JPS6058594B2 - Planar photothyristor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photothyristor, and particularly to a planar type photothyristor with high photosensitivity.

A so-called photocoupler, which combines a light-emitting element and a light-receiving element, is a unique device that has excellent functions such as insulation separation between input and output, impedance conversion, broadband amplification, and high-speed switching.

When a photothyristor is used as a light-receiving element of a photocoupler, the light-emitting element is usually made of GaA from the viewpoint of wavelength characteristics.
s Light emitting diode (GaAs LED) is used. Ga
As-LEDs have a certain size and emit light in a planar shape in a normal structure, but the directivity is not very sharp, so when a light emitting element and a light receiving element are combined, the light on the light receiving surface of the photothyristor is The illumination intensity is reduced, the light utilization rate is poor, and the ignition sensitivity is lower than that of electric gate type thyristors. In order to increase the illuminance on the light-receiving surface, it is possible to guide the light from the light-emitting element to the light-receiving element through a condenser lens or the like, but if the photocoupler is small, assembly is difficult and the cost is high. Therefore, a photothyristor for a photocoupler needs to have a large light-receiving area. There is a limit to the area due to the size of the thyristor and the current capacity of the thyristor itself. On the other hand, in order to increase the ignition sensitivity, it is necessary to devise ways to increase the photoelectric conversion efficiency itself. In order to increase the photoelectric conversion efficiency, it is possible to increase the absorption coefficient α, the diffusion distance Lp of minority carriers, and the width d of the depletion layer. Of these, the absorption coefficient α and minority carrier diffusion length Lp are determined by the material, but the width d of the depletion layer can be controlled by the manufacturing conditions and usage conditions of the element. If the impurity density in the n base region is Nd and the impurity density in the p base region is extremely high, the applied voltage in the forward blocking state is
On the other hand, the width d of the depletion layer is approximately expressed by the following equation. Here, E is the dielectric constant of silicon, and e is the charge of electrons, which is a constant.

In the case of a thyristor, the applied voltage V is about several volts,
In a normal structure, since the impurity concentration Nd of the n-base region is constant, the width d of the depletion layer is also constant from equation (1), and the photoelectric conversion efficiency is fixed. The optical ignition sensitivity of a photothyristor is greatly influenced not only by the photoelectric conversion efficiency but also by the junction dimensions of each layer, impurity concentration, and especially the resistance of the p base region directly below the n emitter region, so these should be selected appropriately. The ignition sensitivity can be improved by
Usually, it is limited due to the balance with other characteristics, such as DV/Dt withstand capacity and blocking withstand voltage. Therefore, in order to increase the optical ignition sensitivity without impairing other electrical properties, it is necessary to lower the impurity concentration in the n-base region. SUMMARY OF THE INVENTION An object of the present invention is to provide a novel planar photothyristor with high light ignition sensitivity without impairing other electrical characteristics. The planar photothyristor of the present invention that achieves the above object is characterized by an n-type layer having a higher resistivity (lower impurity concentration) than the n-base layer near the light-receiving surface side of the n-base layer with good photosensitivity. (referred to as the ν base layer).

The ν base layer is arranged adjacent to the p base layer and adjacent to the n base layer on the surface opposite to the light receiving surface. As a result, the depletion layer near the surface, which has high photosensitivity, expands into a high resistivity v layer, thereby increasing the photoelectric conversion efficiency and increasing the light ignition sensitivity. DESCRIPTION OF THE PREFERRED EMBODIMENTS The planar photothyristor of the present invention will be specifically explained below with reference to drawings showing embodiments thereof. FIG. 1 shows a first embodiment of the planar photothyristor of the present invention. n base layer 2 (NB
) consists of a ν base layer 3 (VB) near the light irradiation surface. In order to realize this, a silicon wafer in which a low concentration ν layer (ν base layer) is formed on a high concentration n layer (n base layer) may be used as the semiconductor substrate 1. A p+ region 4 is formed on this wafer by long-term p-type impurity diffusion (for example, boron diffusion), and then a p emitter layer 5 (PE) and a p
A base layer 6'' (PB) is formed by the same p-type impurity diffusion.Next, an n-emitter layer 7 (NE) is formed by n-type impurity diffusion (phosphorous diffusion), and then an anode electrode 8 and a cathode electrode 9 are provided. The thyristor is completed.Jl, J2
, J3 is PE, . This is a Pn junction formed between the nB layer and the PBli layers. The dimensions and impurity concentration of each part of the thyristor of this example manufactured by the above-mentioned process are as follows. The thyristor pellet has a square main surface with a side of 1.5 m and a thickness of 180 pTrt. The n emitter layer has a thickness of 20 μm and an impurity concentration of about 5 to 10 per surface! Da
tOmslc! 1,. The p base layer has a thickness of 20 μm just below the n emitter layer.1 The impurity concentration is approximately 1×1017at0.
ms'D. ．． The thickness of the n-base layer directly below the p-base layer is 1
00μm1 impurity concentration is 2.5×1014at0msI
d. ．． The p emitter layer has a thickness of 40 μm1 and an impurity concentration of approximately 1×1017at0msIc! It is l. Note that the shape of the exposed portion of the semiconductor substrate surface of the n emitter layer is 350 μm x 8
It is a rectangle of 00 μm. Also, the thickness of the ν base layer is approximately 30 μm1, and the impurity concentration is 5×1013at0msIc!
It is l. The advantage of photosensitivity is that the depletion layer 10 near the J2 junction is widened. In other words, since the lifetime of the p-base layer is short, the minority carrier electrons generated by light irradiation cannot diffuse long distances and do not become an effective photo-trigger current, but the holes generated in the n-base layer have a long lifetime and are therefore effective. It is used as a photo-triggered current. From this, the depletion layer should be expanded as far as possible to the n-base layer side. Therefore, by forming the surface of the n-base layer into a v-base layer having a higher specific resistance, the depletion layer can be expanded to the n-side, and the photosensitivity can be improved. However, if all n base layers are replaced with ν base layers, the main current path (
ν base layer of the part projected in the stacking direction of the n emitter layer)
The disadvantage of the ν base layer is that the on-resistance and on-voltage become high. Moreover, since light does not reach this ν base layer 0-L junction (most of the light is absorbed by the n emitter layer), even if the depletion layer there is widened, the photosensitivity will not improve. Therefore, as in the embodiment shown in FIG. 1, it is advisable to make the thickness of the ν base layer smaller than the depth of the b junction. For example, if the impurity concentration of the n-base layer is 2.5×1014at0msIcI1 and V=10V from equation (1), the depletion layer will expand by about 7μ, but it will be 5×1013at0ms1c! above the n-base layer. ν of about l
When the base layer is provided, it expands to about 16μ. The effects of this embodiment will be specifically explained using numerical values.

In the light receiving part of the thyristor of this example, an ordinary GaAs-based ED is used.
The light-emitting surfaces of the two were opposed to each other, and light was incident as shown by the arrow in FIG. As a result, the thyristor of this example is made of GaAs.
It ignited when an input current of 3771,A was applied to the upper ED. In contrast, a thyristor (conventional example) was prepared in which the impurity concentration of the ν base layer of the thyristor of this example was made the same as that of the n base layer, and the other configuration was the same as that of the thyristor of this example. The upper ED was ignited in the same manner as described above. As a result, the conventional thyristor fired when an input current of 5 TrLA was applied to the GaAs 1ED. As is clear from the above comparative experiments,
The ignition sensitivity of the thyristor of this example was improved by about 1.7 times compared to the thyristor of the conventional example.

FIG. 2 shows a second embodiment of the present invention, which provides a device with higher voltage resistance than the first embodiment.

Since the ν base layer has a low impurity concentration, it is easily inverted to p-type. If the ν base layer directly under the SiO2 layer 11 serving as a surface stabilizing film is inverted to p-type, the p base layer and the p+ region will be connected, increasing leakage current and possibly lowering the withstand voltage. Therefore, as shown in FIG. 1, the ν base layer is selectively epitaxially grown only in the vicinity of the L junction, so as not to contact the J1 junction. Alternatively, even if the portion in contact with the J1 junction is selectively n+ diffused later, the effect remains the same. 3 and 4 show a third embodiment of the present invention, which is an apparatus having a structure that further improves photosensitivity compared to the first embodiment.

It has a structure in which the b-junction penetrates through a part of the p-base layer and emerges from the surface. Also in this case, a part of the n base layer near the surface is made into a ν base layer. In this way, as shown in the figure, the depletion layer spreads over the entire light irradiation area and the photosensitivity improves.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a first embodiment of the planar photothyristor of the invention, FIG. 2 is a sectional view showing a second embodiment of the invention, and FIG. 3 is a sectional view of a third embodiment of the invention. A plan view showing
FIG. 4 is a sectional view taken along line I-1 in FIG. 3. Explanation of symbols, 1...Semiconductor substrate, 2...
・n base layer, 3...v base layer, 5...
...p emitter layer, 6...p base layer, 7...
...n emitter layer, 8... anode electrode, 9...
...Cathode electrode.

Claims (1)

[Claims] 1 A pair of main surfaces located on opposite sides of each other, and a first region of one conductive electrode that is mostly adjacent to one main surface and partially extends to the other main surface side and is adjacent to the other main surface. , extending from the other main surface into the first region and having a lower impurity concentration than the first region forming a first pn junction between the first region and the first region terminating at the other main surface. a second region of the other conductivity type; and a second pn junction formed extending from the other main surface into the second region and terminating at the other main surface between the second region and the second region. a third region of one conductivity type having a higher impurity concentration than the second region; and a second region extending from the other main surface into the second region and partially adjacent to the third region. a fourth region of the other conductivity type having a low impurity concentration; and a third pn formed extending from the other main surface into the third region and terminating at the other main surface between the third region and the third region. a fifth region of the other conductivity type having a higher impurity concentration than the third region forming the junction; a first main electrode in contact with the first region on one main surface of the semiconductor substrate; A planar photothyristor characterized in that the second main electrode contacts the fifth region on the other main surface of the semiconductor substrate.