Integrated optical sensor with pinned photodiode

Abstract

Embodiments of the present disclosure relate to an integrated optical sensor with a pinned photodiode. The integrated optical sensor is formed by a pinned photodiode. A semiconductor substrate includes a first semiconductor region having a first conductivity type, the first semiconductor region being located between a second semiconductor region and a third semiconductor region, the second semiconductor region having a second conductivity type opposite to the first conductivity type, and the third semiconductor region having the second conductivity type. The third semiconductor region is thicker, less doped, and deeper in the substrate than the second region. The third semiconductor region includes silicon and germanium. In one implementation, the germanium in the third semiconductor region has at least one concentration gradient. In another implementation, the germanium concentration in the third semiconductor region is substantially constant.

Description

[0001] Priority declaration

[0002] This application claims the priority of French Patent Application No. 2005537, filed on May 26, 2020, the contents of which are incorporated herein by reference in their entirety to the maximum extent permitted by law. Technical Field

[0003] Implementations and embodiments relate to integrated optical sensors, particularly integrated optical sensors including pinned photodiodes. Background Art

[0004] In recent years, an increasing number of applications, such as facial recognition, virtual reality, and active automotive safety, require high-performance, low-profile, and low-cost imaging systems.

[0005] In this respect, imaging systems based on the use of indirect time-of-flight (iToF) measurement technology and benefiting from a highly integrated structure as well as precise and fast performance meet these expectations particularly well.

[0006] More specifically, using periodically modulated excitation obtained from a laser, it is possible, for example, to indirectly measure the distance separating an object to be measured from an imaging system (referred to as an "iToF" imaging system) via phase shift measurement of a signal which is received after reflection at the object relative to the emitted radiation, and to extend data collection of the optical signal over several excitation and emission cycles in order to improve the accuracy of the measurement.

[0007] This type of detector is particularly useful in applications using radiation having a wavelength in the near infrared (eg, 0.94 micrometers).

[0008] Thus, in particular these applications are being implemented more and more not only in time-of-flight sensors but also in CMOS imagers.

[0009] Typically, the sensors used are integrated silicon-based sensors.

[0010] However, silicon has low absorption power in the infrared and even in the near infrared (eg, 0.94 microns).For example, a silicon substrate having a thickness of 1 micron has an absorption of 1.7% at a wavelength of 0.94 microns.

[0011] The absorbed power increases with greater thickness, for example a thickness on the order of 6 microns is a typical thickness for a pinned photodiode of an integrated optical sensor.

[0012] But silicon devices have low sensitivity in the near infrared. For example, a silicon substrate with a thickness of 6 microns has a quantum efficiency in the range of 7% to 8% at a wavelength of 0.94 microns.

[0013] Furthermore, at this thickness, the collection of minority carriers in the pinned photodiode is very slow, which is detrimental.

[0014] Therefore, there is a need to improve the performance of optical sensors implementing in particular one or more pinned photodiodes, in particular in terms of absorption and / or sensitivity and / or collection speed of minority carriers, most in particular in the near infrared range. Summary of the invention

[0015] The aforementioned requirements are met by replacing silicon with a material having in particular better infrared absorption while satisfying strict constraints such as, for example, the following: compatibility with microelectronic components located on the front end of the substrate and with single-crystalline silicon; integrability in the active parts of semiconductor devices (diodes and pinned diodes); sufficiently small generation of minority carriers; and a defect rate that is as low as possible.

[0016] This material is then advantageously temperature-resistant, has good interface qualities with silicon and with dielectric materials (such as silicon dioxide), and is generally of good quality (in particular no or only few dislocations, no or only few contaminants).

[0017] The pinned photodiode includes a first semiconductor region, for example, of N type, sandwiched between two semiconductor regions, for example, of P+ type, a surface region and a thicker and deeper P type region, within a semiconductor substrate.

[0018] For example, it has been proposed to incorporate less substantial amounts of germanium in the P-type region in order to improve the performance of the optical sensor, in particular in terms of absorption and sensitivity, in particular in the near infrared range, while minimizing the risk of dislocation formation.

[0019] Furthermore, it is proposed to incorporate germanium, for example in a P-type region having a positive concentration gradient from the bottom of the P region to the N region, in order to improve the performance of the optical sensor, in particular in terms of the collection speed of minority carriers, in particular in the near infrared range.

[0020] In both cases mentioned above (not too large, for example constant, amount of germanium and positive concentration gradient), the germanium concentration profile preferably stops at the beginning of the depletion region of the P region.

[0021] Therefore, according to one aspect, an integrated optical sensor is proposed, comprising at least one detection module comprising a pinned photodiode.

[0022] The photodiode includes a first semiconductor region in a semiconductor substrate, which has a first conductivity type (for example, N-type conductivity). The first semiconductor region is located between a second semiconductor region and a third semiconductor region, the second semiconductor region has a second conductivity type (for example, P-type conductivity, opposite to the first conductivity type), and the third semiconductor region also has the second conductivity type.

[0023] The third region is thicker than the second region.

[0024] The third region is less doped than the second region. Thus, the third region may be P-doped, while the second region may be P+ doped.

[0025] Furthermore, the third region is located deeper in the substrate than the second region.

[0026] This third region comprises silicon and germanium, the germanium advantageously in a small amount or atomic percentage, for example with an atomic percentage comprised between 3% and 6%, and preferably with at least a first concentration gradient.

[0027] The first concentration gradient is advantageously a positive gradient, the atomic percentage of germanium increasing towards the first region.

[0028] The presence of germanium allows improving the absorption coefficient of the semiconductor material.

[0029] Furthermore, the presence of a favorable positive concentration gradient allows reducing the space between the valence band and the conduction band of the semiconductor material and causes a tilting of the conduction band towards the surface of the photodiode, which will give rise to an electric field that will accelerate the movement of minority carriers from the third region to the first region.

[0030] Therefore, the duration of collection of minority carriers is reduced.

[0031] The atomic percentage of germanium is preferably increased from 0% to 6%.

[0032] Furthermore, limiting the atomic percentage of germanium to 6% allows limiting the risks of dislocation appearance and generally allows the detection module to remain compatible with the other steps of manufacturing the optical sensor and with other components of an integrated circuit incorporating the optical sensor.

[0033] Furthermore, the growth may occur in any possible manner, such as linearly or in (one or more) steps.

[0034] The third region generally includes a depletion region and a non-depletion region (referred to as a neutral region), the depletion region being in contact with the first region and being located above the non-depletion region, and the first concentration gradient is preferably located in the non-depletion region.

[0035] In addition, it is also preferred that germanium has a second negative concentration gradient in the depletion region.

[0036] This negative gradient in germanium concentration does create an electric field that opposes the electric field caused by the conduction band tilt.

[0037] By placing a negative germanium gradient in the depletion region, it becomes negligible compared to the electric field created by the diode itself.

[0038] For example, the atomic percentage of germanium may decrease from 6% to 0% in the depletion region.

[0039] The reduction in the atomic percentage of germanium according to the second gradient may be gradual or abrupt (second “infinite” gradient), although in practice it is mitigated by the phenomenon of interdiffusion of germanium and silicon atoms.

[0040] According to another aspect, an integrated optical sensor is provided, comprising at least one pinned photodiode, which includes a first semiconductor region having a first conductivity type within a semiconductor substrate, the first semiconductor region being located between a second semiconductor region and a third semiconductor region, the second semiconductor region having a second conductivity type opposite to the first conductivity type, the third semiconductor region having the second conductivity type, the third semiconductor region being thicker, less doped and located deeper in the substrate than the second region, and the third semiconductor region including germanium having an atomic percentage less than or equal to 6% (for example, included between 3% and 6%).

[0041] Indeed, as indicated above, and independently of the presence of a germanium concentration gradient, the presence of a small amount of germanium allows improving the absorption coefficient while minimizing the risk of dislocations appearing and generally allowing the detection module to remain compatible with the other manufacturing steps of the optical sensor and with other components of an integrated circuit incorporating the optical sensor.

[0042] According to one embodiment, the non-depleted region includes germanium having a substantially constant atomic percentage.

[0043] The constant atomic percentage of germanium is, for example, comprised between 4% and 5%.

[0044] The third region may contain a silicon-germanium alloy, which is obtained, for example, by a ramp gradient in the concentration of the dopant (germanium) in the epitaxial reactor, or by an alternation of silicon and silicon-germanium layers.

[0045] As described above, the first conductivity type may be the N type and the second conductivity type may be the P type, but it is also possible that the second conductivity type is the N type and the first conductivity type is the P type.

[0046] According to one embodiment, the substrate may be a silicon-on-insulator type substrate comprising a buried insulating layer known to those skilled in the art by the acronym BOX (“Buried Oxide”), which is capped by a semiconductor film containing the pinned photodiode.

[0047] The sensor may comprise several detection modules arranged, for example, in rows or in a matrix.

[0048] According to another aspect, an imaging system, such as a camera, is proposed, comprising at least one sensor as defined above.

[0049] According to another aspect, an electronic device is proposed, for example of tablet computer or mobile cellular telephone type, comprising at least one imaging system as defined above.

[0050] According to another aspect, a method for manufacturing an integrated pinned photodiode is provided, for example in the context of manufacturing an integrated optical sensor incorporating the photodiode, the method comprising embodiments of a first semiconductor region, a second semiconductor region, and a third semiconductor region within a semiconductor substrate, the first semiconductor region having a first conductivity type (e.g., N-type conductivity) and being located between the second semiconductor region and the third semiconductor region, the second semiconductor region having a second conductivity type (e.g., P-type conductivity, as opposed to the first conductivity type), the third semiconductor region also having the second conductivity type, the third semiconductor region being thicker and less doped than the second region and being located deeper in the substrate than the second region.

[0051] According to a variant of this aspect, the production of the third region comprises forming a material comprising silicon and germanium, the germanium advantageously in a small amount or atomic percentage, for example with an atomic percentage comprised between 3% and 6%, and preferably with at least a first concentration gradient.

[0052] According to another variant of this aspect, the production of the third region comprises forming a material comprising silicon and germanium, the germanium having an atomic percentage less than or equal to 6%, for example comprised between 3% and 6%.

[0053] Regardless of the variation, the formation of the material may include silicon germanium epitaxy or continuous epitaxy of silicon and continuous epitaxy of silicon germanium. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other advantages and features of the present invention will become apparent by examining the detailed description of embodiments and implementations and the accompanying drawings, in which:

[0055] Figure 1 illustrates a cross section of a pinned photodiode located within a semiconductor substrate and also illustrates dopant concentration information;

[0056] Figure 2 illustrates a cross section of a pinned photodiode located within a semiconductor substrate and also illustrates the alternation of doped layers;

[0057] Figure 3 An integrated optical sensor is schematically illustrated;

[0058] Figure 4 schematically illustrates an imaging system including an integrated optical sensor; and

[0059] Figure 5 An electronic device comprising an integrated optical sensor is schematically illustrated. DETAILED DESCRIPTION

[0060] exist Figure 1 On the right part of FIG. 1 , reference numeral MD generally denotes a detection module comprising a pinned photodiode PPD located within a semiconductor substrate, here a silicon-on-insulator (SOI) type substrate.

[0061] The module MD is integrated in the integrated circuit IC.

[0062] The SOI type substrate comprises a semiconductor film 1 which is situated above a buried insulating layer BX which in turn is situated above a carrier substrate 3 .

[0063] The thickness Ep of the semiconductor film 1 may be comprised between approximately 3 and 6 micrometers, and in this example is of the order of 6 micrometers.

[0064] The photodiode PPD is a buried photodiode formed by a double junction (here, a double P+NP junction).

[0065] Here, the photodiode PPD is electrically insulated from the rest of the semiconductor film 1 by the deep insulating trench 4 .

[0066] More specifically, the photodiode PPD includes, within the semiconductor film 1 , a first semiconductor region RG1 having N-type conductivity, located between a second semiconductor region RG2 having P-type conductivity (or pinning implantation) and a third semiconductor region RG3 having P-type conductivity.

[0067] The first region RG1 may advantageously be formed in the middle of the module and not extend to the deep insulation trench 4 .

[0068] The second region RG2 has a thickness e2 of the order of 0.07 micrometers.

[0069] The second region RG2 has a concentration of about 10 20 atoms / cm 3 The dopant is P+ doped.

[0070] This pinning injection allows to significantly reduce the dark current of the detection module MD.

[0071] The first region RG1 has a thickness e1 of the order of 0.3 micrometers.

[0072] The first region RG1 has a concentration of about 2*10 17 atoms / cm 3 The dopant is N-doped.

[0073] The third region RG3 has a thickness e3 of the order of 6 micrometers.

[0074] Compared to the second region RG2 , the third region RG3 is less doped and is located deeper in the substrate.

[0075] It is P-doped, where the dopant concentration is between 10 14 -10 15 atoms / cm 3 in the range.

[0076] The third region RG3 may be very lightly doped over more than 90% of its thickness, but may include a more heavily doped P-type P layer at its base (10 17 Up to 10 18 atoms / cm 3 ), that is, it is adjacent to the buried insulating layer BX or on the buried insulating layer BX.

[0077] The third region RG3 includes a depletion zone Z30 contacting the first region RG1 and a non-depletion zone Z31 below the depletion zone Z30 .

[0078] The depletion zone Z30 has a thickness e30 of the order of 2 to 3 micrometers, the doping of which corresponds to the P doping of the non-depletion zone Z31 (at 10 14 Up to 10 15 atoms / cm3 range) with the N-doped “tail” of the second region RG2.

[0079] The non-depleted region Z31 has a thickness e31 of the order of 3 to 4 microns and, as indicated above, has a thickness of 10 14 Up to 10 15 atoms / cm 3 The dopant concentration is of the order of magnitude.

[0080] Furthermore, the module MD comprises a portion 2 above the upper surface FS of the semiconductor film 1, which comprises the (conventional structure and known per se) processing circuitry of the photodiode, in particular the collection allowing the accumulation of minority carriers in the first region N, and interconnection regions known to those skilled in the art by the acronym BEOL (“Back End Of Line”).

[0081] like Figure 1 As illustrated in the left portion of , the third region RG3 includes silicon and germanium, and the silicon and germanium may have different concentration distributions.

[0082] Thus, according to a first embodiment, preferably in the non-depleted zone Z31, the germanium concentration may have a distribution PRF corresponding to a substantially constant germanium concentration. In this context, substantially constant means within + / - 1 to 3% of the target dopant concentration level of the entire region of interest (i.e., zone Z31).

[0083] As an example, the atomic percentage of germanium is of the order of 4% to 5% throughout the thickness of the non-depletion zone Z31 and then drops abruptly to 0 in the depletion zone Z30 .

[0084] The presence of this small amount of germanium (typically with an atomic percentage of germanium of less than 6% in the third region RG3 ) allows in particular to improve the absorption coefficient while minimizing the risk of dislocations occurring.

[0085] However, the third region RG3 may include silicon and germanium, which advantageously have the first concentration gradient GR1 (or GR10 ) and the second concentration gradient GR2 (or GR20 ).

[0086] Gradients GR1 , GR2 , GR10 and GR20 are possible but non-limiting examples.

[0087] The first concentration gradient GR1 or GR10 is a positive gradient, meaning that the atomic percentage of germanium increases from the buried oxide layer BX toward the first region RG1 .

[0088] With respect to the gradient GR1 , the atomic percentage of germanium increases from 0% to 6% from the bottom of the non-depletion zone Z31 to the limit of the depletion zone Z30 .

[0089] With regard to the gradient GR10 , from the bottom of the non-depletion zone Z31 to the limit of the depletion zone Z30 , the atomic percentage of germanium increases, for example, from 3% to 6%.

[0090] The second germanium concentration gradient GR2 or GR20 located in the depletion zone Z30 is a negative gradient, meaning that the atomic percentage of germanium decreases from the limit of the depletion zone Z30 towards the first region RG1 .

[0091] More specifically, for each of the second germanium concentration gradients GR2 or GR20 , the atomic percentage of germanium decreases from 6% to 0% in the depletion zone Z30 .

[0092] Alternatively, this second gradient may be "infinite", which corresponds to an abrupt transition, here from 6% to 0% (similar to what is illustrated with respect to the change in the distribution PRF).

[0093] In practice, however, the interdiffusion phenomenon of germanium and silicon atoms softens this abrupt transition.

[0094] The presence of the concentration gradient GR1 or GR10 allows reducing the space between the valence band and the conduction band of the semiconductor material and causes the conduction band to tilt towards the surface of the photodiode, which will result in an electric field that will accelerate the movement of minority carriers from the third region to the first region and therefore reduce the duration of collection of minority carriers.

[0095] However, the second germanium concentration gradient creates an electric field that opposes the electric field of the first gradient.

[0096] By placing this second negative gradient GR2 or GR20 of germanium in the depletion zone Z30, it can become negligible compared to the electric field created by the diode itself.

[0097] Therefore, the duration of minority carrier collection will not be negatively affected.

[0098] Moreover, here again, the presence of small amounts of germanium (for example with an average atomic percentage of between 3% and 6%) allows the absorption coefficient to be improved while minimizing the risk of dislocations occurring.

[0099] Provides the presence of a germanium concentration gradient Figure 1 Embodiments of thus allow obtaining a fast detection modulus with an improved absorption coefficient and a reduced risk of dislocations.

[0100] Despite Figure 1 In the embodiment of the present invention, the third region RG3 is formed of a homogeneous silicon-germanium alloy. Figure 2 As illustrated in FIG. 1 , the third region RG3 may be formed by alternation of silicon layers 11 and silicon germanium layers 10 .

[0101] The volume percentage of germanium for each of these layers 11 is chosen so that the final atomic percentage of germanium in the region RG3 follows the gradient considered.

[0102] The method for making Figure 1 An embodiment of the method of module MD.

[0103] In the case of an SOI type substrate, epitaxy is performed over the buried layer BX (and where appropriate the silicon thin layer more heavily doped forming the substrate of the third region RG3 ) in order to form the third region RG3 , which comprises silicon and germanium.

[0104] Silicon germanium epitaxy is a step well known to those skilled in the art.

[0105] As an example, SiGe epitaxy can be performed by chemical vapor deposition (CVD) using dichlorosilane + germanium + hydrogen chemistry at 900 to 950° C. and reduced pressure (10-60 Torr).

[0106] A low partial pressure of diborane (B2H6) can also be added to obtain P doping.

[0107] In order to obtain the desired concentration gradient for germanium, the amounts of germanium can be adjusted in the epitaxial reactor so that they follow the ramp.

[0108] The SiGe epitaxy is then continued by another epitaxy (this time only conventional and per se known silicon epitaxy) in order to form, after local ion implantation of N-type dopants, first regions RG1 and then, after local implantation of P-type dopants, second P+ doped regions RG2.

[0109] As an example, the conditions for this further epitaxy are substantially the same as those for SiGe epitaxy, optionally with the temperature being increased from 50°C to 100°C.

[0110] It should be noted that these two epitaxies, often performed at the same step, can be performed in the same epitaxy run and thus can be performed in the same epitaxy reactor with the same recipe and thus often without cooling of the wafer between the two types of deposition.

[0111] About Figure 2 Production of the third region RG3 illustrated in FIG. 1 , in which case a successive epitaxy of silicon and silicon germanium is performed in order to obtain a stack of layers 11 and 10 .

[0112] The volume percentage of germanium for each of these epitaxies is chosen so that the average final volume percentage of germanium is comprised between 3% and 6%, and where appropriate follows the concentration gradient considered.

[0113] Production then continues with the conventional formation of deep and shallow trenches and other components of the detection module, regardless of the variant used.

[0114] Instead of performing these full wafer epitaxy, it would also be possible to perform a first full wafer silicon epitaxy to form the silicon film 1, then locally etch the semiconductor film (corresponding to the pixels) in the area where the detection module is produced, and then proceed with the SiGe and Si epitaxy mentioned above, and then produce the insulating trenches and the various electronic components of the module MD.

[0115] Furthermore, everything that has just been described for SOI type substrates applies to solid (ie bulk) substrates.

[0116] like Figure 3 As illustrated in , the integrated optical sensor SNS may include several detection modules MD1 -MDn arranged, for example, in a row or a matrix.

[0117] like Figure 4 As illustrated in FIG. 1 , the sensor SNS may be incorporated in an imaging system CM, such as a camera, which in turn may be incorporated in an electronic device APP (eg a tablet or cellular mobile phone type). Figure 5 )Inside.

Claims

1. An integrated optical sensor, comprising a pinned photodiode, the integrated optical sensor comprising: Semiconductor substrate, comprising: A first semiconductor region having a first conductivity type; a second semiconductor region having a second conductivity type opposite to the first conductivity type; and a third semiconductor region having the second conductivity type; wherein the first semiconductor region is located between the second semiconductor region and the third semiconductor region; wherein the third semiconductor region is thicker, less doped, and located deeper in the semiconductor substrate than the second semiconductor region; wherein the third semiconductor region comprises silicon and germanium, wherein the germanium has a first concentration gradient; wherein the third semiconductor region is formed of alternating silicon layers and silicon germanium layers; and The first concentration gradient is a positive gradient in which the atomic percentage of germanium in the third semiconductor region increases from the bottom of the third semiconductor region toward the first semiconductor region. 2 . The sensor of claim 1 , wherein the atomic percentage of the germanium for the first concentration gradient increases from 0% to 6%. 3 . The sensor of claim 1 , wherein the atomic percentage of the germanium for the first concentration gradient increases from 3% to 6%. 4 . The sensor of claim 1 , wherein the third semiconductor region includes a depletion region and a non-depletion region, the depletion region being in contact with the first semiconductor region and located above the non-depletion region, and wherein the first concentration gradient is located in the non-depletion region. 5 . The sensor of claim 4 , wherein the first concentration gradient is a positive gradient in which the atomic percentage of germanium in the non-depletion region increases from a bottom of the non-depletion region toward the depletion region. 6 . The sensor of claim 5 , wherein the atomic percentage of the germanium for the first concentration gradient increases from 0% to 6%.

7. The sensor of claim 5, wherein the atomic percentage of germanium for the first concentration gradient increases from 3% to 6%.

8. The sensor of claim 4 , wherein the third semiconductor region further comprises silicon and germanium in the depletion region, wherein the germanium has a second concentration gradient, wherein the second concentration gradient is a negative concentration gradient, wherein the atomic percentage of germanium in the depletion region decreases from the non-depletion region toward the first semiconductor region.

9. The sensor of claim 8, wherein the atomic percentage of germanium decreases from 6% to 0% in the depletion region.

10. The sensor of claim 4, wherein the depletion region in the third semiconductor region does not include germanium. The sensor of claim 1 , wherein the third semiconductor region comprises a silicon-germanium alloy. 12 . The sensor of claim 1 , wherein the first conductivity type is an N-type, and the second conductivity type is a P-type.

13. The sensor of claim 1, wherein the semiconductor substrate is a silicon-on-insulator type substrate comprising a buried insulating layer capped by a semiconductor film, and wherein the pinned photodiode is contained within the semiconductor film.

14. The sensor of claim 1, comprising at least one detection module including the pinned photodiode.

15. The sensor of claim 1, wherein the pinned photodiode is a component of an imaging system.

16. The sensor of claim 15, wherein the imaging system is a time-of-flight (ToF) system.

17. The sensor of claim 15, wherein the imaging system is a component of an electronic device.

18. The sensor of claim 17, wherein the electronic device is selected from the group consisting of: a tablet computer and a cellular mobile phone.

19. An integrated optical sensor comprising a pinned photodiode, the integrated optical sensor comprising: Semiconductor substrate, comprising: A first semiconductor region having a first conductivity type; a second semiconductor region having a second conductivity type opposite to the first conductivity type; and a third semiconductor region having the second conductivity type; wherein the first semiconductor region is located between the second semiconductor region and the third semiconductor region; wherein the third semiconductor region is thicker, less doped, and located deeper in the semiconductor substrate than the second semiconductor region; wherein the third semiconductor region comprises silicon and germanium, the germanium having a substantially constant atomic percentage of germanium less than or equal to 6%; and wherein the third semiconductor region is formed of alternating silicon layers and silicon germanium layers; wherein the third semiconductor region comprises a depletion region and a non-depletion region, the depletion region contacts the first semiconductor region and is located above the non-depletion region, and the non-depletion region comprises germanium having the substantially constant atomic percentage; and The depletion region does not include germanium.

20. The sensor of claim 19, wherein the constant atomic percentage of germanium in the non-depleted region is between 4% and 5%.

21. The sensor of claim 19, wherein the third semiconductor region comprises a silicon-germanium alloy.

22. The sensor of claim 19, wherein the first conductivity type is N-type and the second conductivity type is P-type.

23. The sensor of claim 19, wherein the semiconductor substrate is a silicon-on-insulator type substrate comprising a buried insulating layer capped by a semiconductor film, and wherein the pinned photodiode is contained within the semiconductor film.

24. The sensor of claim 19, comprising at least one detection module comprising the pinned photodiode.

25. The sensor of claim 19, wherein the pinned photodiode is a component of an imaging system.

26. The sensor of claim 25, wherein the imaging system is a time-of-flight (ToF) system.

27. The sensor of claim 25, wherein the imaging system is a component of an electronic device.

28. The sensor of claim 27, wherein the electronic device is selected from the group consisting of: a tablet computer and a cellular telephone.

29. An integrated optical sensor comprising a pinned photodiode, the integrated optical sensor comprising: Semiconductor substrate, comprising: A first semiconductor region having a first conductivity type; a second semiconductor region having a second conductivity type opposite to the first conductivity type; and a third semiconductor region having the second conductivity type; wherein the first semiconductor region is located between the second semiconductor region and the third semiconductor region; wherein the third semiconductor region is thicker, less doped, and located deeper in the semiconductor substrate than the second semiconductor region; wherein the third semiconductor region includes a depletion region and a non-depletion region, the depletion region contacts the first semiconductor region and is located above the non-depletion region; and The non-depletion region of the third semiconductor region includes silicon and germanium, wherein the germanium has a positive concentration gradient, wherein the atomic percentage of germanium increases from a bottom of the non-depletion region toward the depletion region.

30. The sensor of claim 29, wherein the atomic percentage of germanium for the positive concentration gradient increases from 0% to 6%.

31. The sensor of claim 29, wherein the atomic percentage of germanium for the positive concentration gradient increases from 3% to 6%.

32. The sensor of claim 29, wherein the depletion region comprises silicon and germanium, wherein the germanium has a negative concentration gradient, wherein the atomic percentage of germanium in the depletion region decreases from the non-depleted region toward the first semiconductor region.

33. The sensor of claim 32, wherein the atomic percentage of germanium decreases from 6% to 0% in the depletion region.

34. The sensor of claim 29, wherein the depletion region in the third semiconductor region does not include germanium.

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