JP4223774B2 - Semiconductor photo detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor light receiving element, and more particularly to a semiconductor light receiving element for optical communication in a 1 μm band.
[0002]
[Prior art]
  In optical communication systems, optical signals with wavelengths of 1.3 μm, 1.55 μm, etc. are used, and the light receiving element selectively receives only 1.3 μm light, and selectively selects only 1.55 μm light. It is required to receive light.
[0003]
  In order to selectively receive short wavelength (eg, 1.3 μm) light without receiving long wavelength (eg, 1.55 μm) light, the band gap wavelength (λg) of the light receiving layer is set to long wavelength light and short wavelength light. This can be easily realized by setting the interval between (for example, λg = 1.4 μm).
[0004]
  It is relatively difficult to selectively receive only long-wavelength (for example, 1.55 μm) light without receiving short-wavelength (for example, 1.3 μm) light. And those disclosed in Patent Document 2.
[0005]
  In the light receiving elements of Patent Documents 1 and 2 described above, an optical filter layer and a light receiving layer are sequentially formed in the light incident direction. In the optical filter layer, a band gap is larger than that of the light receiving layer (for example, an InGaAs layer). The wavelength is shortened (for example, in the InGaAsP layer).
[0006]
  When the InGaAs light receiving layer and the InGaAsP optical filter layer are combined, 1.3 μm light (primary light) is absorbed by the optical filter layer to generate carriers. When no voltage is applied to the optical filter layer, carriers remain, recombine light emission, and emit light (secondary light) having a wavelength substantially equal to the band gap wavelength of the InGaAsP optical filter layer. Since the secondary light is absorbed by the InGaAs light receiving layer, it behaves as if 1.3 μm light is received by the InGaAs light receiving layer. Therefore, the light selection ratio of 1.55 μm decreases.
[0007]
  As the above countermeasures, in both Patent Documents 1 and 2, taking advantage of the characteristic that the secondary light is emitted in all directions, the distance between the optical filter layer and the light receiving layer is increased, and a light receiving region (PD: Photo Diode) is obtained. The solid angle of the secondary light incident on is reduced, and the selectivity of 1.55 μm light is improved.
[Patent Document 1]
  JP 2000-252511 A
[Patent Document 2]
  JP 2000-036615 A
[0008]
[Problems to be solved by the invention]
  In the above-mentioned Patent Document 1, since two elements are bonded together, it becomes impossible to receive light if the bonding accuracy is poor, and since two elements are required, the manufacturing cost is doubled, and the mounting cost is also higher than that of a normal light receiving element. There were problems such as becoming higher.
[0009]
  Further, in Patent Document 1, when a voltage is applied to the InGaAsP optical filter layer to forcibly exclude carriers in order to prevent light emission recombination (generation of secondary light), in an ordinary light receiving element, the electrodes are p, n However, there is a problem that it is necessary to provide three or more electrodes, which places a heavy burden on the module design.
[0010]
  In the above-mentioned Patent Document 2, it is difficult to epi-grow on the back surface of an epitaxially grown (epi-grown) wafer (epi-wafer), and the yield of non-defective products of the light-receiving element is extremely reduced. Although the device thickness is about 150 μm by polishing, epi-growth on the back surface makes back-surface polishing difficult and dicing is difficult, and epi-growth after polishing the back surface to reduce device thickness When trying to do so, there is a problem that the diffusion of p + -InP (selective diffusion region) proceeds and the device characteristics deteriorate due to the high temperature during epi growth.
[0011]
[Means for Solving the Problems]
  The semiconductor light-receiving element according to claim 1 is an n-type semiconductor light-receiving element that receives only the second incident light among the first incident light having the first wavelength and the second incident light having the second wavelength longer than the first wavelength. Alternatively, a p-type first conductivity type semiconductor substrate, a first conductivity type buffer layer bonded to one end of the semiconductor substrate, and a first conductivity bonded to the opposite side of the buffer layer from the semiconductor substrate. Type optical filter layer, a barrier layer of the first conductivity type bonded to the opposite side of the buffer layer of the optical filter layer, and a second layer of the barrier layer bonded to the opposite side of the optical filter layer. A first conductive type light receiving layer for receiving incident light, a first conductive type cap layer and a p-type or n-type second conductive type contact layer bonded to the opposite side of the light receiving layer to the barrier layer A positive electrode joined to the contact layer of the second conductivity type, and the half And a negative electrode bonded to the other end of the body substrateThe optical filter layer includes a first semiconductor layer of a first conductivity type having a band gap wavelength having an intermediate length between the first incident light and the second incident light, and a band gap wavelength longer than that of the first semiconductor layer. And a first conductivity type second semiconductor layer bonded to the first semiconductor layer and a first conductivity type third semiconductor having a band gap wavelength longer than that of the light receiving layer and bonded to the second semiconductor layer A first, second, and third optical filter layers made of optical filter layers each including the first, second, and third semiconductor layers are joined in series as the optical filter layer, A dopant of the first conductivity type is contained in at least the third semiconductor layer of the first optical filter layer.It is characterized by that.
[0012]
  ContractClaim2The semiconductor light receiving elementIn the semiconductor light receiving element that receives only the second incident light out of the first incident light having the first wavelength and the second incident light having the second wavelength longer than the first wavelength, the n-type or p-type first conductivity type Semiconductor substrate, and a first conductivity type buffer bonded to one end of the semiconductor substrate A first conductivity type optical filter layer bonded to the opposite side of the buffer layer to the semiconductor substrate, and a first conductivity type barrier bonded to the optical filter layer opposite to the buffer layer. A first conductive type light-receiving layer that is bonded to the opposite side of the barrier layer to the optical filter layer and receives second incident light, and is bonded to the opposite side of the light-receiving layer to the barrier layer A first conductivity type cap layer and a p-type or n-type second conductivity type contact layer; a positive electrode joined to the second conductivity type contact layer; and the other end of the semiconductor substrate. A negative electrode, and the optical filter layer includes a first conductive type first semiconductor layer having a band gap wavelength having an intermediate length between the first incident light and the second incident light, and the first semiconductor layer. Having a long bandgap wavelength and being bonded to the first semiconductor layer Comprising electrically a conductive type second semiconductor layer, and a first conductivity type third semiconductor layer which is bonded to the light receiving layer and the second semiconductor layer has a long band gap wavelength than the previousAs the optical filter layer, first, second, third, and fourth optical filter layers comprising optical filter layers each including the first, second, and third semiconductor layers are joined in series, and the first The second and fourth optical filter layers are inverted so that the incident side and the outgoing side are opposite to the traveling direction of the incident light, and are joined to the first and third optical filter layers.AndIt is characterized in that a dopant of the first conductivity type is contained in at least the third semiconductor layer of the first optical filter layer.
  Claim3The semiconductor light receiving element is a semiconductor light receiving element that receives only the second incident light out of the first incident light having the first wavelength and the second incident light having the second wavelength longer than the first wavelength. An n-type or p-type first conductivity type buffer layer bonded to one end of the semi-insulating substrate, and a first conductivity type buffer layer bonded to the opposite side of the buffer layer from the semi-insulating substrate. An optical filter layer, a first contact layer of a first conductivity type bonded to the opposite side of the optical filter layer to the buffer layer, and an optical filter layer of the first contact layer bonded to the opposite side of the optical filter layer; A first conductivity type light-receiving layer that receives the second incident light, a first conductivity type cap layer and a p-type or n-type second conductivity bonded to the light-receiving layer on the opposite side of the first contact layer. The second contact layer of the mold and the second contact layer of the second conductivity type. A positive electrode and a negative electrode joined to the first contact layer of the first conductivity type, the optical filter layer having a longer band gap wavelength than the light receiving layer and joined to the buffer layer A third semiconductor layer of the first conductivity type, and a second semiconductor of the first conductivity type having a band gap wavelength of an intermediate length between the first incident light and the second incident light and joined to the third semiconductor layer And a first conductivity type first semiconductor layer having a band gap wavelength shorter than that of the second semiconductor layer and bonded to the second semiconductor layer.e,It is characterized in that a dopant of the first conductivity type is contained in at least the third semiconductor layer of the optical filter layer.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the best mode for carrying out the present invention will be described based on examples.
[Example 1]
  FIG. 1 is a light-receiving element cross section and energy band diagram of the semiconductor light-receiving element of Example 1. The semiconductor light-receiving element has a wavelength of 1.3 μm (corresponding to a first incident light having a first wavelength) and 1.55 μm. Light (corresponding to second incident light of the second wavelength) is incident from the back surface of the element and selectively receives only 1.55 μm light.
[0014]
  On an n + type InP semiconductor substrate 101, an n + type InP buffer layer 102, an n type optical filter layer 103, an n type InP barrier layer 104, and an n− type InGaAs light receiving layer 105 (band gap wavelength (λg): λga = 1.65 μm) and an n − -type InP cap layer 106 are sequentially formed. Note that “n-type” corresponds to the first conductivity type, and “p-type” corresponds to the second conductivity type.
[0015]
  The n-type optical filter layer 103 includes an InGaAsP first semiconductor layer 107 (1.3 μm <λg1 <1.55 μm: λg1 = 1.40 μm) and an InGaAsP second semiconductor layer 108 (λg2> λg1: λg2 = 1.45 μm). And an InGaAs third semiconductor layer 109 (λg3> λga: λg3 = 1.70 μm).
[0016]
  The n + -type InP buffer layer 102 functions as a buffer (buffer) layer for lattice-matching the InGaAsP first semiconductor layer 107 and the n + -type InP substrate 101 constituting the n-type optical filter layer 103, and n The type InP barrier layer 104 has a function of preventing holes generated in the n-type optical filter layer 103 from flowing out to the n− type InGaAs light receiving layer 105 (see the energy band diagram of FIG. 1).
[0017]
  A p + type InP contact layer 110 is formed in the light receiving region in the n− type InP cap layer 106 by a selective diffusion method.
[0018]
  A p-electrode 111 is formed on the p + -type InP contact layer 110, and an n-electrode 112 is formed on the n + -type InP substrate 101.
[0019]
  A silicon nitride film (SiN film) 113 is formed as a passivation film on the p + type InP contact layer 110 and the n − type InP cap layer 106 other than the p electrode 111.
[0020]
  An antireflection film (AR coat film) 114 for 1.55 μm is formed on the n + type InP substrate 101 other than the n electrode 112, that is, on the incident light incident surface.
[0021]
  Next, the operation of the light receiving element will be described with reference to FIG.
[0022]
  FIG. 2 is a diagram in which a reverse applied voltage is applied through the p-electrode 111 and the n-electrode 112 of the element of FIG.
[0023]
  Light having a wavelength of 1.3 μm and 1.55 μm incident from the back surface of the element passes through the n + type InP substrate 101 and the n + type InP buffer layer 102 and enters the n type optical filter layer 103.
[0024]
  The 1.3 μm light is absorbed by the InGaAsP first semiconductor layer 107 in the n-type optical filter layer 103 to generate carriers (see FIG. 2A).
[0025]
  Of the 1.3 μm light, the light that has not been absorbed by the InGaAsP first semiconductor layer 107 is absorbed by the next InGaAsP second semiconductor layer 108 to generate carriers (see FIG. 2A).
[0026]
  Of the 1.3 μm light, light that has not been absorbed by the InGaAsP second semiconductor layer 108 is absorbed by the next InGaAs third semiconductor layer 109 to generate carriers (see FIG. 2A).
[0027]
  Of the 1.3 μm light, light that has not been absorbed by the InGaAs third semiconductor layer 109 is received by the n − -type InGaAs light receiving layer 105 (see FIG. 2A).
[0028]
  The light of 1.55 μm is hardly absorbed by the InGaAsP first semiconductor layer 107 and the InGaAsP second semiconductor layer 108 in the n-type optical filter layer 103, and the layer thickness of the InGaAs third semiconductor layer 109 is set sufficiently thin. Most of the light is received by the n − -type InGaAs light receiving layer 105 with only slight absorption (see FIG. 2B).
[0029]
  Of the carriers generated in the InGaAsP first semiconductor layer 107 in the n-type optical filter layer 103, electrons 201 drift to the n + -type InP buffer layer 102, and holes 202 drift to the InGaAsP second semiconductor layer 108 (FIG. 2 ( c)).
[0030]
  The electrons 201 generated in the InGaAsP second semiconductor layer 108 drift to the InGaAsP first semiconductor layer 107, and the holes 202 drift to the InGaAs third semiconductor layer 109 (see FIG. 2C).
[0031]
  The holes 202 generated in the n − type InGaAs light receiving layer 105 reach the p electrode 111 as an electric signal as they are, and the generated electrons 201 drift to the InGaAs third semiconductor layer 109 through the n type InP barrier layer 104 (FIG. 2 (c)).
[0032]
  Since the holes generated in the InGaAs third semiconductor layer 109 and the holes 202 moved to the InGaAs third semiconductor layer 109 cannot move because the gap of the valence band 115 is large, the holes 202 remain. Light emission is recombined in the InGaAs third semiconductor layer 109 and carriers disappear (see FIG. 2D).
[0033]
  Since the wavelength of the light recombined by the InGaAs third semiconductor layer 109 is longer than the band gap wavelength of the n − type InGaAs light receiving layer 105, it passes through the n − type InGaAs light receiving layer 105 (see FIG. 2D). ).
[0034]
  Further, when the thickness of the InGaAsP first semiconductor layer 107 is increased in order to improve the selection ratio of 1.55 μm light, emission or recombination occurs before the carriers that have generated or moved completely drift, but they are emitted. Light is absorbed by the InGaAsP second semiconductor layer 108 to generate carriers and drift in the same manner as described above (see FIG. 2E).
[0035]
  In addition, light emitted by recombination of light emitted from the InGaAsP second semiconductor layer 108 is absorbed by the InGaAs third semiconductor layer 109.
[0036]
  Hereinafter, in FIG. 3, FIG. 6, FIG. 7, and FIG. 9, a light receiving element in which the optical filter layer 103 of Example 1 is partially changed is introduced, and this will be described with reference to FIG. To do.
[0037]
  FIG. 3 shows the light receiving element of FIG. 1 in which the thickness of each layer forming the optical filter layer 103 is reduced, a set is formed from each layer, and the optical filter layer 103 is formed by the plurality of sets. It is an energy band figure of the light receiving element which can improve the selection ratio of 1.55 micrometer light efficiently.
[0038]
  In the light receiving element of the first example shown in FIG. 3A, an InGaAsP first semiconductor layer 107, an InGaAsP second semiconductor layer 108, and an InGaAs third semiconductor layer 109 form a set, and the set is an n-type optical filter. Three sets are formed in series in the layer 103.
[0039]
  In the light receiving element shown in FIG. 3A, the thickness of each layer in the optical filter layer 103 can be reduced as compared with the optical filter layer 103 in FIG. The probability of light emission recombination during carrier drift in the semiconductor layer 108 can be lowered, and as a result, the selectivity of 1.55 μm light can be improved.
[0040]
  In the light receiving element of the second example shown in FIG. 3B, an InGaAsP first semiconductor layer 107 and an InGaAsP second semiconductor layer 108 form a set, and the set includes three sets and an InGaAs third semiconductor layer 109. The n-type optical filter layer 103 is formed in series.
[0041]
  In the light receiving element shown in FIG. 3B, the total thickness of the third semiconductor layer 109 in the optical filter layer 103 can be made thinner than the optical filter layer 103 in FIG. As a result, it is possible to reduce the absorption loss in the inside, and as a result, the selectivity of 1.55 μm light can be improved.
[0042]
  In the light receiving element of the third example shown in FIG. 3C, a pair is formed by the InGaAsP first semiconductor layer 107, the InGaAsP second semiconductor layer 108, and the InGaAs third semiconductor layer 109, and the middle pair of the pair is formed. Are combined so that the incident side and the emission side are reversed with respect to the traveling direction of the incident light, thereby forming the n-type optical filter layer 103.
[0043]
  In the light receiving element shown in FIG. 3C, the carriers generated in the optical filter layer 103 are moved to the third semiconductor layer 109 by the drift due to the electric field and the diffusion of the carriers themselves to recombine light.
[0044]
  In the light receiving element illustrated in FIG. 3C, light emission recombination other than the third semiconductor layer 109 is suppressed to a low level even when a sufficient electric field for drifting generated carriers is not applied in the optical filter layer 103. It becomes possible.
[0045]
  Here, in order to explain the effect of the second semiconductor layer 108, a pair is formed by the first semiconductor layer 107 and the third semiconductor layer 109 except for the second semiconductor layer 108, and 3 in the optical filter layer 103. FIG. 4 shows an example in which the groups are formed in series.
[0046]
  FIG. 5 is a graph in which the selection ratio of 1.55 μm light between the light receiving element in FIG. 3A and the light receiving element in FIG. 4 is calculated and compared.
[0047]
  Here, the secondary light generated when the carriers generated in the optical filter layer 103 by the 1.3 μm light recombine with light other than the third semiconductor layer 109 and the optical filter layer 103 were not completely absorbed. The selection ratio of 1.55 μm light transmitted through the optical filter layer 103 to 3 μm light was R (= 10 * Log (light-receiving sensitivity due to 1.3 μm light / light-receiving sensitivity of 1.55 μm light)).
[0048]
  The thickness of the third semiconductor layer 109 is X. In FIG. 3A, the thickness of the first semiconductor layer 107 is 20X, the thickness of the second semiconductor layer 108 is 10X, and in FIG. The thickness of the optical filter layer 103 was made equal to 30X. 3A and 4 show the case where there are three sets in the optical filter layer 103. Here, five sets are set, and the thickness of the light receiving layer 105 is set to 2.0 μm.
[0049]
  From FIG. 5, when the thickness of the third semiconductor layer 109 is 500 mm and the light emission recombination probability of the first semiconductor layer 107 and the second semiconductor layer 108 is 0%, R = −27. 90 dB (see calculated value 501) and R = −26.85 dB (see calculated value 502) in FIG. 4, which is not much different. However, when this light emission recombination probability is 10%, R = −15 in FIG. 3A. .00 dB (refer to the calculated value 503) and R = -12.11 dB (refer to the calculated value 504) in FIG. 4, indicating that the second semiconductor layer 108 has effectively improved the selectivity of 1.55 μm.
[0050]
  FIG. 6 shows a fourth example in which the second semiconductor layer 108 of the light receiving element of the first example shown in FIG. 3A of Example 1 is made into a plurality of layers, and light emission recombination other than the third semiconductor layer 109 is further reduced. It is an energy band figure of the light receiving element of an example.
[0051]
  As shown in FIG. 5, since the light emission recombination other than the third semiconductor layer 109 in the optical filter layer 103 deteriorates the selectivity of 1.55 μm light, the second semiconductor layer 108 is changed as shown in FIG. By using a plurality of layers and making each layer thin, it is possible to reduce the light emission recombination probability other than in the third semiconductor layer 109, and the selectivity of 1.55 μm light is further improved.
[0052]
  FIG. 7 shows the light emission recombination probability in the third semiconductor layer 109 by reducing the light emission recombination probability in the first semiconductor layer 107 and the second semiconductor layer 108 of the light receiving element of the first example shown in FIG. It is an energy band figure of the light receiving element which is improving.
[0053]
  In the light receiving element of FIG. 7, the first semiconductor layer 107, the second semiconductor layer 108, and the third semiconductor layer 109 form a set, and three sets are formed in series in the optical filter layer 103.
[0054]
  3A, the thickness of each layer in the optical filter layer 103 is equal. In FIG. 7, the thickness of each layer gradually increases with respect to the traveling direction of light. The absorptance of 1.3 μm light is approximately equal.
[0055]
  Based on FIG. 8, the operation of the light receiving element of FIG. 3 (a) and FIG. 7 will be described.
[0056]
  In discussing the light selection ratio of 1.55 μm, the generation of secondary light caused by 1.3 μm light is the most important, so only the case where 1.3 μm light is incident is shown here.
[0057]
  8A and 8B show a case where 1.3 μm light is incident on the light receiving element of FIG. 3A from the back side of the element, and FIGS. 8C and 8D show the light receiving element of FIG. In this case, 1.3 μm light is incident from the back side of the element.
[0058]
  In FIG. 8A, most of the 1.3 μm light is absorbed in the optical filter layer 103 by the first optical filter layer 801 which is the foremost in the light traveling direction, and a large amount of carriers are generated.
[0059]
  When the thickness of the first semiconductor layer 107 is 1.2 μm, the thickness of the second semiconductor layer 108 is 1.0 μm, and the thickness of the third semiconductor layer 109 is 500 mm, the incident 1.3 μm light is The optical filter layer 801 absorbs 86%, the second optical filter layer 802 absorbs 12%, and the third optical filter layer 803 absorbs 2%.
[0060]
  8B, among the generated carriers, the electrons 201 drift to the InP substrate 101 side and the holes 202 drift to the light receiving layer 105 side. Therefore, the third semiconductor layer 109 of the first optical filter layer 801 is used. 86% of the generated holes 202 enter and 12% of the generated electrons 201 enter.
[0061]
  That is, in the third semiconductor layer 109 of the first optical filter layer 801, only about 12% of the generated carriers are recombined for light emission, and the remaining 74% of the holes 202 are the second.Light filter layerThere is a possibility of leakage to the 802 side.
[0062]
  There is no problem if all of the holes 202 leaking to the second optical filter layer 802 stay in the third semiconductor layer 109 in the second optical filter layer 802, but the drifting first semiconductor layer 107, 2 There is a risk of recombination of light emission in the semiconductor layer 108.
[0063]
  In FIG. 8C, 1.3 μm light is absorbed almost evenly in each set in the optical filter layer 103, and the number of generated carriers is almost the same in each set.
[0064]
  The thickness of the first semiconductor layer 107 of the first optical filter layer 801 is 0.21 μm, the thickness of the second semiconductor layer 108 is 0.18 μm, the thickness of the first semiconductor layer 107 of the second optical filter layer 802 is 0.34 μm, The semiconductor layer 108 has a thickness of 0.30 μm, the third optical filter layer 803 has a first semiconductor layer 107 of 3.05 μm, and the second semiconductor layer 108 has a thickness of 2.52 μm. As a result, the absorptance of 1.3 μm light in each group is about 33%.
[0065]
  In FIG. 8D, when carriers drift in the same manner as described above, since the number of carriers generated in each pair is substantially equal, the light emission recombination probabilities in the third semiconductor layers 109 of each pair are also substantially equal. The number of holes 202 drifting to the set is drastically reduced, and the light emission recombination probability outside the third semiconductor layer 109 is extremely low.
[0066]
  FIG. 9 is a diagram showing an example of the light-receiving element shown in FIG. 3A or FIG. 8A according to the first embodiment. The third semiconductor layer 109 efficiently emits and recombines carriers generated in a large amount in the first optical filter layer 801. It is an energy band figure of the photo acceptance unit made to do.
[0067]
  In FIG. 9, the third semiconductor layer 109 of the first optical filter layer 801 is heavily doped with a donor, and the number of electrons, which are major carriers, is increased in the conduction band 116 in advance.
[0068]
  As a result, it is possible to efficiently recombine the generated holes in the third semiconductor layer 109 with light emission.
[0069]
  Although the donor is doped in FIG. 9, the acceptor is doped in the structure in which the p-type and n-type are inverted.
[0070]
  An example in which the light receiving element (FIGS. 1, 3, 6, 7, and 9) of Example 1 described above is partially changed will be described. Although the pn electrodes are formed on the front and back surfaces of these elements, the pn electrodes may be formed on the element surface by utilizing carrier diffusion in the optical filter layer 103. Further, the n-type InP barrier layer 104 may be exposed by etching to form an n-electrode.
[0071]
  Further, in the light receiving element of Example 1 described above, the more complicated the structure, the higher the epi wafer cost. Therefore, considering the balance between the characteristics required by the customer and the cost, the structure that seems to be optimal is adopted. It is desirable.
[0072]
[Example 2]
  FIG. 10 is a cross-sectional view and a schematic diagram of the energy band of the semiconductor light-receiving element of Example 2. In the present invention, optical signals with wavelengths of 1.3 μm and 1.55 μm are incident from the back of the element, and 1.55 μm light. In this case, only light is selectively received.
[0073]
  On a semi-insulating InP substrate 1001, an InP buffer layer 1002, an optical filter layer 1003, an n + type InP contact layer 1004 (corresponding to a first contact layer), and an n− type InGaAs light receiving layer 105 (band gap wavelength (λg ): Λga = 1.65 μm), and an n − -type InP cap layer 106 are sequentially formed.
[0074]
  Here, the reason why the semi-insulating substrate is used for the InP substrate is that the transmittance of 1.55 μm light is higher than that of the n-type, so that an increase in the light receiving sensitivity of 1.55 μm light can be expected.
[0075]
  The optical filter layer 1003 includes an InGaAs third semiconductor layer 109 (λg3> λga: λg3 = 1.70 μm), an InGaAsP second semiconductor layer 108 (λg2> λg1: λg2 = 1.45 μm), and an InGaAsP first semiconductor layer 107 (1 3 μm <λg1 <1.55 μm: λg1 = 1.40 μm).
[0076]
  A p + type InP contact layer 110 (corresponding to the second contact layer) is formed in the light receiving region in the n − type InP cap layer 106 by a selective diffusion method.
[0077]
  The n − type InP cap layer 106 and the n − type InGaAs light receiving layer 105 have a mesa shape formed by etching.
[0078]
  A p-electrode 111 is formed on the p + -type InP contact layer 110, and an n-electrode 112 is formed on the n + -type InP contact layer 1004.
[0079]
  A passivation film is formed on the surface of the p + type InP contact layer 110 other than the p electrode 111 and the surface and side surfaces of the n− type InP cap layer 106, the side surface of the n− type InGaAs light receiving layer 105, and the surface of the n + type InP contact layer 1004 other than the n electrode 112. A SiN film 113 is formed.
[0080]
  An AR coating film 114 for 1.55 μm is formed on the semi-insulating InP substrate 1001, that is, on the light incident surface.
[0081]
  Next, the operation of the light receiving element of Example 2 will be described with reference to FIG.
[0082]
  FIG. 11 is a diagram in which a reverse applied voltage is applied through the p-electrode 111 and the n-electrode 112 of the element of FIG.
[0083]
  Light having a wavelength of 1.3 μm and 1.55 μm incident from the back surface of the element passes through the semi-insulating InP substrate 1001 and the InP buffer layer 1002 and enters the optical filter layer 1003.
[0084]
  The 1.3 μm light is absorbed in the optical filter layer 1003 to generate carriers, and the 1.55 μm light is hardly absorbed by the optical filter layer 1003, and most is received by the n− type InGaAs light receiving layer 105 (FIG. 11 ( a)).
[0085]
  The holes 202 generated in the n − -type InGaAs light receiving layer 105 reach the p electrode 111 as they are as electrical signals, and the generated electrons 201 reach the n electrode 112 (see FIG. 11B).
[0086]
  Carriers generated in the optical filter layer 1003 move to the InGaAs third semiconductor layer 109 by diffusion and recombine with light emission (see FIG. 11B).
[0087]
  In the case of this light receiving element, since the InGaAs third semiconductor layer 109 that recombines light emission is separated from the n − -type InGaAs light receiving layer 105, the solid angle incident on the light receiving region is reduced and the selection ratio of 1.55 μm is improved. .
[0088]
  Here, as an explanation of the solid angle, FIG. 12 shows a case where the secondary light emitted from the point light source in all directions enters the light receiving region.
[0089]
  The distances L1 and L2 from the point light source 1201 to the light receiving region 1202 are L1 <L2, and the area of the light receiving region 1202 is S.
[0090]
  The ratio of light incident on the light receiving area 1202 at the distance L1 is S / 4πL12, the ratio of light incident on the light receiving area 1202 at the distance L2 is S / 4πL22, and the ratio of light incident on the light receiving area is the emission recombination position. And inversely proportional to the square of the distance of the light receiving area.
[0091]
  That is, when the distance between the light emission recombination position and the light receiving region is doubled, the ratio of light incident on the light receiving region is reduced to ¼.
[0092]
  FIG. 13 is an energy band diagram of a light receiving element in which the selection ratio of 1.55 μm light is improved more efficiently than in the second embodiment.
[0093]
  In FIG. 13, a plurality of InGaAsP second semiconductor layers 108 are formed, and the band gap wavelength is gradually shortened with respect to the light traveling direction.
[0094]
  In the light receiving element shown in FIG. 13, although the cost of the epi-wafer is increased, the thickness of each layer can be reduced, so that the light emission recombination probability can be lowered and carrier diffusion can be made smooth.
[0095]
  14A is an example in which the optical filter layer 103 of Example 1 is partially changed, and FIG. 14B is an example in which the optical filter layer 1003 of Example 2 is partially changed. FIG. 6 is an energy band diagram when carriers drift to the third semiconductor layer 109 even when there is no electric field.
[0096]
  14A shows the n-type optical filter layer 103, and FIG. 14B shows that the optical filter layer 1003 contains a dopant.
[0097]
  Since the built-in potential is determined by the band gap energy and the carrier concentration of the heterojunction, an appropriate amount of dopant is added to each layer to increase the built-in potential so that carriers can drift to the third semiconductor layer 109 even when there is no electric field. In particular, since the mobility of holes is slow, the holes are designed to easily drift.
[0098]
  As a result, since at least two pn junctions can be formed, parasitic capacitance is generated and the response speed may be lowered. However, even when no electric field is applied in the optical filter layer, carriers are not recombined by light emission, so that the selection ratio is improved. In addition, since the optical filter layer and the PD are electrically separated, electrical noise is reduced, and further improvement in the selection ratio can be expected.
[0099]
  As described above, in the light receiving elements of the first and second embodiments, the PIN photodiode type light receiving element is exemplified in the light receiving region. However, a similar selection ratio can be obtained even if a light receiving region such as an avalanche type or a phototransistor type is provided. .
[0100]
【The invention's effect】
  According to invention of Claim 1, since this semiconductor light receiving element can be manufactured with one element which consists of one semiconductor substrate, mounting cost can be suppressed. In addition, a buffer layer for lattice matching with the optical filter layer can be provided by the buffer layer, and holes generated in the optical filter layer can be prevented from flowing out to the light receiving layer by the barrier layer. .
[0101]
  AlsoThe first incident light is absorbed by the optical filter layer, recombined in the third semiconductor layer, converted into light that passes through the light receiving layer, and the light recombined in the first semiconductor layer is further reflected in the second semiconductor layer. , And the light is recombined in the third semiconductor layer to be converted into light that passes through the light receiving layer, so that only the second incident light that has passed through the optical filter layer can be selectively received by the light receiving layer.
  furtherSince each layer in the optical filter layer can be made thinner and formed from a plurality of layers, the light emission recombination probability during carrier drift in the first semiconductor layer and the second semiconductor layer is lowered, and as a result In addition, the selection ratio of the second incident light having the second wavelength can be improved.Since the first third semiconductor layer is highly doped with a donor or an acceptor and electrons or holes that are major carriers are increased in advance in the conduction band, a large number of holes or electrons generated in the third band are added to the third semiconductor layer. Emission recombination can be efficiently performed in the semiconductor layer.
  Claim2According to this invention, carriers generated in the optical filter layer can be moved to the third semiconductor layer by the drift due to the electric field and the diffusion of the carriers themselves, and can be recombined for light emission. For this reason, even when a sufficient electric field for drifting carriers generated in the optical filter layer is not applied, recombination other than in the third semiconductor layer can be pushed down.
  AlsoSince the first third semiconductor layer is highly doped with a donor or an acceptor and electrons or holes that are major carriers are increased in advance in the conduction band, a large number of holes or electrons generated in the third band are added to the third semiconductor layer. Emission recombination can be efficiently performed in the semiconductor layer.
  Claim3According to the invention, the band gap wavelength becomes shorter with respect to the light traveling direction in order from the third semiconductor layer, and the short wavelength light can be absorbed in the optical filter layer. Since the third semiconductor layer in the optical filter layer is located away from the light receiving region, the solid angle is reduced, the ratio of incident secondary light due to short wavelengths to the light receiving region is reduced, and the optical filter layer and the PD Are electrically separated from each other, so that electrical noise is reduced, and as a result, a semiconductor element that selectively receives long wavelength light is realized.
  AlsoThe built-in potential can be increased by adding a dopant of the first conductivity type or the second conductivity type to the optical filter layer, and carriers generated in the optical filter layer can be efficiently transported to the third semiconductor layer even without an electric field. Accordingly, the solid angle with the light receiving region (PD) can be reduced by increasing the distance between the third semiconductor layer and the light receiving layer.
[Brief description of the drawings]
FIGS. 1A and 1B are a cross-sectional view and an energy band diagram of a semiconductor light receiving element according to a first embodiment of the present invention.
2 is an energy band diagram for explaining the operation of the light receiving element of FIG. 1, wherein (a) is a diagram showing a state in which 1.3 μm light is absorbed by the optical filter layer and the light receiving layer to generate carriers; (B) is a diagram showing a state in which 1.55 μm light is absorbed by the optical filter layer and the light receiving layer to generate carriers, (c) is a diagram showing a drift state of the generated carriers, and (d) is generated. The figure which shows the state in which the carrier recombined luminescence in the 3rd semiconductor layer, (e) is the figure which shows the state in which the carrier which was absorbed and generated in the 2nd semiconductor layer was radiatively recombined in the 1st semiconductor layer.
FIGS. 3A and 3B are energy band diagrams in which the optical filter layer of Example 1 is partially changed, where FIG. 3A is a light receiving element of the first example, FIG. 3B is a light receiving element of the second example, and FIG. It is an energy band figure of the light receiving element of 3 examples.
FIG. 4 is an energy band diagram of a light receiving element in which an optical filter layer is constituted by a first semiconductor layer and a third semiconductor layer except for a second semiconductor layer.
5 is a diagram showing a calculation result of a selection ratio of 1.55 μm light of the light receiving elements of FIG. 3 (a) and FIG. 4;
6 is an energy band diagram of a light receiving element of a fourth example in which the optical filter layer of Example 1 is partially changed. FIG.
7 is an energy band diagram of a light receiving element of a fifth example in which the optical filter layer of Example 1 is partially changed. FIG.
8 is an energy band diagram for explaining the operation of the light receiving element of the first example of FIG. 3A and the light receiving element of the fifth example of FIG. 7, and FIG. 8A is 1.3 μm in the light receiving element of the first example. The figure which shows the state which light was absorbed by the optical filter layer, and generate | occur | produced the carrier, (b) is the figure which shows the drift of the produced | generated carrier and the light emission recombination state, (c) is 1 in the light receiving element of a 5th example. FIG. 5D is a diagram showing a state in which .3 μm light is absorbed by the optical filter layer to generate carriers, and FIG. 6D is a diagram showing a drift of the generated carriers and a light emission recombination state.
FIG. 9 is an energy band diagram of a sixth example light receiving element in which a third semiconductor layer 109 in the first optical filter layer 801 in FIG. 8A is heavily doped with a donor.
FIGS. 10A and 10B are a cross-sectional view and an energy band diagram of the semiconductor light receiving element according to the second embodiment of the present invention. FIGS.
11 is an energy band diagram for explaining the operation of the light receiving element of FIG. 10, wherein (a) is a diagram showing a state in which 1.3 μm light and 1.55 μm light are absorbed by the filter layer to generate carriers. (B) is a figure which shows the drift state of the generate | occur | produced carrier.
FIG. 12 is a schematic diagram showing a case where light emitted from a point light source in all directions enters a light receiving region.
FIG. 13 is an energy band diagram of a light receiving element in which the optical filter layer according to the second embodiment of the present invention is partially changed.
14A is an energy band diagram showing a state where a dopant is contained in each layer of the optical filter layer of FIG. 3A, and FIG. 14B is a diagram containing a dopant in each layer of the optical filter layer of FIG. It is an energy band figure which shows the state made to do.
[Explanation of symbols]
101 n + type InP substrate
102 n + type InP buffer layer
103 n-type optical filter layer
104 n-type InP barrier layer
105 n-type InGaAs absorption layer
106 n-type InP cap layer
107 InGaAsP first semiconductor layer
108 InGaAsP second semiconductor layer
109 InGaAs third semiconductor layer
110 p + type InP contact layer
111 p electrode
112 n electrode
113 Silicon nitride film
114 1.55μm Antireflection Film
115 Valence band
116 conduction band
201 electrons
202 holes
203 Electron annihilated by radiative recombination
204 Holes annihilated by radiative recombination
501 Calculated value when the light emission recombination probability is 0% in the structure of FIG.
502 Calculated value when the light emission recombination probability is 0% in the structure of FIG.
503 Calculated value when the light emission recombination probability is 10% in the structure of FIG.
504 Calculated value when the light emission recombination probability is 10% in the structure of FIG.
801 First set of optical filter layers
802 Second set of optical filter layers
803 Third optical filter layer
1001 Semi-insulating InP substrate
1002 InP buffer layer
1003 Optical filter layer
1004 n + type InP contact layer
1201 Point light source
1202 Light receiving area

Claims (3)

In the semiconductor light receiving element that receives only the second incident light among the first incident light of the first wavelength and the second incident light of the second wavelength longer than the first wavelength,
an n-type or p-type first conductivity type semiconductor substrate;
A buffer layer of a first conductivity type joined to one end side of the semiconductor substrate;
A first conductivity type optical filter layer bonded to the opposite side of the buffer layer from the semiconductor substrate;
A barrier layer of a first conductivity type bonded to the side of the optical filter layer opposite to the buffer layer;
A light-receiving layer of a first conductivity type that is bonded to the opposite side of the barrier layer from the optical filter layer and receives the second incident light;
A first conductivity type cap layer and a p-type or n-type second conductivity type contact layer bonded to the opposite side of the light-receiving layer from the barrier layer;
A positive electrode bonded to the second conductivity type contact layer;
A negative electrode joined to the other end of the semiconductor substrate ,
The optical filter layer has a first semiconductor layer of a first conductivity type having a band gap wavelength having an intermediate length between the first incident light and the second incident light, and a band gap wavelength longer than that of the first semiconductor layer. A first conductive type second semiconductor layer that is held and bonded to the first semiconductor layer; and a first conductive type third semiconductor layer that has a band gap wavelength longer than that of the light receiving layer and is bonded to the second semiconductor layer. And
As the optical filter layer, first, second, and third optical filter layers made of optical filter layers each including the first, second, and third semiconductor layers are joined in series,
A semiconductor light receiving element, wherein a dopant of the first conductivity type is contained in at least a third semiconductor layer of the first optical filter layer . In the semiconductor light receiving element that receives only the second incident light among the first incident light of the first wavelength and the second incident light of the second wavelength longer than the first wavelength,
an n-type or p-type first conductivity type semiconductor substrate;
A buffer layer of a first conductivity type joined to one end side of the semiconductor substrate;
A first conductivity type optical filter layer bonded to the opposite side of the buffer layer from the semiconductor substrate;
A barrier layer of a first conductivity type bonded to the side of the optical filter layer opposite to the buffer layer;
A light-receiving layer of a first conductivity type that is bonded to the opposite side of the barrier layer from the optical filter layer and receives the second incident light;
A first conductivity type cap layer and a p-type or n-type second conductivity type contact layer bonded to the opposite side of the light-receiving layer from the barrier layer;
A positive electrode bonded to the second conductivity type contact layer;
A negative electrode joined to the other end of the semiconductor substrate,
The optical filter layer has a first semiconductor layer of a first conductivity type having a band gap wavelength having an intermediate length between the first incident light and the second incident light, and a band gap wavelength longer than that of the first semiconductor layer. A first conductive type second semiconductor layer that is held and bonded to the first semiconductor layer; and a first conductive type third semiconductor layer that has a band gap wavelength longer than that of the light receiving layer and is bonded to the second semiconductor layer. And
As the optical filter layer, first, second, third, and fourth optical filter layers made of optical filter layers each including the first, second, and third semiconductor layers are joined in series,
The second and fourth optical filter layers are inverted so that the incident side and the outgoing side are opposite to the traveling direction of incident light, and are joined to the first and third optical filter layers ,
Semiconductors receiving element characterized that it contained at least the first first-conductivity type dopant into the third semiconductor layer of the optical filter layer. In the semiconductor light receiving element that receives only the second incident light among the first incident light of the first wavelength and the second incident light of the second wavelength longer than the first wavelength,
A semi-insulating substrate;
An n-type or p-type first conductivity type buffer layer bonded to one end of the semi-insulating substrate;
A first conductivity type optical filter layer bonded to the opposite side of the buffer layer from the semi-insulating substrate;
A first contact layer of a first conductivity type bonded to the side of the optical filter layer opposite to the buffer layer;
A light-receiving layer of a first conductivity type that is bonded to the side opposite to the optical filter layer of the first contact layer and receives second incident light;
A first conductivity type cap layer and a p-type or n-type second conductivity type second contact layer bonded to the opposite side of the light-receiving layer to the first contact layer;
A positive electrode bonded to the second contact layer of the second conductivity type;
A negative electrode joined to the first contact layer of the first conductivity type,
The optical filter layer has a band gap wavelength longer than that of the light receiving layer and a first conductive type third semiconductor layer bonded to the buffer layer, and an intermediate length between the first incident light and the second incident light. A second semiconductor layer of the first conductivity type having a thickness of a band gap and bonded to the third semiconductor layer, and a band gap wavelength shorter than that of the second semiconductor layer and bonded to the second semiconductor layer. A first semiconductor layer of a first conductivity type,
A semiconductor light receiving element, wherein a dopant of the first conductivity type is contained in at least the third semiconductor layer of the optical filter layer .

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