Photodiode

Abstract

The invention relates to a photodiode. The photodiode includes a carrier generation region of a semiconductor having a band gap that absorbs light of a given wavelength such that charge carriers are generated therein. The photodiode further includes n-doped and p-doped semiconductor regions, each of which has a higher band gap than the band gap of the carrier generation region, each of which is transparent to light of a given wavelength, the n-doped and p-doped semiconductor regions being along different sides of the carrier generation region. The photodiode further includes an interface region between the carrier generation region and a given doped region of the n-doped and p-doped semiconductor regions, the interface region including one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, the band offset is selected to reduce band offset between the carrier generation region and a given doped region adjacent to the interface region.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 542,553 filed on October 5, 2023 and U.S. Provisional Patent Application Serial No. 63 / 544,286 filed on October 16, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present description relates generally to telecommunication devices and, more particularly, to photodiodes having an interface region to reduce a band offset between a carrier generation region and a doped region. Background Art

[0004] Saturation of a photodiode and / or a reduction in the linear power range of the photodiode may be due to a reduction in the electric field in the absorption region where carriers are generated, which absorption region may also be referred to as a carrier generation region and / or an active layer and / or an active region. This electric field reduction is typically caused by "carrier screening," where the charge carriers (electrons and holes) generated by the absorption of light in the absorption region generate their own electric field that is opposite to the electric field applied to the photodiode. The linearity of a photodiode may be increased at the expense of responsivity. For example, a photodiode may be designed to reduce the amount of light absorbed per unit length (fewer charge carriers per unit volume), or to increase the volume of the absorption region. However, reducing the amount of light absorbed per unit length increases linearity at the expense of reduced responsivity. In addition, increasing the volume of the absorption region reduces the modulation bandwidth (speed) of the photodiode. Summary of the invention

[0005] A photodiode is provided, the photodiode comprising: a carrier generation region, the carrier generation region comprising a semiconductor having a band gap that absorbs light of a given wavelength, so that charge carriers are generated in the carrier generation region by the light of the given wavelength; an n-doped semiconductor region and a p-doped semiconductor region, the n-doped semiconductor region and the p-doped semiconductor region having respective band gaps higher than the band gap of the carrier generation region, the respective band gaps being transparent to the light of the given wavelength, the n-doped semiconductor region and the p-doped semiconductor region being along different sides of the carrier generation region; and an interface region between the carrier generation region and a given doped region of the n-doped semiconductor region or the p-doped semiconductor region, the interface region comprising one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, the one or more of the semiconductor alloy and the semiconductor sequence being selected to reduce a band offset between the carrier generation region and the given doped region adjacent to the interface region. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In order to better understand the various implementations described herein and to more clearly illustrate how they may be effected, reference will now be made by way of example only, wherein:

[0007] Figure 1 A Si-Ge-Si heterostructure photodiode according to the prior art is shown.

[0008] Figure 2 A photodiode having an interface region of a graded semiconductor alloy to reduce a band offset between a carrier generation region and a doped region is depicted according to a non-limiting example.

[0009] Figure 3 A photodiode having an interface region of a stepped semiconductor sequence to reduce a band offset between a carrier generation region and a doped region is depicted according to a non-limiting example.

[0010] Figure 4 Photodiodes having an interface region of a graded semiconductor alloy to reduce a band offset between a carrier generation region and a doped region are depicted according to other non-limiting examples.

[0011] Figure 5 Photodiodes having a stacked architecture with an interface region of a graded semiconductor alloy to reduce a band offset between a carrier generation region and a doped region are depicted according to other non-limiting examples.

[0012] Figure 6 Plotted is a graph of the band gap of silicon / germanium alloys as a function of fractional germanium content.

[0013] Those skilled in the art will appreciate that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the size of some elements in the drawings may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention.

[0014] In the drawings, apparatus and method components are represented by conventional symbols where appropriate, and only those specific details relevant to an understanding of embodiments of the invention are shown so as not to obscure the disclosure with details that would be apparent to one of ordinary skill in the art having the benefit of the description herein. DETAILED DESCRIPTION

[0015] High modulation bandwidth optical receivers must typically operate over a standardized range of input powers. Over the range where the photocurrent increases linearly with input optical power, a decrease is measured in some high modulation bandwidth optical receivers. Concurrently with this decrease in differential responsivity (which can be characterized, for example, by a changed slope of the change in photocurrent with respect to optical input power), a decrease in modulation bandwidth (photodiode response speed) is measured. The decrease in slope of responsivity and / or modulation bandwidth as optical input power increases can be referred to as "saturation".

[0016] The present specification provides a photodiode that increases the optical input power at which the photodiode saturates; for example, such a photodiode increases the range over which the photocurrent increases linearly with the input optical power. In addition, the photodiode provided herein generally allows for maintaining a given modulation bandwidth (photodiode response speed). Specifically, the photodiode provided herein includes an interface region between a carrier generation region and a given doping region (e.g., an n-doped semiconductor region or a p-doped semiconductor region); the interface region includes one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, and the semiconductor alloy and / or semiconductor sequence is selected to reduce the band offset between the carrier generation region and a given doping region adjacent to the interface region.

[0017] For example, in the interface region closest to the carrier generation region, an alloy of the corresponding semiconductors used in the manufacture of the carrier generation region and the given doping region can be used, which has a band gap (the difference between the valence band energy and the conduction band energy) that is larger than the band gap of the carrier generation region but still smaller than the band gap of the given doping region. This configuration reduces the band offset between the carrier generation region and the given doping region and reduces the carrier screening effect overall. In addition, the semiconductors of the interface region can be changed in their respective contents (e.g., by gradients and / or steps, as described herein) to increase the modulation bandwidth by reducing the carrier transmission time over the distance from the carrier generation region to the given doping region. In addition, the semiconductor of the interface region is selected so that the interface region is transparent to light absorbed by the carrier generation region, so that carrier generation is contained in the carrier generation region.

[0018] Such an interface region may also generally increase the responsivity of the photodiode and reduce undesirable dark current relative to prior art photodiodes that do not include such an interface region.

[0019] Moreover, in some specific examples, such an interface region may be included in a photodiode of a photonic integrated circuit (PIC), which may be made of intrinsic germanium (e.g., as a carrier generation region) deposited between an n-doped silicon electronic contact region and a p-doped silicon electronic contact region (e.g., as a doping region).

[0020] In addition, using germanium and silicon as examples, the photodiodes provided herein may generally include a "gradient" and / or "step" of a normal abrupt interface between a silicon region and a germanium region. For example, a gradient may be understood to mean that the alloy of silicon and germanium provided in the interface region is gradually changed over a limited and / or given distance, so that the closer to the germanium region, the higher the germanium content of the interface region between the silicon region and the germanium region, and the closer to the silicon region, the silicon content gradually becomes higher. In addition, a step may be understood to mean that a continuous layer of a combination of silicon and germanium is provided in the interface region in a sequence of steps and / or layers over a limited and / or given distance, so that the closer to the germanium region, the higher the germanium content of the interface region between the silicon region and the germanium region on average, and the closer to the silicon region, the silicon content gradually becomes higher on average.

[0021] Continuing with the example of silicon and germanium, in order to manufacture the photodiodes provided herein, processes that allow for the generation of steps of silicon / germanium alloyed materials and / or combinations of silicon and germanium can be introduced into the manufacture of the photodiodes and / or PICs. Any suitable method for generating silicon / germanium alloyed materials and / or steps is within the scope of this specification, including but not limited to growing graded silicon / germanium alloyed materials and / or steps, and / or implantation techniques that generate graded silicon / germanium alloyed materials.

[0022] The photodiodes provided herein may be similar to prior art photodiodes made of doped silicon and intrinsic germanium, but have a "gradient" and / or "step" of a normal abrupt interface between a p-doped silicon region and an intrinsic germanium region. Such photodiodes provided herein generally exhibit improved linearity and responsivity compared to prior art photodiodes made of doped silicon and intrinsic germanium with an abrupt interface.

[0023] In other words, the photodiodes provided herein may include an alloyed interface between an absorbing germanium carrier generation region and a p-doped silicon contact region to reduce the valence band offset and thus reduce the barrier to hole transport. This structure generally increases the linear range (power at which saturation occurs) in germanium-on-silicon PIC photodiodes.

[0024] Although certain examples herein are described with respect to an interface region between an absorbing germanium carrier generation region and a p-doped silicon contact region, more generally, such a corresponding interface region may be provided between a carrier generation region and a corresponding given doped semiconductor region (e.g., a contact region), whether n-doped or p-doped, to reduce any corresponding band offset.

[0025] In some examples, where the photodiodes provided herein include an alloyed interface between an absorbing intrinsic germanium carrier generation region and a p-doped silicon contact region, the interface alloy composition may include: a graded and / or stepped non-absorbing higher bandgap material disposed near or within a doped region, or near or within a germanium region, that generally increases responsivity due to light absorbed by the absorbing intrinsic germanium carrier generation region. This transparency generally reduces and / or eliminates the number of carriers generated in the interface region. The reduction in carrier concentration in turn reduces light wasted due to free-carrier absorption (FCA), for example because FCA cannot be utilized to generate photocurrent and may generate undesirable heat.

[0026] Such graded and / or stepped non-absorbing higher bandgap materials can further reduce dark current in germanium-on-silicon PIC photodiodes. In other words, for example, an abrupt interface between an absorbing region and a doped contact region of a prior art photodiode can be replaced by an interface region of graded and / or stepped non-absorbing higher bandgap materials, and the dark current can be reduced overall due to the increased thermal activation energy.

[0027] Although certain examples herein are described with respect to an interface layer between an absorbing germanium region and a p-doped silicon contact region, such an interface layer may be used with photodiodes made from other semiconductors and / or materials.

[0028] In fact, more generally, the photodiode provided in the present specification may include: a carrier generation region, which includes a semiconductor having a band gap that absorbs light of a given wavelength, so that charge carriers are generated in the carrier generation region by the light of the given wavelength; an n-doped semiconductor region and a p-doped semiconductor region, whose respective band gaps are higher than the band gap of the carrier generation region, and the respective band gaps are transparent to the light of the given wavelength, and the n-doped semiconductor region and the p-doped semiconductor region are along different sides of the carrier generation region; and an interface region between the carrier generation region and a given doped region of the n-doped semiconductor region or the p-doped semiconductor region, the interface region including one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, which is selected to reduce the band offset between the carrier generation region and the given doped region adjacent to the interface region.

[0029] Next follow Figure 1 , which depicts a prior art photodiode 100, and specifically (as labeled) depicts a top view, a plan view, and an energy band diagram 102 of the prior art photodiode 100. For example, the top view shows the prior art photodiode 100 together with an input waveguide 104 (e.g., interchangeably referred to herein as waveguide 104), which can provide modulated light 105 to a carrier generation region 106 of the prior art photodiode 100, and such modulated light 105 can have a signal encoded therein that can be converted by the carrier generation region 106 into a modulated signal and / or current. The waveguide 104 can be one end of a longer waveguide (not shown), and / or the waveguide 104 can be in optical communication with such a longer waveguide. Regardless, in use, the waveguide 104 can be in optical communication with a transmitter of an optical communication system, i.e., data is transmitted to the photodiode 100 in the form of modulated light 105 input to the carrier generation region 106. The photodiode 100 may be a component of a receiver (eg, a PIC receiver) in such an optical communication system.

[0030] The photodiode 100 also includes contacts for receiving current generated by the carrier generation region 106, specifically, as shown, a p-doped semiconductor region 108 and an n-doped semiconductor region 110. As depicted, in both the top view and the plan view, the doped semiconductor regions 108, 110 are located on opposite sides of the carrier generation region 106, but other architectures are possible.

[0031] When the transmitted light provided by the waveguide 104 is understood to be modulated, the current generated by the carrier generation region 106 may also be modulated, so that the data encoded in the transmitted light provided by the waveguide 104 is determined by other components (not shown) that receive the modulated current.

[0032] In practice, as best seen in a plan view depicting the photodiode 100 from the direction of the waveguide 104 and / or modulated light 105 (depicted as a circle with an inner cross to indicate that the modulated light 105 is "entering" the page of the plan view), the carrier generation region 106 may be fabricated by etching a cavity in the semiconductor that forms both doped semiconductor regions 108, 110, depositing the semiconductor of the carrier generation region 106 into the cavity, and using implantation techniques to p-dope and n-dope the doped semiconductor regions 108, 110, respectively. As best seen in the plan view, a portion of the semiconductor may be retained "underneath" the semiconductor of the carrier generation region 106 as the "bottom" of the cavity.

[0033] Next, attention is paid to the band diagram 102, which depicts the valence band 112 and conduction band 114 of the regions 106, 108, 110. It should be understood that the bands 112, 114 are depicted in the presence of an electric field 116 (e.g., a reverse bias electric field) between the doped regions 108, 110 (e.g., from the n-doped semiconductor region 108 to the p-doped semiconductor region 110). As such, the bands 112, 114 are tilted. It should also be understood that the bands 112, 114 are not drawn to scale, but rather to show their general trend.

[0034] As also shown in the energy band diagram 102, when the modulated light 105 from the waveguide 104 is absorbed by the carrier generation region 106, holes 115 and electrons 117 are generated. Figure 1 In the figure, the positive sign ("+") and the negative sign ("-") are represented respectively. This convention will be used throughout the specification. Holes 115 are understood to be generated in the valence band 112 of the carrier generation region 106, and electrons 117 are understood to be generated in the conduction band 114 of the carrier generation region 106 (for example, as the electrons 117 are excited by the modulated light 105, when the modulated light 105 is absorbed by the carrier generation region 106, the electrons 117 transition from the valence band 112 to the conduction band 114, forming holes 115 in the valence band 112). Holes 115 and electrons 117 may be collectively referred to as carriers 115, 117. Holes 115 and electrons 117 are separated by the applied electric field 116 and flow to the respective sides of the carrier generation region 106. At the sides of the carrier generation region, holes 115 encounter a potential barrier represented by band offset 122 and electrons 117 encounter a potential barrier represented by band offset 124 .

[0035] Once the carriers 115, 117 have left the carrier generation region 106, a photocurrent is formed by the corresponding flow of holes 118 and electrons 120 outside the carrier generation region 106. In other words, as shown, the holes 115 and electrons 117 are inside the carrier generation region 106, and the holes 118 and electrons 120 are outside the carrier generation region 106 and form the photocurrent. However, it should be understood that the holes 118 outside the carrier generation region 106 represent the holes 115 inside the carrier generation region 106 flowing across the potential barrier represented by the band offset 122, and the electrons 120 outside the carrier generation region 106 represent the electrons 115 inside the carrier generation region 106 flowing across the potential barrier represented by the band offset 122. Furthermore, as indicated by respective adjacent arrows, holes 115 flow to p-doped semiconductor region 108 via valence band 112 and electrons 117 flow to n-doped semiconductor region 110 via conduction band 114 due at least in part to electric field 116 .

[0036] In a specific example, the semiconductor of carrier generation region 106 may include germanium, and specifically intrinsic (e.g., undoped) germanium, and the semiconductor of both doped regions 108, 110 may include silicon, such that photodiode 100 includes a Si-Ge-Si heterostructure photodiode having an abrupt interface, wherein a partially etched Si region forms a silicon cavity, inside which intrinsic germanium is deposited (e.g., and with reference to a plan view, silicon may remain “underneath” the germanium, as shown by the portion of the semiconductor “underneath” carrier generation region 106).

[0037] However, any suitable semiconductor may be used for each of regions 106, 108, 110, as long as the respective band gaps satisfy the conditions mentioned herein. Another limitation may be that such semiconductors may have similar lattice constants and / or generally matched lattice constants for deposition and overall stability.

[0038] Furthermore, although the doped regions 108 , 110 are described herein as comprising the same semiconductor, such as silicon, the doped regions 108 , 110 may comprise any suitable semiconductor, including the doped regions 108 , 110 comprising the same semiconductor but doped differently, or comprising different semiconductors.

[0039] Typically, the semiconductor of the carrier generation region 106 can be selected so that the band gap between the valence band 112 and the conduction band 114 absorbs the modulated light 105, which is understood to have a given wavelength that can be compatible with an optical communication system. In a specific example, the given wavelength of the modulated light 105 can be 1310 nm and / or about 1310 nm, which is a typical wavelength used in optical communication systems, although other wavelengths are within the scope of this description.

[0040] Similarly, the semiconductor of regions 108 , 110 may be selected such that the band gap between the valence band 112 and the conduction band 114 is transparent to a given wavelength of modulated light 105 .

[0041] In fact, a general requirement for a photodiode is that the band gap of the carrier generation region (e.g., carrier generation region 106) is smaller than the corresponding energy of the light to be absorbed by the carrier generation region. In the case of 1310 nm, with an energy of about 0.95 eV, intrinsic germanium generally meets this requirement, having a band gap of about 0.66 eV at room temperature (e.g., 300 K or 27° C. to allow for some heating of the photodiode incorporated into the PIC). In addition, semiconductor materials with lower band gap energies generally have higher optical refractive indices.

[0042] Similarly, a general characteristic of photoconductor structures, at least in PIC waveguides, is that contact regions, such as doped regions 108, 110, have a relatively low optical refractive index and a corresponding bandgap energy greater than the photon energy of light 105, such that the contact region is generally transparent to light. This characteristic can ensure that light absorption in the contact region is minimized, and / or this characteristic can ensure that carrier generation and / or current generation is localized to the carrier generation region. In the case of 1310 nm, silicon generally meets this requirement, having a bandgap of about 1.12 eV at room temperature (e.g., 300 K or 27°C to allow for some heating of photodiodes incorporated in PICs).

[0043] Thus, as seen in the band diagram 102, there are discontinuities in the respective valence bands 112 and respective conduction bands 114 of the carrier generation region 106 and the doped regions 108, 110. The band discontinuities, which may also be referred to as band offsets, may be larger or smaller depending on the semiconductors used in the regions 106, 108, 110. Furthermore, such band offsets may be different between the carrier generation region 106 and each of the doped regions 108, 110, and further, the band offsets may be different for the regions 112, 114, respectively.

[0044] Returning to the energy band diagram 102, and using germanium and silicon as exemplary respective materials for the carrier generation region 106 and the doped regions 108, 110, due to the abrupt interface therebetween, the band offset 122 in the valence band 112 between the carrier generation region 106 and the p-doped semiconductor region 108 is relatively high, for example, compared to the band offset represented by the barrier 124 in the conduction band 114 between the carrier generation region 106 and the n-doped semiconductor region 110. This results in carrier screening and other effects mentioned herein.

[0045] In practice, the barrier due to band offset 122 for holes 115 may be more problematic than the barrier due to band offset 124 for electrons 117 because the band offset fraction between germanium and silicon is generally biased toward valence band 112 (e.g., the band gap difference for valence band 112 is greater than the band gap difference for conduction band 114). Furthermore, holes 115 are generally heavier than electrons 117, so holes 117 are less likely to be thermally excited beyond the barrier due to band offset 122.

[0046] It is the accumulation of holes 115 at the barrier due to the band offset 122 (and to a lesser extent, the accumulation of electrons 117 at the barrier due to the band offset 124) that causes carrier screening, rather than the presence of the band offsets 122, 124 themselves. For example, at low levels of light, there is still a barrier due to the band offsets 122, 124, but there are not enough carriers 115, 117 to effectively screen the electric field 116.

[0047] Regardless, under normal operating conditions and / or normal intensity of light 105, due to carrier screening (e.g., holes 118 and electrons 120 that form photocurrent can contribute to carrier screening), holes 115, 118 and electrons 117, 120 can generally form an electric field that opposes the applied electric field 116, which can reduce the current, overall responsivity, and linearity of the photodiode 100. Furthermore, while the applied electric field 116 can generally be increased to provide enough energy to the holes 115 to overcome the band offset 122, the band offset 122 still remains. Thus, the band offset 122 causes the overall performance of the photodiode 100 to be reduced.

[0048] Next, pay attention Figure 2 , Figure 2 The photodiode 200 is shown to solve the technical challenges of the prior art photodiode 100. Specifically, Figure 2 Shown are a top view, a plan view, and an energy band diagram 202 of photodiode 200. In effect, photodiode 200 represents a modified version of prior art photodiode 100, where like components have like numbers, but in the "200" series rather than the "100" series.

[0049] Thus, for example, a photodiode 200 is depicted along with an input waveguide 204 (e.g., interchangeably referred to herein as waveguide 204) that provides modulated light 205 to a carrier generation region 206 of the photodiode 200, and the photodiode 200 includes the carrier generation region 206, a p-doped semiconductor region 208 that serves as a contact with the carrier generation region 206, and an n-doped semiconductor region 210. However, in contrast to the prior art photodiode 100, the photodiode 200 also includes an interface region 211 between the carrier generation region 206 and a given doped region (e.g., the p-doped semiconductor region 208 as shown). Typically, the interface region 211 includes one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, which is selected to reduce a band offset between the carrier generation region 206 and the given doped region adjacent to the interface region 211.

[0050] The depicted example assumes that carrier generation region 206 comprises germanium and doped regions 208 , 210 comprise silicon, which are respectively and therefore doped and will therefore have a band diagram similar to band diagram 102 of prior art photodiode 100 without interface region 211 .

[0051] However, because the interface region 211 is located between the carrier generation region 206 and the p-doped semiconductor region 208 , the energy band diagram 202 of the photodiode 200 is modified compared to the energy band diagram 102 of the photodiode 100 , as described below.

[0052] Specifically, the band diagram 202 depicts valence bands 212 and conduction bands 214 of regions 206, 208, 210, 211. It should be understood that the bands 212, 214 are depicted in the presence of an electric field 216 (e.g., a reverse bias electric field) between the doped regions 208, 210 (e.g., from the n-doped semiconductor region 208 to the p-doped semiconductor region 210). As such, the bands 212, 214 are tilted. It should also be understood that the bands 212, 214 are not drawn to scale, but rather to show their general trend.

[0053] As also shown in the energy band diagram 202, when the modulated light 205 from the waveguide 204 is absorbed by the carrier generation region 206, holes 215 and electrons 217 are generated. The holes 215 are understood to be formed in the valence band 212 of the carrier generation region 206, and the electrons 217 are understood to be formed in the conduction band 214 of the carrier generation region 206 (e.g., as the electrons 217 are excited by the modulated light 205, when the modulated light 205 is absorbed by the carrier generation region 206, the electrons 220 transition from the valence band 212 to the conduction band 214, forming holes 215 in the valence band 212). Hereinafter, similar conventions will be used to refer to the holes 215 and electrons 217 in the carrier generation region 206, and the holes 218 and electrons 218 in the p-doped semiconductor region 208 and the n-doped semiconductor region 210.

[0054] In particular, holes 218 and electrons 220 flowing through the respective band offsets 222, 224 are understood to form a photocurrent generated by the carrier generation region 206. In addition, as shown by the adjacent arrows, holes 215 flow to the p-doped semiconductor region 208 via the valence band 212 and electrons 217 flow to the n-doped semiconductor region 210 via the conduction band 214, at least in part due to the electric field 216.

[0055] Continuing with the example of a semiconductor including a carrier generating region 206 of germanium, particularly intrinsic (e.g., undoped) germanium, and a semiconductor including doped regions 208 , 210 of silicon, photodiode 200 may include a Si—Ge—Si heterostructure photodiode, which may be formed in a manner similar to photodiode 100 .

[0056] However, any suitable semiconductor may be used for each of the regions 206, 208. Likewise, although reference is made to the interface region 211 between the carrier generation region 206 and the p-doped semiconductor region 208, Figure 2 , but in other examples, depending on the materials thereof, an interface region may be provided between the carrier generation region 206 and the n-doped semiconductor region 210 .

[0057] Compared to the photodiode 100 , the photodiode 200 further includes an interface region 211 , which may be fabricated by growing and / or forming the interface region 211 between the carrier generation region 206 and the p-doped semiconductor region 208 in any manner.

[0058] The interface region 211 generally reduces the band offset between the carrier generation region 106 and a given doped region adjacent to the interface region 211 (eg, p-doped semiconductor region 208 as depicted).

[0059] like Figure 2As shown, the interface region 211 may include a graded alloy of the semiconductor of the carrier generation region 206 and the corresponding semiconductor of the p-doped semiconductor region 208. For example, again using germanium and silicon as an example, the semiconductor composition of the interface region 211 may be represented as Si 1-x Ge x :p: where "x" represents the fraction of germanium in the graded semiconductor region 211 (e.g., replacing p-doped silicon with p-doped germanium). In particular, at the interface between the p-doped semiconductor region 208 and the interface region 211, the semiconductor composition of the interface region 211 is a combination of p-doped silicon and p-doped germanium, with the p-doped germanium having a higher silicon content than the germanium content (e.g., Si 1-x Ge x :p is higher than "x"), and at the interface between the carrier generation region 206 and the interface region 211, the semiconductor composition of the interface region 211 is a combination of p-doped silicon and p-doped germanium, and the germanium content of the p-doped germanium is higher than the silicon content (for example, in Si 1- x Ge x :p where "x" is higher than "1-x"). For example, the interface region 211 may include a graded alloy of silicon and germanium with increasing germanium content and decreasing silicon content from the p-doped semiconductor region 208 to the carrier generation region 206. The entire interface region 211 may be p-doped using implantation techniques or the like (e.g., when the silicon of the p-doped semiconductor region 208 is p-doped). Furthermore, as best seen in a plan view, the interface region 211 may not be a "planar" layer of uniform thickness, but may be fabricated in any suitable manner (e.g., using ion implantation and / or crystal growth), as long as the interface region 211 is between respective portions of the regions 206, 208 in which holes 218 flow from the carrier generation region 206 to the p-doped semiconductor region 208.

[0060] The width of the interface region 211 can be any suitable value, but can be between about 5% and about 50% of the width of the carrier generation region 206, although such width of the interface region 211 can depend on the process used to manufacture the photodiode 100 and / or can be relatively independent of the width of the carrier generation region 206; for example, using crystal growth, the width of the interface region 211 can be in the range of about 0.1 μm to about 0.3 μm, although any suitable width is within the scope of the present description. In addition, using germanium as an example of a material for the carrier generation region 206, in a waveguide-coupled PIC, the width of the carrier generation region 206 (e.g., between regions 208, 210) can be in the range of about 0.4 μm to about 1 μm, although any suitable width is within the scope of the present description; in addition, the width of the interface region 211 can be adjusted accordingly. In addition, the width of the carrier generation region 206 can depend on its material and / or its manufacturing process; therefore, other suitable widths will occur to those skilled in the art within the scope of the present description.

[0061] Similarly, “x” may vary linearly with distance from the p-doped semiconductor region 208 , however, “x” may vary in any suitable manner including, but not limited to, parabolically with distance from the p-doped semiconductor region 208 , among other possibilities.

[0062] Similarly, the width and / or the change of semiconductor composition in the interface region 211 can be heuristically selected to reduce the band offset 222 between the carrier generation region 206 and the p-doped semiconductor region 208, as described below, for example relative to the band offset 122 of the prior art photodiode 100. In particular, such a heuristic selection can be, for example, controlling the band offset 222 by heuristically selecting the width and / or changing the semiconductor composition in the interface region 211.

[0063] For example, referring to the energy band diagram 202, there are discontinuities in the respective valence bands 212 and the respective conduction bands 214 of the carrier generation region 206 and the doped regions 208, 210. For example, as can be clearly seen in the energy band diagram 202, due to the presence of the interface region 211, the band offset 222 between the carrier generation region 206 and the p-doped semiconductor region 208 is smaller than the corresponding band offset 122 of the prior art photodiode 100.

[0064] In particular, due to the semiconductor alloy grading of the interface region 211, and / or due to the semiconductor composition of the interface region 211 adjacent to the carrier generation region 206 being a graded alloy comprising the same semiconductor as the carrier generation region 206 (e.g., although such semiconductor may be p-doped and / or non-intrinsic and / or non-doped and / or intrinsic in the interface region 211), the band offset 222 is reduced relative to the band offset 122.

[0065] Furthermore, the semiconductor composition gradation of the interface region 211 may be selected such that the band gap of the interface region 211 makes the interface region 211 transparent to the modulated light 205. For example, next turning our attention to Figure 6 , Figure 6 The band gap (in eV) of the germanium / silicon alloy is depicted as a function of the germanium fraction ranging from "0" to "1", for example, at 300K (e.g., and which may be determined according to Vegard's law and / or heuristically). In addition, the energy of 1310 nm light is depicted at 0.95 eV. It should be understood that above 0.95 eV, the corresponding band gap is transparent to 1310 nm light, while below 0.95 eV, the corresponding band gap absorbs 1310 nm light. From Figure 6 It is also understood that below a germanium fraction of 0.2 (e.g., a fraction with a band gap of 0.95 eV), the alloy of silicon and germanium absorbs light at 1310 nm. Figure 2 , the graded alloy of the interface region 211 may have a germanium content of less than 0.2, such as about 0.195, or any other suitable fraction, adjacent to the carrier generation region 206, and may change linearly to a germanium content of 0.0, or any other suitable fraction, from the carrier generation region 206 to the p-doped semiconductor region 208. In practice, Figure 6 The graph of can be used to select the band gap of the graded alloy in the interface region 211 adjacent to the carrier generation region 206 to be as small as possible, but still transparent to 1310 nm light.

[0066] In other words, similar to the p-doped semiconductor region 208, the interface region 211 is transparent to the modulated light 205 of a given wavelength, and the interface region 211 may form part of the p-doped semiconductor region 208, as described in more detail below. In other words, the band gap of the interface region 211 increases from the carrier generation region 206 to the p-doped semiconductor region 208 (e.g., and / or increases as "x" decreases), and may be transparent to the modulated light 205 of a given wavelength.

[0067] Furthermore, a step in the valence band 212 due to the band offset 222 is depicted and is reduced relative to the band offset 122 .

[0068] As such, the holes 215 have a smaller energy barrier to overcome (e.g., represented by the band offset 222) relative to the prior art photodiode 100. For example, carrier accumulation of the holes 215 in the carrier generation region 206 (e.g., on the valence band side) is reduced, resulting in reduced p-doped semiconductor region 208 and carrier screening. In other embodiments, a corresponding interface region can be introduced to reduce the barrier caused by the band offset 224, which can reduce carrier accumulation of the electrons 217 in the carrier generation region 206 directed to the conduction band side of the n-doped semiconductor region 210, as described below.

[0069] It should also be understood that while regions 206, 208, 210, 211 have been described for germanium and silicon, regions 206, 208, 210, 211 may include any suitable respective semiconductors. In addition, while doped regions 208, 210 are described herein as including the same semiconductor, such as silicon, doped regions 208, 210 may include any suitable different semiconductors.

[0070] In addition, although Figure 2 Interface region 211 is depicted in FIG. 2 as being between carrier generation region 206 and p-doped semiconductor region 208 , but in other examples that may depend on the semiconductor used to fabricate photodiode 200 , interface region 211 may be between carrier generation region 206 and n-doped semiconductor region 210 .

[0071] In addition, Figure 2 In the example of FIG. 1 , the band offset 224 in the conduction band 214 between the carrier generation region 206 and the n-doped semiconductor region 210 formed by the abrupt physical interface between the carrier generation region 206 and the n-doped semiconductor region 210 is small enough to allow electrons 220 to flow from the carrier generation region 206 to the n-doped semiconductor region 210 without carrier screening problems. However, such a band offset 224, which is similar to and / or the same as the band offset 124, may be caused by the semiconductors of the photodiode 200 being germanium and silicon. When other semiconductors are used, the band offset 224 may be similar to the band offset 122 and / or large enough to make carrier screening a problem, and thus a corresponding interface region may be provided between the carrier generation region 206 and the n-doped semiconductor region 210. In practice, a corresponding interface region may be provided between the carrier generation region 206 and one or both of the doped regions 208, 210 to reduce the corresponding band offset between the carrier generation region 206 and the p-doped semiconductor region 208 (e.g., in the valence band 212) and / or between the carrier generation region 206 and the n-doped semiconductor region 210 (e.g., in the conduction band 214).

[0072] In addition, although Figure 2The example is described for an interface region 211 of a graded alloy of respective semiconductors including the carrier generation region 206 and the p-doped semiconductor region 208, but in other examples, an interface region including a semiconductor sequence with stepped compositions may be provided, as described below for Figure 3 as described.

[0073] Specifically, Figure 3 A photodiode 300 is shown that is similar to the photodiode 200, and like components have like reference numerals except as noted herein. Specifically, Figure 2 A top view, a plan view, and an energy band diagram 302 of a photodiode 300 are shown.

[0074] Compared with the photodiode 200, the photodiode 300 further includes an interface region 311 between the carrier generation region 206 and the p-doped semiconductor region 208, and the interface region 311 includes a semiconductor sequence with a stepped composition. For example, as shown, the interface region 311 includes four layers, and again using germanium and silicon as an example, the semiconductor composition of the interface region 311 can be expressed as Si 1-xn Ge xn :p: where "x" represents the fraction of germanium in layer "n" of the step interface region 311, so "n" is one of 1, 2, 3 and 4, where "n=1" represents the first layer whose composition is x=x1 in the interface region 311 closest to the p-doped semiconductor region 208, and "n=4" represents the last layer whose composition is x=x4 in the interface region 311 closest to the carrier generation region 206. In general, as "n" increases, the fraction "(1-x)" of the p-doped silicon content of the step interface region 311 decreases, and the fraction "x" of the p-doped germanium content of the step interface region 311 increases. Similarly, it can be used Figure 6 The corresponding contents of the various layers are selected based on the graph of , similar to what is described above with respect to the photodiode 200 , and similar conditions apply.

[0075] In other words, the semiconductor composition variation between layers of the interface region 311 may be similar to the semiconductor composition variation of the graded alloy of the interface region 211 , but provided in a stepped configuration rather than a graded configuration.

[0076] Furthermore, while four steps are shown, interface region 311 may have any suitable number of steps.

[0077] Next, attention is paid to the band diagram 302 , and in particular the band offset 322 which has been modified relative to the band offset 222 due to the stepped structure of the interface region 311 .

[0078] Likewise, the semiconductor composition of the interface region 311 can be selected such that the band gap makes the interface region 311 substantially transparent to the modulated light 205. In other words, similar to the p-doped semiconductor region 208, the interface region 311 is generally transparent to the modulated light 205 of a given wavelength. In other words again, the band gap of the interface region 311 increases from the carrier generation region 206 to the p-doped semiconductor region 208 (e.g., and / or decreases from the p-doped semiconductor region 208 to the carrier generation region 206) and can be generally transparent to the modulated light 205 of a given wavelength.

[0079] In addition, the band offset 322 is provided with a step corresponding to the step of the interface region 311. The step of the band offset 322 of the photodiode 200 may be equal to the band offset 222 of the photodiode 200. In other words, the effect of the stepped interface region 311 is similar to that of the graded interface region 211 in reducing the band offset and reducing carrier accumulation or trapping and carrier screening.

[0080] It should also be understood that aspects of interface regions 211, 311 may be combined. For example, one or more steps of interface region 311 may be graduated similarly to interface region 211, while one or more other steps of interface region 311 may not be graduated.

[0081] Furthermore, the steps of the interface region 311 may be arranged as alternating layers of germanium and silicon, where again the germanium content decreases closer to the p-doped semiconductor region 208 and the silicon content increases closer to the p-doped semiconductor region 208. In this example, the layers are selected such that similar to Figure 3 (and / or Figure 2 ), the average band gap increases from the carrier generation region 206 to the p-doped semiconductor region 208 at the interface region 311.

[0082] Therefore, the present invention provides a photodiode, which includes: a carrier generation region, which includes a semiconductor having a band gap that absorbs light of a given wavelength, so that charge carriers are generated in the carrier generation region by the light of the given wavelength; an n-doped semiconductor region and a p-doped semiconductor region, each of which has a band gap higher than the band gap of the carrier generation region, and the respective band gaps are transparent to the light of the given wavelength, and the n-doped semiconductor region and the p-doped semiconductor region are along different sides of the carrier generation region; and an interface region between the carrier generation region and a given doped region of the n-doped semiconductor region or the p-doped semiconductor region, the interface region including one or more of a semiconductor alloy and a semiconductor sequence that is one or more of a gradient and a step in composition, which is selected to reduce the band offset between the carrier generation region and the given doped region adjacent to the interface region.

[0083] In addition, the semiconductor of the carrier generation region may include a carrier generating and / or absorbing semiconductor (e.g., absorbing the wavelength of the incident light 205), and a given doped region may include a transparent semiconductor different from the carrier generating and / or absorbing semiconductor (e.g., generally transparent to the wavelength of the incident light 205), and the interface region may include a graded alloy of the carrier generating and / or absorbing semiconductor and the transparent semiconductor, and in the interface region, the content of the carrier generating and / or absorbing semiconductor in the graded alloy may decrease from the carrier generating region to the given doped region, and the corresponding content of the doped semiconductor in the graded alloy may increase from the carrier generating region to the given doped region.

[0084] Therefore, in this article, the semiconductor of the carrier generation region is understood to generate carriers, for example by absorbing incident light. Although intrinsic germanium is used as an example of such a semiconductor, such a semiconductor may not be intrinsic, and in fact even germanium may be, for example, lightly doped, as long as germanium generates carriers by absorbing incident light. Therefore, the semiconductor of the carrier generation region may be interchangeably referred to as a carrier generating semiconductor and / or an absorbing semiconductor and / or a carrier generating absorbing semiconductor, etc.

[0085] Similarly, in this article, a given doped region is understood to be generally transparent to light absorbed by the semiconductor of the carrier generation region for which it serves as a contact. Therefore, the semiconductor of a given doped region can be interchangeably referred to as a transparent semiconductor and / or a contact semiconductor and / or a transparent contact semiconductor, etc.

[0086] Alternatively or additionally, the semiconductor of the carrier generating region may include a carrier generating and / or absorbing semiconductor, and the given doped region may include a transparent semiconductor different from the carrier generating and / or absorbing semiconductor, and in the interface region, the content of the carrier generating and / or absorbing semiconductor in the step decreases from the carrier generating region to the given doped region, and the corresponding content of the transparent semiconductor in the step increases from the carrier generating region to the given doped region.

[0087] More generally, the semiconductor of the carrier generating region may include a carrier generating and / or absorbing semiconductor, and a given doped region may include a transparent semiconductor different from the carrier generating and / or absorbing semiconductor, and the interface region may include at least one step in the respective contents of the carrier generating and / or absorbing semiconductor and the transparent semiconductor.

[0088] In other words, refer to Figure 3In the specific example shown in , although the interface region 311 is described with respect to four steps and / or layers, the interface region 311 may include as few as one step and / or one layer as long as a reduction in band offset is achieved, which has a semiconductor component that is a mixture of an intrinsic semiconductor of the carrier generation region 206 and a p-doped semiconductor of the p-doped semiconductor region 208.

[0089] Furthermore, more generally, referring to the band offset 222 and / or the band offset 322 , the interface region 211 , 311 may provide one or more band offset steps in the band offset between the carrier generation region 206 and a given doped region (eg, p-doped semiconductor region 208 ).

[0090] Furthermore, the semiconductor of the carrier generation region 206 may include intrinsic germanium, and the given doping region may include a p-doped semiconductor region 208 , and the p-doped semiconductor region 208 may include p-doped silicon.

[0091] In practice, the interface region provided herein may be between a carrier generating region and a p-doped semiconductor region such that the carriers with reduced band offset include holes.

[0092] However, the interface region provided herein may be between the carrier generating region and the n-doped semiconductor region such that the carriers for which the band offset is reduced include electrons.

[0093] like Figure 2 and Figure 3 As shown, it can be appreciated that the interface region 211, 311 can be formed by the portion of a given doped region that is closest to the carrier generation region 206, as shown by the p-doped semiconductor region 208. In other words, the interface region 211, 311 can be formed during the formation of at least a portion of the p-doped semiconductor region 208, such as in combination with at least the p-doping of the interface region 211, 311 and the p-doped semiconductor region 208.

[0094] However, in other examples, the interface region may be formed as part of the carrier generation region. For example, next note Figure 4 , which is basically similar to Figure 2 , wherein the same components have the same reference numerals.

[0095] Specifically, Figure 4 A photodiode 400 is shown that is similar to the photodiode 200, and like components have like reference numerals except as noted herein. Specifically, Figure 4 A top view, a plan view, and an energy band diagram 402 of a photodiode 400 are shown.

[0096] However, at the photodiode 400, an interface region 411 (which may include a graded alloy similar to interface region 211 (e.g., as depicted)) and / or a stepped semiconductor sequence of composition similar to interface region 311 may be incorporated (e.g., as depicted) into the portion of the carrier generation region 206 that is closest to the p-doped semiconductor region 208 (e.g., again using germanium and silicon as examples).

[0097] As in the depicted example, the interface region 411 includes a graded alloy and the band diagram 402 is similar to the band diagram 202, but the band offset 422 is shifted toward the carrier generation region 206 relative to the band offset 322 of the band diagram 302. When the interface region 411 includes a semiconductor sequence similar to the interface region 311, the band diagram 402 can be similar to the band diagram 302, with the stepped band offset and the sloped region shifted toward the carrier generation region 206.

[0098] Furthermore, again using germanium and silicon as an example, the semiconductor component of the interface region 411 can be represented as Si 1-x Ge x :p: Similar to the interface region 211, it is assumed that the semiconductor of the interface region 411 is p-doped.

[0099] Alternatively, again using germanium and silicon as an example, the semiconductor component of the interface region 411 can be represented as Si 1- x Ge x :i, when the silicon and germanium of interface region 411 are intrinsic (e.g., as shown by “i”), although “x” can vary similarly to that described herein with respect to interface region 211.

[0100] Figure 2 , Figure 3 and Figure 4 The example shows an n-doped semiconductor region and a p-doped semiconductor region on opposite sides of a carrier generation region with an interface region between the carrier generation region and the p-doped semiconductor region, although such an interface region may be between the carrier generation region and the n-doped semiconductor region.

[0101] However, other architectures are also within the scope of this description.

[0102] For example, note next Figure 5 , which shows a plan view of a photodiode 500 having a stacked architecture as described below.

[0103] The photodiode 500 is further depicted along with an input waveguide 504 (e.g., interchangeably referred to herein as waveguide 504), which provides modulated light 505 to a carrier generation region 506 of the photodiode 500, and the photodiode 500 includes the carrier generation region 506, a p-doped semiconductor region 508, and an n-doped semiconductor region 510, which acts as a contact to the carrier generation region 506. The photodiode 500 also includes an interface region 511 located between the carrier generation region 506 and the p-doped semiconductor region 508. The interface region 511 can be similar to any of the interface regions 211, 311, 411, etc. Furthermore, alternatively or additionally, the photodiode 500 can include an interface region located between the carrier generation region 506 and the n-doped semiconductor region 510.

[0104] However, in contrast to the photodiodes 200, 300, 400, the photodiode 500 has a stacked architecture in which the interface region 511 is grown on the carrier generation region 506, for example, on a side of the carrier generation region 506 that is adjacent to the side of the carrier generation region 506 where the n-doped semiconductor region 510 is located. In addition, the p-doped semiconductor region 508 is grown on the interface region 511. However, it should be understood that the interface region 511 and the p-doped semiconductor region 508 are fabricated such that the interface region 511 and the p-doped semiconductor region 508 do not contact and / or short-circuit the n-doped semiconductor region 510. In other words, the n-doped semiconductor region 510 extends only along a portion of the side of the carrier generation region 506 and ends before the adjacent side of the carrier generation region 506 where the interface region 511 is located.

[0105] In addition, the photodiode 500 also includes conductive regions 550, 554 in electrical communication with the p-doped semiconductor region 508 to conduct holes generated by the carrier generation region 506 to the side of the carrier generation region 506 opposite the n-doped semiconductor region 510. In this example, an insulating region 552 is provided that extends from the conductive region 550 and along the regions 506, 508, 511, and further between portions of the conductive region 550 along the sides of the regions 506, 511 (e.g., with portions of the p-doped semiconductor region 508), and further between the conductive region 554 and (as depicted) at least the carrier generation region 506.

[0106] Insulating region 552 generally prevents contact and / or shorting between conductive regions 550 , 554 and sides of regions 506 , 511 .

[0107] Conductive regions 550, 554 are provided only to ensure that the current generated by carrier generation region 506 can be accessed from opposite sides of photodiode 500. Conductive region 550 may include conductive epoxy or conductive metal or wire bonding, and conductive region 554 may include silicon. Similarly, insulating region 552 may include any suitable material, such as silicon oxide, etc., although the material of insulating region 522 may depend on the material of the substrate on which photodiode 500 is formed.

[0108] Furthermore, although the band diagram of photodiode 500 is not depicted, the band diagram of photodiode 500 may be similar to either of band diagrams 202 , 302 , depending on whether interface region 511 is gradient and / or stepped and assuming that a reverse bias electric field is applied to photodiode 500 .

[0109] therefore, Figure 5 The example shows an n-doped semiconductor region and a p-doped semiconductor region on adjacent sides of a carrier generation region, wherein an interface region is between the carrier generation region and the p-doped semiconductor region, although such an interface region may be between the carrier generation region and the n-doped semiconductor region.

[0110] Although the present examples of photodiodes 200, 300, 400, 500 are described with respect to silicon and germanium, other materials are also within the scope of the present description. For example, one or more of the photodiodes 200, 300, 400, 500 may be adapted to include a suitable combination of InGaAs (indium gallium arsenide) and InP (indium phosphide). For example, one or more of the photodiodes 200, 300, 400, 500 may include an absorption layer (e.g., carrier generation layer 206, 506) that includes InGaAs (e.g., having any suitable relative content of indium and gallium), a contact layer (e.g., regions 208, 210 and / or regions 508, 510) of appropriately doped InP, and Ga 1-x In x As 1-y P y Graded contact layers with graded and / or stepped interface regions, all grown on InP. 1-x In x As 1-y P y, “x” is the fraction of indium decreased from the InP contact layer to the InGaAs carrier generation layer, “1-x” is the fraction of gallium increased from the InP contact layer to the InGaAs carrier generation layer, “y” is the fraction of phosphorus decreased from the InP contact layer to the InGaAs carrier generation layer, and “1-y” is the fraction of arsenic increased from the InP contact layer to the InGaAs carrier generation layer.

[0111] In this specification, an element may be described as being "configured to" perform one or more functions or "configured to" such functions. Generally, an element configured to perform or configured to perform a function is capable of performing the function, or is suitable for performing the function, or is adapted to perform the function, or is operable to perform the function, or is otherwise capable of performing the function.

[0112] It should be understood that for the purposes of this specification, the phrases "at least one of X, Y, and Z" and "one or more of X, Y, and Z" can be interpreted as only X, only Y, only Z, or any combination of two or more items X, Y, and Z (e.g., XYZ, XY, YZ, XZ, etc.). Similar logic can be applied to two or more items in any occurrence of "at least one." and "one or more."

[0113] The terms "about," "substantially," "substantially," "approximately," and the like are defined as "close to," such as understood by one skilled in the art. In some examples the phrase should be read as "within 10%, in other examples as "within 5%, in other examples as "within 1%, and in other examples as "within 0.5%."

[0114] Those skilled in the art will appreciate that there are many more alternative examples and possible modifications, and the above examples are only illustrations of one or more embodiments. Therefore, the scope of the present invention is limited only by the appended claims.

Claims

1. A photodiode, comprising: a carrier generation region comprising a semiconductor having a bandgap that absorbs light of a given wavelength such that charge carriers are generated in the carrier generation region by the light of the given wavelength; an n-doped semiconductor region and a p-doped semiconductor region, the n-doped semiconductor region and the p-doped semiconductor region having respective band gaps higher than the band gap of the carrier generation region, the respective band gaps being transparent to the given wavelength of light, the n-doped semiconductor region and the p-doped semiconductor region being along different sides of the carrier generation region; as well as In an interface region between the carrier generation region and a given doped region of the n-doped semiconductor region or the p-doped semiconductor region, the interface region includes one or more of a semiconductor alloy and a semiconductor sequence that are one or more of gradients and steps in composition, and the one or more of the semiconductor alloy and the semiconductor sequence are selected to reduce a band offset between the carrier generation region and the given doped region adjacent to the interface region.

2. The photodiode according to claim 1, wherein: the semiconductor of the carrier generating region comprises a carrier generating semiconductor, and the given doped region comprises a transparent semiconductor different from the carrier generating semiconductor, wherein the interface region comprises a graded alloy of the carrier generating semiconductor and the transparent semiconductor, Wherein, in the interface region, the content of the carrier generating semiconductor in the graded alloy decreases from the carrier generating region to the given doping region, and the corresponding content of the transparent semiconductor in the graded alloy increases from the carrier generating region to the given doping region.

3. The photodiode according to claim 1, wherein: the semiconductor of the carrier generating region comprises a carrier generating semiconductor, and the given doped region comprises a transparent semiconductor different from the carrier generating semiconductor, Wherein, in the interface region, the content of the carrier generating semiconductor in the step decreases from the carrier generating region to the given doping region, and the corresponding content of the transparent semiconductor in the step increases from the carrier generating region to the given doping region.

4. The photodiode according to claim 1, wherein: the semiconductor of the carrier generating region comprises a carrier generating semiconductor, and the given doped region comprises a transparent semiconductor different from the carrier generating semiconductor, And wherein the interface region includes at least one step in the respective contents of the carrier generating semiconductor and the transparent semiconductor.

5. The photodiode according to claim 1, wherein: The interface region provides one or more band offset steps in the band offset between the carrier generating region and the given doped region.

6. The photodiode according to claim 1, wherein: The interface region is formed by a portion of the carrier generation region that is closest to the given doping region.

7. The photodiode according to claim 1, wherein: The interface region is formed by a portion of the given doped region that is closest to the carrier generation region.

8. The photodiode according to claim 1, wherein: The semiconductor of the carrier generating region includes carrier generating germanium, and the given doped region includes the p-doped semiconductor region including p-doped silicon.

9. The photodiode according to claim 1, wherein: The interface region is located between the carrier generating region and the p-doped semiconductor region such that the carriers with reduced band offset include holes.

10. The photodiode according to claim 1, wherein: The interface region is located between the carrier generating region and the n-doped semiconductor region such that the carriers with reduced band offset include electrons.

11. The photodiode according to claim 1, wherein: The n-doped semiconductor region and the p-doped semiconductor region are located at opposite sides of the carrier generation region, and the interface region is located between one of the n-doped semiconductor region and the p-doped semiconductor region and the carrier generation region.

12. The photodiode according to claim 1, wherein: The n-doped semiconductor region and the p-doped semiconductor region are located at adjacent sides of the carrier generation region, and the interface region is located between one of the n-doped semiconductor region and the p-doped semiconductor region and the carrier generation region.

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