JP4127815B2 - Avalanche photodiode - Google Patents

Description

  The present invention relates to an avalanche photodiode, and is suitable for a long wavelength band, for example.

  An avalanche photodiode (hereinafter abbreviated as APD) is widely used as a highly sensitive light receiving element in optical measurement and optical communication because the element itself has an amplification function. In general, the 1.55 μm band InGaAs / InP-APD used for large-capacity long-distance optical communication separates the avalanche multiplication region from the light absorption layer, and reduces the dark current. A SACM (Separated Absorption, Charge and Multiplication) structure in which a charge layer for electric field control is introduced between the absorption layer / avalanche multiplication region is used. However, in the case of an electron injection type APD, it is necessary to use a low-concentration p-type InGaAs semiconductor in order to deplete the light absorption layer when a reverse bias is applied.

In recent years, attention has been focused on an electron injection type APD in which a low concentration p-type InGaAs light absorption layer having a SACM structure is formed at a high concentration (see FIG. 4A).
As shown in FIG. 4A, the electron injection type APD includes a high-concentration n-type semiconductor electrode layer 403 on a semi-insulating InP substrate 401 via a semi-insulating buffer layer 402 made of an undoped semiconductor. An avalanche multiplication layer 404 made of an undoped semiconductor, an electric field control layer 405, an electric field relaxation layer 406 made of an undoped semiconductor, a band gap inclined layer 407, a light absorption layer 408, a high-concentration p-type semiconductor diffusion barrier layer 409, Then, a high-concentration p-type semiconductor electrode layer 410 is sequentially laminated to form a mesa structure, and an n-electrode 411 and a p-electrode 412 are formed on the n-type electrode layer 403 and the p-type electrode layer 410, respectively. It is.

With the above structure, since the light absorption layer 408 is neutralized even when a reverse bias is applied, an electric field required for depletion of the light absorption layer 408 is unnecessary, and an electron injection type APD that can be driven at a relatively low voltage is provided. It is attracting attention because it can be realized.
FIG. 4B shows the band structure of the electron injection APD having the above structure. As shown in FIG. 4B, the band gap gradient layer 407, the electric field relaxation layer 406, the electric field control layer 405, and the avalanche multiplication layer 404 on the lower layer side of the light absorption layer 408 are depleted, so that the avalanche operation is performed. In addition to being in a possible state, the light absorption layer 408 itself is substantially neutralized.
However, in the electron injection type APD, it is difficult to form an n-type diffusion electrode region in the avalanche multiplication layer 404, and it is arranged on the semi-insulating InP substrate 401 side to reduce the resistance of the n-electrode layer 403. In general, a mesa structure as shown in FIG.

Japanese Patent No. 3141847

  Since the electron injection type APD adopts a mesa structure, in a reliability test (for example, a bias condition of an atmospheric temperature of 200 ° C. and a reverse current of 100 μA), a dark current due to surface degradation (see arrow c in FIG. 4A) ) Increase. This is because in the mesa structure, crystal defects increase in the vicinity of the element surface due to heating and energization in the reliability test, and the dark current flowing through the surface gradually increases due to the accompanying increase in the surface state density. is there. The dark current flowing on the surface increases at an accelerated rate because the progress of surface degradation depends on the dark current value of the surface. For this reason, how to suppress the increase in dark current flowing on the surface is a problem in realizing the electron injection APD, and is a major factor that affects the stability and life of the electron injection APD.

  The present invention has been made in view of the above problems, and an object thereof is to provide a stable and long-life electron injection avalanche photodiode.

An avalanche photodiode according to claim 1 of the present invention for solving the above-described problems is provided.
Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
The film thickness on the outer peripheral side of the electric field relaxation layer is formed thicker than the film thickness of the central portion of the electric field relaxation layer.

An avalanche photodiode according to claim 2 of the present invention for solving the above-described problem is provided.
Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
High-concentration n-type semiconductor electrode layer, avalanche multiplication layer made of undoped semiconductor, p-type electric field control layer, first electric field relaxation layer made of undoped semiconductor, and second electric field made of undoped semiconductor having a hollow portion A relaxation layer, a band gap inclined layer, a p-type semiconductor light absorption layer, a high-concentration p-type semiconductor diffusion barrier layer, and a high-concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure.
The hollow portion of the second electric field relaxation layer is formed inside the outer periphery of the p-type semiconductor light absorption layer.

An avalanche photodiode according to claim 3 of the present invention for solving the above-described problem is provided.
In the avalanche photodiode,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
The width of the outer periphery of the electric field relaxation layer or the second electric field relaxation layer is made larger than the width of the outer periphery of the p-type semiconductor light absorption layer.
That is, a thick portion of the electric field relaxation layer or a ring-shaped second electric field relaxation layer is inserted immediately below the peripheral portion of the mesa structure portion on the p-type semiconductor light absorption layer and the band gap inclined layer side, and the ring shape This portion is disposed with a width that traverses from the inside to the outside with respect to the position of the outer periphery of the mesa structure portion on the p-type semiconductor light absorption layer and band gap inclined layer side. An upper band gap gradient layer is formed in the thin portion of the central portion of the electric field relaxation layer or the hollow portion of the second electric field relaxation layer.

An avalanche photodiode according to claim 4 of the present invention for solving the above-described problem is provided.
Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
The film thickness on the outer peripheral side of the p-type electric field control layer is formed thicker than the film thickness of the central portion of the p-type electric field control layer.

An avalanche photodiode according to claim 5 of the present invention for solving the above-described problem is provided.
Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
High-concentration n-type semiconductor electrode layer, avalanche multiplication layer made of undoped semiconductor, first p-type electric field control layer, second p-type electric field control layer having a hollow portion, and electric field relaxation layer made of undoped semiconductor And a mesa structure by sequentially stacking a band gap inclined layer, a p-type semiconductor light absorption layer, a high-concentration p-type semiconductor diffusion barrier layer, and a high-concentration p-type semiconductor electrode layer,
The hollow portion of the second p-type electric field control layer is formed inside the outer periphery of the p-type semiconductor light absorption layer.

An avalanche photodiode according to claim 6 of the present invention for solving the above-described problem is provided.
In the avalanche photodiode,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
The outer width of the p-type electric field control layer or the second p-type electric field control layer is made larger than the outer width of the p-type semiconductor light absorption layer.
That is, a thick portion of the p-type electric field control layer or a ring-shaped second p-type electric field control layer is inserted immediately below the peripheral edge of the p-type semiconductor light absorption layer and the mesa structure portion on the band gap inclined layer side. The ring-shaped portion is arranged with a width that traverses from the inside to the outside with respect to the position of the outer periphery of the mesa structure portion on the p-type semiconductor light absorption layer and the band gap inclined layer side. An upper electric field relaxation layer is formed in the thin portion at the center of the p-type electric field control layer or the hollow portion of the second p-type electric field control layer.

An avalanche photodiode according to claim 7 of the present invention for solving the above-described problem is provided.
Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
In the p-type electric field control layer, a p-type electric field control region having a higher concentration than the p-type electric field control layer is formed in a hollow shape along the peripheral edge of the p-type semiconductor light absorption layer,
The position inside the high-concentration p-type electric field control region is arranged inside the outer periphery of the p-type semiconductor light absorption layer.

An avalanche photodiode according to claim 8 of the present invention for solving the above-described problem is provided.
In the avalanche photodiode,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
The width of the outer periphery of the p-type electric field control layer is made larger than the width of the outer periphery of the p-type semiconductor light absorption layer, and the position outside the high-concentration p-type electric field control region is positioned at the p-type semiconductor light absorption layer. It has arrange | positioned outside the outer periphery of.
That is, the ring-shaped high-concentration p-type electric field control region is arranged with a width that traverses from the inside to the outside with respect to the position of the outer periphery of the mesa structure portion on the p-type semiconductor light absorption layer and the band gap inclined layer side. Is done.

  According to the present invention, in the electron injection type APD, since the electric field strength between the light absorption layer and the electric field control layer at the periphery of the mesa structure is relaxed, or the neutralized region is formed at the periphery of the mesa structure, the mesa structure The dark current flowing on the surface of the peripheral portion and the dark current inside the peripheral portion of the mesa structure can be reduced. As a result, the surface deterioration due to the dark current is suppressed, and a long-life electron injection type APD with stable device characteristics is obtained. Can do.

  The present invention relates to an electron injection type avalanche photodiode (APD) having a mesa structure, using a technique such as crystal regrowth or ion implantation, immediately below the periphery of a mesa structure including a light absorption layer and a band gap layer. By providing a ring-shaped second electric field relaxation layer (undoped layer) or second electric field control layer (P-type layer) at the periphery of the mesa structure, or by increasing the layer thickness, or the mesa structure By increasing the doping concentration of the electric field control layer in the peripheral part, the electric field strength in the peripheral part of the mesa structure including the light absorption layer is relaxed, and darkness of the peripheral part of the mesa structure or the peripheral part of the mesa structure is reduced. It reduces the current and reduces the surface degradation.

  Hereinafter, some embodiments of the APD according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example of an embodiment of an APD according to the present invention.
FIG. 1 (a) is a schematic diagram thereof, and FIG. 1 (b) is a band structure diagram along line E1-E2 of FIG. 1 (a).
As shown in FIG. 1A, the APD of this example includes a high-concentration n-type semiconductor electrode layer 103 on a semi-insulating InP substrate 101 via a semi-insulating buffer layer 102 made of an undoped semiconductor, An avalanche multiplication layer 104 made of an undoped semiconductor, a p-type electric field control layer 105, a first electric field relaxation layer 106 made of an undoped semiconductor, an etch stop layer 107, and a second electric field made of an undoped semiconductor having a hollow portion. The relaxation layer 108, the band gap inclined layer 109, the p-type semiconductor light absorption layer 110, the high-concentration p-type semiconductor diffusion barrier layer 111, and the high-concentration p-type semiconductor electrode layer 112 are sequentially laminated to be semi-insulating. A stepwise mesa structure with a large outer peripheral width of the layer on the InP substrate 101 side is formed, and an n electrode 113 and a p electrode 114 are formed on the n type electrode layer 103 and the p type electrode layer 112, respectively. is there.

  The hollow portion of the second electric field relaxation layer 108 is formed inside the outer periphery of the band gap inclined layer 109 and the p-type semiconductor light absorption layer 110, and the width of the outer periphery of the second electric field relaxation layer 108 is The band gap gradient layer 109 and the p-type semiconductor light absorption layer 110 are formed to be larger than the outer peripheral width. That is, the second electric field relaxation layer 108 has a ring shape, and the position inside the ring-shaped second electric field relaxation layer 108 is the outer periphery on the mesa structure side including the p-type semiconductor light absorption layer 110. The position outside the ring-shaped second electric field relaxation layer 108 is located outside the position of the outer periphery on the mesa structure side including the p-type semiconductor light absorption layer 110.

The APD having the above structure is produced by the following method, for example.
First, each layer from the semi-insulating buffer layer 102 to the second electric field relaxation layer 108 is epitaxially grown sequentially on the semi-insulating InP substrate 101, and then the central portion of the second electric field relaxation layer 108 is formed as an etch stop layer. It removes to 107 by etching, and makes it a ring shape which has a hollow part in the center part. Next, the band gap inclined layer 109, the p-type semiconductor light absorption layer 110, the high-concentration p-type semiconductor diffusion barrier layer 111, and the high-concentration p-type semiconductor electrode layer 112 are epitaxially regrown. After the regrowth, each layer including the light absorption layer 109, the electric field relaxation layer 108, and the avalanche multiplication layer 104 is etched to produce a stepped mesa structure as shown in FIG. The n-electrode 113 and the p-electrode 114 are formed at an appropriate time between processes or at the end of the process.

  In the mesa structure APD, in consideration of further suppressing the dark current and the electric field intensity on the element surface, the mesa structure is formed in a stepped mesa structure, and the distance (path) between the n electrode 113 and the p electrode 114 is increased. They are placed as far away as possible. Note that this embodiment can be applied even when the mesa structure is not stepped. For example, in the case of a mesa structure having a vertical side wall surface, the position outside the second electric field relaxation layer 108 is mesa. It may be up to the position of the side wall surface of the structure.

In the case of a structure that does not use the etch stop layer 107, the second electric field relaxation layer 108 is also eliminated. Instead, the first electric field relaxation layer 106 is formed to a thickness of about twice, and then the first electric field relaxation layer 106 is formed. Only the central portion of the electric field relaxation layer 106 is etched to a thickness of about half, and then the band gap inclined layer 109, the p-type semiconductor light absorption layer 110, and the high-concentration p-type semiconductor diffusion barrier layer 111 are epitaxially regrown. A mesa-structured APD may be used, and an equivalent to the mesa-structured APD shown in FIG.
That is, in the APD having the mesa structure, the film thickness on the lower layer side of the light absorption layer 110 and on the outer peripheral side of the electric field relaxation layer 106 that is the peripheral portion of the mesa structure is smaller than the film thickness of the central portion of the electric field relaxation layer 106. Thus, the structure is formed about twice as thick.

  In the central part of the mesa structure, the operating state of the APD of this example is the avalanche multiplication layer 104, the electric field control layer 105, the first electric field relaxation layer 106, the etch stop layer 107, which are on the lower layer side of the light absorption layer 110, The band gap gradient layer 109 is depleted and is in a state where avalanche operation is possible, and the light absorption layer 110 at this time is almost neutral, so that the APD can be driven at a low voltage. That is, the central portion of the mesa structure (for example, the portion of the S1-S2 line in FIG. 1A) has a band structure equivalent to the band structure shown in FIG.

Here, for comparison, the band structure of the peripheral portion of the mesa structure of the APD of this embodiment is shown in FIG. This corresponds to the portion of line E1-E2 in FIG.
In FIG. 1B, the potential difference Vb in the height direction indicates the difference between the Fermi level on the p-type light absorption layer 110 side and the Fermi level of the n-type electrode layer 103. Each layer is illustrated on a scale correlating with its thickness along line E1-E2 in FIG.

  As shown in FIG. 1B, the first electric field relaxation layer is located on the lower side of the light absorption layer 110 at the periphery of the mesa structure and between the light absorption layer 110 and the electric field control layer 105, which is the periphery of the mesa structure. Since the second electric field relaxation layer 108 is inserted in addition to 106, the electric field relaxation region A (see FIG. 1A) is formed at the peripheral edge of the mesa structure, and the peripheral edge of the mesa structure with respect to the potential difference Vb. The electric field strength of the portion becomes smaller than the central portion of the mesa structure by the thickness of the inserted second electric field relaxation layer 108.

  The decrease in the electric field intensity at the peripheral edge of the mesa structure due to the insertion of the second semiconductor electric field relaxation layer 108 decreases the electric field intensity at the surface in the vicinity of the mesa structure including the light absorption layer 110 and at the terrace region immediately adjacent to the mesa structure. The dark current flowing on the surface in the vicinity is reduced, and the generation rate of surface crystal defects in the vicinity of the mesa structure is reduced due to the decrease in the dark current flowing on the surface. As a result, the deterioration due to the surface dark current is alleviated and the reliability can be improved. In addition, due to the decrease in the electric field strength at the peripheral edge of the mesa structure due to the insertion of the second electric field relaxation layer 108, the dark current flowing inside the peripheral edge of the mesa structure is also reduced, which also alleviates the deterioration of the crystal and improves the reliability. Will contribute. The relaxation of the electric field at the periphery of the mesa structure increases as the layer thickness of the second electric field relaxation layer 108 increases.

  As described above, according to the APD of the present embodiment, the main factor of deterioration in the reliability test is due to the relaxation of the electric field strength between the light absorption layer and the electric field control layer at the periphery of the mesa structure including the light absorption layer. Since the dark current on the surface flowing in the vicinity of a peripheral portion of a certain mesa structure can be reduced, the reliability can be improved.

FIG. 2 is a diagram showing another example of the embodiment of the APD according to the present invention.
FIG. 2A is a schematic view thereof, and FIG. 2B is a band structure diagram taken along line E1-E2 of FIG.
As shown in FIG. 2A, the APD of this example includes a high-concentration n-type semiconductor electrode layer 203 on a semi-insulating InP substrate 201 via a semi-insulating buffer layer 202 made of an undoped semiconductor. An avalanche multiplication layer 204 made of an undoped semiconductor, a first p-type electric field control layer 205, an etch stop layer 206, a second p-type electric field control layer 207 having a hollow portion, and an electric field relaxation layer made of an undoped semiconductor 208, a band gap inclined layer 209, a p-type semiconductor light absorption layer 210, a high-concentration p-type semiconductor diffusion barrier layer 211, and a high-concentration p-type semiconductor electrode layer 212 are sequentially laminated to form a semi-insulating InP substrate. In this structure, a stepwise mesa structure having a large outer peripheral width of the 201 side layer is formed, and an n electrode 213 and a p electrode 214 are formed on the n type electrode layer 203 and the p type electrode layer 212, respectively. The difference from the first embodiment (see FIG. 1) is that the second electric field relaxation layer 108 is replaced with the second electric field control layer 207.

  The hollow portion of the second p-type electric field control layer 207 is formed inside the outer periphery of the band gap gradient layer 209 and the p-type semiconductor light absorption layer 210. The outer peripheral width is formed larger than the outer peripheral width of the band gap inclined layer 209 and the p-type semiconductor light absorbing layer 210. In other words, the second p-type electric field control layer 207 has a ring shape, and a position inside the ring-shaped second p-type electric field control layer 207 is a mesa including the p-type semiconductor light absorption layer 210. It is inside the outer peripheral position on the structure side, and the outer position of the ring-shaped second p-type electric field control layer 207 is outer than the outer peripheral position on the mesa structure side including the p-type semiconductor light absorption layer 210. Placed in.

The APD having the above structure is produced by the same method as in Example 1, for example.
Specifically, the layers from the semi-insulating buffer layer 202 to the second electric field control layer 207 are sequentially epitaxially grown on the semi-insulating InP substrate 201, and then the central portion of the second electric field control layer 207 is formed. The etch stop layer 208 is removed by etching to form a ring shape having a hollow portion at the center. Next, the band gap inclined layer 209, the p-type semiconductor light absorption layer 210, and the high-concentration p-type semiconductor diffusion barrier layer 211 are epitaxially regrown, and the mesa structure and the electrode after the epitaxial regrowth are produced in the same manner as in the first embodiment. It can produce by performing to.

  The APD having the mesa structure is also formed in a stepped mesa structure in consideration of further suppressing the dark current and electric field intensity on the element surface so that the distance between the n electrode 213 and the p electrode 214 is as far as possible. Is arranged. Even when the mesa structure is not stepped, this embodiment can be applied. For example, in the case of a mesa structure having a vertical side wall surface, the position outside the second p-type electric field control layer 207 is Further, it may be up to the position of the side wall surface of the mesa structure.

In the case where the etch stop layer 206 is not used, the second electric field control layer 207 is also eliminated, and instead, the first electric field control layer 205 is about twice as thick as in the first embodiment. After that, only the central portion is etched to a thickness of about half, and then the electric field relaxation layer 208, the band gap inclined layer 209, the p-type semiconductor light absorption layer 210, and the high-concentration p-type semiconductor diffusion barrier layer 211 are epitaxially formed. A regrown mesa APD may be used, and an APD having the mesa structure shown in FIG. 2A can be produced.
That is, in the APD having the mesa structure, the film thickness on the lower side of the light absorption layer 210 and on the outer peripheral side of the electric field control layer 205 that is the peripheral part of the mesa structure is smaller than the film thickness of the central part of the electric field control layer 205. Thus, the structure is formed about twice as thick.

  The operating state of the APD of this embodiment is the same as that of the first embodiment. In the central portion of the mesa structure, the avalanche multiplication layer 204, the first electric field control layer 205, the etch stop layer, which are on the lower layer side of the light absorption layer 210. 206, the electric field relaxation layer 208, and the band gap gradient layer 209 are depleted, and an avalanche operation is possible (see FIG. 4B).

  On the other hand, in the peripheral portion of the mesa structure, as is apparent from the band structure of the peripheral portion of the mesa structure of the APD of this embodiment shown in FIG. 2B, in addition to the first electric field control layer 205, the second electric field control is performed. Since the layer 207 is present and the substantial thickness of the electric field control layer is increased, the neutralization region B (see FIG. 2A) extends from the light absorption layer 110 to the second electric field control at the periphery of the mesa structure. It is expanded to the vicinity of the layer 207. For this reason, at the peripheral edge of the mesa structure, it is difficult for electrons to be extracted from the light absorption layer 110, and even if the electric field strength between the electric field control layers 205 and 207 and the n-electrode layer 203 increases, an avalanche state does not occur.

  Since the neutralization region B of the mesa structure peripheral portion reduces the electric field strength of the mesa structure peripheral portion of the electric field relaxation layer 208, the dark current flowing on the surface of the mesa structure peripheral portion also decreases. Further, since the light absorption layer 210 is substantially neutral and the electric field strength between the light absorption layer 210 and the electric field control layers 205 and 207 is relaxed, the dark current flowing inside the peripheral portion of the mesa structure can also be reduced. These reductions in dark current alleviate the deterioration of the element surface caused by dark current, as in Example 1, and contribute to improving the reliability of APD.

FIG. 3 is a diagram showing still another example of the embodiment of the APD according to the present invention.
FIG. 3A is a schematic diagram thereof, and FIG. 3B is a band structure diagram taken along line E1-E2 of FIG.
As shown in FIG. 3A, the APD according to the present invention includes a high-concentration n-type semiconductor electrode layer 303 and an undoped semiconductor layer on a semi-insulating InP substrate 301 via a semi-insulating buffer layer 302 made of an undoped semiconductor. An avalanche multiplication layer 304 made of a semiconductor, a p-type electric field control layer 305 having a ring-shaped high-concentration p-type electric field control region 306, an electric field relaxation layer 307 made of an undoped semiconductor, a band gap inclined layer 308, Type semiconductor light absorption layer 309, high-concentration p-type semiconductor diffusion barrier layer 310, and high-concentration p-type semiconductor electrode layer 311 are sequentially stacked, and the step width of the outer periphery of the layer on the semi-insulating InP substrate 301 side is large. A mesa structure is formed, and an n-electrode 312 and a p-electrode 313 are formed on the n-type electrode layer 303 and the p-type electrode layer 311, respectively.

  In the APD of the present embodiment, the width of the outer periphery of the electric field control layer 305 is made larger than the width of the outer periphery of the band gap inclined layer 308 and the p-type semiconductor light absorption layer 309, and the position inside the p-type electric field control region 306 is The gap gradient layer 308 and the p-type semiconductor light absorption layer 309 are arranged inside the outer periphery, and the position outside the p-type electric field control region 306 is outside the band gap gradient layer 308 and the p-type semiconductor light absorption layer 309 outer periphery. Arranged. That is, the high-concentration p-type electric field control region 306 in the electric field control layer 305 is formed in a ring-shaped hollow shape along the peripheral edge of the band gap layer 308 on the lower layer side. The electric field control region 306 is doped with a higher concentration of p-type than the electric field control layer 305.

  As a method for manufacturing the APD having the above-described structure, for example, each layer is sequentially epitaxially grown from the substrate side from the semi-insulating buffer layer 302 to the electric field control layer 305 on the semi-insulating InP substrate 301, and thereafter, in the electric field control layer 305 Zn is selectively thermally diffused at the periphery of the mesa structure to form a high-concentration electric field control region 306, followed by an electric field control layer 307, a band gap inclined layer 308, a p-type semiconductor light absorption layer 309, a high concentration The p-type semiconductor diffusion barrier layer 310 is produced by epitaxial regrowth.

  Further, in the APD having the mesa structure, the n-electrode 312 and the p-electrode 313 are arranged such that the distance between the n-electrode 312 and the p-electrode 313 is as far as possible in consideration of further suppressing the dark current and electric field intensity on the element surface.

  In the second embodiment, the second electric field control layer 207 is provided on the periphery of the mesa structure, and the thickness of the electric field control layer is substantially increased. However, in this embodiment, instead of the second electric field control layer 207, In addition, the neutralization region B is formed in the peripheral portion of the mesa structure by providing a higher concentration electric field control region 306 in the peripheral portion of the mesa structure.

  Therefore, the operating state of the APD of the present embodiment does not reach the avalanche state due to the neutralization region B even if the mesa structure central portion reaches the avalanche state as in the second embodiment. As a result, as in the second embodiment, it is possible to improve the dark current at the peripheral edge of the mesa structure and the reliability associated with the dark current. For reference, the band structure of the E1-E2 line in FIG. 3A is shown in FIG. As is clear from this, the neutralized region B extends from the light absorption layer 309 to the electric field control layer 305.

As described in the first, second, and third embodiments, in the present invention, as a method for reducing the current flowing inside the peripheral portion of the mesa structure including the light absorption layer and the dark current flowing on the surface of the peripheral portion of the mesa structure, The following structures are shown respectively.
1. The electric field strength between the light absorption layer and the electric field control layer at the mesa structure periphery is increased by inserting a new electric field relaxation layer only at the periphery of the mesa structure or by increasing the thickness of the electric field relaxation layer only at the periphery of the mesa structure. (Embodiment 1) in which an electric field relaxation region is formed.
2. A new electric field control layer is inserted only at the peripheral edge of the mesa structure to increase the layer thickness of the substantial electric field control layer, or the thickness of the electric field control layer is increased only at the peripheral edge of the mesa structure. A structure (Example 2) in which a neutralized region is widened at the peripheral edge of the structure.
3. Example 3 in which a high-concentration electric field control layer is provided only at the periphery of the mesa structure to widen the neutralization region at the periphery of the mesa structure

  The present invention is not limited to the case where each of the first, second, and third embodiments is used alone, but by combining these embodiments, the electric field between the light absorption layer and the electric field control layer can be further relaxed, The control layer may be more easily neutralized. For example, in Example 2, it is possible to build a high-concentration p-type electric field control region by making the doping concentration of the second p-type electric field control layer 207 higher than that of the first p-type electric field control layer 205. is there. In this case, due to the increase in the layer thickness and the p-type doping concentration, the neutralized region can be formed more easily than in the second and third embodiments, and the dark current at the periphery of the mesa structure can be further reduced.

An example of embodiment of APD which concerns on this invention is shown, (a) is the schematic of the structure, (b) is a band block diagram of the E1-E2 line (mesa peripheral part) of (a). . The other example of embodiment of APD which concerns on this invention is shown, (a) is the schematic of the structure, (b) is a band block diagram of the E1-E2 line (mesa peripheral part) of (a). It is. The further another example of embodiment of APD which concerns on this invention is shown, (a) is the schematic of the structure, (b) is the band of E1-E2 line (mesa peripheral part) of (a). It is a block diagram. (A) is the schematic which shows the structure of the conventional APD, (b) is a band block diagram of the S1-S2 line (mesa center part) of (a).

Explanation of symbols

101 semi-insulating InP substrate, 102 buffer layer made of undoped semiconductor, 103 n electrode layer, avalanche multiplication layer made of 104 undoped semiconductor, 105 electric field control layer, first electric field relaxation layer made of 106 undoped semiconductor, 107 etch stop Layer, 108 second electric field relaxation layer made of undoped semi-base, 109 band gap relaxation layer, 110 light absorption layer, 111 diffusion barrier layer, 112 p electrode layer, 113 n-type electrode, 114 p-type electrode
201 semi-insulating InP substrate, 202 buffer layer made of undoped semiconductor, 203 n electrode layer, 204 avalanche multiplication layer made of undoped semiconductor, 205 first electric field control layer, 206 etch stop layer, 207 second electric field control layer , 208 Electric field relaxation layer made of undoped semiconductor, 209 band gap relaxation layer, 210 light absorption layer, 211 diffusion barrier layer, 212 p electrode layer, 213 n-type electrode, 214 p-type electrode
301 Semi-insulating InP substrate, 302 buffer layer made of undoped semiconductor, 303 n electrode layer, 304 avalanche multiplication layer made of undoped semiconductor, 305 electric field control layer, 306 high concentration electric field control layer, electric field relaxation made of 307 undoped semiconductor Layer, 308 band gap relaxation layer, 309 light absorption layer, 310 diffusion barrier layer, 311 p electrode layer, 312 n-type electrode, 313 p-type electrode
401 semi-insulating InP substrate, 402 undoped semiconductor buffer layer, 403 n electrode layer, 404 undoped semiconductor avalanche multiplication layer, 405 electric field control layer, 406 undoped semiconductor electric field relaxation layer, 407 band gap relaxation layer, 408 light absorption layer, 409 diffusion barrier layer, 410 p electrode layer, 411 n-type electrode, 412 p-type electrode

Claims (8)

Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
The avalanche photodiode is characterized in that the film thickness on the outer peripheral side of the electric field relaxation layer is thicker than the film thickness of the central portion of the electric field relaxation layer. Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
High-concentration n-type semiconductor electrode layer, avalanche multiplication layer made of undoped semiconductor, p-type electric field control layer, first electric field relaxation layer made of undoped semiconductor, and second electric field made of undoped semiconductor having a hollow portion A relaxation layer, a band gap inclined layer, a p-type semiconductor light absorption layer, a high-concentration p-type semiconductor diffusion barrier layer, and a high-concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure.
The avalanche photodiode, wherein the hollow portion of the second electric field relaxation layer is formed inside the outer periphery of the p-type semiconductor light absorption layer. The avalanche photodiode according to claim 1 or 2,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
An avalanche photodiode, wherein the outer peripheral width of the electric field relaxation layer or the second electric field relaxation layer is larger than the outer peripheral width of the p-type semiconductor light absorption layer. Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
The avalanche photodiode is characterized in that the film thickness on the outer peripheral side of the p-type electric field control layer is thicker than the film thickness of the central part of the p-type electric field control layer. Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
High-concentration n-type semiconductor electrode layer, avalanche multiplication layer made of undoped semiconductor, first p-type electric field control layer, second p-type electric field control layer having a hollow portion, and electric field relaxation layer made of undoped semiconductor And a mesa structure by sequentially stacking a band gap inclined layer, a p-type semiconductor light absorption layer, a high-concentration p-type semiconductor diffusion barrier layer, and a high-concentration p-type semiconductor electrode layer,
The avalanche photodiode, wherein the hollow portion of the second p-type electric field control layer is formed inside the outer periphery of the p-type semiconductor light absorption layer. The avalanche photodiode according to claim 4 or 5,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
An avalanche photodiode, wherein the outer peripheral width of the p-type electric field control layer or the second p-type electric field control layer is larger than the outer peripheral width of the p-type semiconductor light absorption layer. Through a buffer layer made of an undoped semiconductor on a semi-insulating substrate,
A high-concentration n-type semiconductor electrode layer, an avalanche multiplication layer made of an undoped semiconductor, a p-type electric field control layer, an electric field relaxation layer made of an undoped semiconductor, a band gap inclined layer, a p-type semiconductor light absorption layer, A concentration p-type semiconductor diffusion barrier layer and a high concentration p-type semiconductor electrode layer are sequentially stacked to form a mesa structure,
In the p-type electric field control layer, a p-type electric field control region having a higher concentration than the p-type electric field control layer is formed in a hollow shape along the peripheral edge of the p-type semiconductor light absorption layer,
An avalanche photodiode characterized in that a position inside the high-concentration p-type electric field control region is arranged inside the outer periphery of the p-type semiconductor light absorption layer. The avalanche photodiode according to claim 7,
The mesa structure is stepped so that the width of the outer periphery of the layer on the semi-insulating substrate side is increased,
The width of the outer periphery of the p-type electric field control layer is made larger than the width of the outer periphery of the p-type semiconductor light absorption layer, and the position outside the high-concentration p-type electric field control region is positioned on the p-type semiconductor light absorption layer. An avalanche photodiode characterized in that it is arranged outside the outer periphery.

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