JPH0779009A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To provide an optical waveguide type photodiode, whose delay in response speed of output electric signals and distortion of output signal waveforms are suppressed by maintaining uniform distribution of generated carrier density and preventing distortion of the distribution of electric field strength. CONSTITUTION:An n type InGaAsP optical waveguide layer 7, an n type InP layer 5 and an i type InGaAs optical absorbing layer 4a are interlaid in order and formed in stripe on the center of the surface of the n type InP substrate 5, and a semi-insulating In P layer 3 is formed on both sides of these layers. Since this enables to prevent optical absorption from occurring only in the vinicity of one end when light directly enters the optical absorbing layer, this can prevent the distribution of electric field strength from distorting at the optical absorbing layer, thus suppressing a delay in response speed of output electric signals and distortion in output electric signal waveforms due to distortion of the distribution of electric field strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light receiving element,
In particular, the present invention relates to a semiconductor light receiving element suitable for a waveguide type photodiode having a low distortion response characteristic.

[0002]

2. Description of the Related Art FIG. 13 shows Electronics Lett., Vol.22, P90.
FIG. 6 is a perspective view showing a waveguide type photodiode described in 6,1986. In FIG. 13, i-type InG is formed in stripes as a high-resistance intrinsic semiconductor layer in the central portion of the surface of the n-type InP substrate 5.
An aAs light absorption layer 4 is formed, and a semi-insulating InP layer 3 is formed on both sides of the layer. The p-type InP layer 2 is formed on the surface of these. The Ti / Au electrode 1 is formed on the surface of the p-type InP layer 2, and the n-type InP substrate 5 is formed.
An AuGe / Au electrode 6 is formed on the lower surface side of the.
Further, the output signal is taken out as an RF output through the capacitor.

Next, the operation will be described with reference to FIGS. 13 and 14. FIG. 14 is a sectional view taken along line AB of the waveguide type photodiode shown in FIG. As shown in FIG. 14, the Ti / Au electrode 1 is set to a negative potential, and AuGe
When a voltage (about 5 V) is applied with the / Au electrode 6 as a positive potential, the pn junction formed by the p-type InP layer 2 and the n-type InP substrate 5 is in a reverse bias state, and a high resistance intrinsic semiconductor between them is formed. A high electric field is generated in the i-type InGaAs light absorption layer 4, which is a layer. In FIG. 14, from the A-side end surface, i-type InG
The light incident on the aAs light absorption layer 4 is absorbed and extinguished while propagating to the inside of the device using the layer as a waveguide.

In the i-type InGaAs light absorption layer 4, electron-hole pairs are generated by photoexcitation by incident light. The generated electrons and holes are accelerated by the high electric field of the i-type InGaAs light absorption layer 4 to the n-type InP substrate 5 and the p-type InP layer 2 and output to the outside as a photocurrent.

FIG. 15 shows an attenuation characteristic in which the light incident from the A-side end face is exponentially attenuated as it advances toward the B-side end face. In FIG. 15, the vertical axis represents i-type InG
The light intensity P at the aAs light absorption layer 4 is shown, and the horizontal axis shows the distance x from the A-side end face. The attenuation characteristic is represented by the amount of change in the light intensity P and is represented by P = P ₀ e ^−ax . Here, a represents the absorption coefficient, and P ₀ represents the light intensity at x = 0 (A-side end face).

The number N of electron-hole pairs generated by photoexcitation is proportional to the light intensity P, and the relational expression is N = PλaΓ / h
Given in C. Here, λ represents the wavelength of light, a represents the absorption coefficient, Γ represents the confinement coefficient of light in the light absorption layer, h is the Planck's constant, and C is the speed of light. Therefore,
Since the light intensity P is higher as it is closer to the incident end face, many electron-hole pairs are generated. Hereinafter, the electrons and holes are collectively called carriers.

FIGS. 16 and 17 show the moving state of carriers generated in the i-type InGaAs light absorption layer 4. FIG.
17, the vertical axis represents the electric field intensity E, the horizontal axis corresponds to the thickness direction (y direction) of the i-type InGaAs light absorption layer 4, the center represents the i-type InGaAs light absorption layer 4, and the left side thereof is p. Type InP layer 2 and the right side is an n type InP substrate 5
Represents

Since carriers have electric charges, they shield an electric field, but when the number of carriers is small, the electric field shielding effect (space charge effect) by the carriers is small, and as shown in FIG. 16, the electric field is proportional to the distance. Strength E decreases. However, in a place where a large number of carriers are generated, such as in the vicinity of the end face on the A side, the influence of the space charge effect is large,
As shown in FIG. 17, the electric field strength distribution will be distorted. The space charge effect is expressed by the following equation.

[0009]

[Equation 1]

In the above equation, E is the electric field strength, p is the hole density, n is the electron density, and ε ₀ is the dielectric constant in vacuum.

The carrier moving speed V is proportional to the electric field strength E and is represented by V = μE. Here, μ represents the mobility of carriers. Therefore, the carrier moving speed changes due to the distortion of the electric field strength distribution, which causes the delay of the response speed of the output electric signal extracted from the electrode and the distortion of the output signal waveform.

As an example, FIGS. 18 and 19 show pulse waveforms of an input optical signal and an output electric signal when the electric field strength distribution is distorted. 18 and 19,
The vertical axis indicates the input light intensity and the output current, and the horizontal axis indicates the time change. Here, the input optical signal is given as a rectangular pulse, but it can be seen that the output electric signal from the photodiode is blunted at the falling edge.

[0013]

Since the conventional waveguide type photodiode is constructed as described above, a large amount of carriers are generated in the vicinity of the light incident end face, and an electric field inside the i-type InGaAs light absorption layer 4 is generated. There have been problems that the response speed of the output electric signal is delayed and the output signal waveform is distorted due to the distortion of the intensity distribution.

The present invention has been made in order to solve the above-mentioned problems. The carrier density is kept uniform by making the light intensity uniform in the waveguide direction, and the electric field intensity distribution is distorted. It is an object of the present invention to obtain a waveguide type photodiode in which the delay of the response speed of the output electric signal and the distortion of the output signal waveform are suppressed and prevented.

[0015]

A first aspect of a semiconductor light receiving element according to the present invention is a first semiconductor layer of a first conductivity type, a second semiconductor layer of a second conductivity type, and the first semiconductor layer. And a high-refractive-index light absorbing layer formed between the second semiconductor layer and light entering from one end face, in the semiconductor light-receiving element, the intermediate layer having a low refractive index is adjacent to the light absorbing layer. And an optical waveguide layer having a lower refractive index than the light absorption layer and a higher refractive index than the intermediate layer, and is formed in parallel with the light absorption layer via the intermediate layer. To do.

According to a second aspect of the semiconductor light receiving element of the present invention, a first conductive type first semiconductor layer, a second conductive type second semiconductor layer, and the first semiconductor layer and the second semiconductor layer are provided. In a semiconductor light receiving element having a light absorption layer formed between them, and light is incident from one end face thereof, the light absorption layer reaches the inside of the light absorption layer from the surface of the first semiconductor layer, and from the one end face side. It is characterized in that a plurality of diffusion regions of the first conductivity type are arranged in order so that the respective reaching depths become deeper.

According to a third aspect of the semiconductor light receiving element of the present invention, a first conductive type first semiconductor layer, a second conductive type second semiconductor layer, and the first semiconductor layer and the second semiconductor layer are provided. In a semiconductor light receiving element having a light absorption layer formed between them, and light is incident from one end face thereof, the light absorption layer reaches the inside of the light absorption layer from the surface of the first semiconductor layer, and from the one end face side. It is characterized in that a plurality of diffusion regions of the first conductivity type are arranged in order so that the respective impurity concentrations become higher.

According to a fourth aspect of the semiconductor light receiving element of the present invention, the first conductivity type first semiconductor layer, the second conductivity type second semiconductor layer, and the first semiconductor layer and the second semiconductor layer are included. Each of which has a first electrode and a second electrode for applying a bias voltage, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer, which is provided on each end face. In the semiconductor light receiving element on which light is incident, the first electrodes are divided and aligned so that different bias voltages that sequentially increase from the one end face side can be independently applied.

A fifth aspect of the semiconductor light receiving element according to the present invention is the first semiconductor layer of the first conductivity type, the second semiconductor layer of the second conductivity type, and the first semiconductor layer and the second semiconductor layer. In a semiconductor light receiving element having a light absorption layer formed between them and light is incident from one end face, the light absorption layer is inclined so that the thickness gradually increases from the one end face side. It is characterized by being formed by holding it.

A sixth aspect of the semiconductor light receiving element according to the present invention is a first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, the first semiconductor layer and the second semiconductor layer. A high-refractive-index light-absorbing layer formed between, and a semiconductor light-receiving element in which light is incident from one end face, adjacent to the light-absorbing layer, a low-refractive-index intermediate layer, and the intermediate An optical waveguide layer having a refractive index higher than that of the layer is sequentially formed, and a surface of the optical waveguide layer opposite to the intermediate layer has a wavy shape in which irregularities are repeated, and the depth and height of the irregularities are It is characterized in that it gradually increases from one end face side.

[0021]

According to the first aspect of the semiconductor light receiving element of the present invention, when light is incident on the optical waveguide layer formed in parallel with the light absorption layer through the intermediate layer having a low refractive index, the incident light travels. However, the light intensity in the light absorption layer becomes maximum when the light is gradually transmitted from the optical waveguide layer to the light absorption layer through the intermediate layer and travels a certain distance from the incident end face. Therefore, it is possible to prevent light absorption only in the vicinity of one end face that occurs when light is directly incident on the light absorption layer and suppress a phenomenon in which carriers are partially biased. Distortion can be prevented.

According to the second aspect of the semiconductor light receiving element of the present invention, the reaching depth of each reaches the inside of the light absorption layer from the surface of the first semiconductor layer and becomes deeper in order from one end face side. In the plurality of diffusion regions of the first conductivity type formed as follows,
The bandgap becomes narrower than the undiffused light absorption layer,
Since the absorption coefficient is large, the light can be efficiently absorbed even when the light intensity is low. Furthermore, by changing the arrival depth of the diffusion region, the proportion of the diffusion region in the light absorption layer increases in order, and the proportion of the absorbed light also increases accordingly. Therefore, the amount of carriers generated in the light absorption layer becomes uniform, so that the distortion of the electric field strength distribution can be prevented.

According to the third aspect of the semiconductor light receiving element of the present invention, the impurity concentration of each of the first semiconductor layers reaches the inside of the light absorption layer and is sequentially increased from the one end face side on which light is incident. In the plurality of first-conductivity-type diffusion regions formed so as to have a high absorption coefficient, the band gap is narrower and the absorption coefficient is larger than that of the undiffused light absorption layer, so that the efficiency is improved even when the light intensity is low. It can absorb light well. Further, as the impurity concentration is increased, the probability of light absorption between the conduction band and the acceptor is also increased in order, so that the absorption coefficient is increased and the proportion of the absorbed light is increased accordingly. Therefore, the amount of carriers generated in the light absorption layer becomes uniform, so that the distortion of the electric field strength distribution can be prevented.

According to the fourth aspect of the semiconductor light receiving element of the present invention, the first electrode is divided and formed so that a high bias voltage can be independently applied in order from one end face side. By applying a voltage such that the voltage is higher toward the electrode located farther from the one end surface on which the light enters, the absorption coefficient of the light absorption layer can be increased toward the back. Therefore, the absorption coefficient can be increased as the light intensity decreases, and the amount of carriers generated in the light absorption layer can be made uniform to prevent distortion of the electric field intensity distribution.

According to the fifth aspect of the semiconductor light receiving element of the present invention, the light absorption layer is formed with an inclination so that the thickness gradually increases from one end face side, whereby the light intensity is increased. Since the thickness of the light absorption layer is thin near one end face of high
Even if the light intensity is high, the amount of carriers generated by absorption of light is suppressed. On the other hand, the light intensity decreases as the distance from the one end surface on which light is incident increases, but since the light absorption layer becomes thicker, the amount of light absorption does not decrease sharply and the amount of carriers generated in the light absorption layer It becomes uniform and can prevent the distortion of the electric field strength distribution.

According to the sixth aspect of the semiconductor light receiving element of the present invention, when light is incident on the corrugated optical waveguide layer having irregularities, the optical waveguide layer acts as a second-order diffraction grating and the incident direction. Light is emitted in a direction perpendicular to, and light is given to the light absorption layer formed in the direction. further,
Since the depth and height of the unevenness increase stepwise from the side of the one end face, the diffraction efficiency is increased stepwise according to the depth and height of the unevenness, and light absorption even when the light intensity is low. It is possible to prevent the electric field intensity distribution from being distorted by making the amount of carriers generated in the light absorption layer uniform without abruptly reducing the amount of light applied to the layer.

[0027]

1 is a perspective view showing a first embodiment of a waveguide type photodiode according to the present invention. In FIG. 1, n
N-type I in a stripe shape at the center of the surface of the InP substrate 5.
An nGaAsP optical waveguide layer 7, an n-type InP layer 5a, and an i-type InGaAs optical absorption layer 4a are formed in this order, and a semi-insulating InP layer 3 is formed on both sides thereof. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described with reference to FIGS. FIG. 2 is a sectional view taken along line AB of the waveguide type photodiode shown in FIG. The light incident from the A-side end face is the i-type I formed above and below with the n-type InP layer 5a interposed therebetween.
The nGaAs light absorption layer 4a and the n-type InGaAsP optical waveguide layer 7 are used as waveguides and propagated to the back of the device (in the B-side end face direction).

The propagation of light will be described with reference to FIG. 3, in which the i-type InGaAs light absorption layer 4a and the n-type InGaAsP optical waveguide layer 7 are referred to as the waveguide A and the waveguide B, respectively. As shown in FIG. 3, when the two waveguides X and Y are arranged in parallel with a narrow interval (up to several μm), the light is incident from the waveguide Y (that is, the n-type InGaAsP optical waveguide layer 7). The light gradually moves to the waveguide X (that is, the i-type InGaAs light absorption layer 4a) as it travels, and travels a certain distance (several tens to several hundreds of μm) from the end face on the A side. Maximum strength. If the waveguide X is not a light absorption layer but a layer having a small refractive index like the waveguide Y, the light incident on the waveguide Y has a small refractive index (high transmittance). (The n-type InP layer 5a in this embodiment) travels while alternately traveling back and forth between the waveguides X and Y.

The composition of the n-type InGaAsP optical waveguide layer 7 is
For example, for incident light having a wavelength of 1.55 μm, In _0.76 Ga _0.24 As _0.55 P having an absorption wavelength range of 1.3 μm is used.
The composition of the n-type InGaAsP optical waveguide layer 7, such as _0.45, is configured to have a band gap that does not absorb incident light.

FIG. 4 shows the light intensity distribution in the i-type InGaAs light absorption layer 4a. In FIG. 4, the vertical axis represents the i-type I
The light intensity P at the nGaAs light absorption layer 4a is shown, and the horizontal axis is A.
The distance x from the side end face is shown. In FIG. 4, since the light is incident on the n-type InGaAsP optical waveguide layer 7 near the end face on the A side, the light intensity P at the i-type InGaAs light absorption layer 4a is small, but the incident light is gradually increased. 4a
Since the light intensity in the i-type InGaAs light absorption layer 4a increases and reaches the maximum in the central portion of the device,
The light intensity P is attenuated by being absorbed while advancing through the i-type InGaAs light absorption layer 4a.

In this embodiment, since the light absorption only near the light incident end face can be prevented and the phenomenon that the carriers are partially biased can be suppressed, the distortion of the electric field intensity distribution in the i-type InGaAs light absorption layer 4a is prevented. Therefore, it is possible to suppress the delay of the response speed of the output electric signal and the distortion of the output signal waveform.

FIG. 5 shows a second embodiment of the waveguide type photodiode according to the present invention. In the first embodiment, the waveguides are provided vertically in parallel, but the waveguides may be provided so as to be parallel in the left and right as shown in this embodiment.

In FIG. 5, a semi-insulating InP layer 3 is formed in a stripe shape in the central portion of the surface of an n-type InP substrate 5, and an i-type InGaAs light absorption layer 4b and an n-type InGaAsP optical waveguide layer 7 are formed on both left and right sides thereof. The semi-insulating InP layers 3 are formed on the outer sides of the respective layers so as to sandwich them. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described. As described with reference to FIG. 3 in the first embodiment, the light incident from the waveguide Y is the light incident from the waveguide Y (that is, the n-type InGaAsP optical waveguide layer 7), and the light gradually enters the waveguide X while proceeding.
(Ie i-type InGaAs light absorption layer 4b),
The intensity of the light in the waveguide X becomes maximum in a portion that has traveled a fixed distance (several tens to several hundreds of μm) from the A-side end face. here,
An intermediate layer formed between the waveguides (semi-insulating I in this embodiment)
The nP layer 3) has a lower refractive index than the layer forming the waveguide,
Any material having a high light transmittance may be used, such as InGaAsP.

In this embodiment, since the n-type InGaAsP optical waveguide layer 7 and the i-type InGaAs optical absorption layer 4b are formed in parallel with each other on the left and right sides, they are highly independent of each other, and the optical elements are connected by a waveguide to achieve optical When forming a circuit, the waveguides can be easily connected to each other.

FIG. 6 shows a third embodiment of the waveguide type photodiode according to the present invention. In FIG. 6, an In _1-X Ga _X As _Y P _1-Y light absorption layer 4c is formed on an n-type InP substrate 5, and a p-type InP layer 2 is formed thereon.
From the surface of the p-type InP layer 2, p-type diffusion regions 8a, 8b, and 8c whose reaching depths are increased in order are formed by using Zn as an impurity, for example. Ti is formed on the surface of the p-type InP layer 2.
The / Au electrode 1 is formed, and the AuGe / Au electrode 6 is formed on the lower surface side of the n-type InP substrate 5. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described. Since the In _1-X Ga _X As _Y P _1-Y light absorption layer 4c formed on the n-type InP substrate 5 contains P, InGa containing no P is used.
The absorption coefficient is smaller than that of the As layer. Therefore, compared with the case where the light absorption layer is made of InGaAs, light is less likely to be absorbed, and the light reaches the inside of the In _1-X Ga _X As _Y P _1-Y light absorption layer 4c. On the other hand, In _1-X Ga
The inside of the _X As _Y P _1-Y light absorption layer 4c is a p-type diffusion region 8
By providing a, 8b, and 8c, In _1-X Ga _X As _Y
The band gap is narrower and the absorption coefficient is larger than that of the undiffused region of the P _{1 -Y} light absorption layer 4c. Since the p-type diffusion regions 8a, 8b, and 8c are formed so that the reaching depth becomes deeper and the width becomes wider, In _1-X Ga _X A
s _Y P _1-Y p-type diffusion regions 8a and 8 in the light absorption layer 4c
The proportion occupied by b and 8c increases in order, and the amount of light absorbed does not decrease sharply. Therefore, In _1-X Ga _X A
The generated carrier density distribution in the s _Y P _{1 -Y} light absorption layer 4c changes gently as shown in FIG. 7 to show a substantially uniform distribution. If the generated carrier density distribution becomes uniform, it is possible to prevent the distortion of the electric field strength distribution, and it is possible to suppress the delay of the response speed of the output electric signal and the distortion of the output signal waveform.

FIG. 8 shows a fourth embodiment of the waveguide type photodiode according to the present invention. In FIG. 8, the In _1-X Ga _X As _Y P _1-Y light absorption layer 4c is formed on the n-type InP substrate 5, and the p-type InP layer 2 is formed thereon.
From the surface of the p-type InP layer 2, p-type diffusion regions 9a, 9b and 9c are formed in which the impurity concentration is gradually increased. p
The Ti / Au electrode 1 is formed on the surface of the type InP layer 2,
An AuGe / Au electrode 6 is formed on the lower surface side of the n-type InP substrate 5. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described. Since the In _1-X Ga _X As _Y P _1-Y light absorption layer 4c formed on the n-type InP substrate 5 contains P, InGa containing no P is used.
The absorption coefficient is smaller than that of the As layer. Therefore, compared with the case where the light absorption layer is made of InGaAs, light is less likely to be absorbed, and the light reaches the inside of the In _1-X Ga _X As _Y P _1-Y light absorption layer 4c. On the other hand, In _1-X Ga
The inside of the _X As _Y P _1-Y light absorption layer 4c is a p-type diffusion region 9
By providing a, 9b, and 9c, In _1-X Ga _X As _Y
The band gap is narrower and the absorption coefficient is larger than that of the undiffused region of the P _{1 -Y} light absorption layer 4c. further,
As the impurity concentration increases in order, the probability of light absorption between the conduction band and the acceptor also increases in order, so the absorption coefficient also increases, and the width of each region is increased. Type diffusion regions 9a, 9b, 9c
The amount of light absorbed at does not decrease sharply. Therefore, I
The generated carrier density distribution in the n _1-X Ga _X As _Y P _1-Y layer 4c changes gradually and shows a substantially uniform distribution, as in the third embodiment shown in FIG. Become. If the generated carrier density distribution becomes uniform, it is possible to prevent the electric field strength distribution from being distorted, and the delay in the response speed of the output electric signal,
Distortion of the output signal waveform can be suppressed.

FIG. 9 shows a fifth embodiment of the waveguide type photodiode according to the present invention. In FIG. 9, the light absorption layer 4d is formed on the n-type InP substrate 5, and the p-type In is formed thereon.
The P layer 2 is formed. 4 on the surface of the p-type InP layer 2
Divided Ti / Au electrodes 1a, 1b, 1c, 1d are formed, and AuGe / Au is formed on the lower surface side of the n-type InP substrate 5.
The electrode 6 is formed. Ti / Au electrodes 1a, 1b,
Power supplies V1, V2, V3, and V4 for independently applying a voltage are connected to 1c and 1d through protective elements (coils in this figure), and the voltage distribution is V1 <V2.
<V3 <V4.

Next, the operation will be described. When the bias voltage is increased, the absorption coefficient of the light absorption layer 4d can be increased. Therefore, Ti / A is set such that the voltage is increased as the electrode is located farther from the end surface on the A side of the light absorption layer 4d.
By independently applying a voltage to the u electrodes 1a, 1b, 1c, and 1d, the absorption coefficient of the light absorption layer 4d can be increased as it goes deeper. Here, the light absorption layer 4
d is, for example, i-type In, as described in Examples 1 to 4.
A bulk type may be formed by using GaAs, In _1-X Ga _X As _Y P _1-Y, or the like. For example, In _0.47
A quantum well structure which is formed by alternately stacking Ga _0.53 As layers and In _0.82 Ga _0.18 As _0.40 P _0.60 layers, and which can obtain a large difference in absorption coefficient by giving a slight potential difference,
Alternatively, it is preferable to form a strained quantum well structure having strain in a crystal by stacking semiconductor layers having different lattice constants.

As a result, since the bias voltage is low near the A-side end face on which light is incident, the absorption coefficient is also small, so that the amount of carriers generated by light absorption is suppressed even if the light intensity is high. On the other hand, although the light intensity is low inside the light absorption layer 4d away from the A-side end face on which light is incident, the absorption coefficient can be increased by increasing the bias voltage, so that regardless of the decrease in light intensity. A uniform carrier distribution can be achieved to prevent distortion of the electric field strength distribution, and delay of the response speed of the output electric signal and distortion of the output signal waveform can be suppressed.

FIG. 10 shows a sixth embodiment of the waveguide type photodiode according to the present invention. In FIG. 10, n-type I
The light absorption layer 4e is formed on the nP substrate 5 so that the thickness of the light absorption layer 4e increases from the end face on the A side toward the back, and the p-type InP layer 2 is formed thereon. Here, the light absorption layer 4e is, for example, the i-type InGaA described in Examples 1 to 4.
s, In _1-X Ga _X As _Y P _1-Y, or the like is formed by selective growth. Ti / A is formed on the surface of the p-type InP layer 2.
The u electrode is formed, and Au is formed on the lower surface side of the n-type InP substrate 5.
The Ge / Au electrode 6 is formed. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described. Since the light absorption layer 4e is thin in the vicinity of the A-side end face on which light with high light intensity enters, the amount of carriers generated by light absorption is suppressed even with high light intensity. On the other hand, although the light intensity is low inside the light absorption layer 4e far from the light incident end face, the amount of light absorbed is not proportional to the attenuation characteristic of the light intensity because the light absorption layer 4e becomes thicker. A uniform carrier distribution can be obtained regardless of the decrease in strength. Therefore, the distortion of the electric field strength distribution can be prevented, and the delay of the response speed of the output electric signal and the distortion of the output signal waveform can be suppressed.

FIG. 11 shows a seventh embodiment of the waveguide type photodiode according to the present invention. In FIG. 11, n-type In
In the P substrate 5, a surface opposite to the light emitting surface of the optical waveguide layer 7a is formed by crystal growth of n-type InGaAsP or the like in a wavy shape in which irregularities are repeated. With this configuration, the optical waveguide layer 7a has a function as a secondary diffraction grating. In this embodiment, the shape of the unevenness is a sine wave, and this diffraction grating is a sine wave grating type. Further, the depth of the valley and the height of the peak of the sine wave are formed so as to gradually increase from the A-side end face on which light is incident.

Here, the stepwise increase means that
The depth and height of the unevenness (in this embodiment, the depth of the valley of the sine wave and the height of the peak) are not constant over the entire area of the optical waveguide layer 7a, and the optical waveguide layer 7a is divided into a plurality of areas. However, the depth and height of the concavities and convexities in the regions adjacent to each other in the light traveling direction are formed to be larger, although they are formed to have a constant depth and height in the same region.

As an example, an enlarged view of the optical waveguide layer 7a of FIG. 11 is shown in FIG. In FIG. 12, the height and the depth of the sine wave are increased stepwise by about 10 nm at intervals of about 10 μm.

Although several wavelengths are formed in one region in FIG. 12, one region may be formed in half wavelength. Generally, the sine wave period Λ and the incident light wavelength λ in the second-order diffraction grating
The relationship with and is determined by Λ = λ / n. n is a refractive index. Therefore, the period of the sine wave and the like are determined from the wavelength λ of the incident light and the refractive index n of the optical waveguide layer 7a.

On the optical waveguide layer 7a, a light absorption layer 4f is formed between the n-type InP layer 5b and the i-type InGaAs or In.
It is formed by using _1-X Ga _X As _Y P _1-Y or the like.
A p-type InP layer 2 is formed on the surface of this layer. A Ti / Au electrode 1 is formed on the surface of the p-type InP layer 2,
An AuGe / Au electrode 6 is formed on the lower surface side of the type InP substrate 5. Other configurations are the same as those of the conventional waveguide type photodiode described with reference to FIGS. 13 and 14.

Next, the operation will be described. The light incident on the optical waveguide layer 7a having a function as a diffraction grating is emitted perpendicularly to the incident direction and given to the light absorption layer 4f. Further, since the depth and height of the sine wave are formed so as to increase stepwise from the A-side end surface on which light is incident, the diffraction efficiency also increases stepwise, and the optical intensity decreases.
Even in the back, the amount of light given to the light absorption layer 4f does not decrease sharply. Therefore, it is possible to achieve a uniform carrier distribution and prevent distortion of the electric field strength distribution regardless of the decrease in light intensity, delaying the response speed of the output electric signal, and
Distortion of the output signal waveform can be suppressed.

In this embodiment, an example in which the optical waveguide layer 7a is formed with a sine wave grating type diffraction grating structure and the uneven shape is a sine wave has been described. The same effect can be obtained with a triangular shape or a rectangular shape.

[0053]

According to the semiconductor light receiving element of the first aspect, the light intensity in the light absorption layer becomes maximum when the light has traveled a certain distance from the incident end face. Therefore, it is possible to prevent light absorption only in the vicinity of one of the end faces and to suppress the phenomenon in which the carriers are partially biased, so that the distortion of the electric field strength distribution in the light absorption layer can be prevented, and the distortion of the electric field strength distribution can be prevented. There is an effect of suppressing the delay of the response speed of the output electric signal and the distortion of the output signal waveform due to.

According to the semiconductor light receiving element of the second aspect,
In the diffusion region of the first conductivity type, the band gap is narrower and the absorption coefficient is larger than that of the undiffused light absorption layer, so that light can be efficiently absorbed even when the light intensity is low. Furthermore, since the diffusion regions are formed so that the arrival depth becomes deeper in order, the proportion of the diffusion regions in the light absorption layer becomes larger in order, and the proportion of absorbed light also increases accordingly. . Therefore, the amount of carriers generated in the light absorption layer becomes uniform and the distortion of the electric field strength distribution can be prevented, and the delay of the response speed of the output electric signal due to the distortion of the electric field strength distribution and the output signal waveform Has the effect of suppressing the distortion.

According to the semiconductor light receiving element of claim 3,
In the diffusion region of the first conductivity type, the band gap is narrower and the absorption coefficient is larger than that of the undiffused light absorption layer, so that light can be efficiently absorbed even when the light intensity is low. Furthermore, by increasing the impurity concentration, the absorption coefficient also increases, and the proportion of light absorbed increases accordingly. Therefore, the amount of carriers generated in the light absorption layer becomes uniform and the distortion of the electric field strength distribution can be prevented, and the delay of the response speed of the output electric signal due to the distortion of the electric field strength distribution and the output signal waveform Has the effect of suppressing the distortion.

According to the semiconductor light receiving element of the fourth aspect,
By increasing the voltage applied to the divided first electrode to the electrode located farther from one end face on which light is incident, the absorption coefficient in the light absorption layer is increased as it goes deeper. You can Therefore, the absorption coefficient is increased according to the decrease in light intensity, the amount of carriers generated in the light absorption layer becomes uniform, and the distortion of the electric field strength distribution can be prevented. It has the effect of suppressing the delay of the response speed of the output electric signal and the distortion of the output signal waveform.

According to the semiconductor light receiving element of the fifth aspect,
Since the thickness of the light absorption layer is formed so as to gradually increase from one end face side, even if the light intensity decreases by separating from the one end face on which light is incident, The amount of carriers generated in the light absorption layer becomes uniform and the distortion of the electric field strength distribution can be prevented without abruptly decreasing the absorption amount of the electric field, and the response of the output electric signal due to the distortion of the electric field strength distribution can be prevented. It has the effect of suppressing the delay in speed and the distortion of the output signal waveform.

According to the semiconductor light receiving element of claim 6,
When light is incident on the corrugated optical waveguide layer that repeats irregularities, the optical waveguide layer acts as a second-order diffraction grating, and the light is emitted in a direction perpendicular to the incident direction. Light is provided to the absorption layer. Furthermore, since the depth and height of the unevenness gradually increase from the side of the one end face, the diffraction efficiency is increased stepwise according to the depth and height of the unevenness, and the light intensity becomes low. The amount of light generated in the light absorption layer does not decrease sharply, the amount of carriers generated in the light absorption layer becomes uniform, and the distortion of the electric field strength distribution can be prevented. It has the effect of suppressing the delay of the response speed of the electric signal and the distortion of the output signal waveform.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of a semiconductor light receiving element according to the present invention.

FIG. 2 is a sectional view showing a first embodiment of a semiconductor light receiving element according to the present invention.

FIG. 3 is a conceptual diagram for explaining light propagation of the first embodiment of the semiconductor light receiving element according to the present invention.

FIG. 4 is a diagram showing a light intensity distribution of a first embodiment of a semiconductor light receiving element according to the present invention.

FIG. 5 is a perspective view showing a second embodiment of the semiconductor light receiving element according to the present invention.

FIG. 6 is a sectional view showing a third embodiment of the semiconductor light receiving element according to the present invention.

FIG. 7 is a diagram showing a generated carrier density distribution of a third embodiment of the semiconductor light receiving element according to the present invention.

FIG. 8 is a sectional view showing a fourth embodiment of the semiconductor light receiving element according to the present invention.

FIG. 9 is a sectional view showing a fifth embodiment of a semiconductor light receiving element according to the present invention.

FIG. 10 is a sectional view showing a sixth embodiment of a semiconductor light receiving element according to the present invention.

FIG. 11 is a sectional view showing a seventh embodiment of a semiconductor light receiving element according to the present invention.

FIG. 12 is a partially enlarged view of the seventh embodiment of the semiconductor light receiving element according to the present invention.

FIG. 13 is a perspective view showing a conventional semiconductor light receiving element.

FIG. 14 is a sectional view showing a conventional semiconductor light receiving element.

FIG. 15 is a diagram showing a light intensity distribution of a conventional semiconductor light receiving element.

FIG. 16 is a diagram showing a carrier moving state of a conventional semiconductor light receiving element.

FIG. 17 is a diagram showing a carrier moving state of a conventional semiconductor light receiving element.

FIG. 18 is a waveform diagram showing an input optical signal and an output electrical signal of a conventional semiconductor light receiving element.

FIG. 19 is a waveform diagram showing an output electric signal of a conventional semiconductor light receiving element.

[Explanation of symbols]

1a~1d negative electrode 4a~4f light absorbing layer 5a n-type InP layer (intermediate layer) 7, 7a optical guide layer 8a to 8c p-type diffusion region 9a p-type diffusion region ^(p -) 9b p-type diffusion region (p) 9c p-type diffusion region (p ⁺ )

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshitaka Aoyagi 4-1-1 Mizuhara, Itami City, Hyogo Prefecture Mitsubishi Electric Corp. Optical & Microwave Device Development Laboratory

Claims (6)

[Claims] 1. A first-conductivity-type first semiconductor layer, a second-conductivity-type second semiconductor layer, and a high-refractive-index light-absorbing layer formed between the first and second semiconductor layers. In the semiconductor light receiving element having light incident from one end face, the intermediate layer having a low refractive index is formed adjacent to the light absorbing layer, and the refractive index is lower than that of the light absorbing layer, A semiconductor light receiving element, wherein an optical waveguide layer having a refractive index higher than that of the layer is formed in parallel with the light absorption layer via the intermediate layer. 2. A first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer. In the semiconductor light receiving element in which light is incident from one end face, it reaches the inside of the light absorption layer from the surface of the first semiconductor layer, and the arrival depth of each becomes deeper in order from the one end face side. A semiconductor light-receiving element comprising a plurality of first-conductivity-type diffusion regions formed in alignment. 3. A first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer. In a semiconductor light receiving element in which light is incident from one end surface, the semiconductor light receiving element is arranged so that the impurity concentration increases in order from the surface of the first semiconductor layer to the inside of the light absorption layer and from the one end surface side. A semiconductor light-receiving element comprising a plurality of formed diffusion regions of the first conductivity type. 4. A first conductive type first semiconductor layer, a second conductive type second semiconductor layer, and a bias voltage provided to each of the first semiconductor layer and the second semiconductor layer, for applying a bias voltage. First electrode and second
In a semiconductor light receiving element that has an electrode and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer, and in which light is incident from one end face, the height increases in order from the one end face side. 1. A semiconductor light receiving device, characterized in that the first electrodes are divided and aligned so that different bias voltages can be applied independently. 5. A first conductivity type first semiconductor layer, a second conductivity type second semiconductor layer, and a light absorption layer formed between the first semiconductor layer and the second semiconductor layer. In the semiconductor light receiving element in which light is incident from one end face, the light absorption layer is formed with an inclination so that the thickness gradually increases from the one end face side. element. 6. A first-conductivity-type first semiconductor layer, a second-conductivity-type second semiconductor layer, and a high-refractive-index light absorption layer formed between the first-semiconductor layer and the second-semiconductor layer. In the semiconductor light receiving element having a layer and light is incident from one end face thereof, an intermediate layer having a low refractive index and an optical waveguide layer having a refractive index higher than that of the intermediate layer are adjacent to the light absorbing layer. The surface of the optical waveguide layer opposite to the intermediate layer, which is formed in order, has a wavy shape in which irregularities are repeated, and the depth and height of the irregularities gradually increase from the one end face side. A semiconductor light receiving element characterized by.