JP4058921B2 - Semiconductor photo detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light-receiving element that converts an optical signal into an electric signal, and more particularly to an avalanche multiplication type semiconductor light-receiving element that is excellent in high-speed response and has low dark current and high sensitivity characteristics.
[0002]
[Prior art]
In optical communication / measurement technology, high speed and large capacity are indispensable. Therefore, a semiconductor light receiving element having excellent high speed response and low noise and high sensitivity characteristics is indispensable. A superlattice avalanche photodiode (superlattice APD) in which a superlattice structure is applied to an avalanche multiplication layer has been developed as a high-speed and high-sensitivity semiconductor light-receiving element having a wavelength band of 1 to 1.6 μm.
[0003]
Chin et al., Electron. Lett., 16 (12), P.467-469, 1980, in the superlattice structure, which is the basic principle of superlattice APD. Only proposed a structure in which electrons are selectively ionized by acquiring potential energy (conduction band discontinuity) ΔEc. Regarding the structure that artificially increases the ionization rate ratio α / β by using the conduction band discontinuity of the superlattice for collisional ionization of electrons, F. Capasso et al. In the GaAs / GaAlAs superlattice actually An increase in the ionization rate ratio α / β was confirmed [Appl. Phys. Letters, 40 (1), P.38-40, 1982]. Furthermore, a superlattice APD in which a superlattice multiplication layer is formed using an InAlAs / InGaAsP superlattice having a light receiving sensitivity at a wavelength of 1.3 to 1.6 μm or an InAlAs / InAlGaAs superlattice used for long-distance optical communication. Has been developed to achieve higher speed and higher sensitivity than conventional semiconductor photodetectors. [For example, Kagawa et al .: Journal of Quantum Electronics (J.Quantum.Electronics), 28 (6), P 1419-1423, 1992, Watanabe et al .: Photonics Technol. Letters, 5 (6), P.675-677, 1993, Watanabe et al .: Photonics Technol. Lett.), 8 (6), P.827-829, 1996].
[0004]
8 [1] and [2] are element structure diagrams of the InAlAs / InAlGaAs superlattice APD reported by Watanabe et al. 8 [1] is a mesa structure element, and FIG. 8 [2] is a planar structure element. In FIG. 8 [1] [2], the same number is attached | subjected to the component of the same function.
[0005]
This superlattice APD is formed on an InP substrate 807, an InP buffer layer 801, an InAlAs / InAlGaAs superlattice avalanche multiplication layer 802, p⁺Type InP electric field relaxation layer 803, p⁻Type InGaAs light absorption layer 804 and p⁺A type InGaAs light absorption layer 805 is laminated.
[0006]
The operation principle will be described. First, only electrons among the optical carriers generated in the light absorption layers 804 and 805 travel to the electric field relaxation layer 803 by a drift electric field and are injected into the avalanche multiplication layer 802. Subsequently, in the avalanche multiplication layer 802, since a high electric field is applied, the injected electrons collide with the lattice to cause ionization, thereby causing avalanche multiplication. Here, the InAlAs / InAlGaAs superlattice structure constituting the avalanche multiplication layer 802 has a large conduction band discontinuity, which increases the ionization rate of electrons, thereby increasing the ionization rate ratio α / β and the resulting low noise. It is planned.
[0007]
8 [1] and [2], an InP cap layer 806, a p-side electrode 808, an n-side electrode 809, a surface passivation film 810, an antireflection film 811, and the like are attached. Further, in FIG. 8 [2], the high resistance region 812, p⁺A region 813 and the like are attached.
[0008]
FIG. 9 shows a basic configuration of a conventional APD having a light absorption layer 90 having a two-layer structure with different carrier concentrations.
[0009]
The APD shown in FIG. 9 is formed by laminating a buffer layer 91, an avalanche multiplication layer 92, an electric field relaxation layer 93, a light absorption layer 90, a cap layer 96, and the like. The light absorption layer 90 includes a depleted light absorption layer 94 and a light absorption layer 95 having a certain concentration of carrier concentration that is not depleted. The carrier concentration of the light absorption layer 94 is 1 × 10.¹⁶cm^-3The carrier concentration of the light absorption layer 95 is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3It is. The main function of the light absorbing layer 95 which is a non-depleted layer is to terminate depletion of the light absorbing layer 94. Here, the light absorption layer 94 responsible for light absorption is desired to be thin in order to improve the carrier traveling time and increase the speed. However, since the reduction in the thickness of the light absorption layer 94 is accompanied by a decrease in quantum efficiency, there is a trade-off relationship between higher speed and higher quantum efficiency.
[0010]
[Problems to be solved by the invention]
The main factors governing the high-speed response in a conventional semiconductor light-receiving element having an avalanche multiplication layer are the CR circuit constant limitation due to the capacitance and resistance of the element itself and the multiplication of optical carriers in the avalanche multiplication layer. For example, the time required for the multiplication (multiplication time) and the carrier travel time generated by the optical carrier traveling in the depleted light absorption layer. Here, the limitation on the CR circuit constant can be dealt with by improving the capacitance by reducing the pn junction area, reducing the contact resistance by optimizing the electrodes, and the like. The multiplication time is largely due to the ionization rate ratio α / β, which is a physical property constant inherent to the material. Regarding the carrier transit time in the light absorption layer, in principle, the carrier transit time is shortened by reducing the thickness of the light absorption layer in order to increase the speed. However, the quantum efficiency depends on the thickness of the light absorption layer and decreases as the film becomes thinner. Therefore, there is a trade-off relationship between the carrier travel time and the quantum efficiency, and it is difficult to achieve both.
[0011]
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to achieve both high-speed response and high quantum efficiency in a semiconductor light-receiving element having an avalanche multiplication layer.
[0012]
[Means for Solving the Problems]
  A semiconductor light-receiving element according to the present invention includes a light absorption layer that absorbs light to generate electron-hole pairs, and an avalanche multiplication layer that causes avalanche multiplication by electrons generated in the light absorption layer. . The light absorption layer includes a depletion layer that is depleted during operation, and a depletion termination layer that terminates depletion of the depletion layer. Further, the carrier concentration of the depletion termination layer is higher than the carrier concentration of the depletion layer and is distributed so as to generate a pseudo electric field that accelerates electrons in the depletion termination layer toward the depletion layer..
[0013]
  AndThe carrier concentration of the depleted layer is 1 × 10¹⁶cm^-3The carrier concentration of the depletion termination layer is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3Is.Where 1 × 10¹⁶cm^-3Is a lower limit concentration for preventing depletion (that is, an upper limit concentration for depletion) and is 1 × 10¹⁹cm^-3Is an upper limit concentration for preventing “high carrier concentration → non-light emission center increase → quantum efficiency decrease”. The “carrier concentration” here is, of course, a value measured at room temperature with no light irradiation, no voltage applied.In addition, the thickness of the depleted termination layer is 1μ m Is less than.
[0014]
  The depletion termination layer consists of two or more layers with different carrier concentrations.,Carrier concentrationIn logarithmic notationIt consists of a single layer that changes linearly, or it consists of two or more layers with different linear changes.,Or carrier concentrationIn logarithmic notationExponentially changing,It is good. Furthermore, the pseudo electric field may be generated by using the electron affinity of the depletion termination layer instead of the carrier concentration of the depletion termination layer..
[0015]
For example, the present invention is a semiconductor light receiving element in which at least a light absorption layer, an electric field relaxation layer, and an avalanche multiplication layer are stacked on a semi-insulating semiconductor substrate or a high concentration semiconductor substrate. The light absorption layer has a low carrier concentration (1 × 10¹⁶cm^-3Below) depleted layer and high carrier concentration (1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3)) And a depleted termination layer that is not depleted.
[0016]
In addition to this, the carrier concentration of the depletion termination layer changes sequentially in the layer thickness direction. Or the electron affinity of the depleted termination layer is expressed as eχ₁, Eχ the electron affinity of the depleted layer₂Eχ₁> Eχ₂And the electron affinity of the depletion termination layer changes sequentially in the layer thickness direction.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an energy band diagram showing the structure of the first embodiment of the semiconductor light-receiving element according to the present invention. Hereinafter, description will be given based on this drawing.
[0018]
The semiconductor light receiving element of this embodiment includes a light absorption layer 10 that absorbs light to generate electron e-hole h pairs, an avalanche multiplication layer 12 that causes avalanche multiplication by electrons generated in the light absorption layer 10, and And a buffer layer 11, an avalanche multiplication layer 12, an electric field relaxation layer 13, a light absorption layer 10 and a cap layer 16 are laminated. The light absorption layer 10 includes a depletion layer 14 that is depleted during operation, and a depletion termination layer 15 that terminates depletion of the depletion layer 14. Further, the carrier concentration of the depletion termination layer 15 is higher than the carrier concentration of the depletion layer 14 and is distributed so as to generate a pseudo electric field that accelerates electrons in the depletion termination layer 15 toward the depletion layer 14. is doing.
[0019]
The light absorption layer 10 is composed of two layers: a depleted layer 14 with a low carrier concentration and a depleted termination layer 15 with a high carrier concentration that is not depleted. Then, the carrier concentration of the depletion termination layer 15 changes stepwise or continuously. With such an element structure, in the depletion termination layer 15, the Fermi level is inclined due to the difference in carrier concentration, and a pseudo electric field corresponding to the ratio of carrier concentration and the film thickness is generated. Electrons e, which are photocarriers generated in the depletion termination layer 15, are accelerated by this pseudo electric field and drift to the end of the depletion layer 14, thereby contributing as a photocurrent.
[0020]
For this reason, in the semiconductor light receiving element of this embodiment, the depletion termination layer 15 is actually optically light as compared with the conventional structure in which the light absorption layer 95 shown in FIG. 9 functions only as a termination of the depletion layer (light absorption layer 94). By functioning as a layer that absorbs light, the effective light absorption layer thickness increases. Here, since the actual thickness of the light absorption layer is not increased, the response speed is maintained, and high-speed response and high quantum efficiency characteristics can be realized. In addition, since the hole h having a low drift velocity responds to the dielectric relaxation time in a short time and is collected by the p-type electrode, only high-speed electrons e having a small effective mass and a high thermal diffusion rate are involved in the photocurrent as photocarriers. . Moreover, the electric field relaxation layer 13 has the effect | action which reduces a dark current component.
[0021]
2 is a graph showing the carrier concentration of the light absorption layer in the semiconductor light receiving element of FIG. 1, FIG. 2 [1] is the first example, FIG. 2 [2] is the second example, and FIG. 2 [3] is the third. It is an example. Hereinafter, a description will be given based on FIG. 1 and FIG.
[0022]
The depletion layer 14 and the depletion termination layer 15 in FIG.⁻Layer and p⁺Indicated as layer. p⁻The carrier concentration of the layer is 1 × 10¹⁶cm^-3And p⁺The carrier concentration of the layer is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3It is.
[0023]
In the first example of FIG.⁺The layer is composed of two layers p1 and p2 having different carrier concentrations. That is, the two layers p1, p2 to p having different carrier concentrations⁺By forming the layer, a pseudo electric field is generated, and thereby the above-described characteristics of high-speed response and high quantum efficiency can be realized.
[0024]
  In the second example of FIG. 2 [2], p⁺The carrier concentration of the layerIn logarithmic notationIt consists of a single layer that varies linearly. At this time, it is good also as what consists of two or more layers from which the linear variation | change_quantity differs. Also in this configuration, a pseudo electric field is generated due to the Fermi level gradient, so that the same effect as the first example is realized.
[0025]
  In the third example of FIG. 2 [3], p⁺The carrier concentration of the layerIn logarithmic notationIt changes exponentially. Also in this configuration, a pseudo electric field is generated due to the Fermi level gradient, so that the same effect as the first example is realized. P⁺P in the layer⁻Since a high pseudo electric field is applied to the opposite end of the layer, p⁻Since acceleration for electrons (photocarriers) far from the layer becomes larger, characteristics of higher response and higher quantum efficiency are realized.
[0026]
FIG. 3 is a graph showing calculation results of the quantum efficiency increase rate Δη and the travel time increase amount Δt with respect to the layer thickness X of the depletion termination layer 15 in FIG. Hereinafter, a description will be given based on FIG. 1 and FIG.
[0027]
Here, the thickness of the depletion layer 14 is 1.0 μm, the absorption coefficient α is 10,000 / cm, and the electron velocity obtained by the pseudo electric field is 3 × 10.⁷cm / sec. Accordingly, when the layer thickness X of the depletion termination layer 15 is 0.5 μm, for example, the quantum efficiency increase rate Δη is 15% and the travel time increase Δt is 1.67 psec. In this case, the time for the electrons to travel through the depletion layer 14 and the depletion termination layer 15 is 5 psec, and shows a response that does not deteriorate sufficiently for an optical signal of 10 Gbps or more.
[0028]
However, when the layer thickness X of the depletion termination layer 15 is about 1 μm, the carrier concentration is 1 × 10 5.¹⁶cm^-3~ 1x10¹⁹cm^-3However, since the pseudo electric field is 2 kV / cm or less, a sufficient electric field is not applied to the depletion termination layer 15. For this reason, the electron velocity is deteriorated, and the traveling time in the depletion termination layer 15 is rapidly deteriorated.
[0029]
Where 1 × 10¹⁶cm^-3Is the lower limit of carrier concentration for preventing depletion termination layer 15 from being depleted (that is, the upper limit for depletion layer 14 being depleted). 1 × 10¹⁹cm^-3Is the upper limit carrier concentration for preventing the depletion termination layer 15 from becoming “high carrier concentration → non-emission center increase → quantum efficiency decrease”.
[0030]
FIG. 4 is an energy band diagram showing the structure of the second embodiment of the semiconductor light receiving element according to the present invention. Hereinafter, description will be given based on this drawing.
[0031]
The semiconductor light receiving element of this embodiment includes a light absorption layer 50 that absorbs light to generate electron e-hole h pairs, an avalanche multiplication layer 52 that causes avalanche multiplication by electrons generated in the light absorption layer 50, and The buffer layer 51, the avalanche multiplication layer 52, the electric field relaxation layer 53, the light absorption layer 50, and the cap layer 56 are laminated. The light absorption layer 50 includes a depletion layer 54 that is depleted during operation, and a depletion termination layer 55 that terminates depletion of the depletion layer 54. Further, the electron affinity of the depletion termination layer 55 is smaller than the electron affinity of the depletion layer 54 and is distributed so as to generate a pseudo electric field that accelerates electrons in the depletion termination layer 55 toward the depletion layer 14. is doing.
[0032]
The light absorption layer 50 is composed of two layers: a depleted layer 54 that is depleted with a low carrier concentration, and a depleted termination layer 55 that is not depleted with a high carrier concentration. In addition, the electron affinity of the depletion termination layer 55 changes stepwise or continuously. With such an element structure, a pseudo electric field is generated in the depletion termination layer 55 due to the conduction band discontinuity ΔEc, and thus a high-speed response and high quantum efficiency characteristics are realized as in the first embodiment.
[0033]
5 and 6 are energy band diagrams showing the structure of the light absorption layer in the semiconductor light-receiving element of FIG. 4. FIG. 5 [1] is the first example, FIG. 5 [2] is the second example, and FIG. ] Is a third example, and FIG. 6 [2] is a fourth example. Hereinafter, a description will be given with reference to FIGS.
[0034]
The depletion layer 54 and the depletion termination layer 55 in FIG.⁻Light absorbing layer and p⁺This is expressed as a light absorption layer. p⁻The carrier concentration of the light absorption layer is 1 × 10¹⁶cm^-3And p⁺The carrier concentration of the light absorption layer is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3It is.
[0035]
In the first example and the second example shown in FIGS. 5 [1] and [2], two layers having different electron affinities are used.⁺A light absorption layer is formed. The same effect as described above is realized by the pseudo electric field generated from the conduction band discontinuity (difference in electron affinity) ΔEc of these two layers.
[0036]
In the third example shown in FIG. 6 [1], p is changed from a single layer whose electron affinity changes linearly.⁺A light absorption layer is formed. This p⁺The light absorption layer can be formed in a mixed crystal semiconductor such as InAlGaAs, InGaAsP, and AlGaAsSb by sequentially changing the composition ratio and changing the band gap linearly. Also in this structure, the same effect as described above is realized by the generation of the pseudo electric field.
[0037]
In the fourth example shown in FIG. 6 [2], p is changed from a single layer whose electron affinity changes exponentially.⁺A light absorption layer is formed. This p⁺The light absorption layer can be formed in a mixed crystal semiconductor such as InAlGaAs, InGaAsP, and AlGaAsSb by sequentially changing the composition ratio and changing the band gap exponentially. Also in this structure, the same effect as described above is realized by the generation of the pseudo electric field.
[0038]
As described above, the semiconductor light-receiving elements of the first and second embodiments can realize an operation that achieves both high-speed response and high quantum efficiency, and improve the performance of an optical communication device and an optical measurement device equipped with the operation. It is valid.
[0039]
【Example】
Hereinafter, examples that further embody the above embodiment will be described in detail with reference to the drawings.
[0040]
FIG. 7 [1] is a cross-sectional view showing an example of the first embodiment. Hereinafter, description will be given based on this drawing.
[0041]
The semiconductor light receiving element of this example is a mesa type having a depleted termination layer in which the carrier concentration changes sequentially in the layer thickness direction. The depletion layer and the depletion termination layer in the first embodiment are embodied as the light absorption layers 404 and 405, respectively.
[0042]
A manufacturing method will be described. First, on an InP substrate 407, an InP buffer layer 401, an InAlAs / InAlGaAs superlattice avalanche multiplication layer 402 (layer thickness 0.3 μm), an InP electric field relaxation layer 403, p^-Type InGaAs light absorption layer 404 (layer thickness: 1.0 μm), p⁺A type InGaAs light absorption layer 405, an InP cap layer 406, and an InGaAs contact layer (not shown) are sequentially stacked by a gas source MBE (Molecular Beam Epitaxy). Subsequently, a mesa is formed by wet etching, a p-side electrode 408 and an n-side electrode 409 are formed, and a surface passivation film 410 is formed. Subsequently, after mirror polishing, an antireflection film 411 is formed on the back surface of the InP substrate 407, thereby completing a semiconductor light receiving element.
[0043]
p⁻The type InGaAs light absorption layer 404 is 1 × 10 so as to be depleted.¹⁶cm^-3Set the following low carrier concentration. P which is a characteristic part of the present embodiment⁺The type InGaAs light absorption layer 405 has a structure that generates a pseudo electric field by the gradient of the carrier concentration. This carrier concentration is p⁻The concentration is set so as to increase in the layer thickness direction from the side in contact with the type InGaAs light absorption layer 404.
[0044]
For example, the carrier concentration shown in FIG. 2 [1] (p1 = 1 × 10¹⁷cm^-3, P2 = 1 × 10¹⁹cm^-3P) with a total film thickness W = 0.5 μm.⁺In the type InGaAs light absorption layer 405, a pseudo electric field of 2.36 kV / cm is generated. FIG. 2 [1] shows a configuration with two InGaAs layers, but it is formed of two or more semiconductor layers and has a carrier concentration of 1 × 10 6.¹⁶cm^-3~ 1x10¹⁹cm^-3P tilting in the range⁺A similar pseudo electric field is also generated in the type semiconductor light absorption layer 405.
[0045]
  Also, the carrier concentration p shown in FIG.⁺A similar pseudo electric field is also generated in the type InGaAs light absorption layer 405. This carrier concentration is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3In the range p⁻From the side in contact with the InGaAs light absorption layer 404 to the thickness directionIn logarithmic notationIt changes so as to increase the concentration linearly. As shown in Fig. 2 [2]In logarithmic notationP formed of two or more semiconductor layers having a linear carrier concentration change⁺A similar pseudo electric field is also generated in the type InGaAs light absorption layer 405.
[0046]
Further, the carrier concentration p shown in FIG.⁺A similar pseudo electric field is also generated in the type InGaAs light absorption layer 405. This carrier concentration is 1 × 10¹⁶cm^-3~ 1x10¹⁹cm^-3In the range p⁻From the side in contact with the type InGaAs light absorption layer 404, the thickness changes in a nonlinear manner in the layer thickness direction.
[0047]
P having the carrier concentration gradient of this embodiment⁺In the semiconductor light receiving element to which the type InGaAs light absorption layer 405 is applied, a quantum efficiency improvement of 15% or more was confirmed without impairing the high-speed characteristics as compared with the conventional semiconductor light receiving element having the same carrier concentration profile.
[0048]
FIG. 7 [2] is a cross-sectional view showing an example of the second embodiment. Hereinafter, description will be given based on this drawing.
[0049]
The semiconductor light receiving element of this example is a mesa type having a depleted termination layer in which electron affinity changes sequentially in the layer thickness direction. The depletion layer and the depletion termination layer in the second embodiment are embodied as the light absorption layers 704 and 705, respectively.
[0050]
A manufacturing method will be described. First, on an InP substrate 707, an InP buffer layer 701, an InAlAs / InAlGaAs superlattice avalanche multiplication layer 702 (layer thickness: 0.3 μm), an InP electric field relaxation layer 703, p^-Type InGaAs light absorption layer 704 (layer thickness: 1.0 μm), p⁺A type InGaAs light absorption layer 705, an InP cap layer 706, and an InGaAs contact layer (not shown) are sequentially stacked by a gas source MBE (Molecular Beam Epitaxy). Subsequently, a mesa is formed by wet etching, a p-side electrode 708 and an n-side electrode 709 are formed, and a surface passivation film 710 is formed. Subsequently, after mirror polishing, an antireflection film 711 is formed on the back surface of the InP substrate 707, thereby completing a semiconductor light receiving element.
[0051]
p⁻The type InGaAs light absorption layer 704 is 1 × 10 so as to be depleted.¹⁶cm^-3Set the following low carrier concentration. P which is a characteristic part of the present embodiment⁺The type InGaAs light absorption layer 705 has a structure that generates a pseudo electric field due to a difference in electron affinity. This electron affinity is p⁻The thickness is set so as to increase in the layer thickness direction from the side in contact with the type InGaAs light absorption layer 704.
[0052]
For example, p shown in FIG.⁺1 layer and p⁺Consider a light absorption layer 705 having a total film thickness of 0.5 μm composed of two layers. In this case, p⁺1 layer is p⁺Type In_0.53Ga_0.47As layer (bandgap energy Eg₁= 0.75 eV), p⁺2 layers are p⁺Type In_0.53Al_0.06Ga_0.41As layer (bandgap energy Eg₂= 0.83 eV), the conduction band discontinuity ΔEc is 57 meV, which generates a pseudo electric field of 1.1 kV / cm. In FIG. 5 [1], p⁺Type InGaAs layer and p⁺The light absorption layer 705 having two layers with the type InAlGaAs layer is shown.⁺Similarly, a pseudo electric field is generated in the type semiconductor light absorption layer.
[0053]
Similarly, a pseudo electric field is generated in the light absorption layer 705 having the electron affinity shown in FIG. This linearly changing electron affinity is, for example, In_0.53(Al_xGa_0.47-x) It is obtained by continuously changing the composition ratio of As and linearly changing the band gap energy in the layer thickness direction. At this time, by continuously changing the composition ratio x from x = 0 to x = 0.06, the bandgap energy becomes Eg₁= 0.75eV to Eg₂= Continuously changes to 0.83 eV. In addition, p formed from two or more semiconductor layers having different amounts of linear change in band gap energy.⁺Similarly, a pseudo electric field is generated in the type semiconductor light absorption layer.
[0054]
Furthermore, a pseudo electric field is generated in the same manner in the light absorption layer 705 having the electron affinity shown in FIG. This electron affinity is obtained by exponentially changing the band gap energy in the layer thickness direction.
[0055]
In each of the above embodiments, a mesa-type semiconductor light-receiving element is shown, but the same applies to the case of a planar-type semiconductor light-receiving element. In each of the above embodiments, an element structure using an InAlAs / InAlGaAs superlattice as an avalanche multiplication layer and InP as an electric field relaxation layer has been described. In the case of an element structure using a superlattice layer made of or a single bulk layer, an element structure using InAl (Ga) As, InGaAs (P) as an electric field relaxation layer, or an element structure composed of a combination thereof Are all the same. Furthermore, in the embodiment of FIG. 7 [2], the element structure using the InAlGaAs layer as the light absorption layer 705 has been described. However, the same applies to the element structure using InGaAsP or AlGaAsSb.
[0056]
【The invention's effect】
According to the semiconductor light receiving element of the present invention, the light absorption layer is composed of a depletion termination layer and a depletion layer, and the carrier concentration or electron affinity of the depletion termination layer is changed stepwise or continuously, thereby depletion. A pseudo electric field that accelerates electrons in the termination layer to the depletion layer can be generated. Therefore, since the electron transit time can be shortened, high-speed response can be achieved, and high quantum efficiency can be achieved by increasing the effective thickness of the light absorption layer. Therefore, high-speed response and high quantum efficiency characteristics can be realized. Further, by mounting the semiconductor light receiving element according to the present invention on an optical communication device or an optical measurement device, a high-speed and high-sensitivity optical receiver can be realized.
[Brief description of the drawings]
FIG. 1 is an energy band diagram showing a structure of a first embodiment of a semiconductor light receiving element according to the present invention.
2 is a graph showing the carrier concentration of the light absorption layer in the semiconductor light receiving element of FIG. 1, FIG. 2 [1] is a first example, FIG. 2 [2] is a second example, and FIG. 2 [3] is a first example. Three examples.
3 is a graph showing calculation results of a quantum efficiency increase rate Δη and a travel time increase amount Δt with respect to the layer thickness X of the depletion termination layer in FIG. 1;
FIG. 4 is an energy band diagram showing a structure of a second embodiment of a semiconductor light receiving element according to the present invention.
5 is an energy band diagram showing a structure of a light absorption layer in the semiconductor light receiving element of FIG. 4, in which FIG. 5 [1] is a first example and FIG. 5 [2] is a second example.
6 is an energy band diagram showing a structure of a light absorption layer in the semiconductor light receiving element of FIG. 4, in which FIG. 6 [1] is a third example, and FIG. 6 [2] is a fourth example.
FIG. 7 [1] is a cross-sectional view showing an example of the first embodiment, and FIG. 7 [2] is a cross-sectional view showing an example of the second embodiment.
8 is a cross-sectional view showing a conventional semiconductor light-receiving element, in which FIG. 8 [1] is a mesa structure element, and FIG. 8 [2] is a planar structure element.
FIG. 9 is an energy band diagram showing a structure of a conventional semiconductor light receiving element.
[Explanation of symbols]
10, 50 Light absorption layer
11, 51 Buffer layer
12,52 Avalanche multiplication layer
13,53 Electric field relaxation layer
14,54 Depleted layer
15,55 Depleted termination layer
16, 56 Cap layer
401,701 InP buffer layer
402,702 InAlAs / InAlGaAs superlattice avalanche multiplication layer
403,703 InP electric field relaxation layer
404,704 p⁻Type light absorption layer (depletion layer)
405,705 p⁺Type light absorption layer (depletion termination layer)
406,706 InP cap layer
407,707 InP substrate
408, 708 p-side electrode
409, 709 n-side electrode
410,710 Surface passivation film
411,711 Antireflection film

Claims (8)

A light absorbing layer;
An avalanche multiplication layer,
The light absorbing layer is
A depletion layer having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or less,
A depletion termination layer having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ ,
The carrier concentration of the depletion termination layer changes continuously or stepwise toward the depletion layer, generating a pseudo electric field in which electrons of the depletion termination layer accelerate toward the depletion layer,
The thickness of the depletion termination layer, a semiconductor light-receiving element and less than 1 [mu] m. The semiconductor light-receiving element according to claim 1, wherein the depletion termination layer includes two or more layers having different carrier concentrations. 2. The semiconductor light receiving element according to claim 1, wherein the depletion termination layer is formed of a single layer whose carrier concentration linearly changes in a logarithmic notation , or two or more layers having different linear change amounts. . The semiconductor light receiving element according to claim 1, wherein the carrier concentration of the depletion termination layer varies exponentially in logarithmic notation . A light absorbing layer;
An avalanche multiplication layer,
The light absorbing layer is
A depletion layer having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or less,
A depletion termination layer having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ ,
The electron affinity of the depletion termination layer is smaller than the electron affinity of the depletion layer and changes continuously or stepwise toward the depletion layer, and the electrons of the depletion termination layer are depleted. Generate a pseudo electric field that accelerates toward the
The thickness of the depletion termination layer, a semiconductor light-receiving element and less than 1 [mu] m. The semiconductor light receiving element according to claim 5, wherein the depletion termination layer includes two or more layers having different electron affinity. 6. The semiconductor light receiving element according to claim 5, wherein the depletion termination layer is composed of a single layer whose electron affinity changes linearly, or is composed of two or more layers having different linear change amounts. The air-electron affinity of depleted termination layer is characterized by changes exponentially, the semiconductor light receiving device according to claim 5.

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