JPH026232B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the optical firing sensitivity of an optical trigger switching element consisting of four pnpn layers.

The element that is switched by the optical trigger signal is the first
As shown in the figure, a semiconductor substrate 1 includes a continuous four-layer region of p _E , n _B , p _B , and n _E , and a cathode electrode in contact with the exposed surface of the n _E layer and p _B on one main surface 11. 2, an anode electrode 3 in contact with the exposed surface of the _pE layer on the other main surface 12, and one main surface 11
and means 4 for irradiating an optical trigger signal onto the surface of the _nE layer on which the cathode electrode 2 is not formed.

In the configuration shown in Figure 1, the thickness of the p _B layer is uniform below the n _E layer. The thickness of this p _B layer is determined approximately in proportion to the magnitude of the forward blocking voltage of the switching element. On the other hand, the magnitude of the optical trigger signal required for ignition is p _B
It is determined in proportion to the thickness of the layer. Therefore, the configuration shown in FIG. 1 has the disadvantage that as the withstand voltage increases, the optical trigger signal increases in proportion.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved optical trigger/switching element which eliminates the above-mentioned drawbacks and is capable of switching with a substantially constant optical trigger signal and high firing sensitivity without being affected by withstand voltage. be.

The optical trigger switching device of the present invention that achieves the above object is characterized by a semiconductor substrate comprising four consecutive pnpn layers in which adjacent layers have different conductivity types, and at least one layer on the surface of the semiconductor substrate. A device comprising a pair of electrodes in low-resistance contact with an outer layer and a means for irradiating the surface of the semiconductor substrate with an optical trigger signal for switching between the pair of electrodes, in which one intermediate layer and one outer layer are electrodes. are short-circuited and have a channel region in one intermediate layer having the same conductivity type as the other intermediate layer, one end of which is connected to the other intermediate layer, and the other end of which extends through one intermediate layer to one outer layer. The width of the channel region is set so that it pinches off at the depletion layer formed when the pn junction between one intermediate layer and the other intermediate layer is reverse biased with the main power supply voltage, and one outer layer The point is to irradiate an optical trigger signal to a location on the surface corresponding to a channel region.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on drawings showing examples thereof.

In FIGS. 2 and 3, 1 indicates n _E , p _B ,
A semiconductor substrate having four consecutive layers of n _B and p _E ; 2 is a cathode electrode in low resistance contact with the exposed surface of the p _B layer and the exposed surface of the p _B layer on one main surface 11; 2; 4 is an anode electrode in low resistance contact with the exposed surface of the _pE layer on the other main surface 12, and 4 is a means for irradiating a light trigger signal. Reference numeral 5 denotes a channel region in which a part of _nB penetrates the _pB layer and protrudes until it reaches the _nE layer at a location on one main surface 11 corresponding to the irradiation location of the optical trigger signal. As shown in FIG. 4, this channel region 5 is n _B
The width W is such that when the pn junction formed between the pn layer and the _pb layer is reverse biased, the entire region becomes a depletion layer and becomes a pinch-off state. The depletion layer is indicated by 6. If formed in this way, n _E layer and n _B
Even if the layers are in contact, they are electrically isolated by the depletion layer, so there is no worry that load current i _L will flow. Next, the switching operation will be explained. By means of the means 4, when an optical trigger signal is applied to the exposed surface of the _nE layer, the light passes through the _nE layer and enters the channel region 5. As a result, electron-hole pairs proportional to the number of light quanta are generated in the channel region 5, and the p _E , n _B , n _E diode regions including the channel region enter a low impedance state, causing the diode region to flow. Become. Furthermore, this diode current causes the peripheral area of the channel region 5 to
The p _E , n _B , p _B , n _E four-layer regions are turned on, and the conduction region through which the load current flows becomes wider. Figures 2 and 3
In the element with the structure shown in the figure, since the depletion layer formed in the _nB layer is in contact with the _nE layer in the channel region 5, the distance from the light incidence surface to this depletion layer is equal to the thickness of the _nE layer. That is, it can be made as small as about 2 to 3 μm. Therefore, since the light can enter the channel region 5 with less attenuation from the light source, the light energy required to bring the element into a conductive state can be reduced. Also, p _E including channel region 5,
n _B , n _E The diode region has a four-layer structure p _E , n _B ,
It has the characteristic that it can be turned on about 1/2 or more faster than in the p _B and n _E regions. This is because the _nB layer is in contact with the _nE layer through the channel region 5 with a high electric field, so the electrons generated in the depletion layer by light,
The travel time of a hole toward the p _E layer and n _E layer is p _E ,
This is because the travel time within the p _B layer is faster than in the case of n _B , p _B , and n _E thyristors.

The above-mentioned effects are significantly greater than in the case of conventional high-voltage devices that require a thick p _B layer.

Figure 5 shows that the impurity concentration of the n _B layer is 1×10 ¹⁴ cm ^-3 ,
When the thickness is 5 μm, the width of the channel region 5 is 2 μm, and the lengths of the channel region 5 are 75 μm and 10 μm, the potential passing through the center of the channel region 5 when a voltage of 65 V is applied between the anode electrode and the cathode electrode The distribution was obtained by numerically calculating and solving the basic semiconductor equations (Poisson's equation, carrier flow continuity equation). A negative potential, ie, a barrier against electrons flowing from the _nE layer to the _nB layer, is formed in the channel region 5, and the channel region 5 is in a blocking state. This barrier can be increased by narrowing the width of the channel region and by increasing the length of the channel region.

FIG. 6 shows forward blocking characteristics corresponding to the case of FIG. When the length of the channel region is 10 μm, the voltage applied between the anode electrode and the cathode electrode V _AK
The leakage current at =150V is 1.2×10 ^-7 A/cm ² , which is very small. When the length of the channel region is 7.5 μm, it is 3×10 ⁻⁵ A/cm ² , which is small. As described above, with the structures shown in FIGS. 2 and 3, it is possible to realize a high-speed optical trigger switching element that can obtain the target breakdown voltage and has high optical ignition sensitivity.

FIG. 7 shows another embodiment of the invention. The embodiment shown in FIG. 7a is characterized in that in the embodiments shown in FIGS. 2 and 3, a p-type semiconductor layer 7, which is thinner than the p _B layer, is formed between the channel region 5 and the _nE layer. It is said that By providing this p layer 7, the target breakdown voltage can be obtained even if the width of the channel region 5 is increased or the thickness of the p _B layer is decreased. Therefore, this embodiment is useful when the width of the channel region is widened to increase the effective light incident area, or when p _B
Suitable for thinning.

In the embodiment shown in FIG. 7b, the shape of the thin p-type semiconductor layer 7 shown in FIG. 7a is changed so that the same effect can be obtained. For example, when forming the p _B layer by diffusion, this structure narrows the gap between the exposed parts of one main surface 11 of the semiconductor substrate 1 when diffusing the p-type impurity, and the lateral diffusion from both sides causes the optical trigger signal to be transmitted. This is realized by forming a thin p-layer 7a corresponding to a p-type semiconductor layer with a low impurity concentration so as to overlap each other under the irradiated surface. That is, p layer 7
A can be formed at the same time as the p and _B layers.

FIG. 8 shows the example of FIG. 7a, with the thickness of the p _B layer being 5 μm, the surface impurity concentration being 1×10 ¹⁸ cm ^-3 , and the n _B
The layer thickness is 5 μm, the impurity concentration is 1×10 ¹⁴ cm ^-3 , p
The thickness of layer 7 is 2 μm, and the surface impurity concentration is 5×10 ¹⁵ cm.
This is an example of forward blocking characteristics when the value is ⁻³ . Even if the length of the channel region 5 is shortened to 5 μm, 150V can be blocked if the width of the channel region 5 is 2 μm.
Also, even if the width of channel region 5 is widened to 11 μm,
Can block 100V. In this case, the thickness of p layer 7 is 2μ
Since the light source 4 is as thin as m, the light from the light source 4 enters the channel region 5 without being attenuated on the way. Also, the p layer
Since it is as thin as 2 μm, the intensity of light required to ignite the four layer regions p _E , n _B , p _B , and n _E can be reduced. This effect is extremely large in the case of high voltage switching devices that require a thick _pB layer. For example, if the lifetime of the p _B layer is 0.5 μs, the thickness of the p _B layer is
As the thickness decreases from 100 μm to 30 μm, the minimum ignition light input decreases by a factor of 6. In this way, in the present invention, by providing the thin p layer 7 on the channel region 5 and putting the channel region 5 in a pinch-off state with the voltage between the anode electrode and the cathode electrode, a high breakdown voltage switching element with high light ignition sensitivity is realized. can.

FIGS. 9 and 10 show an example in which a large number of switching elements shown in FIGS. 2 and 3 are arranged in parallel within the same semiconductor substrate. Channel area 5
is widened to widen the turn-on area by light ignition. For this purpose, the pattern of the channel region 5 viewed from the cathode electrode side can be circular, radial, or any other arbitrary shape.

FIGS. 11 and 12 show other embodiments of the present invention. Compared to the embodiments shown in FIGS. 9 and 10, only the structure of the cathode electrode 2 is different. In this embodiment, the cathode electrode 2 is not connected to the entire surface of the central part of the _nE layer. Since the light also enters the four-layer region p _E , n _B , p _B , n _E surrounding the channel region 5, these four-layer region turns on quickly. Therefore, a rapidly rising current can be passed through the switching element.

FIG. 13 shows another embodiment of the invention. Second
This is an example in which the embodiment shown in the figures and FIG. 3 is applied to an auxiliary switching element portion Th _A of a switching element employing an amplified gate method. Th _M is the main switching element. It is possible to realize an optical trigger switching device with high optical ignition sensitivity and high forward current increase rate tolerance during turn-on.

FIG. 14 shows a case where the embodiment shown in FIG. 7 is used as an auxiliary switching element portion Th _A of a switching element employing an amplification type gate method. The same effect as in the case of FIG. 13 can be obtained. Furthermore, by using the embodiments shown in FIGS. 9 and 10, as well as FIGS. 11 and 12 as an auxiliary element part of an element that employs an amplification type gate method, it is possible to make a light beam with a large forward current increase rate at turn-on. A trigger switching device can be realized.

Note that instead of the light source 4, electrons such as γ rays and α rays can be used.
It goes without saying that similar effects can be obtained when a hole pair generation source is used.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a conventional optical trigger switching device, FIG. 2 is a schematic plan view showing an embodiment of the optical trigger switching device of the present invention, and FIG. 3 is a cross-sectional view taken along the line - in FIG. 4 is a cross-sectional view of the device in FIG. 3 in a blocked state, FIG. 5 is a potential distribution diagram passing through the center of the channel region in FIG. 4, and FIG. Forward blocking characteristic diagram of the element,
FIGS. 7a and 7b are cross-sectional views showing other embodiments of the present invention, FIG. 8 is a forward blocking characteristic diagram of the element in FIG. 7a, and FIG. 9 is a diagram showing another embodiment of the present invention. A plan view, FIG. 10 is a sectional view taken along the line - in FIG. 9,
FIG. 11 is a plan view showing still another embodiment of the present invention, FIG. 12 is a sectional view taken along line XII-XII in FIG. 11, and FIG. 13 is a sectional view showing still another embodiment of the present invention. , and FIG. 14 are cross-sectional views showing different embodiments of the present invention. DESCRIPTION OF SYMBOLS 1... Semiconductor base, 2... Cathode electrode, 3... Anode electrode, 4... Light trigger signal irradiation means, 5... Channel region.

Claims (1)

[Claims] 1. Four consecutive pnpn layers are formed between a pair of main surfaces so that the adjacent layers have different conductivity types, and one main surface has an outer n layer and an adjacent intermediate layer. a semiconductor substrate in which a p-layer is exposed and an outer p-layer is exposed on the other main surface; a pair of electrodes each in low resistance contact with at least each outer layer on both main surfaces of the semiconductor substrate; and means for irradiating an optical trigger signal for switching onto one main surface of the semiconductor substrate, wherein one electrode is in low resistance contact with the periphery of the outer n-layer excluding the center and the intermediate p-layer. It is located just below the part of the outer n-layer that is not in contact with one of the electrodes, has a lower impurity concentration than the outer n-layer, and penetrates the middle p-layer so that one end is connected to the outer n-layer.
Each layer has an n-type channel region whose other end is connected to the intermediate n-layer, and the width of the channel region is set between the intermediate p-layer and the intermediate n-layer by applying a rated voltage between a pair of electrodes. of
The optical trigger is characterized in that the dimensions are such that the p-n junction is pinched off at the depletion layer formed when the p-n junction is reverse biased, and the optical trigger signal is irradiated onto the exposed surface of the outer n-layer corresponding to the channel region. switching element.