Patent Application
20230114395
The subject matter herein generally relates to semiconductors, specifically to a photodetector and an integrated circuit.
A photodetector's response time should be as short as possible. The shorter the response time, the faster the speed of the photodetector in responding. With the development of science and technology, the response speed of current photodetectors needs to be improved.
Therefore, there is room for improvement in the art.
Implementations of the present disclosure will now be described, by way of embodiment, with reference to the attached figures.
It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiments described herein. However, it will be understood by those of ordinary skill in the art that the exemplary embodiments described herein may be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the exemplary embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.
The term “comprising” when utilized, means “including, but not necessarily limited to”; it specifically indicates open-ended inclusion or membership in the so-described combination, group, series, and the like. The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references can mean “at least one”. The term “circuit” is defined as an integrated circuit (IC) with a plurality of electric elements, such as capacitors, resistors, amplifiers, and the like.
Specifically, the photodetector forms a depletion region under the action of reverse bias, and transit time (td) of photogenerated carriers in the depletion region is one of the main factors affecting the response time of the photodetector. The relationship between the transit time (td) of the photogenerated carriers in the depletion region and the mobility (μd) of the carriers can be expressed by formula td=W/vd; vd=μdE, where W is the width of the depletion region, vd is the drift velocity of the carriers s, μd is the mobility of the carriers, and E is the electric field strength in the depletion region.
The transit time (td) of the photogenerated carriers in the depletion region is inversely proportional to the mobility (μd) of the carriers. When the mobility of the carriers is increased the transit time of the photogenerated carriers is reduced, the response time of the photodetector is accordingly reduced, and the response speed of the photodetector is improved.
In the photodetector 12, the light absorption layer 124 includes a strained layer including a heterostructure, and the strain generated in the strained layer increases the mobility of carriers in the light absorption layer 124. This reduces the response time of the photodetector 12, the modulation frequency of the photodetector 12 is accelerated, and the response speed of the photodetector 12 is improved.
In some embodiments, the strained layer is a layer having a compressive strain. The compressive strain generated in the strained layer is configured for increasing the mobility of holes in the light absorption layer 124. For example, the strained layer is in direct contact with the P-type semiconductor layer 126, and a lattice spacing of a material of the P-type semiconductor layer 126 is less than a lattice spacing of a material of the strained layer. The P-type semiconductor layer 126 induces compressive strain in the strained layer, so that the mobility of the holes in the light absorption layer 124 is increased, thereby increasing the response speed of the photodetector 12.
In some other embodiments, the strained layer is a layer having a tensile strain. The tensile strain generated in the strained layer is configured for increasing the mobility of electrons in the light absorption layer 124. For example, the strained layer is in direct contact with the N-type semiconductor layer 122, and a lattice spacing of the material of the N-type semiconductor layer 122 is greater than the lattice spacing of the material of the strained layer. The N-type semiconductor layer 122 induces tensile strain in the strained layer, so that the mobility of electrons in the light absorption layer 124 is increased, thereby increasing the response speed of the photodetector 12.
In some embodiments, the strained layer is a multiple quantum well (MQW) layer, a superlattice layer, or a quantum dots (QDs) layer. The MQW layer and the superlattice layer are both periodic heterostructures made of alternating semiconductors with different bandgaps, each thin alternating material layer containing several or a great many atomic layers. A superlattice is a periodic heterostructure made of alternating materials with different bandgaps. The thickness of each of these periodically alternating material layers is generally about a few nanometers. The band structure that results from such a configuration is a period series of quantum wells.
These non-conductive barriers must be thin enough such that carriers can tunnel through the barrier regions of the multiple wells. A defining property of superlattices is that the barriers between wells are thin enough for adjacent wells to couple. Periodic structures made of repeated quantum wells with barriers that are too thick for adjacent wave functions to couple are called MQW structures. In other words, in superlattices, the potential barriers are thin, or the heights of the potential barriers are low, increasing the probability of electrons in the well tunneling through the potential barrier due to the tunnel effect, and the discrete sub-levels in the potential well form sub-bands with a certain width.
When the barrier thickness (i.e., a thickness of the material with a wider bandgap in the alternating materials with different bandgaps) in a periodic structure made of repeated quantum wells is greater than 20 nm and the barrier height is greater than 0.5 eV, the electrons in multiple wells behave as the sum of the electrons in a single well, this periodic structure is called MQW structure. The quantum well has the potential well of electrons or holes with obvious quantum confinement effect. Generally, quantum well structures with a size below 100 nm in only one dimension can be approximated as a two-dimensional material.
QDs are semiconductor particles only a few nanometers in size, having optical and electronic properties that operate differently from larger particles due to quantum mechanics. QDs are quasi-zero-dimensional nanomaterials composed of a small number of atoms. Generally, a size of the QDs in three dimensions are all below 100 nm, and the appearance of QDs is like a small point-like object. The movement of electrons in QDs is restricted in all directions, so the quantum confinement effect is particularly significant in QDs.
It should be noted that, due to the introduction of strain in the MQW layer, the superlattice layer, or the QDs layer, the energy band structure of the photodetector 12 is changed, enhancing the photon quantum efficiency of the photodetector 12 and expanding the detecting wavelength range of the photodetector 12.
In some embodiments, the N-type semiconductor layer 122 includes N-type silicon (Si); the strained layer includes a silicon/germanium (Si/Ge) heterostructure, a germanium/silicon germanium (Ge/SiGe) heterostructure, a silicon/silicon germanium (Si/SiGe) heterostructure, a heterostructure composing of a group III-V compound semiconductor, a heterostructure composing of a group II-VI compound semiconductor, and a heterostructure composing of the group III-V compound semiconductor and the group II-VI compound semiconductor. The strained layer can be grown epitaxially on the N-type Si.
For example, in one embodiment, the strained layer includes the Si/Ge heterostructure. The Si/Ge heterostructure is epitaxially grown on N-type Si by forming a periodic multi-layer structure of alternating Si layers and Ge layers, each Si layer alternating with one Ge layer. In another embodiment, the strained layer includes the Ge/SiGe heterostructure. The Ge/SiGe heterostructure is epitaxially grown on the N-type Si by forming a periodic multi-layer structure of alternating Ge layers and the SiGe layers, each Ge layer alternating with one SiGe layer. Similarly, the Si/SiGe heterostructure included in the strained layer can be epitaxially grown on N-type Si by forming a periodic multi-layer structure of alternating Si layers and SiGe layers, each Si layer alternating with one SiGe layer. Additionally, the group III-V compound semiconductor of the heterostructure can be, for example, GaAs, InGaAs, InP, GaN, etc., which can also be epitaxially grown on N-type Si. The group II-VI compound semiconductor can be, for example, CdTe.
In some embodiments, the P-type semiconductor layer 126 includes a P-type silicon germanium (SiGe) layer. The P-type SiGe layer is gradient-doped, or different locations of the P-type SiGe layer have different silicon-germanium (Si—Ge) ratios.
For example, in some embodiments, the doping concentration of Ge in the P-type SiGe layer is least at the location which is in contact with the strained layer, and gradually increases along a thickness direction of the P-type SiGe layer.
In some embodiments, the doping concentration of Ge in the P-type SiGe layer is greatest at the location in contact with the strained layer, and gradually increases along the thickness direction of the P-type SiGe layer.
In some embodiments, the doping concentration of Ge in the P-type SiGe layer first increases and then decreases along the thickness direction of the P-type SiGe layer.
In some embodiments, different locations of the P-type SiGe layer may have different SiGe ratios to improve device performance. In other embodiments, the doping concentration of Ge in the P-type SiGe layer may be fixed and constant, and the SiGe ratio in the P-type SiGe layer is fixed and constant.
In some embodiments, the strained layer is a Ge/SiGe heterostructure or a Si/SiGe heterostructure, and the photodetector 12 is sensitive from 400 nm to 1600 nm. In other words, a working wavelength range (i.e., a detectable wavelength range of light) of the photodetector 12 is from 400 nm to 1600 nm.
Since the band gap of Si is 1.12 eV, the detectable wavelength range of traditional Si-based photodetectors is from 400 nm to 1100 nm, as shown in
In some embodiments, the photodetector 12 is a PIN photodiode or an avalanche diode. The light absorption layer 124 serves as an intrinsic layer (I-type layer) of the PIN photodiode or the avalanche diode. When the photodetector 12 is an avalanche diode, the photodetector 12 further includes an avalanche region, to utilize the avalanche multiplication effect of carriers to amplify the photoelectric signal, to improve sensitivity of detection.
In some embodiments, an integrated circuit 100 is provided. As shown in
It is to be understood, even though information and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the present exemplary embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the present exemplary embodiments to the full extent indicated by the plain meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202111190683.8 | Oct 2021 | CN | national |
