Light detector with array of light absorbing materials
By employing an array structure of light absorption regions and a bias circuit in the photodetector, the problem of low responsivity caused by insufficient thickness of the light absorption layer was solved, achieving higher light absorption and current generation.
Patent Information
- Application Number
- CN202510388259.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-04-15
- Filing Date
- 2025-03-31
- Publication Date
- 2025-10-24
AI Technical Summary
Existing free-space photodetectors have low responsivity because the thickness of the light absorption layer is smaller than the wavelength of the sensitive light, resulting in the absorption layer being unable to absorb a large amount of light.
An array structure of light absorption regions is adopted. Multiple light absorption layers are formed on the surface of a semiconductor substrate. The interference effect between the light absorption regions is used to increase the amount of light absorption, and the generation of photocurrent is improved by a bias circuit.
This improved the responsivity of the photodetector, enhanced its absorption capacity for specific wavelengths of light, and increased the amount of photocurrent generated.
Smart Images
Figure CN120835625A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates generally to semiconductors, and in particular to a light detector having an array of light absorbing materials. BACKGROUND
[0002] A free space light detector can include a light absorbing layer in which electron hole pairs can be generated due to photons of light entering the absorbing layer. The light absorbing layer can be fabricated as a thin film material, but the thickness of the light absorbing layer can be substantially less than the wavelength of light for which the free space light detector is intended to be sensitive. Thus, the absorbing layer can not be able to absorb a significant amount of light, thereby causing the free space light detector to have a low responsivity. SUMMARY
[0003] In one example, a semiconductor device includes a semiconductor substrate having a surface. The semiconductor device includes a first region in the semiconductor substrate having a first dopant, a second region in the semiconductor substrate having a second dopant, and a third region in the semiconductor substrate having the first dopant. A first light absorbing layer is on the surface and over a fourth region of the semiconductor substrate between the first region and the second region. The first light absorbing layer is configured to absorb a particular wavelength of light. A second light absorbing layer is on the surface and over a fifth region of the semiconductor substrate between the second region and the third region. The second light absorbing layer is configured to absorb the light of the particular wavelength. At least one of a respective lateral dimension of the first light absorbing layer and the second light absorbing layer or a lateral separation between the first light absorbing layer and the second light absorbing layer is based on the particular wavelength.
[0004] In another example, a semiconductor device includes a semiconductor substrate having a surface, a first region in the semiconductor substrate having a first dopant, a second region in the semiconductor substrate having a second dopant, and a third region in the semiconductor substrate having the first dopant. The semiconductor device also includes an array of light absorbing regions on the surface.
[0005] In yet another example, a light detection circuit includes a light detector having a semiconductor substrate having a surface, a first region in the semiconductor substrate having a first dopant, a second region in the semiconductor substrate having a second dopant, a third region in the semiconductor substrate having the first dopant, and an array of light absorbing regions on the surface. The light detection circuit also includes a biasing circuit coupled to a first terminal and a second terminal. BRIEF DESCRIPTION OF DRAWINGS
[0006] Figure 1 A cross-sectional view of a light detector having a continuous absorbing layer in one example.
[0007] Figure 2 A cross-sectional view of a photodetector having an array of light-absorbing regions in an example.
[0008] Figure 3 A schematic diagram showing photons of light passing through a light-absorbing region and reflecting off an interface between the light-absorbing region and adjacent dielectric material in an example.
[0009] Figure 4 A top view of a photodetector in an example. Figure 2 A top view of a photodetector in an example.
[0010] Figure 5 A top view of a photodetector in an example. Figure 2 A top view of a photodetector in an example.
[0011] Figure 6 A plot showing the absorption index at different wavelengths of light for a photodetector having an array of light-absorbing regions and a photodetector having a continuous absorption layer in an example.
[0012] Figure 7 A cross-sectional view of an example of a photodetector having an array of light-absorbing regions and an avalanche diode in an example.
[0013] Figure 8 A top view of a photodetector in an example. Figure 8 A top view of a photodetector in an example.
[0014] Figure 9 A circuit in which a photodetector having an array of light-absorbing regions can be used. DETAILED DESCRIPTION
[0015] The same reference numbers or other reference designators in the drawings and the following description represent the same or similar elements.
[0016] Figure 1 A cross-sectional view of a photodetector 100 in an example. The photodetector 100 includes a semiconductor substrate 102. The semiconductor substrate 102 can include, for example, p-doped or n-doped silicon or another suitable material. In the example of FIG. 1, the semiconductor substrate 102 includes a p-doped silicon substrate. Figure 1 In the example of FIG. 1, a buried dielectric layer 104 is formed in the semiconductor substrate 102. The buried dielectric layer 104 can be silicon oxide or another suitable dielectric material.
[0017] The photodetector 100 also includes a first region 121, a second region 122, and a third region 123. The first region 121, the second region 122, and the third region 123 are in the semiconductor substrate 102. The first region 121 and the third region 123 have a first dopant, and the second region 122 has a second dopant. In one example, the first dopant is a type that increases the number of mobile negative charge carriers (electrons) in the corresponding region (e.g., phosphorus, arsenic). The second dopant is a type that increases the number of mobile positive charge carriers (holes) in the corresponding region (e.g., boron). The first region 121 and the third region 123 can be N-type silicon, and the second region 122 can be P-type silicon. The first region 121 and the second region 123 have portions 131 and 133 that have a higher dopant concentration than the surrounding portions (N-type), as indicated by the notation "N++". Similarly, the second region 122 has a portion 132 that has a higher dopant concentration than the surrounding portions (P-type), as indicated by the notation "P++". A region 124 of the semiconductor substrate 102 is between the regions 121 and 122. A region 125 of the semiconductor substrate 102 is between the regions 122 and 123. Figure 1 The example cross-sectional view also includes a sixth region 126 (P-type) that is separated from the region 121 by a region 127 along the x-axis through the semiconductor substrate 102. The photodetector 100 can have multiple P-type regions, such as the regions 122 and 126, and multiple n-type regions, such as the regions 121 and 123. The P-type region 122 and the N-type region 121 form a PN junction.
[0018] The semiconductor substrate 102 has a surface 102a. The photodetector 100 includes a light-continuously-absorbing layer 140 on the surface 102a of the semiconductor substrate 102. A protective dielectric layer 160 (e.g., silicon dioxide) can cover the continuously-absorbing layer 140. Conductive vias 147 and 148 provide electrical connectivity between the corresponding terminals 151 and 152 and the respective regions 121 and 122. The terminal 151 can be a cathode, and the terminal 152 can be an anode. Similarly, terminals 153 (cathode) and 154 (anode) can be coupled to the regions 123 and 124, respectively. The terminals 151 and 153 can be coupled together, and the terminals 152 and 154 can be coupled together. A bias voltage can be applied between the cathode terminals (e.g., terminals 151, 153) and the anode terminals (e.g., terminals 152, 154) such that the voltage at the cathode terminals 151, 153 is more positive than the voltage at the anode terminals 152, 154, in turn reverse-biasing the PN junction formed by the p-type second region 122 and the n-type first region 121. The reverse-biased PN junction creates an electric field that penetrates the absorbing layer 140.
[0019] Photons of light 170 may pass through dielectric layer 160 and enter light absorbing layer 140. Any given photon of light 170 may pass through light absorbing layer 140 or be absorbed by light absorbing layer 140. If photon 170 is absorbed by light absorbing layer 140, electron-hole pairs may be generated in the light absorbing layer. The electric field generated by the voltage difference between the cathode and anode causes the electrons and holes to separate. As more and more electron-hole pairs are generated by photons in light absorbing region 140, a current is generated between terminals 151 and 152. The magnitude of this current varies with the intensity of the light received by photodetector 100.
[0020] The material forming the light absorbing layer 140 may depend on the wavelength of light to which the light detector 100 is intended to be sensitive. For example, the absorption layer 140 may include germanium (Ge), which can absorb light having a wavelength in the range of approximately 1200 nm to 1600 nm. In another example, the absorption layer 140 may include silicon, which can absorb light having a wavelength in the range of 400 nm to 1100 nm.
[0021] Light absorbing layer 140 has a thickness D1. Light absorbing layer 140 is a thin film, meaning D1 is relatively small. In one example, D1 is less than 1000 nm, which is substantially smaller than the wavelength of light to which the photodetector is intended to be sensitive (e.g., 1200 nm to 1600 nm). Because the thickness D1 of light absorbing layer 140 is substantially smaller than the wavelength of light to be detected, light absorbing layer 140 is unable to absorb significant amounts of light, and too few photons generate electron-hole pairs to generate a significant level of current. Consequently, the responsivity of photodetector 100 with its continuous light absorbing layer 140 is relatively low.
[0022] Figure 2 is a cross-sectional view of a photodetector 200 in one example. Photodetector 200 includes a semiconductor substrate 102, a dielectric layer 104, regions 121, 122, 123, and 126, and conductive vias (e.g., vias 147 and 148) coupled between regions 121, 122, 123, and 126 and respective terminals 151, 152, 153, and 154. Terminals 151 and 153 are cathode terminals in this example, and terminals 152 and 154 are anode terminals.
[0023] Not as Figure 1 The continuous absorption layer 140 in the photodetector 100, Figure 2The photodetector 200 in FIG. 1 includes an array 240 of light absorbing regions (also referred to as layers) 241, 242, and 243. The array 240 of light absorbing regions 241-243 is on the surface 102a of the semiconductor substrate 102. The light absorbing layer 241 is on the surface 102a and over a region 124 of the semiconductor substrate 102 between regions 121 and 122. The light absorbing layer 242 is on the surface 102a and over a region 125 between regions 122 and 123. Similarly, the light absorbing layer 243 is on the surface 102a and over a region 127.
[0024] Each light absorption region 241-243 may include germanium, silicon, a III-V compound, or a II-VI compound. Examples of III-V compounds include GaAs and InGaAsP. Examples of II-VI compounds include ZnSe and WSe2. The type of material used for the light absorption region is based on the specific wavelength of light to which the photodetector is intended to be sensitive. For example, the light absorption regions 241-243 may include germanium for detecting light having a wavelength in the range of 1200 nm to 1600 nm, or may include silicon for detecting light having a wavelength in the range of 400 nm to 1100 nm.
[0025] The thickness D1 of the light absorbing regions 241-243 may be less than 1000 nm, which is substantially less than the wavelength of light to which the light detector 200 is sensitive. The diameter of each light absorbing region 241-243 is d and the pitch of the array 240 is p. Figure 2 The array of light absorbing regions 241-243 of the light detector 200 creates a cavity in which the light can be absorbed. Figure 1 The continuous absorption layer 140 of the photodetector 100 absorbs more light. Light from any given light absorption region 241-243 destructively interferes with adjacent light absorption regions, forming a cavity with a particular quality factor, Q, which indicates how much light can be absorbed in the cavity. The quality factor, Q, varies with the ratio of the diameter, d, to the pitch, p, of the array 240. The greater the number of light absorption regions 241-243 in the array 240, the greater the quality factor, Q. Because photons are collected in the light absorption regions 241-243, there is a greater probability of generating electron-hole pairs. Therefore, all other conditions being equal, the current generated by the photodetector 200 with its array of light absorption regions is greater than the current generated by the photodetector 100 with its continuous light absorption layer.
[0026] Figure 3A cross-sectional view of the photodetector 200 is shown for the regions 241 and 242. A possible path of the light 170 is shown entering the light absorption region 241 at an interface 241a between the light absorption region and the dielectric layer 160. Since the refractive index of the light absorption region 241 / 242 is higher than the refractive index of the dielectric layer 160, some of the light 170 can be reflected as 170a at the interface 241b, and some of the light 170 can pass through the interface 241b and reach the interface 242a as light 170b. Some of the light 170b can be reflected at the interface 242a and propagate back into the light absorption region 241 as 170c. The spacing (p) between adjacent light absorption layers (e.g., 241 and 242) and the lateral width (d) of each light absorption layer can be configured so that there is destructive interference between the light 170b and 170c to reduce the power of the light that radiates away from the light absorption layer (e.g., 240), and to keep the reflected light (e.g., light 170a) for an increased duration to facilitate absorption. Thus, the pattern of regions with different refractive indices can cause the incoming electromagnetic wave (light 170) to be confined to a high-refractive-index semiconductor (absorption layer) cavity.
[0027] In some examples, the width d of each light absorption region 241-243 and the spacing p of the array of light absorption regions are set based on the wavelength of light that the photodetector 200 will be sensitive to. For example, for values of d and p of approximately 800 nm and 1000 nm, respectively, and using germanium to form the light absorption regions 241, 242, and 243, the photodetector 200 with the array of light absorption regions 241-243 can have an operating range from 1200 to 1600 nm.
[0028] Figure 4 A top view of the photodetector 200 is shown. The regions 121, 122, 123, and 126 extend laterally along the y-axis on the surface 102a of the semiconductor substrate 102. The region 122 is laterally between the regions 121 and 123 along the x-axis, which is orthogonal to the y-axis. Similarly, the region 121 is laterally between the regions 126 and 122 along the x-axis. In Figure 4 In the example, the array 240 of light absorption regions 242-243 is a one-dimensional array extending along the x-axis. The light absorption region 241 is laterally between the light absorption regions 242 and 243. The polarization of the light includes transverse electric (horizontal) polarization and transverse magnetic (vertical) polarization. Depending on the angle of incidence of the light into the one-dimensional array of light absorption regions 241-243, one polarization type or the other will be dominant for the absorption of the light.
[0029] Figure 5 A top view of the photodetector 200 is shown in another example in which the array 240 of light absorption regions is a two-dimensional array. In Figure 5Array 240 of light absorption regions in the example of EMBODIMENT 1 includes, for example, light absorption regions 511, 512, 513, and 514, all of which are above surface 102a of semiconductor substrate 102. Light absorption regions 511 and 513 are above region 124 of semiconductor substrate 102. Light absorption regions 512 and 514 are above region 125 of semiconductor substrate 102.
[0030] exist Figure 5 In the example of FIG, each light absorption region 511-514 includes a circular pillar. The diameter d of the pillar is the same in all light absorption regions 511-514. In other examples, the diameter d of one or more of the light absorption regions 511-514 is different from the diameter d of one or more of the other light absorption regions 511-514. In addition, in other examples, the shape of each pillar may not be circular. For example, the shape of each pillar may be square, rectangular, oval, etc. The pitch of the array is determined by the p along the x-axis. x and p along the y-axis y In some instances, p x Equal to p y In other examples, p x Not equal to p y . Make p x Equal to p y results in a cavity that absorbs a large amount of light but in a narrow bandwidth, e.g. Figure 5 As shown in 610 in (described below). x Different from p y This can be caused by the incomplete cancellation of interference in adjacent blocks, which is similar to the case when p x Equal to p y The cavity absorbs less light than the cavities above, but has wider bandwidth absorption / responsivity performance.
[0031] Figure 6 is a graph of the absorption coefficient of the light absorbing layer relative to the wavelength of light. Curve 601 represents the absorption coefficient of the continuous layer of germanium on the silicon substrate 102 without the buried dielectric layer 104. Curve 602 represents the absorption coefficient of the continuous layer of germanium on the silicon substrate 102 with the buried dielectric layer 104. Curve 602 corresponds to Figure 1Curve 603 represents the absorption coefficient of a germanium-based light absorption region array on a silicon substrate 102 without a buried dielectric layer 104. Curve 604 represents the absorption coefficient of a germanium-based light absorption region array on a silicon substrate 102 with a buried dielectric layer 104. Curve 604 corresponds to the photodetector 200 described above. Curves 603 and 604 have a higher absorption index than curves 601 and 602 for wavelengths in the range of approximately 1530 nm to 1550 nm. Thus, the photodetector 200 having a light absorption region array has a higher absorption index than the photodetector having a continuous layer of light absorption material, particularly where the silicon substrate includes a buried dielectric layer 104. For example, the absorption index of curve 604 is approximately 0.9, as indicated by reference numeral 610 at wavelengths in the range of 1530 to 1550 nm, while the absorption index of curves 601 and 602 is approximately 0.1 for the same wavelength range. Thus, the photodetector having a light absorption region array can have a higher responsivity than the photodetector having a continuous layer of light absorption material.
[0032] Figure 7 A cross-sectional view of an example of the photodetector 200 implementing an avalanche photodiode. Figure 7 The structure of the photodetector 200 is largely the same as that of the photodetector 100. Figure 2 The difference is that regions 701, 702, and 703, which include the multiplication regions, are included. In this example, regions 701, 702, and 703 have P-type dopants. P-type region 702 and N-type region 121 form a PN junction. Similarly, P-type region 702 and N-type region 121 form a PN junction, and P-type region 703 and N-type region 123 form another PN junction. When electron-hole pairs are formed in absorption regions 241, 242, and 243, the electrons and holes separate and enter P-type regions 701, 702, and 703, where the electrons create additional electron-hole pairs by impact ionization. In another example, N-type regions can be formed adjacent to p+ regions 122, 126 of the anode to form APD multiplication regions.
[0033] Figure 8 A top view of the photodetector 200 of Figure 8 The photodetector 200 of
[0034] Figure 9For a schematic of the circuit 900, the circuit includes a biasing circuit 910, a photodetector 100 or 200, a transimpedance amplifier (TIA) 920, and a resistor 924. In this example, the biasing circuit 910 includes a resistor 912 coupled to a capacitor 1014. The resistor 912 is coupled between the voltage input terminal 902 and the cathode 151 of the photodetector 100, 200. A capacitor 914 is coupled between the cathode 151 and ground. The negative input of the TIA 920 is coupled to the anode 152 of the photodetector 100, 200. The resistor 924 is coupled between the negative input of the TIA 920 and the output 921 of the TIA 920.
[0035] The resistor 912 and the capacitor 914 of the biasing circuit 910 form a low-pass filter to filter out higher frequencies (e.g., noise) of the voltage at the voltage input terminal 920. The biasing circuit 910 provides the filtered voltage from the voltage input terminal 902 to the cathode 151 of the photodetector 100, 200. The positive terminal of the TIA 920 is coupled to ground, and thus, the negative terminal of the TIA 920 is also at ground potential. Because the anode 152 of the photodetector 100, 200 is at ground potential and the cathode 151 is at the voltage of the voltage input terminal 902, the photodetector 100, 200 is reverse-biased.
[0036] The photodetector 100, 200 generates a current 930 based on the intensity of the light it receives. The TIA 920 converts the current 930 from the photodetector 100, 200 to a voltage (Vout) at the output 921. The voltage Vout is given as: Vout = -(R924*I930), where R924 is the resistance of the resistor 924 and I930 is the magnitude of the current 930.
[0037] In this specification, the term "coupled" can encompass a connection, communication, or signal path that enables a functional relationship consistent with this specification. For example, if device A generates a signal to control device B to perform an action, then: (a) in a first example, device A is coupled to device B by a direct connection; or (b) in a second example, device A is coupled to device B through an intermediate component C, such that device B is controlled by device A via a control signal generated by device A, if the intermediate component C does not change the functional relationship between device A and device B.
[0038] Also, in this specification, recitation that something is "based on" something else means "based at least in part on" that other thing. Accordingly, if X is based on Y, X can be a function of Y and any number of other factors.
[0039] As used herein, the terms "terminal," "node," "interconnect," "lead," and "pin" are used interchangeably. Unless specifically stated to the contrary, these terms are generally used to denote an interconnection between or terminal end of a device element, circuit element, integrated circuit, device, or other electronic device or semiconductor component.
[0040] In this specification, unless otherwise stated, "about," "approximately," or "substantially" preceding a parameter means within + / - 10% of the stated parameter, or if the parameter is zero, within a reasonable range of values about zero.
[0041] Within the scope of the claims, modifications are possible in the described examples, and other examples are possible.
Claims
1. A semiconductor device comprising: a semiconductor substrate having a surface; a first region in the semiconductor substrate having a first dopant; a second region in the semiconductor substrate having a second dopant; a third region in the semiconductor substrate having the first dopant; a first light-absorbing layer on the surface and over a fourth region of the semiconductor substrate between the first region and the second region, the first light-absorbing layer configured to absorb a particular wavelength of light; and a second light-absorbing layer on the surface and over a fifth region of the semiconductor substrate between the second region and the third region, the second light-absorbing layer configured to absorb the particular wavelength of the light, wherein at least one of a respective lateral dimension of the first and second light-absorbing layers or a lateral separation between the first and second light-absorbing layers is based on the particular wavelength.
2. The semiconductor device of claim 1, wherein: each of the first, second, and third regions extends laterally along a first axis on the surface; the second region extends laterally along a second axis on the surface between the first and third regions; and the second axis is orthogonal to the first axis.
3. The semiconductor device of claim 2, further comprising an array of light-absorbing layers including the first and second light-absorbing layers.
4. The semiconductor device of claim 3, wherein the array is a one-dimensional array extending along the first axis.
5. The semiconductor device of claim 3, wherein: the array is a two-dimensional array including a third light-absorbing layer and a fourth light-absorbing layer; the third light-absorbing layer is on the surface and over the fourth region of the semiconductor substrate; and the fourth light-absorbing layer is on the surface and over the fifth region of the semiconductor substrate.
6. The semiconductor device of claim 5, wherein each of the first, second, third, and fourth light-absorbing layers comprises a circular pillar.
7. The semiconductor device of claim 5, wherein the first light-absorbing layer has a different shape than the second light-absorbing layer.
8. The semiconductor device of claim 5, wherein the first light-absorbing layer has a different size than the second light-absorbing layer.
9. The semiconductor device of claim 5, wherein the first and second light-absorbing layers are separated by a first distance and the third and fourth light-absorbing layers are separated by a second distance.
10. The semiconductor device of claim 1, wherein the first and second light-absorbing layers comprise at least one of germanium, silicon, a III-V compound, and a II-VI compound.
11. The semiconductor device of claim 1, further comprising a sixth region between the first and fourth regions, wherein: the first dopant is an n+ dopant; the first region has a portion with an n++ dopant; the second dopant is a p+ dopant; and the sixth region has a p-type dopant.
12. The semiconductor device of claim 1, further comprising: a first electrical terminal coupled to the first region, configured as a cathode; and a second electrical terminal coupled to the second region, configured as an anode.
13. A semiconductor device, comprising: a semiconductor substrate having a surface; a first region in the semiconductor substrate having a first dopant; a second region in the semiconductor substrate having a second dopant; a third region in the semiconductor substrate having the first dopant; and an array of light-absorbing regions on the surface.
14. The semiconductor device of claim 13, wherein the array is a one-dimensional array.
15. The semiconductor device of claim 13, wherein the array is a two-dimensional array.
16. The semiconductor device of claim 13, wherein the substrate includes a buried silicon oxide layer.
17. The semiconductor device of claim 13, wherein the semiconductor device is a photodetector.
18. A photodetection circuit, comprising: a photodetector having: a semiconductor substrate having a surface; a first region in the semiconductor substrate having a first dopant; a second region in the semiconductor substrate having a second dopant; a third region in the semiconductor substrate having the first dopant; and an array of light-absorbing regions on the surface; and a biasing circuit coupled to the first terminal and the second terminal.
19. The photodetection circuit of claim 18, wherein the array is a two-dimensional array.
20. The photodetection circuit of claim 18, further comprising a fourth region adjacent to the first region and between the first region and the second region, wherein: the first dopant is an n+ dopant; the second dopant is a p+ dopant; and the fourth region is a p-type dopant.