Photodetectors with charge collection regions

Abstract

The techniques described herein relate to photodetectors with charge collection regions. An example photodetector includes a first doped semiconductor region configured to receive light and generate first charge carriers in response to the received light, and a second doped semiconductor region surrounding the first doped semiconductor region and configured to send second charge carriers generated outside the first doped semiconductor region to ground.

Description

Attorney Docket No. 96531021PHOTODETECTORS WITH CHARGE COLLECTION REGIONSRELATED APPLICATION

[0001] This patent claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 63 / 687,433, titled “PHOTODETECTORS WITH CHARGE COLLECTION REGIONS,” fded on August 27, 2024, which is hereby incorporated by reference in its entirety.FIELD

[0002] The techniques described herein relate generally to photodetectors and, more particularly, to photodetectors with charge collection regions.BACKGROUND

[0003] A photodetector is an electric device that detects light or optical power and converts it into an electrical signal. Photodetectors may be used to detect light such as infrared light (IR), ultraviolet (UV), or visible light. Semiconductor photodetectors (e.g., photodiodes) operate in accordance with electron-hole pair generation principles when exposed to light to achieve fast detection speed, high detection efficiency, and small size.SUMMARY

[0004] In accordance with the disclosed subject matter, apparatus, systems, and methods are provided for photodetectors with charge collection regions.

[0005] Some embodiments relate to a photodetector. The photodetector comprises a first doped semiconductor region configured to receive light and generate first charge carriers in response to the received light, and a second doped semiconductor region surrounding the first doped semiconductor region and configured to send second charge carriers generated outside the first doped semiconductor region to ground.

[0006] Some embodiments relate to a diode. The diode comprises a cathode, an anode comprising a first doped semiconductor region and a first metal ring surrounding the first doped semiconductor region, and a second doped semiconductor region surrounding the first doped semiconductor region.

[0007] Some embodiments relate to a package. The package comprises at least one terminal, and a plurality of photodetectors arranged in a matrix. A first one of the plurality of photodetectors comprising an output to the at least one terminal, a cathode, an anodeAttorney Docket No. 96531021 comprising a first doped semiconductor region and a first metal ring surrounding the first doped semiconductor region, and a second doped semiconductor region surrounding the first doped semiconductor region.

[0008] The foregoing summary is not intended to be limiting. Moreover, various aspects of the present disclosure may be implemented alone or in combination with other aspects.BRIEF DESCRIPTION OF FIGURES

[0009] Various aspects and embodiments will be described with reference to the following figures. It should be appreciated that the figures are not necessarily drawn to scale. Items appearing in multiple figures are indicated by the same or a similar reference number in all the figures in which they appear.

[0010] FIG. 1 is an illustration of a cross section of a side view of a first example photodetector with a charge collection region, according to some embodiments.

[0011] FIG. 2 is an illustration of example operation of the first photodetector of FIG. 1, according to some embodiments.

[0012] FIG. 3 is an illustration of a cross section of a side view of a second example photodetector with a charge collection region, according to some embodiments.

[0013] FIG. 4 is an illustration of example operation of the second photodetector of FIG. 3, according to some embodiments.

[0014] FIG. 5 is an illustration of a top view of a photodetector without the charge collection region of FIGS. 1-4, according to some embodiments.

[0015] FIG. 6 is an illustration of a top view of the first photodetector of FIGS. 1-2 and / or the second photodetector of FIGS. 3-4, according to some embodiments.

[0016] FIG. 7 is a graph representative of example operation of the photodetector of FIG. 5, according to some embodiments.

[0017] FIG. 8 is a graph representative of example operation of the photodetector of FIGS. 1, 2, 3, 4, and / or 6, according to some embodiments.DETAILED DESCRIPTION

[0018] The present application generally provides for photodetectors, such as semiconductor photodetectors, configured with an active region for detecting light and a charge collection region (e.g., a diffused charge collection region) around the active region. When light irradiates a semiconductor photodetector outside the active region, electron-hole pairs are generated and resulting charge carriers may diffuse slowly, some of them reaching the activeAttorney Docket No. 96531021 region. In contrast to conventional semiconductor photodetectors, which have a tail in response time due to charge carriers reaching the active region, the charge collection region can be configured to attract and send these charge carriers to electric ground.Advantageously, by sending the charge carriers to electric ground, photodetectors as disclosed herein can eliminate and / or otherwise reduce the tail in response time and thereby achieve improved recovery time and reduced signal noise with respect to a photodetector without the charge collection region.

[0019] A semiconductor photodetector operates such that when irradiated with high or equivalent energy to its bandgap, the absorbed photons induce valence band electrons (e.g., negative charge carriers) in an active region of the photodetector to migrate into the conduction band, leaving positively charged holes (e.g., positive charge carriers) in the valence band. The electrons in the conduction band behave as free electrons that can scatter in the presence of an electric field, which can either be intrinsic or externally imposed.

[0020] When an electric field is applied to the active region, the holes in the valence band diffuse towards the anode of the photodetector and the electrons in the conduction band diffuse towards the cathode of the photodetector. This diffusion towards the cathode / anode generates a photocurrent that can be output and / or measured. The magnitude of photocurrent at a given wavelength corresponds to the intensity of light flooded onto the active region. Thus, the magnitude of the resulting output signal can correspond to the intensity of light measured by the photodetector.

[0021] Photodetectors, such as semiconductor photodetectors, may generally be referred to as optical detectors, opto-electronic devices, or detectors. Examples of semiconductor photodetectors, that may generally be referred to as photodiodes, include avalanche photodiodes (APDs) and p-i-n (PIN) photodiodes. APD detectors are PN or PIN junctiontype photodetection diodes that use the avalanche multiplication effect of carriers to amplify optical signals to improve detection sensitivity. APD detectors have internal gain due to a high electric field and the avalanche effect arrives through impact ionization from charge carriers. For example, an indium gallium arsenide (InGaAs) APD detector has an InGaAs layer that is grown lattice matched on an indium phosphide (InP) substrate. In such an example, the InGaAs layer has the role of absorbing light in a wavelength range of approximately 900-1700 nanometers (nm).

[0022] PIN detectors are photodetection diodes with an intrinsic (I) layer placed between the positive (P) and negative (N) doped layers. The intrinsic layer is highly resistive and increases the electric field strength in the photodiode. For example, an InGaAs PIN detectorAttorney Docket No. 96531021 also has an InGaAs absorber layer but no internal gain. This InGaAs absorber layer absorbs light in a wavelength range of approximately 900-1700 nm. Thus, PIN detectors are very effective in detecting light in the short infrared range that is used for various applications, such as range finding and telecommunications.

[0023] When compared to other types of photodetectors, such as silicon photodetectors, the InGaAs photodetectors (e.g., InGaAs APD photodetectors, InGaAs PIN photodetectors) are much noisier. To keep noise under control, InGaAs photodetectors are manufactured in much smaller sizes (e.g., with respect to silicon photodetectors) and are made with diameter of the active region in a range from 15 micrometers (pm) to 500 pm for InGaAs APD photodetectors and in a range from 30 pm to 10 mm for InGaAs PIN photodetectors. The inventors have recognized that it would be desirable for InGaAs photodetectors to be manufactured with increased active region sizes without incurring signal noise penalties.

[0024] Photodetectors, such as InGaAs photodetectors, can have different designs (e.g., configurations). A first photodetector design is a planar design with a diffused anode. Planar InGaAs photodetectors are reliable and can generate very low dark currents but when light reaches outside the active region, there is an InGaAs layer in those regions as well and charge carriers are generated. There is no electric field outside the active region, and these carriers will slowly diffuse towards the active region generating a slow signal at the end, which may be referred to as a tail (e.g., a tail of the signal, a signal tail). This slow signal, when overlapped on the fast signal from the active region, will appear as a tail (e.g., a small tail) in the recovery time, which increases the recovery time of the photodetector. The inventors have recognized that such a tail is detrimental for various applications, such as range finding or Optical Time Domain Reflectometry (OTDR).

[0025] The response time of a photodiode is the time needed for the photodiode to respond to an optical input. For example, a photon absorbed by the semiconducting material will generate an electron-hole pair, which in turn starts moving in the semiconducting material under the effect of an electric field and thus generate a current. The inventors have recognized that operation and / or performance of photodetectors having a planar design can be improved by removing the tail to improve the response time (e.g., reduce the response time). A conventional technique for reducing the tail in recovery time is to use a planar design with a thicker InGaAs absorber layer. However, the inventors have recognized that increasing the thickness of the InGaAs absorber layer increases the dark current and noise levels because the InGaAs layer provides a significant contribution to the dark current in the photodetector structure. The inventors have recognized that in order to absorb all light throughout theAttorney Docket No. 96531021 absorption spectrum for InGaAs (e.g., an absorption spectrum range of approximately 900- 1700 nm), such as at 1650 nm, a substantially thick InGaAs absorber layer would be needed. However, a thick InGaAs layer causes an increase in the overall response time of the photodetector and reduces its bandwidth.

[0026] The inventors have recognized that when light is focused on the active region with optical fibers and lenses, the tail can be less important at wavelengths efficiently absorbed by the InGaAs absorber layer, such as at 1300 nm or 1550 nm, but the tail can be identified at wavelengths of 1650 nm, which are towards the end range of the absorption spectrum for InGaAs and are less absorbed. For example, a high percentage of the 1650 nm light would pass through the InGaAs layer and has a relatively high probability of being reflected outside the active region in the InGaAs layer. The inventors have recognized that this effect is even more important for small size InGaAs detectors at 1650 nm. The inventors have also recognized that a similar effect would occur at 900 nm or below, which are also not well absorbed by InGaAs.

[0027] A second photodetector design is a mesa design where the material around the active region is physically removed to isolate the active region. Mesa type designs typically have lower noise factor in the APD photodetector design but are more difficult to passivate, often have higher dark currents, and have a lower reliability or less resistance to high electrical powers due to the physical isolation and poor lateral heat conductivity. For a mesa type InGaAs photodetector, due to the physical etch of the InGaAs absorber around, there is no contribution of current generated outside the active region.

[0028] The inventors have developed example photodetectors as disclosed herein that overcome the aforementioned technical challenges of conventional photodetector designs. The inventors have developed example photodetectors with an additional diffused charge collection region, which can be implemented as a ring (e.g., a diffused charge collection ring), that is not electrically connected to the anode and configured for the purpose of collecting charge carriers generated outside the active region and sending them to electrical ground. Beneficially, recovery time of the photodetectors can be reduced by collecting and sending charge carriers to electrical ground instead of allowing them to slowly diffuse to the active region. For example, when light reaches outside the active region or when light is reflected from the back side of the photodetectors disclosed herein, no tail is observed in the response time of the photodetectors.

[0029] In some embodiments, the photodetectors developed by the inventors include InGaAs photodetectors. In such embodiments, the photodetectors are InGaAs photodetectors.Attorney Docket No. 96531021Examples of the InGaAs photodetectors disclosed herein include APD photodetectors and PIN photodetectors.

[0030] In some embodiments, the photodetectors developed by the inventors include an anode, a cathode, an active region, and a charge collection region around the active region. In some embodiments, the charge collection region can be diffused. For example, the active region can be a first diffused region and the charge collection region can be a second diffused region (e.g., a diffused charge collection region). In some embodiments, the charge collection region can be non-diffused as well.

[0031] In example operation, when an electric field is applied between the anode and cathode, charge carriers outside the active region can be generated. In example operation, the electric field is also applied between the cathode and the charge collection region, which enables the charge collection region to attract the charge carriers that are generated outside the active region and send the attracted charge carriers to electrical ground. Beneficially, by sending the charge carriers to ground, the photodetectors disclosed herein ensure that the charge carriers do not contribute to the principal signal generated and / or output by the photodetector. By eliminating the contribution to the principal signal, the tail can be eliminated and / or otherwise reduced to achieve reduced recovery time and improved photodetector performance.

[0032] The techniques described herein may be implemented in any of numerous ways, as the techniques are not limited to any particular manner of implementation. Examples of details of implementation are provided herein solely for illustrative purposes. Furthermore, the techniques disclosed herein may be used individually or in any suitable combination, as aspects of the technology described herein are not limited to the use of any particular technique or combination of techniques.

[0033] Turning to the figures, the illustrated example of FIG. 1 depicts a cross section of a side view of a first example photodetector 100. The first photodetector 100 is a PIN photodetector (e.g., a PIN photodiode). In some embodiments, the first photodetector 100 is an indium-gallium-arsenide (InGaAs) photodetector. For example, the first photodetector 100 can be an InGaAs PIN photodetector.

[0034] The first photodetector 100 is a diode (e.g., a photodiode). The first photodetector 100 of this example includes an active region 102 (identified by “P REGION”), an absorption region 104, which is non-doped and is the intrinsic region of the diode (identified by “ABSORPTION REGION”) and a substrate region 108 (identified by “N REGION”). TheAttorney Docket No. 96531021 active region 102 is an active area and may be referred to as a P region (e.g., a P+ region). For example, the active region 102 can be a highly-doped transparent p-type contact layer.

[0035] The active region 102 is a doped semiconductor region. The doped semiconductor region can be a diffused region. Alternatively, the doped semiconductor region may be an implant having substantially the same electrical characteristics as a diffused region.

[0036] The active region 102 can be an active diffused region that establishes the photodiode active area. For example, the active region 102 can be a defined area that is diffused to create a PN or NP junction, which can convert photons into current. The active region 102 can be a P+ indium phosphide (InP) layer.

[0037] The active region 102 of this example has a circular shape. Alternatively, the active region 102 may be any shape, such as a rectangular (e.g., a square) shape.

[0038] The active region 102 can vary in size from less than a square millimeter (mm) to over a square centimeter. In some embodiments, the active region 102 can have a diameter in a range from 5 pm to 10 mm. Alternatively, the active region 102 can have a diameter in a different range, such as 1 pm to 20 mm.

[0039] The absorption region 104 of this example is constructed from InGaAs. Alternatively, the absorption region 104 may be constructed from one or more different materials.

[0040] The InGaAs layer is non-doped and accounts for the intrinsic region of the diode as well; it is highly resistive and increases the electric field strength in the first photodetector 100. In some embodiments, there can be an added intrinsic region 106 (identified by “I REGION”) that can be constructed from InP. Alternatively, the intrinsic region 106 may be constructed from one or more different materials.

[0041] In some embodiments, the absorption region 104 and the intrinsic region 106 form a depletion region of the first photodetector 100. For example, the absorption region 104 can be a first portion of a depletion region of the first photodetector 100 and the intrinsic region 106 can be a second portion of the depletion region.

[0042] The substrate region 108 is a highly-doped n-type layer. For example, the substrate region can be an N-type bulk InP wafer.

[0043] The first photodetector 100 of this example includes a dielectric portion 110 disposed on a first surface (e.g., a first side) of the first photodetector 100. For example, the dielectric portion 110 can be a dielectric disposed on the first surface of the first photodetector 100.

[0044] Examples of the dielectric portion 110 include aluminum oxide (A12O3), silicon monoxide (SiO), silicon nitride (Si3N4), silicon dioxide (SiO2), and titanium dioxide (TiO2). For example, the dielectric portion 110 can be constructed from SiO2.Attorney Docket No. 96531021

[0045] In some embodiments, the active region 102 is passivated with an antireflection coating (not shown) to reduce the reflection of the light for a specific predefined wavelength. For example, an antireflection coating can be disposed over the dielectric region 110. Alternatively, the dielectric region 110 may be disposed over the antireflection coating such that the antireflection coating is disposed between the dielectric region 110 and the active region 102.

[0046] The first photodetector 100 of this example includes a metal portion 112 disposed on a second surface (e.g., a second side) of the photodetector 100. For example, the metal portion 112 can be on one or more metals disposed on the second surface of the first photodetector 100. The second surface is opposite the first surface. The second side is opposite to the first side.

[0047] Examples of the metal portion 112 include copper, gold, platinum, chrome, tin and titanium. For example, the metal portion 112 can be constructed from gold.

[0048] In some embodiments, one or more contact pads can be disposed over portions of the first surface of the first photodetector 100. For example, the one or more contact pads can be disposed over portions of the active region 102. The one or more contact pads can have any shape. Examples of shapes include circular (e.g., ring, oval, elliptical), rectangular, and square. Alternatively, one or more other types of electrical connections such as traces, wires, or vias may be disposed over portions of the first surface of the first photodetector 100.

[0049] In the illustrated example, the one or more contact pads are implemented at least in part as a metal ring 114 deposited over an outer perimeter of the active region 102. The metal ring 114 can be constructed of one or more metals. Examples of the one or more metals include copper, gold, platinum, chrome, tin, and / or titanium. For example, the metal ring 114 can be a gold metal ring.

[0050] The first photodetector 100 of this example includes a charge collection region 116. The charge collection region 116 of this example is implemented as a ring (e.g., a diffused charge collection ring) surrounding the active region 102. For example, from a birds-eye view of the first surface of the first photodetector 100 (e.g., the surface on which the dielectric 110 is disposed), the active region 102 (e.g., an entirety of the active region 102) can be disposed within an interior of the ring formed by the charge collection region 116.

[0051] The charge collection region 116 is a doped semiconductor region. The doped semiconductor region can be a diffused region (e.g., a diffused semiconductor region). The doped semiconductor region can be a highly-doped transparent p-type contact region. ForAttorney Docket No. 96531021 example, the charge collection region 116 can be a region (e.g., an area) of P+ indium phosphide (InP).

[0052] The diffusion depths of the charge collection region 116 can vary. For example, the charge collection region 116 can be diffused to a depth in a range from 0.1 pm to 20 pm. In such an example, the charge collection region 116 can be diffused to a depth of 1 pm from the first surface of the first photodetector 100. Alternatively, the charge collection region 116 can be diffused to a depth in a different range, such as from 0.1 pm to 350 pm.

[0053] The charge collection region 116 of this example is metalized. For example, a metal region can be disposed over the charge collection region 116 by covering the charge collection region 116. The metal region of this example is a metal layer implemented as a metal ring 118 that can be constructed of one or more metals. The metal ring 118 can be configured such that it can be wire bonded. The metal ring 118 can be configured such that a bias can be applied between a cathode of the first photodetector 100 and the charge collection region 116. For example, the cathode can be configured to be coupled to a voltage source configured to bias the cathode with a positive voltage with respect to the anode of the first photodetector 100 under reverse bias conditions.

[0054] Examples of the one or more metals include copper, gold, platinum, chrome, tin and / or titanium. For example, the metal ring 118 can be a gold metal ring.

[0055] The charge collection region 116 can vary in size. In some embodiments, the charge collection region 116 can have a diameter in a range from 5 pm to 10 mm. For example, the charge collection region 116 can have a diameter of 100 pm. Alternatively, the charge collection region 116 can have a diameter in a different range, such as 1 pm to 20 mm.

[0056] The charge collection region 116 of this example is electrically separated from the active region 102. For example, the charge collection region 116 may not be electrically connected and / or otherwise electrically in circuit with the active region 102.

[0057] The charge collection region 116 of this example is physically separated from the active region 102. For example, a distance between an outer perimeter of the active region 102 and an inner perimeter of the charge collection region 116 can be in a range from 2 pm to 200 pm. Alternatively, the distance may be in a different range, such as a range from 1 pm to 300 pm.

[0058] In some embodiments, the metal ring 114 disposed over the active region 102 can be constructed using the same material(s) as the metal ring 118 disposed over the charge collection region 116. Alternatively, the metal ring 114 disposed over the active region 102Attorney Docket No. 96531021 can be constructed using different material(s) as the metal ring 118 disposed over the charge collection region 116.

[0059] FIG. 2 is an illustration of example operation of the first photodetector 100 of FIG. 1. The first photodetector 100 shown in FIG. 2 is coupled to an anode 202, a cathode 204, and ground 206 (e.g., electrical ground, physical ground, physical earth ground).

[0060] As shown, the metal ring 114 of the active region 102 is coupled to the anode 202.For example, the metal ring 114 of the active region 102 can be wire bonded to the anode 202 of the first photodetector 100.

[0061] As shown, the metal region 112 is over the doped substrate and coupled to the cathode 204. For example, the metal region 112 can be wire bonded to the cathode 204 of the first photodetector 100.

[0062] In some embodiments the metal 112 can be deposited on the front side and coupled with the substrate through an etched via. Such a design is a co-planar design in which the anode and the cathode are on the same side of the photodetector.

[0063] As shown, the metal ring 118 of the charge collection region 116 is coupled to the ground 206. For example, the metal ring 118 of the charge collection region 116 can be wire bonded to the ground 206.

[0064] In the illustrated example, the cathode 204 can be biased with a positive electrical voltage with respect to the anode 202 under reverse bias conditions to cause generation of an electric field 208. The electric field 208 is represented by electric field lines in the absorption region 104. Alternatively, there may be a non-zero voltage between the charge collection region 116 and the cathode 204 to cause generation of the electric field 208.

[0065] In example operation, light 210 can be focused onto the active region 102. For example, the light 210 can be focused onto the active region 102 with optical fibers and / or lenses. In such an example, the active region 102 can be configured to receive the light 210.

[0066] In some embodiments, the light 210 is focused (e.g., focalized) on the active region 102. In some embodiments, the light 210 is flooded more generally on the first photodetector 100.

[0067] In example operation, the light 210 absorbed by the absorption layer 104 can generate electron-hole pairs within the absorption layer 104. The holes can be driven towards the anode 202 by the applied electric field 208 while the electrons can be driven towards the cathode 204.

[0068] The light 210 can be light in a wavelength range of 900 to 1700 nm. For example, the light 210 can be infrared light.Attorney Docket No. 96531021

[0069] In a conventional PIN photodetector, the charge carriers that are generated outside an active region of the photodetector in response to light onto the active region would normally diffuse towards the active region and collected by the anode or the cathode afterwards. The diffusion process is much longer than the drift process in an electric field, which can generate a tail in the response time of a conventional photodetector.

[0070] Beneficially, with the added charge collection region 116, the carriers generated outside of the active region 102 in response to light 210 are collected by this charge collection region 116 and are sent to the ground 206. Beneficially, this signal will not contribute to the signal generated by the active region 102 and eliminate and / or otherwise reduce the tail in the response time of the first photodetector 100. Advantageously, the first photodetector 100 has improved response time with respect to a conventional PIN photodetector at least in part because of the charge collection region 116.

[0071] The first photodetector 100 can implement a front entry photodetector where the cathode 204 is on the back side of the first photodetector 100 and the light 210 reaches the first photodetector 100 on the anode side. Alternatively, in some embodiments, the first photodetector 100 can implement a rear entry photodetector where the anode 202 is on the back side of the first photodetector 100 and the light 210 reaches the first photodetector 100 on the cathode side, but the charge collection region 116 surrounds the anode 202 that is electrically connected.

[0072] FIG. 3 is an illustration of a cross section of a side view of a second example photodetector 300 with the charge collection region 116 of FIGS. 1-2. The second photodetector 300 is a diode (e.g., a photodiode).

[0073] The second photodetector 300 is an avalanche photodetector (e.g., an avalanche photodiode). In some embodiments, the second photodetector 300 is an InGaAs photodetector. For example, the second photodetector 300 can be an InGaAs avalanche photodetector.

[0074] The second photodetector 300 of this example includes the dielectric portion 110, the metal portion 112, the metal ring 114, the charge collection region 116, and the metal ring 118 of the first photodetector 100 of FIGS. 1-2. The second photodetector 300 of this example an active region 302, an absorption region 304, an added optional intrinsic region 306, and a substrate region 308 configured to implement an avalanche photodetector. The active region 302 of this example is a doped semiconductor region. The doped semiconductor region can be a diffused region (e.g., a diffused active region, a diffused semiconductor region).Attorney Docket No. 96531021

[0075] In some embodiments, one or more of the active region 302, the absorption region 304, the intrinsic region 306, and / or the substrate region 308 of the second photodetector 300 of FIG. 3 may be the same as the active region 102, the absorption region 104, the intrinsic region 106, and / or the substrate region 308 of the first photodetector 100 of FIGS. 1-2. For example, the substrate region 308 of FIG. 3 can correspond to and / or be the same as the substrate region 108 of FIG. 1.

[0076] In some embodiments, one or more of the active region 302, the absorption region 304, the intrinsic region 306, and / or the substrate region 308 of the second photodetector 300 of FIG. 3 may be different than the active region 102, the absorption region 104, the intrinsic region 106, and / or the substrate region 308 of the first photodetector 100 of FIGS. 1-2. For example, the intrinsic region 304 of FIG. 3 can be different than the intrinsic region 104 of FIG. 1. In such an example, the intrinsic region 304 of FIG. 3 can be lightly p-doped (and may be referred to as the n layer) while the intrinsic region 104 of FIG. 1 can be lightly n- doped.

[0077] FIG. 4 is an illustration of example operation of the second photodetector 300 of FIG. 3. The second photodetector 300 shown in FIG. 4 is coupled to an anode 402, a cathode 404, and ground 406 (e.g., electrical ground, physical ground, physical earth ground).

[0078] As shown, the metal ring 114 of the active region 302 is coupled to the anode 402.For example, the metal ring 114 of the active region 302 can be wire bonded to the anode 402 of the second photodetector 300.

[0079] As shown, the metal region 112 is coupled to the cathode 404. For example, the metal region 112 can be wire bonded to the cathode 404 of the second photodetector 300.

[0080] As shown, the metal ring 118 of the charge collection region 116 is coupled to the ground 406. For example, the metal ring 118 of the charge collection region 116 can be wire bonded to the ground 406.

[0081] In the illustrated example, the cathode 404 can be biased with a positive electrical voltage with respect to the anode 402 under reverse bias conditions to cause generation of an electric field 408. The electric field 408 is represented by electric field lines in the absorption region 304. Alternatively, there may be a non-zero voltage between the charge collection region 116 and the cathode 404 to cause generation of the electric field 408.

[0082] In example operation, light 410 can be focused onto the active region 302. For example, the light 410 can be focused onto the active region 302 with optical fibers and / or lenses.Attorney Docket No. 96531021

[0083] In example operation, the light 410 absorbed by the absorption layer 304 can generate electron-hole pairs within the absorption layer 304. The holes can be driven towards the anode 402 by the applied electric field 208 while the electrons can be driven towards the cathode 404.

[0084] The light 410 can be light in a wavelength range of 900 to 1700 nm. For example, the light 410 can be infrared light.

[0085] In a conventional avalanche photodetector, the charge carriers that are generated outside an active region of the photodetector in response to light onto the active region would normally diffuse towards the active region and collected by the anode or the cathode afterwards. The diffusion process is much longer than the drift process in an electric field, which can generate a tail in the response time of a conventional photodiode.

[0086] Beneficially, with the added charge collection region 116, the carriers generated outside of the active region 302 in response to light 410 are collected by this charge collection region 116 and are sent to the ground 406. Beneficially, this signal will not contribute to the signal generated by the active region 302 and eliminate and / or otherwise reduce the tail in the response time of the second photodetector 300. Advantageously, the second photodetector 300 has improved response time with respect to a conventional avalanche photodetector at least in part because of the charge collection region 116.

[0087] The second photodetector 300 can implement a front entry photodetector where the cathode 404 is on the back side of the first photodetector 100 and the light 210 reaches the first photodetector 100 on the anode side. Alternatively, in some embodiments, the second photodetector 300 can implement a rear entry photodetector where the anode 402 is on the back side of the second photodetector 300 and the light 210 reaches the second photodetector 300 on the cathode side, but the charge collection region 116 surrounds the anode 402 that is electrically connected.

[0088] FIG. 5 is an illustration of a top view of a photodetector 500 without the charge collection region 116 of FIGS. 1-4. For example, the photodetector 500 can be a PIN photodetector (e.g., an InGaAs PIN photodetector) or an avalanche photodetector (e.g., an InGaAs avalanche photodetector).

[0089] The photodetector 500 includes an active region 502 and a metal layer 504 encircling the active region 502. When the active region 502 absorbs tight, electron-hole pairs can be generated. The charge carriers that are generated outside the active region 502 of the photodetector 500 in response to light onto the active region 502 can diffuse towards the active region 502 and collected by the anode or the cathode afterwards. For example, lightAttorney Docket No. 96531021 reaching outside the active region 502, directly or through reflections from the back side of the photodetector package, create electron-hole pairs of carriers that would diffuse slowly, some of them reaching the active region 502. Once reaching the active region 502, they are collected by the electric field and would give a slow contribution that shows like a tail in response time. This tail in the response time of the photodetector 500 is generated because the diffusion process is much longer than the drift process in an electric field.

[0090] FIG. 6 is an illustration of a top view of an example photodetector 600 as disclosed herein. For example, the photodetector 600 of FIG. 6 can be implemented by the first photodetector 100 of FIGS. 1-2 and / or the second photodetector 300 of FIGS. 3-4.

[0091] The photodetector 600 includes an active region 602 and a metal region 604 encircling the active region 602. In some embodiments, the active region 602 and the metal region 604 correspond to the active region 102 and the metal ring 114, respectively, of FIGS. 1-2. In some embodiments, the active region 602 and the metal region 604 correspond to the active region 302 and the metal ring 114, respectively, of FIGS. 3-4.

[0092] The active region 602 is a doped semiconductor region. The doped semiconductor region can be a diffused region (e.g., a diffused active region, a diffused semiconductor region). The active region 602 of this example has a circular shape. Alternatively, the active region 602 may have a different shape, such as rectangular (e.g., square).

[0093] In some embodiments, the active region 602 can have a diameter in a range from 5 pm to 10 mm. Alternatively, the active region 602 can have a diameter in a different range, such as 1 pm to 20 mm.

[0094] The metal region 604 of this example is a metal layer having a circular shape. As shown, the metal region 604 can be implemented as a metal ring surrounding the active region 602. Alternatively, the metal region 604 may have a different shape, such as rectangular (e.g., square).

[0095] In the illustrated example, the photodetector 600 includes a charge collection region 606 and a metal region 608 covering the charge collection region 606. The metal region 608 is a metal layer. In some embodiments, the charge collection region 606 and the metal region 608 correspond to the charge collection region 606 and the metal ring 118, respectively, of FIGS. 1-4.

[0096] The charge collection region 606 of this example has a circular shape, which is shown as an ellipse; however it can have a non-regular or rectangular shape as well. The charge collection region 606 has varying widths 610 (identified by “W”) along a length 612 (identified by “L”) of the charge collection region 606. Alternatively, the charge collectionAttorney Docket No. 96531021 region 606 may have uniform width (e.g., the same width) along the length 612 of the charge collection region 606.

[0097] As shown, the metal region 608 is a metal layer having a circular shape and covers the charge collection region 606. Alternatively, the metal region 608 may have a different shape, such as rectangular (e.g., square).

[0098] The charge collection region 606 can vary in size. In some embodiments, the largest diameter of the charge collection region 606 can be in a range from 5 pm to 10 mm. For example, the largest diameter of the charge collection region 606 can be 1 mm. Alternatively, the largest diameter of the charge collection region 606 can be in a different range, such as 1 pm to 20 mm.

[0099] In some embodiments, the photodetector 600 can be mounted in a package. For example, the package can be an integrated circuit (IC) package. Examples of packages include a ceramic package and a transistor outline (TO) package. For example, the photodetector 600 can be mounted in a ceramic package as long as the metal region 608 of the charge collection region 606 is electrically connected and separate from anode circuitry.

[0100] In some embodiments, the photodetector 600 is implemented as part of a photodetector array (e.g., a photodetector matrix, a photodiode array / matrix). For example, the photodetector 600 can be included in a single package with multiple other photodetectors. The photodetectors, which include the photodetector 600, included in the package can be configured to form a photodetector array. Alternatively, the photodetector 600 may be part of a photodetector array not included in a package.

[0101] By way of example, the photodetector 600 can be included in a package. The package can include a plurality of terminals (e.g., electrical terminals, electrical connections) and a plurality of photodetectors. The plurality of photodetectors can be arranged in an array (e.g., a matrix). Each of the plurality of photodetectors can be coupled to a respective one of the plurality of terminals such that output from each of the plurality of photodetectors can be provided to another device. Examples of a device include lab measurement equipment, an analog-to-digital converter, and a computer hardware processor.

[0102] Furthering the example, a first one of the plurality of photodetectors can be the photodetector 600 of FIG. 6 (or the first photodetector 100 of FIGS. 1-2 or the second photodetector 300 of FIGS. 3-4). The photodetector 600 can include an output coupled to at least one of the plurality of terminals. The photodetector 600 can include a cathode, an anode, and the charge collection region 606. The anode can include the active region 602 and theAttorney Docket No. 96531021 metal ring 604 surrounding the active region 602. The charge collection region 606 can surround the first active region 602.

[0103] Beneficially, with the added charge collection region 606, the carriers generated outside of the active region 602 in response to light are collected by this charge collection region 606 and are sent to ground connected to the metal region 608. Beneficially, this signal will not contribute to the signal generated by the active region 602 and eliminate and / or otherwise reduce the tail in the response time of the photodetector 600. Advantageously, the photodetector 600 has improved response time with respect to a conventional photodetector, such as the photodetector 500 of FIG. 5, at least in part because of the charge collection region 606.

[0104] The first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and the photodetector 600 of FIG. 6 are improvements over conventional photodetectors and are useful in various applications. Example applications in which the first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and the photodetector 600 of FIG. 6 are useful include range finding (e.g., light detection and ranging (LIDAR)), Optical Time Domain Reflectometry (OTDR), and quantum cryptography. Each of these applications can benefit from a high bandwidth, fast response photodetector, such as the first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and the photodetector 600 of FIG. 6.

[0105] FIG. 7 is a graph 700 representative of example operation of a conventional photodetector, such as the photodetector 500 of FIG. 5. The graph 700 depicts measurements of a photodetector output signal with respect to time when light is focused on the active region 502. The photodetector output signal is represented in volts (V) and time is represented in seconds (s).

[0106] The graph 700 of FIG. 7 depicts the results of light focused on the active region 502 where the light has a wavelength of either 1317 nm (represented by first measurements 702) or 1650 nm (represented by second measurements 704). In some embodiments, the light can be generated using a 1 ps light pulse.

[0107] As depicted, the second measurements 704 show a tail 706 in the response time for wavelengths of 1650 nm, which are less absorbed by an InGaAs layer (e.g., the absorption region 104 of FIGS. 1-4) than wavelengths of 1317 nm.

[0108] FIG. 8 is a graph 800 representative of example operation of (i) the first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and / or the photodetector 600 of FIG. 6 and (ii) a conventional photodetector, such as the photodetectorAttorney Docket No. 96531021500 of FIG. 5. The graph 800 depicts measurements of a photodetector output signal with respect to time when light is focused on an active region (e.g., the active region 102 of FIGS. 1-2, the active region 302 of FIGS. 3-4, the active region 602 of FIG. 6). The photodetector output signal is represented in volts (V) and time is represented in seconds (s).

[0109] In the illustrated example, the graph 800 shows first measurements 802 corresponding to a photodetector output signal from the photodetector 500 when light having a wavelength of 1317 nm is focused on the active region 502. The graph 800 further shows second measurements 804 corresponding to a photodetector output signal from the photodetector 500 when light having a wavelength of 1650 nm is focused on the active region 502. The graph 800 also shows third measurements 806 corresponding to a photodetector output signal from the first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and / or the photodetector 600 of FIG. 6 when light having a wavelength of 1650 nm is focused on its active region.

[0110] As depicted, the second measurements 804 show a tail 808 in the response time for wavelengths of 1650 nm, which are less absorbed by an InGaAs layer (e.g., the absorption region 104 of FIGS. 1-4) than wavelengths of 1317 nm. Beneficially, by sending charge carriers generated outside the active region to ground using a charge collection region, such as the charge collection region 116 of FIGS. 1-4 and / or the charge collection region 606 of FIG. 6, the tail 808 is eliminated and / or otherwise reduced for the third measurements 806 with respect to the second measurements 804.

[0111] Beneficially, the photodetector output signal for the first photodetector 100 of FIGS. 1-2, the second photodetector 300 of FIGS. 3-4, and / or the photodetector 600 of FIG. 6 (represented by the third measurements 806) has similar performance when absorbing light throughout the wavelength range of the photodetector (e.g., a wavelength range of 900 to 1700 nm), which contrasts conventional photodetectors that have the tail 808 at the boundaries of the wavelength range of the photodetector.

[0112] Various aspects of the embodiments described above may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments.

[0113] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both,” of the elements so conjoined, e.g., elements that areAttorney Docket No. 96531021 conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, e.g., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as anon-limiting example, a reference to “A and / or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0114] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0115] As used herein in the specification and in the claims, the phrase, “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently, “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, ,and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0116] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0117] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” “having,”Attorney Docket No. 96531021“containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

[0118] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0119] Having thus described several aspects of at least one embodiment, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the spirit and scope of the principles described herein. Accordingly, the foregoing description and drawings are by way of example only.

Claims

Attorney Docket No. 96531021CLAIMS1. A photodetector comprising: a first doped semiconductor region configured to receive light and generate first charge carriers in response to the received light; and a second doped semiconductor region surrounding the first doped semiconductor region and configured to send second charge carriers generated outside the first doped semiconductor region to ground.

2. The photodetector of claim 1, wherein the first doped semiconductor region is a p- doped portion, the photodetector is a PIN photodetector comprising the p-doped portion, an n-doped portion, and an intrinsic portion, and the intrinsic portion is disposed between the p- doped portion and the n-doped portion.

3. The photodetector of claim 1, wherein the photodetector is an avalanche photodetector.

4. The photodetector of any one of claims 1-3, wherein the photodetector is an indium- gallium-arsenide (InGaAs) photodetector.

5. The photodetector of any preceding claim, further comprising: a first metal portion coupled to a portion of the first doped semiconductor region; and a second metal portion coupled to a portion of the second doped semiconductor region.

6. The photodetector of claim 5, wherein at least one of the first metal portion or the second metal portion is a metal ring.

7. The photodetector of any preceding claim, wherein the second charge carriers are generated outside the first doped semiconductor region in response to the received light.

8. The photodetector of claim 7, wherein the second doped semiconductor region is configured to collect the charge carriers generated outside the first doped semiconductor region.Attorney Docket No. 965310219. The photodetector any preceding claim, further comprising a first side and a second side, the second side opposite the first side, the first side comprising an anode, and the second side comprising a cathode.

10. The photodetector of claim 9, wherein the anode comprises the first doped semiconductor region.

11. The photodetector of claim 9, further comprising a metal portion coupled to a portion of the first doped semiconductor region, and the metal portion is wire bonded to the anode.

12. The photodetector of claim 9, wherein the cathode comprises a metal portion.

13. The photodetector of claim 9, wherein the cathode is configured to be coupled to a voltage source configured to bias the cathode with a positive voltage with respect to the anode under reverse bias conditions.

14. The photodetector of claim 9, wherein the cathode is configured to have a non-zero voltage with respect to the second doped semiconductor region.

15. The photodetector of any preceding claim, further comprising an absorption region.

16. The photodetector of claim 15, wherein the absorption region comprises indium- gallium-arsenide (InGaAs).

17. The photodetector of claim 16, wherein the absorption region is configured to absorb light having a wavelength in a range of 900 to 1700 nanometers.

18. The photodetector of any preceding claim, wherein the first doped semiconductor region and the second doped semiconductor region are electrically isolated.

19. The photodetector of any preceding claim, wherein the first doped semiconductor region has a diameter in a range of 5 micrometers to 10 millimeters.Attorney Docket No. 9653102120. The photodetector of any preceding claim, wherein an outer perimeter of the first doped semiconductor region and an inner perimeter of the second doped semiconductor region are separated by a distance in a range of 2 to 300 micrometers.

21. The photodetector of any preceding claim, wherein the second doped semiconductor region is diffused to a depth in a range from 0.1 micrometers to 350 micrometers22. A diode comprising: a cathode; an anode comprising a first doped semiconductor region and a first metal ring surrounding the first doped semiconductor region; and a second doped semiconductor region surrounding the first doped semiconductor region.

23. The diode of claim 22, wherein the cathode is configured to be biased with a positive voltage with respect to the anode under reverse bias conditions.

24. The diode of any preceding claim, wherein the second doped semiconductor region is configured to be electrically coupled to ground.

25. The diode of any preceding claim, wherein the cathode and the second doped semiconductor region are configured to have a non-zero voltage therebetween.

26. The diode of any preceding claim, wherein the first doped semiconductor region and the second doped semiconductor region are electrically isolated.

27. The diode of any preceding claim, wherein the second doped semiconductor region is configured to send charge carriers generated outside the first doped semiconductor region to ground.

28. A package comprising: at least one terminal; and a plurality of photodetectors arranged in a matrix, a first one of the plurality of photodetectors comprising:Attorney Docket No. 96531021 an output to the at least one terminal; a cathode; an anode comprising a first doped semiconductor region and a first metal ring surrounding the first doped semiconductor region; and a second diffused region surrounding the first doped semiconductor region.

29. The package of claim 28, wherein the cathode is configured to be biased with a positive voltage with respect to the anode under reverse bias conditions.

30. The package of any preceding claim, wherein the second doped semiconductor region is configured to be electrically coupled to ground.

31. The package of any preceding claim, wherein the cathode and the second doped semiconductor region are configured to have a non-zero voltage therebetween.

32. The package of any preceding claim, wherein the first doped semiconductor region and the second doped semiconductor region are electrically isolated.

33. The package of any preceding claim, wherein the second doped semiconductor region is configured to send charge carriers generated outside the first doped semiconductor region to ground.

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