical fiber 30, and a second region which is an auxiliary thyristor which is ignited by the current of the light receiving thyristor and further amplifies the current. and a third region, which is the main thyristor which fires with the current up to the auxiliary thyristor.

Of the above regions, the second region may be omitted, or a region having the same structure as the second region may be provided between the first region and the second region or between the second region and the third region. It is also possible to increase it.

This structure prevents the large current from concentrating on the light irradiation area, which is the initial ignition area, when controlling a large current. This is to spread the heat to the thyristor, thereby preventing element destruction due to Joule heat.

This allows the ignition sensitivity to be increased by the light receiving thyristor.
The auxiliary thyristor can be increased in order of the main thyristor.
It is possible to increase the sensitivity of the light receiving thyristor.

According to the results of research on the ignition phenomenon caused by light conducted by the present inventors, in an optical thyristor having a light-receiving part thyristor that irradiates light through the _nE layer 14L as shown in FIG. generated by light, p _E layer 11, n _B layer 12 and p _B layer 13
In addition to the current i _b flowing to the cathode electrode 22 of the main thyristor through J ₃ between the p _B layer 13 and the n _E layer 14L
It has been found that there is a current i _p that is generated by the solar cell effect due to the junction and flows through the light receiving section cathode electrode 24 .

Due to the sum of these currents (i _b + i _p ) and the lateral resistance _R of the p _B layer ₁₃ , _a forward voltage {(i _b + i _p )×R} is added. When this voltage becomes larger than the threshold voltage of the _J3 junction, a large amount of electrons are injected from the _nE layer 14L,
The depletion layer at the _J2 junction, which was blocking the voltage applied between the anode and cathode electrodes, disappears, and the photothyristor fires.

As described above, the minimum amount of light irradiation when the optical thyristor fires will be referred to as the minimum firing light input P _GT .

By the way, even with the amplification gate structure as shown in FIG. 1, in an optical thyristor having a blocking voltage of about 4 kV, the minimum ignition light input P _GT is about 5 mW. In order to reduce the turn-on time of the optical thyristor, a light amount of five times or more than the above-mentioned P _GT is required.

However, it is difficult to stably supply such a large amount of light using a light emitting element, and it is desired to reduce P _GT . In order to reduce P _GT , it is conceivable to increase the resistance R so that the J ₃ junction reaches the threshold voltage with a small current ( _ib + i _p ).

However, increasing the resistance R causes another problem in that it is undesirable because the dv/dt tolerance, which is one of the other important device characteristics, decreases. The dv/dt tolerance will be explained below.

When a positive, steeply rising voltage is applied to the anode electrode 21 of the optical thyristor as shown in FIG. 1 and negative to the cathode electrode 22, a displacement current similar to i _b flows through the junction J ₂ .

By this displacement current and resistance R, p _B layer 13 and n _E
Layer 14 is forward biased. Therefore, if the value of the forward bias exceeds the threshold value, the optical thyristor will be erroneously fired even if no light is irradiated through the _nE layer 14. The limit value of the voltage rise rate that will not cause false ignition.
It is called dv/dt tolerance.

To summarize the above, when the resistance R is increased in order to reduce P _GT , the dv/dt withstand capacity decreases, that is, the P _GT and the dv/dt withstand capacity are in an antinomic relationship. Therefore, it is desired to develop a means to reduce P _GT without impairing the dv/dt tolerance.

(Object of the invention) The object of the invention is to provide a highly sensitive optical thyristor that can reduce P _GT without impairing dv/dt tolerance by controlling the current generated by the solar cell effect. There is a particular thing.

(Summary of the Invention) A feature of the present invention is that the current i _p is dispersed by narrowing the flow path of the current i p generated between the p _B layer and the n _E layer in the light irradiation area due to the solar _cell effect. The present invention is provided with means for preventing (in other words, concentrating the current i _p ) and increasing the current density to reduce the minimum ignition light input P _GT .

Next, the basic principle of the present invention will be described in detail using an optical thyristor as an example.

FIG. 2 is a plan view of the optical thyristor shown in FIG. 1, viewed from the cathode electrodes 22-24 side.
As shown in the figure, the current i _b generated in the _pE layer 11, _nB layer 12, and _pB layer 13 due to light irradiation flows from the first region (light receiving thyristor region) to the short circuit part of the cathode electrode 22. It flows radially towards the p _B layer 13.

On the other hand, the current i _p generated by the solar cell effect of the p _B layer 13 and the n _E layer 14L similarly flows in a radially dispersed manner from the light irradiation region toward the short circuit part of the light receiving section cathode electrode 24. After reaching the electrode 24, on the contrary, the light is concentrated toward the light irradiation area.
n Flows within _{the E} layer 14L.

If the current density J _p can be increased without damaging this current i _p , even if the electrical conductivity δ of the p _B layer 13 is constant, Ohm's law (E = J _p /
δ), it is possible to increase the electric field E due to the current i _p between the light irradiation region and the short-circuited portion of the cathode electrode 24.

As a result, the voltage drop during this period can be increased, and photosensitivity can be improved. On the other hand, if the flow path of the current i _b is not changed, dv/dt related to i _b
The tolerance should not change.

As described above, if the current density of the current i _p can be increased without changing the flow of the current i _b , the photosensitivity can be improved without impairing the dv/dt tolerance.

The present invention has been made based on the above considerations.

(Embodiment of the Invention) FIG. 3 shows an enlarged plan view of a light-receiving portion thyristor (ie, first region) of an optical thyristor that is an embodiment of the present invention.

The _nE layer 14L and the _pB layer 13 of the light receiving thyristor are only partially short-circuited by the cathode electrode 24.

To be more specific, in the conventional example shown in _FIGS .
4, but in this example,
Only part of it is shorted.

With this structure, the current i _b of the light receiving thyristor flows radially from the light irradiation region toward the cathode electrode 22 of the main thyristor to which a negative voltage is applied, but the current i b due to the solar cell effect _p
flows concentratedly in the p _B layer 13 toward the cathode electrode 24, and further flows through the n _E layer 14L toward the light irradiation region.

As a result, the current density of i _p increases, and the voltage drop due to the current i _p in the p _B layer 13 increases accordingly. As a result, the _nE layer 14L under the light irradiation area and
Since the p _B layer 13 is forward biased with a larger voltage, photosensitivity is improved.

On the other hand, since the flow of the current i _b related to the dv/dt withstand capacity does not change, the dv/dt withstand capacity does not decrease.

According to experiments conducted by the present inventors, this embodiment can reduce light sensitivity by about 20% without impairing DV/DT tolerance.
I was able to improve.

FIG. 4 is an enlarged plan view similar to FIG. 3 of another embodiment of the present invention, in which a current flows through the _nE layer 14L.
A structure is shown in which a part of the _nE layer 14L is removed in order to limit the area of i _p .

The _nE layer generally has a high carrier concentration and low resistance, so the voltage drop across the _nE layer is small. Therefore, n _E
The effect of forward biasing the layer 14L and the p _B layer 13 is small, and its contribution to improving photosensitivity is also small.

However, if the structure shown in Figure 4 is adopted and the cross-sectional area of the current i _p is made smaller, the current density of i _p in the n _E layer 14L will further improve, so even if the resistance of the n _E layer 14L is small, , the voltage drop in the n _E layer becomes large. Thereby, photosensitivity can be further improved. Needless to say, in this case, the dv/dt tolerance does not decrease.

FIG. 5 shows yet another embodiment of the present invention.
FIG. 4 is an enlarged plan view similar to FIG. 3;

This embodiment differs from the embodiment shown in FIG.
The point is that the number of cathode electrodes 24 that partially short-circuit the _nE layer 14L and the _pB layer 13 (the number of formation locations) is further increased, and these are evenly distributed around the light irradiation area.

With this configuration and arrangement, when the light receiving thyristor fires, the _pB layer 1 under the light irradiation area
3. It is possible to improve the dispersion of the ignition current flowing through the _nE layer 14L and the cathode electrode 24, and to fire the auxiliary thyristors in the second region shown in FIG. 1 almost simultaneously under the annular _nE layer. can. As a result, element destruction due to concentration of ignition current can be prevented.

Although there is a concern that the current density of i _p may decrease due to increasing the number of cathode electrodes 24, the decrease in current density can be prevented by reducing the short circuit width of the cathode electrodes 24. It goes without saying that the number of partially short-circuited cathode electrodes 24 can be further increased beyond the three shown.

According to this embodiment, it is possible to increase the sensitivity of optical ignition without impairing the dv/dt tolerance while preventing element destruction due to concentration of ignition current during ignition.

In addition, although the optical thyristor in which the second region (auxiliary thyristor) and the third region (main thyristor) are sequentially formed around the first region (light-receiving thyristor) has been described above, the second region is omitted. It will be readily understood that it is also possible to form two or more second regions.

(Effects of the Invention) As is clear from the above description, according to the present invention, the flow path (cross-sectional area) of the current due to the solar cell effect in the p _B layer and n _E layer of the light receiving thyristor is restricted. By doing so, the value of the forward bias applied to the _nE layer and the _pB layer below the light irradiation area can be increased.
It is possible to increase the sensitivity of optical thyristors, etc.

Moreover, concentration of the ignition current of the thyristor formed around the light receiving part thyristor can be prevented.
It does not cause a decrease in dv/dt tolerance. Therefore, according to the present invention, it is possible to simultaneously improve the light ignition sensitivity and prevent a decrease in dv/dt tolerance.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional amplification gate type optical thyristor, Figure 2 is an enlarged plan view of the light irradiation area as seen from the cathode surface of Figure 1, and Figures 3, 4, and 5 are respectively FIG. 3 is an enlarged plan view similar to FIG. 2, showing an embodiment of the invention. 1...Semiconductor substrate, 11...p _E layer, 12...n _B
Layer, 13...p _B layer, 14...n _E layer, 21... anode electrode, 22, 23... cathode electrode, 24...
...Light receiving section cathode electrode, 31...Light.

Claims (1)

[Claims] 1. first emitter regions having different conductivity types;
The first base region, the second base region, and the second emitter region are stacked in the above order, and a pn junction is formed between the adjacent regions, and the second emitter region and the second base region are formed on one of the main surfaces. a semiconductor body which is exposed and further divided into a first part and a second part having a larger area for the second emitter region to be irradiated with at least a light ignition signal; and the other main surface of the semiconductor body. an anode electrode connected with low resistance to a first emitter region exposed to the second emitter region; a cathode electrode connected with low resistance to a second portion of the second emitter region; and a first portion of the second emitter region connected to a second portion. an auxiliary electrode short-circuiting a first portion of the second emitter region to a second base region on an opposite side;
An optical thyristor characterized in that the optical thyristor is divided into a plurality of parts along opposing positions of the first part and the second part. 2 the first portion of the second emitter region is circular;
Claims characterized in that a second portion is formed to surround the first portion, and the auxiliary electrodes are substantially evenly distributed around the first portion of the second emitter region. The optical thyristor according to item 1.