Single-carrier photodiode

Abstract

The application relates to the technical field of semiconductor photoelectric devices, and provides a single-carrier photoelectric diode. The single-carrier photoelectric diode comprises a p-type contact layer, an electron blocking layer, an absorption layer, a spacer layer, a cliff layer, a collection layer, a sub-collection layer, an n-type contact layer which are sequentially connected; and a p electrode located on the p-type contact layer and an n electrode located on the n-type contact layer; wherein the thickness of the collection layer is 1300-1700 nanometers. The single-carrier photoelectric diode is formed by selecting the collection layer with the thickness of 1300-1700 nanometers, sequentially connecting the p-type contact layer, the electron blocking layer, the absorption layer, the spacer layer, the cliff layer, the collection layer, the sub-collection layer and the n-type contact layer, and arranging the p electrode and the n electrode on the p-type contact layer and the n-type contact layer respectively, so that the parasitic capacitance in the single-carrier photoelectric diode is reduced, the total bandwidth of the single-carrier photoelectric diode is improved, and the working efficiency of the single-carrier photoelectric diode is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor optoelectronic devices, in particular to a uni-travelling carrier photodiode. BACKGROUND

[0002] Uni-travelling carrier photodiode (UTC-PD) has become a popular choice in the optical devices of microwave and millimeter wave communication systems due to its excellent performance of high speed and high power. Since millimeter waves face huge transmission loss in long-distance transmission in free space, optical wireless communication systems are usually used to transmit millimeter waves through low-loss optical fibers. In the practical application of RoF (radio-over-fiber) communication systems, photodiodes with a diameter of 14-25 μm are usually used to make the light entrance aperture larger, so as to facilitate the coupling with optical fibers and reduce the coupling loss, but the parasitic capacitance is also larger at this time, and the parasitic capacitance is usually about 100 fF under a diameter of 20 μm. The increase of the parasitic capacitance will lead to the decrease of the total bandwidth of the photodiode, and the working efficiency of the photodiode is low. SUMMARY

[0003] Embodiments of the present application provide a uni-travelling carrier photodiode to solve the problem that the increase of the parasitic capacitance will lead to the decrease of the total bandwidth of the photodiode, and the working efficiency of the photodiode is low.

[0004] Embodiments of the present application provide a uni-travelling carrier photodiode, which comprises a p-type contact layer, an electron blocking layer, an absorption layer, a spacer layer, a cliff layer, a collection layer, a sub-collection layer, an n-type contact layer connected in sequence, and a p electrode located on the p-type contact layer and an n electrode located on the n-type contact layer.

[0005] In an embodiment, the thickness of the collection layer is 1300 nm to 1700 nm.

[0006] In an embodiment, the thickness of the collection layer is 1500 nm.

[0007] In an embodiment, the material of the collection layer comprises InP.

[0008] In an embodiment, the doping concentration of InP in the collection layer gradually changes from 3×1018 cm-3 close to the cliff layer to 1×1018 cm-3 close to the n-type contact layer. 15 cm -3 . 15 cm -3

[0009] In an embodiment, the material of the cliff layer comprises InP. ​

[0010] In one embodiment, the doping concentration of InP in the cliff layer is 4x10 17 cm -3 to 6x10 17 cm -3 .

[0011] In one embodiment, the thickness of the cliff layer is 50nm to 70nm.

[0012] In one embodiment, the thickness of the cliff layer is 70nm.

[0013] In one embodiment, the sub-collection layer at least includes a first sub-collection layer and a second sub-collection layer, the first sub-collection layer and the second sub-collection layer are structure layers with different doping concentrations of InP.

[0014] In one embodiment, the material of the interval layer includes InGaAsP and InP.

[0015] The single-carrier photodiode provided by the embodiments of the present application can reduce the parasitic capacitance in the single-carrier photodiode by selecting the collection layer with a thickness of 1300nm to 1700nm, connecting the p-type contact layer, the electron blocking layer, the absorption layer, the interval layer, the cliff layer, the collection layer, the sub-collection layer, and the n-type contact layer in sequence, and arranging the p-electrode and the n-electrode on the p-type contact layer and the n-type contact layer respectively, thereby improving the total bandwidth of the single-carrier photodiode and the working efficiency of the single-carrier photodiode. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0017] Figure 1 is a structure diagram of the single-carrier photodiode provided by the embodiments of the present application;

[0018] Figure 2 is one of the test result diagrams of the single-carrier photodiode provided by the embodiments of the present application;

[0019] Figure 3 is another of the test result diagrams of the single-carrier photodiode provided by the embodiments of the present application;

[0020] Figure 4 is a third of the test result diagrams of the single-carrier photodiode provided by the embodiments of the present application.

[0021] Reference signs:

[0022] 1, p electrode; 2, p-type contact layer; 3, electron blocking layer; 4, absorption layer; 5, spacer layer; 6, mesa layer; 7, collection layer; 8, first sub-collection layer; 9, second sub-collection layer; 10, n electrode; 11, n-type contact layer. DETAILED DESCRIPTION

[0023] The embodiments of the present application will be further described below in conjunction with the drawings and examples. The following examples are used to illustrate the present application, but cannot be used to limit the scope of the present application.

[0024] In the description of the embodiments of the present application, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0025] In the description of the embodiments of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "connected", "connected" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0026] In the embodiments of the present application, unless otherwise explicitly specified and limited, the first feature is "on" or "under" the second feature, which can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "above" and "above" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "below" and "below" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0027] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0028] During the creation of the inventive application, the applicant has considered the following aspects:

[0029] In the practical application of the RoF communication system, a single-carrier photodiode with a diameter of 14-25 μm and a collecting layer thickness of 500 nanometers is usually used to make the light entrance aperture larger, facilitate coupling with the optical fiber, and reduce the coupling loss, but the parasitic capacitance is also larger, usually about 100 fF under 20 μm diameter.

[0030] Based on the above considerations, the applicant proposes the embodiments of the present application.

[0031] The single-carrier photodiode provided by the application will be described in detail below in combination with embodiments.

[0032] Figure 1 The structure diagram of the single-carrier photodiode provided by the embodiments of the present application is shown in FIG. 1. Referring to FIG. 1, Figure 1 The embodiments of the present application provide a single-carrier photodiode, which can include: a p-type contact layer, an electron blocking layer, an absorption layer, a spacer layer, a cliff layer, a collecting layer, a sub-collecting layer, an n-type contact layer, a p-electrode and an n-electrode.

[0033] The p-electrode can be a positive electrode, and the n-electrode can be a negative electrode.

[0034] In addition, the sub-collecting layer can include a first sub-collecting layer and a second sub-collecting layer.

[0035] The p-type contact layer, the electron blocking layer, the absorption layer, the spacer layer, the cliff layer, the collecting layer, the sub-collecting layer, and the n-type contact layer are connected in sequence.

[0036] The first sub-collecting layer and the second sub-collecting layer in the collecting layer are connected in sequence.

[0037] The electron blocking layer is connected with the p-type contact layer, the absorbing layer is connected with the electron blocking layer, the interval layer is connected with the absorbing layer, the cliff layer is connected with the interval layer, the collecting layer is connected with the cliff layer, the first sub-collecting layer is connected with the collecting layer, the second sub-collecting layer is connected with the first sub-collecting layer, and the n-type contact layer is connected with the second sub-collecting layer.

[0038] Further, metal electrodes are plated on both sides of the n-type contact layer to form ohmic contact and are connected with n electrodes.

[0039] Metal electrodes are plated on both sides of the p-type contact layer to form ohmic contact and are connected with p electrodes.

[0040] Further, the thickness of the collecting layer in the embodiment can be 1300 nm to 1700 nm, for example, can be 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, etc.

[0041] Further, the thickness of the collecting layer in the embodiment can be preferably 1500 nm, but is not specifically limited, and other thicknesses can also be used in other cases to achieve the best effect.

[0042] The material of the collecting layer in the embodiment can include InP. The InP is indium phosphide.

[0043] Further, the doping concentration of InP in the collecting layer can be 3×10 15 cm -3 near the side close to the cliff layer, gradually changes to 1×10 15 cm -3 near the side close to the n-type contact layer. The electric field at the front end of the collecting layer is pre-enhanced so that the electrons at the front end of the collecting layer do not accumulate under high light intensity, and the electric field is still high.

[0044] Further, the material of the cliff layer in the embodiment can include InP.

[0045] The doping concentration of InP in the cliff layer is 4×10 17 cm -3 to 6×10 17 cm -3 . For example, can be 4×10 17 cm -3 , 5×10 17 cm -3 , 6×10 17 cm -3 , etc.

[0046] It should be noted that when the doping concentration decreases from 1×10 18 cm -3 to 5×10 17 cm-3 When the device works, the optimal bias voltage is reduced from 9V to 5V, the maximum value of the cliff layer electric field is significantly reduced from 880kV / cm to 500kV / cm, the power consumption is reduced, and the high-speed performance of the device is improved. If the cliff layer doping concentration is further reduced, the heterojunction barrier at the cliff layer conduction band will be increased, thereby reducing the high-speed performance. Therefore, the doping concentration of InP in the cliff layer is preferably 5x10 17 cm -3 .

[0047] The cliff layer has a high electric field, which can alleviate the heterojunction barrier of InGaAs and InP, and facilitate the electron to cross to the collection layer. InGaAs is gallium indium arsenide.

[0048] Further, the thickness of the cliff layer is 50nm to 70nm. For example, it can be 50nm, 55nm, 60nm, 65nm, 70nm, etc.

[0049] The thickness of the cliff layer in the embodiment can be preferably 70nm, but is not specifically limited, and other thicknesses can also be used in other cases to achieve the best effect.

[0050] It should be further pointed out that the first and second sub-collection layers in the embodiment are structure layers with different doping concentrations of InP. The doping concentration of InP in the first sub-collection layer can gradually increase from low to high, and can be from 1x10 15 cm -3 to 1x10 18 cm -3 . Since it is connected with the n-type contact layer, the doping concentration of InP in the second sub-collection layer is higher, and can be 1x10 18 cm -3 .

[0051] The material of the p-type contact layer in the embodiment can be InGaAs, and the doping concentration thereof can be 2x10 19 cm -3 to 3x10 19 cm -3 , so that an ohmic contact can be formed with the metal electrode thereon.

[0052] The material of the electron blocking layer can be InGaAsP, and the doping concentration thereof can be 1x10 19 cm -3 , which can block the diffusion of electrons to the positive electrode above the p-type contact layer. InGaAsP is gallium indium phosphide arsenide.

[0053] The material of the absorption layer can be InGaAs, which is a layer for light absorption to generate photoelectrons and holes, and the doping concentration thereof can be from 5x10 18cm -3 Linearly graded to 3x10 17 cm -3 ; and, with a certain built-in electric field, which is conducive to the diffusion of electrons.

[0054] The material of the spacer layer can include InGaAsP and InP, which can be graded from InGaAsP to InP. Specifically, it can be graded from InGaAsP near the absorption layer side to InP near the mesa layer side.

[0055] It can be understood that in the single-carrier photodiode structure of the embodiment, the electric field in the collection layer is controlled at 10kV / cm-20kV / cm by adjusting the incident light intensity when working at a 5V bias, so that the electrons in the collection layer cross at the peak speed under different electric fields, so as to improve the transit time bandwidth, and thus improve the total bandwidth of the single-carrier photodiode.

[0056] Further, in the single-carrier photodiode structure, when working at a 5V bias, the electric field distribution of the collection layer is gradually reduced from the side close to the mesa layer to the side close to the n-type contact layer when there is no light injection. With the increase of the incident light intensity, the electric field distribution of the collection layer gradually becomes uniform, and when the incident light intensity is greater than 4x10 4 W / cm 2 , the electric field distribution of the collection layer is reversely tilted.

[0057] Further, in the single-carrier photodiode structure, when working at a 5V bias, with the increase of the incident light intensity, the electric field of the collection layer changes, the average drift speed of the electrons gradually increases, and the capacitance gradually decreases. When the light intensity is 6x10 4 W / cm 2 , the average speed of the electrons crossing the collection layer reaches a maximum (about 3.5x10 7 cm / s), and at this time the capacitance is reduced to a minimum of 10.5fF.

[0058] Further, in the single-carrier photodiode structure, when working at a 5V bias, the high-speed performance is best: when the incident light intensity is 6x10 4 W / cm 2 , the bandwidth reaches 106GHz; when the working bias is reduced, the highest bandwidth decreases, the high-speed performance decreases under high light intensity, and the saturation performance is poor; when the working bias is increased, the highest bandwidth decreases, and the high-speed performance decreases under low light intensity.

[0059] The single-carrier photodiode in the embodiment can also include an active region, and the diameter of the active region can be 20μm. By selecting a collection layer composed of InP material of 1500nm, the parasitic capacitance caused by a larger active region diameter is greatly reduced.

[0060] The single-carrier photodiode provided by the embodiment of the present application can reduce the parasitic capacitance in the single-carrier photodiode, thereby improving the total bandwidth of the single-carrier photodiode, and improving the working efficiency of the single-carrier photodiode.

[0061] The present application proposes a new type of single-carrier photodiode with long collection layer for controlling electron transport and capacitance by light intensity as a detector to obtain excellent high-speed response and high saturation characteristics in the RoF communication system, while greatly reducing the coupling loss with the optical fiber. The high capacitance of the 20 μm diameter photodiode detector can be compensated to improve the response bandwidth; the electron transport and capacitance are controlled based on the incident light intensity to further optimize the high-speed performance, and the doping concentration of the cliff layer is improved to make the electric field distribution more uniform, the power consumption lower, the doping concentration of the collection layer is optimized to bring charge compensation, thereby greatly improving the response bandwidth and saturation performance.

[0062] Figure 2 The test result diagram of the single-carrier photodiode provided by the embodiment of the present application is shown in FIG. 1. Figure 2 Figure 2 When the incident light intensity in the single-carrier photodiode increases from 0 to 6×10 4 W / cm 2 , the change diagram of the electric field distribution of the collection layer is shown in FIG. 2.

[0063] Specifically, in the single-carrier photodiode, when the incident light intensity in the arrow direction is 0, 2×10 4 W / cm 2 , 4×10 4 W / cm 2 , and 6×10 4 W / cm 2 , respectively, the front end electric field intensity of the collection layer gradually decreases, and the rear end electric field intensity of the collection layer gradually increases as the incident light intensity gradually increases.

[0064] Specifically, in the single-carrier photodiode, the initial electric field intensity of the collection layer is 40 kV / cm under no light incidence, and the 3×10 15 cm -3 ~ 1×10 15 cm -3 gradual doping of the collection layer has pre-enhanced the electric field of the front end of the collection layer.

[0065] ​Specifically, in a single-row carrier photodiode, when the incident light intensity is 6 × 10⁻⁶... 4 W / cm 2 At this time, the electric field strength at the front end of the collection layer is higher than 10kV / cm, and there is no electron accumulation at the front end of the collection layer that would affect the high-speed performance of the photodetector.

[0066] In one embodiment, for a single-carrier photodiode, the cliff layer doping concentration along the arrow direction is 1×10 18 cm -3 Reduced to 5×10 17 cm -3 At that time, the electric field distribution of the collecting layer changes: the electric field intensity at the end of the collecting layer increases, and the electric field distribution of the collecting layer becomes more uniform.

[0067] Specifically, for a single-row carrier photodiode, when the cliff layer doping concentration increases from 1×10⁻⁶... 18 cm -3 Reduced to 5×10 17 cm -3 At that time, the electric field strength at the end of the collection layer increased from about 0 kV / cm to 12 kV / cm.

[0068] Figure 3 This is the second schematic diagram of the test results of a single-row carrier photodiode provided in the embodiments of this application, as shown below. Figure 3 As shown, Figure 3 The diagram shows that for a single-row carrier photodiode, the incident light intensity increases from 0 to 6 × 10⁻⁶. 4 W / cm 2 The change in electron velocity distribution in the collection region over time.

[0069] Specifically, for a single-row carrier photodiode, the incident light intensities along the arrow direction are 0 and 2 × 10⁻⁶, respectively. 4 W / cm 2 4×10 4 W / cm 2 6×10 4 W / cm 2 At that time, the electron velocity at the front end of the collection region gradually increases.

[0070] Specifically, for a single-row carrier photodiode, the incident light intensity increases from 0 to 6 × 10⁻⁶. 4 W / cm 2 At that time, the overall electron velocity of the collecting layer gradually increases.

[0071] Figure 4 This is the third schematic diagram illustrating the test results of a single-row carrier photodiode provided in an embodiment of this application. Figure 4 As shown, for a single-row carrier photodiode, at operating voltages of 4V, 5V, and 6V, the bandwidth first increases and then decreases as the incident light intensity increases.

[0072] Specifically, the photoelectric detector working at 4V voltage, with the increase of incident light intensity, the internal electronic pile-up is generated, and the bandwidth decreases quickly; the photoelectric detector working at 5V voltage, with the increase of incident light intensity, the bandwidth reaches the maximum 106GHz when the incident light intensity is 6x10 4 W / cm 2 Then decreases; the photoelectric detector working at 6V voltage, the bandwidth is lower than that of the photoelectric detector working at 5V voltage under the same incident light intensity, and the maximum light intensity is only 92GHz.

[0073] Wherein, Figures 2-4 The horizontal coordinates are all Distance, i.e. thickness, and the unit is μm, i.e. micrometer; the horizontal coordinates are all Electric Field, i.e. electric field, and the unit is V / cm, i.e. volt per centimeter.

[0074] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A single-carrier photodiode, characterized by, The single-row carrier photodiode comprises a p-type contact layer, an electron blocking layer, an absorption layer, a spacer layer, a mesa layer, a collection layer, a sub-collection layer, an n-type contact layer connected in sequence; and a p-electrode on the p-type contact layer and an n-electrode on the n-type contact layer; The thickness of the collection layer is 1500 nm to 1700 nm. The material of the collection layer comprises InP with a gradually changed doping concentration. The material of the mesa layer comprises InP. The doping concentration of InP in the cliff layer is 5x10 17 cm -3 -2 The diameter of the active region of the single-row carrier photodiode is 20 μm. The doping concentration of InP in the collection layer is 3 x 10 15 cm -3 near the side of the mesa layer, gradually changing to 1 x 10 15 cm -3 near the side of the n-type contact layer.

2. The single-carrier photodiode of claim 1, wherein, The thickness of the mesa layer is 50 nm to 70 nm.

3. The single-carrier photodiode of claim 2, wherein, The thickness of the mesa layer is 70 nm.

4. The single-carrier photodiode of claim 1, wherein, The sub-collection layer comprises at least a first sub-collection layer and a second sub-collection layer, and the first sub-collection layer and the second sub-collection layer are structure layers with different doping concentrations of InP.

5. The single-carrier photodiode of claim 1, wherein, The material of the spacer layer comprises InGaAsP and InP.

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