JPS58192B2 - Semiconductor optical detection device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a semiconductor optical detection device.

There are PIN photodiodes, avalanche photodiodes, phototransistors, etc. as semiconductor optical detection devices, but PIN photodiodes have the advantage of being simple in structure and therefore easy to manufacture; However, the avalanche photodiode has the disadvantage of not being able to obtain a detection output with a large gain, and the avalanche photodiode has exactly the opposite advantages and disadvantages to the PIN photodiode, and the disadvantage is that it requires a particularly harsh usage environment. Furthermore, although the phototransistor can provide a detected output with a relatively large gain, it has the disadvantage of slow response speed.

Furthermore, a structure in which a diode is connected between the base and collector of an npn transistor has also been proposed, as shown in a cross-sectional view in FIG. 1 and an equivalent circuit diagram in FIG.

(Japanese Unexamined Patent Publication No. 53-71590) However, even with this type of structured device, the optical detection characteristics have the disadvantage that they can be used only up to a certain frequency, as shown in the part A in Figure 3. had.

The present invention solves these drawbacks and proposes a device suitable for high-frequency optical detection.

That is, the present inventors believe that the skirt pull shown in Figure 3 is caused by recombination of minority carriers, and by introducing impurities that form deep levels that promote recombination,
This is to prevent the hem from pulling.

The present invention will be described in detail below using the drawings. FIG. 4 shows an example of a semiconductor optical detection device according to the present invention, which is designated as a whole by M, and includes, for example, an N-type semiconductor layer 1, an N-type semiconductor layer 2 formed on this layer 1, and this layer. 2, a P-type semiconductor layer 3 formed from the side opposite to the layer 1 side, an N-type semiconductor layer 4 formed within this layer 3 from the side opposite to the layer 1 side, and a layer 2 formed on the layer 2. A light-shielding layer 5 is provided so as to allow light to enter the layer 3 from the side opposite to the layer 1 side as indicated by the arrow, that is, without covering all of the layer 3, and a A terminal 7 led out through an electrode 6 provided on the side, a terminal 8 led out from the layer 3 in such a way that the incidence of light thereon is not substantially blocked, and a terminal 9 led out from the layer 4. and.

The above configuration is the same as the configuration shown in FIG.

The present invention differs from the device shown in FIG. 1 in that impurities are introduced that form deep levels within layer 2.

This impurity is for compensating the carrier concentration and making the carrier concentration of layer 2 sufficiently low.

Furthermore, layer 2 is formed on layer 1 as a substrate by, for example, epitaxial growth, and the specific resistance of layer 2 is
and is selected to be sufficiently large compared to the specific resistance of layer 3,
The thickness D2 under layer 3 is chosen to be greater than the characteristic absorption length of layer 2 for light.

Moreover, for optical detection under optimal conditions, layer 3 is obtained by impurity diffusion into layer 2, and the thickness of layer 3 D
3 is preferably selected to be 1/10 or less of the characteristic absorption length of layer 3 for light, and layer 4 is obtained by diffusing impurities into layer 3, but layer 4 is selected from the side where light is incident. It is preferable that the area as viewed from the same side of the layer 3 is selected to be 115 or less.

The above is an example of the structure of the semiconductor detection device according to the present invention. According to such a structure, layers 1, 2 and 3 and terminals 7 and 8 are used to form layer 1 into N layer and layer 2 into I layer. layer, layer 3 to 2
The PIN photodiode H used as a layer also includes layers 1, 2, and 3.
4 and terminals 7 and 9, it is clear that an NPN phototransistor T having layers 1 and 2 as a collector, layer 3 as a base, and layer 4 as an emitter is constructed.

Therefore, applying the required potentials to terminals 7, 8 and 9 so that the PN junction 11 between layers 2 and 3 is biased in the reverse direction and the PN junction 10 between layers 3 and 4 is biased in the forward direction, Then, when a depletion layer is formed that spreads on both sides of the PN junction 10, and light is incident on the depletion layer through the layer 3, it is converted into electric carriers within the depletion layer, and the electrons are transferred to the layer 3 side. In layers 2 and 1 towards the side opposite to L, holes travel into layer 3 towards the side opposite to layer 1, thus L
A current corresponding to the intensity of the current flows inside between the terminals 7 and 8 as an output current obtained by detecting the incident light of the PIN photodiode H.

By the way, the current that flows internally as the output current of the PIN photodiode H flows through the layer 3 as the base of the NPN transistor T, so it is an NPN transistor.
This is the base input current of the type transistor T.

Therefore, if the forward bias between layers 3 and 4 is set to a value sufficient to turn on the NPN transistor, the amplified output current of the detected incident light of the PIN photodiode H is transferred to the terminals 7 and 9. It can be led out to the outside through the optical detector, thereby providing a function as a photodetecting device.

In this way, the semiconductor optical detection device of the present invention described above can function as a photodetection device, but in this case, the specific resistance of layer 2 is selected to be sufficiently larger than that of layer 3. Therefore, the depletion layer that is obtained by expanding to both sides of the PN junction 11 is obtained by largely expanding to the layer 2 side, and the thickness of layer 2 is the thickness of the layer below layer 3. Since the thickness of the depletion layer is selected to be longer than the characteristic absorption length of the layer 2, the thickness of the depletion layer obtained by expanding to the layer 2 side can be made larger than the characteristic absorption length of the layer 2.

Also, the thickness of layer 3 is 1 of the characteristic absorption length of layer 3 for light.
/10 or less, the light can efficiently enter the depletion layer that has spread widely toward the layer 2 side through the layer 3, and the area of the layer 4 will be smaller than the layer 4 when viewed from the side where the light is incident. 3
If the area is selected to be 115 or less when viewed from the same side of the layer 4, the problem of light incident on the depletion layer, which passes through the layer 3 and spreads widely toward the layer 2 side, will be reduced due to the existence of the layer 4. Therefore, the incident light is converted into electric carriers within the depletion layer with high efficiency.

In addition, the incident light L is converted into electric carriers with high conversion efficiency, and the current based on it is P.
The output current obtained as the IN photodiode H is amplified by the NPN transistor T, and the amplified output current becomes the output current of the device M, so that the detection output of the incident light can be efficiently and large. It has characteristics that can be obtained through gain.

This is even more important since impurities are introduced into layer 2 to form a deep level to compensate for the carrier concentration, so a depletion layer is expected to be formed on the layer 2 side from the above-mentioned location. be.

FIG. 5 is a photodetection waveform diagram showing the effect of introducing an impurity that forms a deep level.

The optical detection device used had the following configuration.

Layer 1: n-type Si substrate with specific resistance 0.015 Ωcm Layer 2: n-type epitaxial growth layer with specific resistance 132 Ωcm, thickness 43 μm Layer 3: Doped with BN at 1000° C. for 30 minutes,
P-type region of Bdope driven at 0°C for 90 minutes, thickness 1 μm, main surface 265 μmφ circular layer 4: N+ type region doped with P at 950°C for 40 minutes thickness 0.5 μm, main surface 50 μmφ deep As the impurity forming the level, Au was heated at 850℃ in an O2 atmosphere for 20
It was diffused.

Furthermore, the irradiation light is pulsed light with a wavelength of 0.85 μm and a pulse width of about 0.5 ns.

The photodetection waveform shown in FIG. 3 uses the above-described configuration except that Au is not diffused as a photodetection device, and the irradiation light is also the same as that described above.

From FIG. 5, it is clear that the optical detection device of the present invention does not exhibit any skirting as shown by A in FIG.

FIG. 6 is a diagram showing the dependence of recovery time on the amount of Au doping.

The recovery time is directly related to the recombination time of minority carriers, and a forward voltage was applied to the PN junction formed by a layer 2°3 between electrodes 8 and 7, and then switched to a reverse voltage. Sometimes, this is the time from when switching to the reverse voltage until the forward current flowing due to minority carriers remaining without recombination disappears.

When measuring Figure 6, the peak current value (current value when forward voltage was applied) was obtained when a forward voltage of 0.5V was applied and the voltage was switched to -4.0V. is 1/10
It shows the time when

In Figure 6, the doping amount was not changed, but the diffusion time was kept constant (20
(min) This shows the doping temperature dependence, but since there is a relationship that the higher the doping temperature, the higher the doping amount, the doping amount dependence is shown.

Note that the values indicated by the dotted line in FIG. 6 are the values when Au is not doped.

As explained using FIGS. 5 and 6, it is clear that the apparatus of the present invention has significantly improved the conventional apparatus with respect to high-frequency optical detection.

Furthermore, in the device M of the present invention as described above, since the light shielding layer 5 is provided on the layer 2, light does not enter the internal region other than the depletion layer as described above, and therefore there is no noise. Although it is possible to obtain a detection output, if the light-shielding layer is made conductive and serves as an electrode, the carriers that have accumulated unnecessarily in layer 2 can be released to the outside through this electrode. This allows light to be detected at high speed.

Further, according to the above-described semiconductor optical detection device M according to the present invention, it is possible to extremely easily configure a configuration in which a plurality of them (these are referred to as M12M2) can be used as an imaging device in which they are arranged side by side.

That is, although a detailed explanation will be omitted, as shown in FIG. It is possible to easily obtain a configuration in which a plurality of devices M are arranged side by side by using a configuration in which the light-shielding layer 5 is commonly used for the devices M12M2..., and in this case, the device M12
Even if layer 2 for each of M2... is common,
During operation of each device, a depletion layer is generated in layer 2 at the location where each device is formed, so that adjacent devices can be electrically isolated from each other without using any other special means. It has great features such as the ability to

The above description is only an example of the present invention, and the above-mentioned "P type" may be replaced with "N type", "N type" may be replaced with "P type", and various other configurations may also be used. Variations may be made.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional optical detection device, Fig. 2 is an equivalent circuit diagram of Fig. 1, Fig. 3 is an optical pulse detection characteristic diagram of the device shown in Figs. 1 and 2, and Fig. 4 5 is a line sectional view showing an example of the semiconductor optical detection device of the present invention, FIG. 5 is a diagram of the optical pulse detection characteristics of the device of the present invention shown in FIG. 4, and FIG. 6 is a diagram showing the doping amount dependence of recovery time. The figure shown in FIG. 7 is a line sectional view showing a juxtaposed structure using a plurality of semiconductor optical detection devices according to the present invention. In the figure, M is a semiconductor optical detection device, L is light, H is a PIN photodiode, T is a phototransistor, 1, 2.3 and 4 are semiconductor layers, 5 is a light shielding layer, 6 is an electrode, 7, 8 and 9 represents a terminal, and 10 and 11 represent a PN junction, respectively.

Claims (1)

[Claims] 1 a first semiconductor layer having a first conductivity type; a second semiconductor layer having the first conductivity type formed on the first semiconductor layer; a third semiconductor layer formed from the side opposite to the first semiconductor layer and having a second conductivity type opposite to the first conductivity type; a fourth semiconductor layer having a first conductivity type formed from the side opposite to the semiconductor layer side;
a light shielding layer provided on the semiconductor layer to allow light to enter the third semiconductor layer from the side opposite to the first semiconductor layer side; first, second and third terminals led out from a fourth semiconductor layer, wherein the second semiconductor layer has a resistivity larger than that of the first and third semiconductor layers. In the semiconductor optical detection device having the above structure, an impurity is introduced into the second semiconductor layer to form a deep level to compensate for the carrier concentration, and the impurity of the layer 2 under the third semiconductor layer is introduced. The thickness is selected to be greater than or equal to the characteristic absorption length of the second semiconductor layer for the incident light, and the first, second, and third semiconductor layers form a PIN photodiode. 2
, a semiconductor optical detection device characterized in that a phototransistor is formed by a third and a fourth semiconductor layer.