High modulation speed PIN photodiode

Abstract

Various embodiments of an improved PIN photodiode are provided. In an example embodiment, the PIN photodiode includes: a p-type contact; an n-type contact; a first absorption layer disposed between the p-type contact and the n-type contact; and a second absorption layer disposed between the first absorption layer and the n-type contact. The first absorption layer is characterized by a first absorption coefficient, and the second absorption layer is characterized by a second absorption coefficient. The second absorption coefficient is greater than the first absorption coefficient. In another example embodiment, the PIN photodiode includes: a p-type contact; an n-type contact; a first absorption layer disposed between the p-type contact and the n-type contact; and a non-absorbing acceleration layer disposed between the absorption layer and the non-absorbing drift layer and the n-type contact.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Greek Application No. 20210100075, filed on February 4, 2021, the contents of which are incorporated herein by reference in their entirety. Background Art

[0003] As data communication demands increase in both volume and speed, optical communications have become an increasingly popular means of communication. To meet these growing demands, optical communications require high-speed transmitters and high-speed receivers. Summary of the invention

[0004] A photodiode is an electro-optical device that is configured to receive light through its aperture and convert the light into an electrical signal. An example type of photodiode is a PIN photodiode. For example, a PIN photodiode may include a PIN junction. Typically, a PIN junction includes a P region in which holes are majority charge carriers, an intrinsic region in which there are no free charge carriers or the least free charge carriers, and an N region in which electrons are majority charge carriers. The intrinsic region is sandwiched between the P region and the N region and acts as an insulator between the P region and the N region. For example, the intrinsic region may have a relatively high resistance (compared to the P region and / or the N region), which may slow down the flow of electrons and / or holes through it, so that the PIN junction acts as a capacitor. Typically, the intrinsic region of a PIN photodiode includes an absorption region of the photodiode, wherein light is absorbed by the material of the intrinsic region and converted into charge carriers (e.g., electrons and / or holes). Therefore, a thicker intrinsic region directly corresponds to a more sensitive PIN photodiode. However, the thicker the intrinsic region of the PIN photodiode, the greater the capacitance of the PIN photodiode, and therefore, the slower the modulation speed of the PIN diode. Embodiments of the present invention provide a PIN photodiode having an appropriate sensitivity level and an increased modulation speed for optical communications. For example, various embodiments provide a PIN photodiode having a sensitivity in the range of 0.4 amperes to 0.8 amperes per watt and a 3-dB modulation bandwidth in the range of 15 GHz to 100 GHz.

[0005] Various embodiments provide a PIN photodiode including a multi-layer intrinsic region. Various embodiments provide a PIN photodiode including a p-type contact, an n-type contact, and a multi-layer intrinsic region therebetween. In various embodiments, the multi-layer intrinsic region includes one or more layers of a second absorbing material embedded in a first absorbing material and / or disposed between the first absorbing material and one of the contact layers. In various embodiments, the first absorbing material and the second absorbing material are semiconductor materials, wherein the second absorbing material has a lower energy band gap than the first absorbing material. In various embodiments, the multi-layer intrinsic region includes an acceleration layer disposed between an absorbing material (e.g., the first absorbing material and / or the second absorbing material) and one of the contact layers. In various embodiments, the acceleration layer is configured not to absorb light, but to cause photoelectrons released by the absorption of light by the first absorbing material or the second absorbing material to have a greater drift velocity. In various embodiments, the multi-layer intrinsic region includes a drift layer disposed between an absorbing material (e.g., the first absorbing material and / or the second absorbing material) and / or the acceleration layer and the n-type contact. In various implementations, the drift layer is configured to reduce the total capacitance of a PIN junction of a PIN-type photodiode.

[0006] According to one aspect of the present disclosure, a PIN photodiode is provided. In an example embodiment, the PIN photodiode includes: a p-type contact; an n-type contact; a first absorption layer disposed between the p-type contact and the n-type contact; and a second absorption layer disposed between the first absorption layer and the n-type contact. The first absorption layer is characterized by a first absorption coefficient, and the second absorption layer is characterized by a second absorption coefficient. The second absorption coefficient is greater than the first absorption coefficient.

[0007] According to another aspect of the present disclosure, a PIN photodiode is provided. In an example embodiment, the PIN photodiode includes: a p-type contact; an n-type contact; a first absorption layer disposed between the p-type contact and the n-type contact; and a non-absorption acceleration layer disposed between the first absorption layer and the n-type contact. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Having thus generally described the invention, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and in which:

[0009] Figure 1 illustrates a cross section of an example PIN-type photodiode according to an example embodiment;

[0010] Figure 2 illustrates a cross section of an example PIN-type photodiode according to another example embodiment;

[0011] Figure 3illustrates a cross-section of an example PIN-type photodiode according to yet another example embodiment; and

[0012] Figure 4 A cross section of an example PIN-type photodiode is illustrated according to yet another example embodiment. DETAILED DESCRIPTION

[0013] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. In practice, these disclosures may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present disclosure satisfies applicable legal requirements. The same reference numerals refer to the same elements throughout. As used herein, terms such as "top," "around," "around," and the like are used for illustrative purposes in the examples provided below to describe the relative positions of certain components or portions of components. As used herein, the terms "substantially" and "approximately" refer to tolerances within manufacturing and / or engineering standards.

[0014] Various embodiments provide a PIN photodiode, wherein the intrinsic region of the PIN photodiode includes a multilayer intrinsic region. In various embodiments, the PIN photodiode includes a p-type contact, an n-type contact, and a multilayer intrinsic region disposed between the p-type contact and the n-type contact. In various embodiments, the multilayer intrinsic region includes one or more layers of a second absorbing material, wherein the one or more layers of the second absorbing material are embedded in a first absorbing material and / or disposed between the first absorbing material and one of the contact layers. In various embodiments, the first absorbing material and the second absorbing material are semiconductor materials, wherein the second absorbing material has a lower energy band gap than the first absorbing material. In various embodiments, the multilayer intrinsic region includes an acceleration layer, wherein the acceleration layer is disposed between an absorbing material (e.g., the first absorbing material and / or the second absorbing material) and one of the contact layers. In various embodiments, the acceleration layer is configured not to absorb light, but to cause photoelectrons released by the absorption of light by the first absorbing material or the second absorbing material to have a greater drift velocity. In various embodiments, the multilayer intrinsic region includes a drift layer disposed between an absorption material (eg, a first absorption material and / or a second absorption material) and / or an acceleration layer and the n-type contact. In various embodiments, the drift layer is configured to reduce a total capacitance of a PIN junction of a PIN photodiode. Figures 1 to 4 Each illustrates a cross-section of an example implementation of a PIN-type photodiode, where the cross-section is taken in a plane including an axis defined by the PIN-type diode.

[0015] Example PIN Photodiode 100

[0016] Figure 1A cross-section of a PIN photodiode 100 is illustrated according to example embodiments, taken in a plane including an axis 195 of the PIN photodiode 100. In various embodiments, the PIN photodiode 100 can be substantially uniform in various planes taken substantially perpendicular to the axis 195. In other words, the composition and / or characteristics of the PIN photodiode 100 can be substantially the same along a first radius extending from the axis 195 and along a different second radius extending from the axis 195 in the same plane as the first radius, the plane being substantially perpendicular to the axis 195.

[0017] In various embodiments, the PIN photodiode 100 includes a multi-layer intrinsic region 105 including two absorption layers characterized by different absorption coefficients. In various embodiments, the PIN photodiode 100 is formed and / or mounted on a substrate 110. In various embodiments, the substrate 110 includes a GaAs substrate or other suitable substrate.

[0018] In various embodiments, the PIN-type photodiode 100 includes a p-type contact 175 and an n-type contact 125. For example, the p-type contact 175 may include a p-type semiconductor contact layer 170 and an anode electrode and / or pad 180B. For example, the n-type contact 125 may include an n-type contact layer 120, an n-type semiconductor contact layer 130, and a cathode electrode and / or pad 180A. In various embodiments, the electrodes and / or pads 180A, 180B are formed by depositing and / or patterning a conductive material on the PIN-type photodiode. For example, the electrodes and / or pads 180A, 180B may include copper, gold, and / or other metals. In various embodiments, the n-type contact layer 120 is made of a conductive material such as copper, gold, or other metals. In various embodiments, the n-type semiconductor contact layer 130 includes a semiconductor material that has been doped with an n-type dopant. For example, the n-type semiconductor contact layer 130 may include n-type doped AlGaAs. In various embodiments, the p-type semiconductor contact layer 170 includes a semiconductor material that has been doped with a p-type dopant. For example, the p-type semiconductor contact layer 170 may include p-type doped AlGaAs. In various embodiments, the PIN-type photodiode includes a mesa structure having a diameter D. One of the cathode electrode and / or pad 180A or the anode electrode and / or pad 180B may be disposed on top of the mesa structure and surround (e.g., define) the hole 190, and the other of the cathode electrode and / or pad 180A or the anode electrode and / or pad 180B may be disposed around the mesa structure and / or around the mesa structure. In various embodiments, the diameter D is in the range of ten to forty microns (e.g., twenty to thirty microns).

[0019] In various embodiments, the PIN photodiode 100 includes a multi-layer intrinsic region 105. In various embodiments, the multi-layer intrinsic region 105 includes an absorption region 155 of the PIN photodiode 100. In various embodiments, the absorption region 155 includes at least one absorption material configured to absorb light in a specific wavelength range. Figure 1 As shown in , when the axis 195 defined by the PIN photodiode 100 is aligned with the z-axis, light (e.g., light of a specific wavelength range) can enter the PIN photodiode 100 through the hole 190 traveling in the negative z-direction and be absorbed by the absorbing material in the intrinsic region. When photons of a specific wavelength are absorbed, photoelectrons are released from the crystal structure of the absorbing material, thereby providing photoelectrons and holes. When a negative reverse bias is applied between the p-contact and the n-contact of the PIN photodiode 100, the holes move generally in the positive z-direction toward the p-type contact, and the photoelectrons move generally in the negative z-direction toward the n-type contact. Holes reaching the p-type contact and / or photoelectrons reaching the n-type contact result in a voltage difference and / or current at the electrodes and / or pads 180A, 180B.

[0020] In various embodiments, the multilayer intrinsic region 105 includes a drift layer 140. In various embodiments, the drift layer 140 is configured not to absorb light of a specific wavelength range. For example, the drift layer 140 can be a non-absorbing drift layer. In various embodiments, the drift layer 140 is disposed between the absorption region of the multilayer intrinsic region 105 and the n-type contact 125 (e.g., the n-type semiconductor contact layer 130). In particular, the PIN-type photodiode can be configured so that only photoinduced electrons pass through the drift layer 140. For example, the PIN-type photodiode can be configured so that holes do not pass through the drift layer 140. For example, the drift layer 140 can be disposed at a boundary of the multilayer intrinsic region 105, the boundary of the multilayer intrinsic region 105 being adjacent and / or directly adjacent to the n-type contact 125.

[0021] In various embodiments, the drift layer 140 is configured to reduce the capacitance of the PIN junction of the PIN photodiode while having a minimal effect on the transit time of the photoinduced electrons. Generally, the transit time of the photoinduced electrons is the time between when the photoinduced electrons are generated and when the photoinduced electrons reach the n-type contact 125. The shorter the photoinduced electron transit time of the PIN photodiode, the faster the modulation speed of the PIN photodiode. In various embodiments, the drift layer includes a material that provides a high mobility of the photoinduced electrons traveling therethrough.

[0022] In various embodiments, the drift layer 140 includes a semiconductor material having a bandgap energy such that the drift layer 140 substantially functions as a carrier transport layer. For example, the bandgap energy of the drift layer 140 may be greater than the bandgap energy of the absorber material (e.g., the first absorber material and / or the second absorber material). In particular, the bandgap energy of the drift layer 140 may be sufficiently large to prevent or at least substantially reduce the absorption of light of a particular wavelength range by the drift layer 140. In the illustrated embodiment, the drift layer 140 includes intrinsic or lightly n-doped AlGaAs (AlGaAs). x Ga 1-x As, x = (0 ... 1)) compound semiconductor alloy. For example, the drift layer 140 may be substantially undoped. In an example embodiment, the drift layer 140 has a thickness (eg, in a direction substantially parallel to the axis 195) T in the sub-micron range. d For example, in an example embodiment, the drift layer 140 has a thickness T in the range of 0.1 to 0.5 micrometers (eg, 0.3 micrometers). d The particular thickness to be used depends on the relative thicknesses of the other layers, particularly the absorber layers 150 , 160 , and can be tailored to the desired properties of the PIN photodiode 100 .

[0023] In various embodiments, the drift layer 140 is configured such that the electric field in the drift layer 140 is lower than the electric field in the absorber layers 150, 160. In various embodiments, the reduction of the electric field in the drift layer 140 relative to the absorber layers 150, 160 is achieved by the distribution of dopant concentrations in the absorber layers 150, 160 and the drift layer 140 and any buffer layers therebetween. In an example embodiment, the electric field in the drift layer 140 is reduced by n-doping a region of the drift layer 140 adjacent to the absorber layers 150, 160 and / or providing an n-type doped buffer layer between the drift layer 140 and the second absorber layer 150. This doped region can be much thinner than the drift layer 140. In various embodiments, thinner doped regions will require higher doping levels, while thicker regions will require lower doping levels to achieve the desired reduction of the electric field in the drift layer 140. It will be appreciated that the main factor achieving a specific reduction in the electric field in the drift layer 140 is the total fixed specific charge due to the n-type dopants introduced in the doped regions of the drift layer 140 and / or the buffer layer between the drift layer 140 and the second absorber layer 150 .

[0024] In various embodiments, the multilayer intrinsic region 105 includes an absorption region 155, which includes a first absorption layer 160 and a second absorption layer 150. In various embodiments, the first absorption layer 160 is configured to absorb light in a specific wavelength range. In various embodiments, the first absorption layer 160 has a thickness T in a direction substantially parallel to the axis 195.a In various embodiments, the first absorption layer 160 includes a first absorption material. In an example embodiment, the first absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the first absorption material may be GaAs.

[0025] In various embodiments, the second absorption layer 150 is configured to absorb light of a specific wavelength range. In various embodiments, the second absorption layer 150 has a thickness T in a direction substantially parallel to the axis 195. in In various embodiments, the second absorption layer 150 includes a second absorption material. In an example embodiment, the second absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the second absorption material may be InGaAs (e.g., In y Ga 1-y As, y = (0 ... 1)). In various embodiments, the second absorber material has a lower band gap energy than the first absorber material. In various embodiments, the second absorber material has a higher absorption coefficient than the first absorber material. For example, the first absorber layer 160 can be characterized by a first absorption coefficient, and the second absorber layer 150 can be characterized by a second absorption coefficient, wherein the second absorption coefficient is greater than the first absorption coefficient. In various embodiments, the thickness T of the second absorber layer 150 is in Less than the thickness T of the first absorption layer 160 a In an exemplary embodiment, the thickness T of the second absorbent layer 150 is in The thickness T of the second absorption layer 150 may have an upper boundary defined by the strain relaxation of the lattice constant of the first absorption material. For example, when the first absorption material is GaAs and the second absorption material is InGaAs, the thickness T of the second absorption layer 150 is in may be equal to or less than a critical thickness governed and / or controlled by the saturation of strain relaxation of the host GaAs lattice constant corresponding to the amount added to GaAs to form InGaAs. In an example embodiment, the absorption region (T a +T in ) may have a thickness in the range of half a micron to two microns (eg, 0.8 microns to 1.8 microns and / or approximately 1.3 microns).

[0026] In various embodiments, the second absorption layer 150 is disposed and / or formed on the boundary of the absorption region, which is adjacent to and / or directly adjacent to the drift layer 140 (or the n-type contact 125 in the embodiment that does not include the drift layer 140). Therefore, due to the higher absorption coefficient of the second absorption layer 150, and this positioning of the second absorption layer 150 can increase the proportion of photoinduced electrons provided to the n-type semiconductor contact layer 130 in a relatively short time, so that the transit time of the photoinduced electrons of the PIN photodiode 100 is reduced, while increasing the 3-dB modulation bandwidth of the PIN photodiode.

[0027] Example PIN photodiode 200

[0028] Figure 2 A cross-section of a PIN photodiode 200 is illustrated according to example embodiments, taken in a plane including an axis 295 of the PIN photodiode 200. In various embodiments, the PIN photodiode 200 can be substantially uniform in various planes taken substantially perpendicular to the axis 295. In other words, the composition and / or characteristics of the PIN photodiode 200 can be substantially the same along a first radius extending from the axis 295 and along a different second radius extending from the axis 295 in the same plane as the first radius, the plane being substantially perpendicular to the axis 295.

[0029] In various embodiments, the PIN photodiode 200 includes a multi-layer intrinsic region 205, which includes multiple (e.g., four or more) absorption layers, wherein adjacent absorption layers are characterized by different absorption coefficients. In various embodiments, the PIN photodiode 200 is formed and / or mounted on a substrate 210. In various embodiments, the substrate 210 includes a GaAs substrate or other suitable substrate.

[0030] In various embodiments, the PIN-type photodiode 200 includes a p-type contact 275 and an n-type contact 225. For example, the p-type contact 275 may include a p-type semiconductor contact layer 270 and an anode electrode and / or pad 280B. For example, the n-type contact 225 may include an n-type contact layer 220, an n-type semiconductor contact layer 230, and a cathode electrode and / or pad 280A. In various embodiments, the electrodes and / or pads 280A, 280B are formed by depositing and / or patterning a conductive material on the PIN-type photodiode. For example, the electrodes and / or pads 280A, 280B may include copper, gold, and / or other metals. In various embodiments, the n-type contact layer 220 is made of a conductive material such as copper, gold, or other metals. In various embodiments, the n-type semiconductor contact layer 230 includes a semiconductor material that has been doped with an n-type dopant. For example, the n-type semiconductor contact layer 230 may include n-type doped AlGaAs. In various embodiments, the p-type semiconductor contact layer 270 includes a semiconductor material that has been doped with a p-type dopant. For example, the p-type semiconductor contact layer 270 may include p-type doped AlGaAs. In various embodiments, the PIN-type photodiode includes a mesa structure having a diameter D. One of the cathode electrode and / or pad 280A or the anode electrode and / or pad 280B may be disposed on top of the mesa structure and surround (e.g., define) the hole 290, and the other of the cathode electrode and / or pad 280A or the anode electrode and / or pad 280B may be disposed around the mesa structure and / or around the mesa structure. In various embodiments, the diameter D is in the range of ten microns to forty microns (e.g., twenty microns to thirty microns).

[0031] In various embodiments, the PIN photodiode 200 includes a multi-layer intrinsic region 205. In various embodiments, the multi-layer intrinsic region 205 includes an absorption region 255 of the PIN photodiode 200. In various embodiments, the absorption region 255 includes an absorption material that is configured to absorb light in a specific wavelength range. Figure 2 As shown in , when the axis 295 defined by the PIN photodiode 200 is aligned with the z-axis, light (e.g., light of a specific wavelength range) can enter the PIN photodiode 200 through the aperture 290 traveling in the negative z-direction and be absorbed by the absorbing material of the intrinsic region. When photons of a specific wavelength are absorbed, photo-induced electrons are released from the crystal structure of the absorbing material, thereby providing photo-induced electrons and holes. The holes move generally in the positive z-direction toward the p-type contact 275, and the photo-induced electrons move generally in the negative z-direction toward the n-type contact 225. The holes reaching the p-type contact 275 and / or the photo-induced electrons reaching the n-type contact 225 result in a voltage difference and / or current at the electrodes and / or pads 280A, 280B.

[0032] In various embodiments, the multilayer intrinsic region 205 includes a drift layer 140. In various embodiments, the drift layer 240 is configured not to absorb light of a specific wavelength range. For example, the drift layer 240 can be a non-absorbing drift layer. In various embodiments, the drift layer 240 is disposed between the absorption region of the multilayer intrinsic region 205 and the n-type contact 225 (e.g., the n-type semiconductor contact layer 230). In particular, the PIN-type photodiode can be configured so that only photoinduced electrons pass through the drift layer 240. For example, the PIN-type photodiode can be configured so that holes do not pass through the drift layer 240. For example, the drift layer 240 can be disposed at a boundary of the multilayer intrinsic region 205, the boundary of the multilayer intrinsic region 205 being adjacent and / or directly adjacent to the n-type contact 225.

[0033] In various embodiments, the drift layer 240 is configured to reduce the capacitance of the PIN junction of the PIN photodiode while having a minimal effect on the transit time of the photoinduced electrons. Generally, the transit time of the photoinduced electrons is the time between when the photoinduced electrons are generated and when the photoinduced electrons reach the n-type contact 225. The shorter the photoinduced electron transit time of the PIN photodiode, the faster the modulation speed of the PIN photodiode. In various embodiments, the drift layer includes a material that provides a high mobility of the photoinduced electrons traveling therethrough.

[0034] In various embodiments, the drift layer 240 includes a semiconductor material having a bandgap energy such that the drift layer 240 substantially functions as a carrier transport layer. For example, the bandgap energy of the drift layer 240 may be greater than the bandgap energy of the absorber material (e.g., the first absorber material and / or the second absorber material). In particular, the bandgap energy of the drift layer 240 may be sufficiently large to prevent or at least substantially reduce the absorption of light of a particular wavelength range by the drift layer 240. In the illustrated embodiment, the drift layer 240 includes intrinsic or lightly n-doped AlGaAs (AlGaAs). x Ga 1-x As, x = (0 ... 1)) compound semiconductor alloy. For example, the drift layer 240 may be substantially undoped. In an example embodiment, the drift layer 240 has a thickness (eg, in a direction substantially parallel to the axis 295) T in a range of half a micron to ten microns. d For example, in an example embodiment, the drift layer T d In the sub-micron range. For example, in an example embodiment, the drift layer 240 has a thickness T in the range of 0.1 to 0.5 microns (eg, 0.3 microns). d The particular thickness to be used depends on the relative thicknesses of the other layers, particularly the absorber layers 250 , 260 , and can be tailored to the desired properties of the PIN photodiode 200 .

[0035] In various embodiments, the drift layer 240 is configured such that the electric field in the drift layer 240 is lower than the electric field in the absorber layers 250, 260. In various embodiments, the reduction of the electric field in the drift layer 240 relative to the absorber layers 250, 260 is achieved by the distribution of dopant concentrations in the absorber layers 250, 260 and the drift layer 240 and any buffer layers therebetween. In an example embodiment, the electric field in the drift layer 240 is reduced by n-doping a region of the drift layer 240 adjacent to the absorber layers 250, 260 and / or providing an n-doped buffer layer between the drift layer 240 and the second absorber layer 250. This doped region can be much thinner than the drift layer 240. In various embodiments, thinner doped regions will require higher doping levels, while thicker regions will require lower doping levels to achieve the desired reduction of the electric field in the drift layer 240. It will be appreciated that the main factor achieving a specific reduction in the electric field in the drift layer 240 is the total fixed specific charge due to the n-type dopants introduced in the doped regions of the drift layer 240 and / or the buffer layer between the drift layer 240 and the second absorber layer 250 .

[0036] In various embodiments, the multilayer intrinsic region 205 includes two or more groups of absorption layers. Each group of absorption layers includes a first absorption layer 260A, 260B and a second absorption layer 250A, 250B. For example, one first absorption layer 260A and one second absorption layer 250A form a first group of absorption layers, and another first absorption layer 260B and another second absorption layer 250B form a second group of absorption layers. In various embodiments, each first absorption layer 260A, 260B is configured to absorb light of a specific wavelength range. In various embodiments, one first absorption layer 260A has a thickness T in a direction substantially parallel to the axis 295. a1 , and the other first absorbent layer 260B has a thickness T in a direction substantially parallel to the axis 295 a2 In various embodiments, depending on the application requirements, T a1 and T a2 can be equal to each other, T a2 Can be greater than T a1 , or T a1 Can be greater than T a2 In various embodiments, each first absorption layer 260A, 260B includes a first absorption material. In an example embodiment, the first absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the first absorption material may be GaAs.

[0037] In various embodiments, each second absorption layer 250A, 250B is configured to absorb light of a specific wavelength range. In various embodiments, one second absorption layer 250A has a thickness T in a direction substantially parallel to the axis 295. in1 , and the other second absorbent layer 250B has a thickness T in a direction substantially parallel to the axis 195 in2 In various embodiments, depending on the application requirements, T in1 and T in2 can be equal to each other, T in2 Can be greater than T in1 , or T in1 Can be greater than T in2 In various embodiments, each second absorption layer 250A, 250B includes a second absorption material. In an example embodiment, the second absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the second absorption material may be InGaAs (e.g., InGaAs). y Ga 1-y As, y = (0 ... 1)). In various embodiments, the second absorber material has a lower band gap energy than the first absorber material. In various embodiments, the second absorber material has a higher absorption coefficient than the first absorber material. For example, the first absorber layer 260A, 260B can be characterized by a first absorption coefficient, and the second absorber layer 250A, 250B can be characterized by a second absorption coefficient, wherein the second absorption coefficient is greater than the first absorption coefficient. In various embodiments, the thickness T of the second absorber layer 250A, 250B is in1 , T in2 Less than the thickness T of the first absorption layer 260A, 260B of the same group of absorption layers a1 , T a2 In an example embodiment, the thickness T of each of the second absorbent layers 250A, 250B is in1 , T in2 Less than the thickness T of each of the first absorbent layers 260A, 260B a1 , T a2 In various embodiments, a specific location of the second absorbent layer 250A (eg, determined by the thickness T of the first absorbent layers 260A, 260B) a1 , T a2 The definition) can be configured to balance the local concentration of photoinduced electrons and holes and their corresponding shortest transit times to the n-type contact 225 and the p-type contact 275.

[0038] In an example embodiment, the thickness T of each of the second absorbent layers 250A, 250B is in1 , Tin2 Or the total thickness (T in1 +T in2 ) may have an upper boundary defined by the strain relaxation of the lattice constant of the first absorber material. For example, when the first absorber material is GaAs and the second absorber material is InGaAs, the thickness T of the second absorber layer 250A, 250B is in1 , T in2 may be equal to or less than a critical thickness governed and / or controlled by the saturation of strain relaxation of the host GaAs lattice constant corresponding to the amount added to GaAs to form InGaAs. In an example embodiment, the absorption region (T a1 +T in1 +T a2 +T in2 ) may have a thickness in the range of half a micron to two microns (eg, 0.8 microns to 1.8 microns and / or approximately 1.3 microns).

[0039] In various embodiments, one of the second absorption layers (e.g., second absorption layer 250B) is disposed and / or formed on a boundary of an absorption region that abuts and / or is directly adjacent to the drift layer 240 (or in embodiments that do not include the drift layer 240, the n-type contact 225). The other second absorption layer (e.g., second absorption layer 250A) can be sandwiched between two first absorption layers 260A, 260B. For example, the absorption region can include alternating layers of first absorption layers and second absorption layers. For example, each first absorption layer can be adjacent to, adjacent to, and / or directly adjacent to (a) the p-type contact 275 and one second absorption layer or (b) two second absorption layers. For example, each second absorption layer can be adjacent to, adjacent to, and / or directly adjacent to (a) two first absorption layers or (b) the drift layer 240 or the n-type contact 225 and one first absorption layer. Therefore, the second absorption layer 250B can increase the proportion of photoinduced electrons provided to the n-type semiconductor contact layer 230 in a relatively short time, thereby reducing the transit time of photoinduced electrons of the PIN photodiode 200 and increasing the 3-dB modulation bandwidth of the PIN photodiode.

[0040] Example PIN Photodiode 300

[0041] Figure 3A cross-section of a PIN photodiode 300 is illustrated according to example embodiments, taken in a plane including an axis 395 of the PIN photodiode 300. In various embodiments, the PIN photodiode 300 can be substantially uniform in various planes taken substantially perpendicular to the axis 395. In other words, the composition and / or characteristics of the PIN photodiode 300 can be substantially the same along a first radius extending from the axis 395 and along a different second radius extending from the axis 395 in the same plane as the first radius, the plane being substantially perpendicular to the axis 395.

[0042] In various embodiments, the PIN photodiode 300 includes a multi-layer intrinsic region 305 including an acceleration layer 335. In various embodiments, the PIN photodiode 300 is formed and / or mounted on a substrate 310. In various embodiments, the substrate 310 includes a GaAs substrate or other suitable substrate.

[0043] In various embodiments, the PIN-type photodiode 300 includes a p-type contact 375 and an n-type contact 325. For example, the p-type contact 375 may include a p-type semiconductor contact layer 370 and an anode electrode and / or pad 380B. For example, the n-type contact 325 may include an n-type contact layer 320, an n-type semiconductor contact layer 330, and a cathode electrode and / or pad 380A. In various embodiments, the electrodes and / or pads 380A, 380B are formed by depositing and / or patterning a conductive material on the PIN-type photodiode. For example, the electrodes and / or pads 380A, 380B may include copper, gold, and / or other metals. In various embodiments, the n-type contact layer 320 is made of a conductive material such as copper, gold, or other metals. In various embodiments, the n-type semiconductor contact layer 330 includes a semiconductor material that has been doped with an n-type dopant. For example, the n-type semiconductor contact layer 330 may include n-type doped AlGaAs. In various embodiments, the p-type semiconductor contact layer 370 includes a semiconductor material that has been doped with a p-type dopant. For example, the p-type semiconductor contact layer 370 may include p-type doped AlGaAs. In various embodiments, the PIN-type photodiode includes a mesa structure having a diameter D. One of the cathode electrode and / or pad 380A or the anode electrode and / or pad 380B may be disposed on top of the mesa structure and surround (e.g., define) the hole 390, and the other of the cathode electrode and / or pad 380A or the anode electrode and / or pad 380B may be disposed around the mesa structure and / or around the mesa structure. In various embodiments, the diameter D is in the range of ten to forty microns (e.g., twenty to thirty microns).

[0044] In various embodiments, the PIN photodiode 300 includes a multi-layer intrinsic region 305. In various embodiments, the multi-layer intrinsic region 305 includes an absorption region 355 of the PIN photodiode 300. In various embodiments, the absorption region 355 includes at least one absorption material configured to absorb light in a specific wavelength range. Figure 3 As shown in , when the axis 395 defined by the PIN photodiode 300 is aligned with the z-axis, light (e.g., light of a specific wavelength range) can enter the PIN photodiode 300 through the hole 390 traveling in the negative z-direction and be absorbed by the absorbing material of the intrinsic region. When photons of a specific wavelength are absorbed, photoelectrons are released from the crystal structure of the absorbing material, thereby providing photoelectrons and holes. The holes generally move in the positive z-direction toward the p-type contact, and the photoelectrons generally move in the negative z-direction toward the n-type contact. The holes reaching the p-type contact and / or the photoelectrons reaching the n-type contact result in a voltage difference and / or current at the electrodes and / or pads 380A, 380B.

[0045] In various embodiments, the multilayer intrinsic region 305 includes a drift layer 340. In various embodiments, the drift layer 340 is configured not to absorb light of a specific wavelength range. For example, the drift layer 340 can be a non-absorbing drift layer. In various embodiments, the drift layer 340 is disposed between the absorption region of the multilayer intrinsic region 305 and the n-type contact 325 (e.g., the n-type semiconductor contact layer 330). In particular, the PIN-type photodiode can be configured so that only photoinduced electrons pass through the drift layer 340. For example, the PIN-type photodiode can be configured so that holes do not pass through the drift layer 340. For example, the drift layer 340 can be disposed at a boundary of the multilayer intrinsic region 305, the boundary of the multilayer intrinsic region 305 being adjacent and / or directly adjacent to the n-type contact 325.

[0046] In various embodiments, the drift layer 340 is configured to reduce the capacitance of the PIN junction of the PIN photodiode while having a minimal effect on the transit time of the photoinduced electrons. Generally, the transit time of the photoinduced electrons is the time between when the photoinduced electrons are generated and when the photoinduced electrons reach the n-type contact 325. The shorter the photoinduced electron transit time of the PIN photodiode, the faster the modulation speed of the PIN photodiode. In various embodiments, the drift layer includes a material that provides a high mobility of the photoinduced electrons traveling therethrough.

[0047] In various embodiments, the drift layer 340 includes a semiconductor material having a bandgap energy such that the drift layer 340 substantially functions as a carrier transport layer. For example, the bandgap energy of the drift layer 340 may be greater than the bandgap energy of the absorber material (e.g., the first absorber material and / or the second absorber material). In particular, the bandgap energy of the drift layer 340 may be sufficiently large to prevent or at least substantially reduce the absorption of light of a particular wavelength range by the drift layer 340. In the illustrated embodiment, the drift layer 340 includes intrinsic or lightly n-doped AlGaAs (AlGaAs). x Ga 1-x As, x = (0 ... 1)) compound semiconductor alloy. For example, the drift layer 340 may be substantially undoped. In an example embodiment, the drift layer 340 has a thickness (eg, in a direction substantially parallel to the axis 395) T in the sub-micron range. d For example, in an example embodiment, the drift layer 340 has a thickness T in the range of 0.1 to 0.5 micrometers (eg, 0.3 micrometers). d The particular thickness to be used depends on the relative thicknesses of the other layers, particularly the absorber layer 360 , and can be tailored according to the desired characteristics of the PIN photodiode 300 .

[0048] In various embodiments, the drift layer 340 is configured such that the electric field in the drift layer 340 is lower than the electric field in the absorption layer 360. In various embodiments, the reduction of the electric field in the drift layer 340 relative to the absorption layer 360 is achieved by the distribution of dopant concentrations in the absorption layer 360 and the drift layer 340 and any buffer layers therebetween. In an example embodiment, the electric field in the drift layer 340 is reduced by n-doping a region of the drift layer 340 adjacent to the absorption layer 360 and / or providing an n-type doped buffer layer between the drift layer 340 and the absorption layer 360. This doped region can be much thinner than the drift layer 340. In various embodiments, thinner doped regions will require higher doping levels, while thicker regions will require lower doping levels to achieve the desired reduction of the electric field in the drift layer 340. It will be appreciated that the primary factor achieving a specific reduction in the electric field in the drift layer 340 is the total fixed specific charge due to the n-type dopants introduced in the doped regions of the drift layer 340 and / or the buffer layer between the drift layer 340 and the absorber layer 360 .

[0049] In various embodiments, the multilayer intrinsic region 305 includes an absorption layer 360. In various embodiments, the absorption layer 360 is configured to absorb light in a specific wavelength range. In various embodiments, the absorption layer 360 has a thickness T in a direction substantially parallel to the axis 395. aIn various embodiments, the absorption layer 360 includes a first absorption material. In an example embodiment, the first absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the first absorption material may be GaAs. In various embodiments, the absorption layer 360 is characterized by a first absorption coefficient.

[0050] In various embodiments, the multilayer intrinsic region 305 further includes an acceleration layer 335. In various embodiments, the acceleration layer 335 is configured to not absorb light within a specific wavelength range. For example, the acceleration layer 335 can be a non-absorbing acceleration layer. In various embodiments, the acceleration layer is configured to cause photoelectrons released by the absorption of light by the first absorbing material or the second absorbing material to have a greater drift velocity. In various embodiments, the acceleration layer is disposed between the absorption layer 360 and the drift layer 340 (or the n-type contact 325 in embodiments that do not include the drift layer 340). In an example embodiment, the acceleration layer 335 includes n-type doped AlGaAs (e.g., Al z Ga 1-z As, z=(0...1)). In an example embodiment, the acceleration layer 335 includes n-type doped AlGaAs including 1×10 15 Up to 1×10 17 In various embodiments, the acceleration layer 335 has a thickness T in a direction substantially parallel to the axis 395. n .

[0051] In various embodiments, the acceleration layer 335 causes an increase in the electric field within the absorption layer 360, resulting in a higher drift velocity of the photoinduced electrons when the electrons are released from the crystal structure of the absorption material. With a higher drift velocity of the photoinduced electrons, the photoinduced electrons take less time to reach the n-type contact 325. Thus, the acceleration layer 335 reduces the transit time of the photoinduced electrons of the PIN photodiode 300, while increasing the 3-dB modulation bandwidth of the PIN photodiode.

[0052] Example PIN Photodiode 400

[0053] Figure 4A cross-section of a PIN photodiode 400 is illustrated according to example embodiments, taken in a plane including an axis 495 of the PIN photodiode 400. In various embodiments, the PIN photodiode 400 can be substantially uniform in various planes taken substantially perpendicular to the axis 495. In other words, the composition and / or characteristics of the PIN photodiode 400 can be substantially the same along a first radius extending from the axis 495 and along a different second radius extending from the axis 495 in the same plane as the first radius, the plane being substantially perpendicular to the axis 495.

[0054] In various embodiments, the PIN photodiode 400 includes a multi-layer intrinsic region 405 including an acceleration layer 435 and a plurality of absorption layers 450, 460. In various embodiments, the PIN photodiode 400 is formed and / or mounted on a substrate 410. In various embodiments, the substrate 410 includes a GaAs substrate or other suitable substrate.

[0055] In various embodiments, the PIN-type photodiode 400 includes a p-type contact 475 and an n-type contact 425. For example, the p-type contact 475 may include a p-type semiconductor contact layer 470 and an anode electrode and / or pad 480B. For example, the n-type contact 425 may include an n-type contact layer 420, an n-type semiconductor contact layer 430, and a cathode electrode and / or pad 480A. In various embodiments, the electrodes and / or pads 480A, 480B are formed by depositing and / or patterning a conductive material on the PIN-type photodiode. For example, the electrodes and / or pads 480A, 480B may include copper, gold, and / or other metals. In various embodiments, the n-type contact layer 420 is made of a conductive material such as copper, gold, or other metals. In various embodiments, the n-type semiconductor contact layer 430 includes a semiconductor material that has been doped with an n-type dopant. For example, the n-type semiconductor contact layer 430 may include n-type doped AlGaAs. In various embodiments, the p-type semiconductor contact layer 470 includes a semiconductor material that has been doped with a p-type dopant. For example, the p-type semiconductor contact layer 470 may include p-type doped AlGaAs. In various embodiments, the PIN-type photodiode includes a mesa structure having a diameter D. One of the cathode electrode and / or pad 480A or the anode electrode and / or pad 480B may be disposed on top of the mesa structure and surround (e.g., define) the hole 490, and the other of the cathode electrode and / or pad 480A or the anode electrode and / or pad 480B may be disposed around the mesa structure and / or disposed around the mesa structure. In various embodiments, the diameter D is in the range of ten to forty microns (e.g., twenty to thirty microns).

[0056] In various embodiments, the PIN photodiode 400 includes a multi-layer intrinsic region 405. In various embodiments, the multi-layer intrinsic region 405 includes an absorption region 455 of the PIN photodiode 400. In various embodiments, the absorption region 455 includes at least one absorption material configured to absorb light in a specific wavelength range. Figure 4 As shown in , when the axis 495 defined by the PIN photodiode 400 is aligned with the z-axis, light (e.g., light of a specific wavelength range) can enter the PIN photodiode 400 through the hole 490 traveling in the negative z-direction and be absorbed by the absorbing material of the intrinsic region. When photons of a specific wavelength are absorbed, photoelectrons are released from the crystal structure of the absorbing material, thereby providing photoelectrons and holes. The holes generally move in the positive z-direction toward the p-type contact, and the photoelectrons generally move in the negative z-direction toward the n-type contact. The holes reaching the p-type contact and / or the photoelectrons reaching the n-type contact result in a voltage difference and / or current at the electrodes and / or pads 480A, 480B.

[0057] In various embodiments, the multilayer intrinsic region 405 includes a drift layer 440. In various embodiments, the drift layer 440 is configured not to absorb light of a specific wavelength range. For example, the drift layer 440 can be a non-absorbing drift layer. In various embodiments, the drift layer 440 is disposed between the absorption region of the multilayer intrinsic region 405 and the n-type contact 425 (e.g., the n-type semiconductor contact layer 430). In particular, the PIN-type photodiode can be configured so that only photoinduced electrons pass through the drift layer 440. For example, the PIN-type photodiode can be configured so that holes do not pass through the drift layer 440. For example, the drift layer 440 can be disposed at a boundary of the multilayer intrinsic region 405, the boundary of the multilayer intrinsic region 405 being adjacent and / or directly adjacent to the n-type contact 425.

[0058] In various embodiments, the drift layer 440 is configured to reduce the capacitance of the PIN junction of the PIN photodiode while having a minimal effect on the transit time of the photoinduced electrons. Generally, the transit time of the photoinduced electrons is the time between when the photoinduced electrons are generated and when the photoinduced electrons reach the n-type contact 425. The shorter the photoinduced electron transit time of the PIN photodiode, the faster the modulation speed of the PIN photodiode. In various embodiments, the drift layer includes a material that provides a high mobility of the photoinduced electrons traveling therethrough.

[0059] In various embodiments, the drift layer 440 includes a semiconductor material having a bandgap energy such that the drift layer 440 substantially functions as a carrier transport layer. For example, the bandgap energy of the drift layer 440 may be greater than the bandgap energy of the absorber material (e.g., the first absorber material and / or the second absorber material). In particular, the bandgap energy of the drift layer 440 may be sufficiently large to prevent or at least substantially reduce the absorption of light of a particular wavelength range by the drift layer 440. In the illustrated embodiment, the drift layer 440 includes intrinsic or lightly n-doped AlGaAs (AlGaAs). x Ga 1-x As, x = (0 ... 1)) compound semiconductor alloy. For example, the drift layer 440 may be substantially undoped. In an example embodiment, the drift layer 440 has a thickness (eg, in a direction substantially parallel to the axis 495) T in the sub-micron range. d For example, in an example embodiment, the drift layer 440 has a thickness T in the range of 0.1 to 0.5 micrometers (eg, 0.3 micrometers). d The particular thickness to be used depends on the relative thicknesses of the other layers, particularly the first absorber layer 460 and the second absorber layer 450 , and can be tailored according to the desired properties of the PIN photodiode 400 .

[0060] In various embodiments, the drift layer 440 is configured such that the electric field in the drift layer 440 is lower than the electric field in the absorption layer 460. In various embodiments, the reduction of the electric field in the drift layer 440 relative to the second absorption layer 450 is achieved by the distribution of dopant concentrations in the second absorption layer 450 and the drift layer 440 and any buffer layers therebetween. In an example embodiment, the electric field in the drift layer 440 is reduced by n-doping a region of the drift layer 440 adjacent to the second absorption layer 450 and / or providing an n-type doped buffer layer between the drift layer 440 and the second absorption layer 450. This doped region can be much thinner than the drift layer 440. In various embodiments, thinner doped regions will require higher doping levels, while thicker regions will require lower doping levels to achieve the desired reduction of the electric field in the drift layer 440. It will be appreciated that the primary factor achieving a specific reduction in the electric field in the drift layer 440 is the total fixed specific charge due to n-type dopants introduced in doped regions of the drift layer 440 and / or in a buffer layer between the drift layer 440 and the second absorber layer 450 .

[0061] In various embodiments, the multilayer intrinsic region 405 further includes an acceleration layer 435. In various embodiments, the acceleration layer 435 is configured to not absorb light within a specific wavelength range. For example, the acceleration layer 435 can be a non-absorbing acceleration layer. In various embodiments, the acceleration layer is configured to cause photoelectrons released by the absorption of light by the first absorbing material or the second absorbing material to have a greater drift velocity. In various embodiments, the acceleration layer is disposed between the second absorbing layer 450 and the drift layer 440 (or the n-type contact 425 in embodiments that do not include the drift layer 440). In an example embodiment, the acceleration layer 435 includes n-type doped AlGaAs (e.g., Al z Ga 1-z As, z=(0...1)). In an example embodiment, the acceleration layer 435 includes n-type doped AlGaAs including 1×10 15 Up to 1×10 17 In various embodiments, the acceleration layer 435 has a thickness T in a direction substantially parallel to the axis 495. n .

[0062] In various embodiments, the acceleration layer 435 causes an increase in the electric field within the first absorption layer 460 and the second absorption layer 450, so that the drift velocity of the photoinduced electrons is higher when the electrons are released from the crystal structure of the absorption material. With the higher drift velocity of the photoinduced electrons, the time taken for the photoinduced electrons to reach the n-type contact 425 is shorter. Therefore, the acceleration layer 435 reduces the transit time of the photoinduced electrons of the PIN photodiode 400 and increases the 3-dB modulation bandwidth of the PIN photodiode.

[0063] In various embodiments, the multi-layer intrinsic region 405 includes an absorption region 455, which includes a first absorption layer 460 and a second absorption layer 450. In various embodiments, the absorption region 455 may include multiple sets of first and second absorption layers, such as Figure 4 In various embodiments, the first absorption layer 460 is configured to absorb light of a specific wavelength range. In various embodiments, the first absorption layer 460 has a thickness T in a direction substantially parallel to the axis 495. a In various embodiments, the first absorption layer 460 includes a first absorption material. In an example embodiment, the first absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the first absorption material may be GaAs.

[0064] In various embodiments, the second absorption layer 450 is configured to absorb light in a specific wavelength range. In various embodiments, the second absorption layer 450 has a thickness T in a direction substantially parallel to the axis 495. in In various embodiments, the second absorption layer 450 includes a second absorption material. In an example embodiment, the second absorption material is a semiconductor material configured to absorb light of a specific wavelength range. For example, the specific wavelength range may include a range of 800nm-900nm and / or a portion thereof, and the second absorption material may be InGaAs (e.g., In y Ga 1-y As, y = (0 ... 1)). In various embodiments, the second absorber material has a lower band gap energy than the first absorber material. In various embodiments, the second absorber material has a higher absorption coefficient than the first absorber material. For example, the first absorber layer 460 can be characterized by a first absorption coefficient, and the second absorber layer 450 can be characterized by a second absorption coefficient, wherein the second absorption coefficient is greater than the first absorption coefficient. In various embodiments, the thickness T of the second absorber layer 450 is in Less than the thickness T of the first absorption layer 460 a In an exemplary embodiment, the thickness T of the second absorbent layer 450 is in The thickness T of the second absorption layer 450 may have an upper boundary defined by the strain relaxation of the lattice constant of the first absorption material. For example, when the first absorption material is GaAs and the second absorption material is InGaAs, the thickness T of the second absorption layer 450 is in may be equal to or less than a critical thickness governed and / or controlled by the saturation of strain relaxation of the host GaAs lattice constant corresponding to the amount added to GaAs to form InGaAs. In an example embodiment, the absorption region (T a +T in ) may have a thickness in the range of half a micron to two microns (eg, 0.8 microns to 1.8 microns and / or approximately 1.3 microns).

[0065] In various embodiments, the second absorption layer 450 is disposed and / or formed on the boundary of the absorption region, which is adjacent to and / or directly adjacent to the drift layer 440 (or the n-type contact 425 in the embodiment that does not include the drift layer 440). Therefore, due to the higher absorption coefficient of the second absorption layer 450, and this positioning of the second absorption layer 450 can increase the proportion of photoinduced electrons provided to the n-type semiconductor contact layer 430 in a relatively short time, so that the transit time of the photoinduced electrons of the PIN photodiode 400 is reduced, while increasing the 3-dB modulation bandwidth of the PIN photodiode.

[0066] In various embodiments, the parameter T of the PIN photodiode is a , Tin , T n And ingredientsIn y Ga 1-y As,y=(0...1) can be configured to provide a reduced and / or minimized capacitance (relative to the capacitance of a conventional PIN photodiode) with reduced and / or minimized photo / hole transit time at a given sensitivity of a PIN photodiode suitable for the application.

[0067] Technical advantages

[0068] Conventional PIN photodiodes often fail to provide modulation speeds sufficient to meet the growing demands of optical communications. The limiting factor for modulation speed is typically the transit time of photoinduced electrons. Various embodiments provide a technical solution to this technical problem by providing a PIN photodiode having a reduced transit time compared to a conventional PIN photodiode. For example, by using one or more second absorption layers having a higher absorption coefficient than (one or more) first absorption layers, wherein one of the one or more second absorption layers is disposed directly adjacent to an acceleration layer, a drift layer, or an n-type contact, the transit time of photoinduced electrons is greatly reduced compared to a conventional PIN photodiode. In another example, by using an acceleration layer disposed between an absorption region and a drift layer or an n-type contact, the drift velocity of photoinduced electrons can be increased compared to the drift velocity of similarly induced photoinduced electrons in a conventional PIN photodiode. Thus, various embodiments provide a PIN photodiode having a reduced transit time. Thus, various embodiments provide a PIN photodiode having an increased 3-dB modulation bandwidth without reducing the sensitivity of the PIN photodiode relative to a conventional PIN photodiode.

[0069] Many modifications and other embodiments of the invention set forth herein will occur to those skilled in the art having benefit of the foregoing description and the teachings given in the associated drawings. Therefore, it should be understood that the invention is not limited to the specific embodiments disclosed, and modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a general and descriptive sense only and not for the purpose of limitation.

Claims

1. A PIN type photodiode, comprising: p-type contact; n-type contact; a first absorbing layer characterized by a first absorption coefficient; as well as a second absorption layer characterized by a second absorption coefficient, wherein the second absorption coefficient is greater than the first absorption coefficient; wherein the first absorption layer is disposed between the p-type contact and the second absorption layer, wherein the second absorption layer is disposed between the first absorption layer and the non-absorption acceleration layer, wherein the non-absorption acceleration layer is in direct contact with the second absorption layer, The non-absorbing acceleration layer is disposed between the second absorbing layer and the non-absorbing drift layer, and the non-absorbing acceleration layer is configured to increase the drift velocity of photoinduced electrons released by the absorption of light by the first absorbing layer and / or the second absorbing layer. The non-absorbing drift layer is disposed between the non-absorbing acceleration layer and the n-type contact, wherein the non-absorbing drift layer is a carrier transport layer having a third absorption coefficient, wherein the third absorption coefficient is smaller than the first absorption coefficient and the second absorption coefficient. 2 . The PIN photodiode of claim 1 , wherein the first absorption layer comprises GaAs, and the second absorption layer comprises InGaAs. 3 . The PIN photodiode according to claim 1 , wherein the non-absorbing drift layer is disposed between the second absorbing layer and the n-type contact. 4 . The PIN photodiode according to claim 1 , wherein the n-type contact comprises an n-type contact and an n-type semiconductor contact layer, and the n-type semiconductor contact layer is disposed between the second absorption layer and the n-type contact.

5. The PIN photodiode according to claim 1, further comprising: a third absorption layer disposed between the second absorption layer and the n-type contact, the third absorption layer being characterized by the first absorption coefficient; as well as A fourth absorption layer is disposed between the third absorption layer and the n-type contact, wherein the fourth absorption layer is characterized by the second absorption coefficient. 6 . The PIN photodiode of claim 1 , further comprising a substrate, wherein the n-type contact is disposed on the substrate.

7. The PIN photodiode of claim 1, further comprising a first electrode in electrical communication with the p-type contact and a second electrode in electrical communication with the n-type contact.

8. The PIN photodiode according to claim 1, wherein the non-absorbing acceleration layer is disposed between (a) the second absorbing layer and the first absorbing layer and (b) the n-type contact, and has an n-type doping concentration of 1×10 15 Up to 1×10 17 within the range.

9. The PIN photodiode of claim 1, wherein the first absorption layer and the second absorption layer are configured to absorb light within a wavelength range that includes at least a portion of a range of 800 nm-900 nm.

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