Asymmetric silicon-based germanium optical waveguide detector

Abstract

The invention provides an asymmetric germanium optical waveguide detector. The asymmetric germanium optical waveguide detector comprises a silicon substrate layer, a silicon oxide buried layer, a waveguide layer, a silicon oxide upper cladding layer and an electrode layer which are sequentially stacked in the first direction. The waveguide layer comprises a germanium absorber and a thin silicon layer, the germanium absorber is located between the thin silicon layer and the silicon oxide upper cladding, light is injected through waveguide coupling along the thin silicon layer below the germanium absorber, and the thin silicon layer comprises a P-type silicon heavily doped region, a P-type silicon lightly doped region, an N-type silicon lightly doped region and an N-type silicon heavily doped region. The distance between the germanium absorber and the N-type lightly doped region is not equal to the distance between the germanium absorber and the P-type lightly doped region; the silicon oxide upper cladding layer comprises a metal through hole structure and is connected with the electrode layer through a through hole. The structure provides a method which is simple in structure and can effectively improve the responsivity or bandwidth of the optical waveguide detector.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon-based optoelectronic devices, and particularly to an asymmetric silicon-based germanium optical waveguide detector. Background Art

[0002] With the rapid development of fields such as 5G communication, artificial intelligence, and the Internet of Things, the demand for data transmission in communication networks is increasing continuously, resulting in the gradual replacement of traditional electrical interconnections in communication by optical interconnections. The continuous improvement of transmission capacity and speed has put forward requirements for miniaturization, high integration, and high performance for key optical devices in optical interconnection systems, which is crucial for achieving higher bandwidth density and lower cost. Silicon-based optoelectronic technology is an on-chip optoelectronic integration technology relying on the silicon-on-insulator (SOI) platform, and its advantage is compatibility with the mature complementary metal-oxide-semiconductor (CMOS) process. The detector is one of the key devices in the optoelectronic integration system, and its function is to convert optical signals into electrical signals. Since silicon does not have the ability to absorb light waves in the communication band, on the contrary, germanium can absorb light waves in these bands well, so germanium detectors have broad development prospects, and at the same time, the characteristics of silicon can be used to make it a waveguide material for the transmission of optical signals.

[0003] The bandwidth of the optical waveguide detector is mainly affected by the carrier transit time and the RC cut-off effect. Currently known germanium optical waveguide detectors inevitably increase the structural complexity or process difficulty in order to reduce the influence of these two factors on the bandwidth. Summary of the Invention

[0004] The present invention provides a germanium optical waveguide detector with an asymmetric structure, which can regulate the carrier transit time without increasing the process difficulty, thereby improving the responsivity or bandwidth of the optical waveguide detector.

[0005] To achieve the above object, the present invention provides the following technical solution: An asymmetric germanium optical waveguide detector includes a silicon substrate layer, a buried silicon oxide layer, a waveguide layer, a silicon oxide upper cladding layer, and an electrode layer stacked in sequence along a first direction. The waveguide layer includes a germanium absorber and a thin silicon layer, and the germanium absorber is located between the thin silicon layer and the silicon oxide upper cladding layer;

[0006] The silicon oxide upper cladding layer includes a metal via structure, and the metal via structure connects the thin silicon layer and the electrode layer.

[0007] Preferably, the thin silicon layer includes a P-type silicon heavily doped region, a P-type silicon lightly doped region, an N-type silicon lightly doped region, and an N-type silicon heavily doped region, and an intrinsic region is between the P-type lightly doped region and the N-type lightly doped region.

[0008] Preferably, the lower surface of the germanium absorber along the first direction overlaps with the intrinsic region between the P-type lightly doped region and the N-type lightly doped region, and the distance between the germanium absorber and the N-type lightly doped region is not equal to the distance between the germanium absorber and the P-type lightly doped region.

[0009] Preferably, the light is injected by waveguide coupling through the thin silicon layer at the position below the germanium absorber.

[0010] Preferably, the via hole structure connects the metal electrode and the P-type heavily doped region and the N-type heavily doped region;

[0011] The metal electrode 06 connected to the P-type heavily doped region 03a is the P electrode, and the metal electrode connected to the N-type heavily doped region is the N electrode, where a reverse bias voltage is applied to the P electrode and the N electrode is grounded.

[0012] Preferably, the germanium absorber is grown and prepared using a low-temperature buffer layer technology.

[0013] Compared with the prior art, the beneficial effects of the present invention are:

[0014] In the present invention, a silicon substrate layer, a buried silicon oxide layer, a waveguide layer, an upper silicon oxide cladding layer, and an electrode layer are sequentially stacked along the first direction; the waveguide layer includes a germanium absorber and a thin silicon layer, the germanium absorber is located between the thin silicon layer and the upper silicon oxide cladding layer, and the position of the germanium absorber is asymmetric; the upper silicon oxide cladding layer includes a metal via hole structure, and the electrode layer is connected through the via hole, effectively improving the responsivity or bandwidth of the optical waveguide detector, specifically including:

[0015] 1. Compatible with the mature CMOS process, and compared with the ordinary transverse optical waveguide detector, there is no need to use a more complex process;

[0016] 2. Since the electron lifetime is greater than the hole lifetime, compared with the symmetric structure where the distances between the germanium absorber and the two electrodes are equal, the asymmetric structure where the germanium absorber is closer to the P electrode reduces the transit distance of the photo-generated holes and increases the transit distance of the photo-generated electrons. Therefore, fewer carriers are recombined in this structure, and the photocurrent is larger, improving the responsivity of the optical waveguide detector;

[0017] 3. Since the mobility of electrons is greater than the mobility of holes and the drift velocity is faster, compared with the symmetric structure where the distances between the germanium absorber and the two electrodes are equal, in the asymmetric structure where the germanium absorber is closer to the N electrode, the distance for the photo-generated electrons in the germanium absorber to be transmitted to the N electrode is shorter, thereby reducing the transit time of electrons and making the response speed of the detector faster, improving the bandwidth of the optical waveguide detector. Description of the Drawings

[0018] Figure 1Schematic cross-sectional structure diagram of an asymmetric germanium optical waveguide detector provided by an embodiment of the present invention along the direction perpendicular to the light propagation direction;

[0019] Figure 2 Optical field distribution of the germanium absorber of an asymmetric germanium optical waveguide detector provided by an embodiment of the present invention;

[0020] Figure 3 Comparison diagram of the responsivity of two asymmetric germanium optical waveguide detectors provided by an embodiment of the present invention under different bias voltages with a symmetric structure;

[0021] Figure 4 Comparison diagram of the bandwidth of two asymmetric germanium optical waveguide detectors provided by an embodiment of the present invention with a symmetric structure under a bias voltage of -1V.

[0022] Reference numerals in the figure: 01, silicon substrate layer; 02, buried silicon oxide layer; 03, thin silicon layer; 03a, heavily doped P-type silicon; 03b, lightly doped P-type silicon region; 03c, lightly doped N-type silicon region; 03d, heavily doped N-type silicon region; 03e, thin silicon layer; 04, germanium absorber; 05, silicon oxide upper cladding layer; 06, electrode layer; 06a, metal via structure. Detailed implementation manners

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Figure 1 Schematic cross-sectional structure diagram of an asymmetric germanium optical waveguide detector provided by an embodiment of the present invention along the direction perpendicular to the light propagation direction. The present invention provides an asymmetric germanium optical waveguide detector, and this structure provides a method with a simple structure and effectively improving the responsivity or bandwidth of the optical waveguide detector.

[0025] An embodiment of the present invention provides an asymmetric germanium optical waveguide detector, including a silicon substrate layer 01, a buried silicon oxide layer 02, a waveguide layer, a silicon oxide upper cladding layer 05, and an electrode layer 06 stacked in sequence along a first direction;

[0026] The waveguide layer includes a germanium absorber 04 and a thin silicon layer 03. The germanium absorber 04 is located between the thin silicon layer 03 and a silicon oxide upper cladding layer 05. The lower surface of the germanium absorber 04 along the first direction overlaps with the intrinsic region between the P-type lightly doped region 03b and the N-type lightly doped region 03c. Light is coupled and injected through the thin silicon layer 03e at the position 03e below the germanium absorber 04. Through etching and epitaxy processes, a part of the germanium absorber 04 is embedded in the silicon waveguide layer. In this way, the electric field strength in the germanium absorber 04 is enhanced, the drift velocity of carriers increases, and the carriers lost due to recombination decrease. Therefore, the bandwidth and responsivity of the optical waveguide detector are also improved.

[0027] The distance between the germanium absorber 04 and the N-type lightly doped region 03c is not equal to the distance between the germanium absorber 04 and the P-type lightly doped region 03b.

[0028] The thin silicon layer 03 includes a P-type heavily doped silicon region 03a, a P-type lightly doped silicon region 03b, an N-type lightly doped silicon region 03c, and an N-type heavily doped silicon region 03d. The intrinsic region between the P-type lightly doped region 03b and the N-type lightly doped region 03c forms a PIN junction.

[0029] The silicon oxide upper cladding layer 05 includes a metal via structure 06a. Through the metal via structure 06a, the thin silicon layer 03 and the electrode layer 06 are connected to form an ohmic contact.

[0030] The via structure 06a connects the metal electrode 06 and the P-type heavily doped region 03a, the N-type heavily doped region 03d. The metal electrode 06 connected to the P-type heavily doped region 03a is the P electrode, and the metal electrode 06 connected to the N-type heavily doped region 03d is the N electrode. Among them, a reverse bias is applied to the P electrode and the N electrode is grounded.

[0031] Since the electron lifetime is greater than the hole lifetime, compared with the symmetric structure where the distances between the germanium absorber 04 and the two electrodes are equal, the asymmetric structure where the germanium absorber 04 is closer to the P electrode reduces the transit distance of photo-generated holes and increases the transit distance of photo-generated electrons. Therefore, fewer carriers are recombined in this structure and the photocurrent is larger, improving the responsivity of the optical waveguide detector. Also, since the mobility of electrons is greater than the mobility of holes and the drift velocity is faster, compared with the symmetric structure where the distances between the germanium absorber 04 and the two electrodes are equal, in the asymmetric structure where the germanium absorber 04 is closer to the N electrode, the distance for photo-generated electrons in the germanium absorber 04 to be transmitted to the N electrode is shorter, thus reducing the transit time of electrons and improving the bandwidth of the optical waveguide detector.

[0032] The germanium absorber 04 is grown and prepared using a low-temperature buffer layer technique. The low-temperature buffer layer technique means that a buffer layer is first grown at a lower temperature, and then an epitaxial layer with high crystal quality is rapidly grown at a high temperature.

[0033] To verify the beneficial effects of the present invention, an asymmetric optical waveguide detector structure with different parameters was used. The parameters of Example 1, Example 2 and the symmetric structure are shown in Table 1 respectively;

[0034] Table 1

[0035]

[0036]

[0037] As Figure 2 shown, light is coupled into the germanium waveguide to generate electrons and holes. The germanium absorber 04 confines the light in the waveguide for absorption. When a reverse bias voltage is applied to the PIN junction, an electric field is generated in the germanium absorber 04 and the silicon intrinsic region below it. Under the action of the electric field, the photo-generated electrons generated in the germanium absorber 04 drift towards the N lightly doped region 03c, and the photo-generated holes generated in the germanium absorber 04 drift towards the P lightly doped region 03b, generating a photocurrent;

[0038] Figure 3 In Example 1, the germanium absorber 04 is close to the N lightly doped region 03c. In Example 2, the position of the germanium absorber 04 is close to the P lightly doped region 03b. In the symmetric structure, the distance between the germanium absorber 04 and the P lightly doped region 03b is equal to the distance between the germanium absorber 04 and the N lightly doped region 03c. The data shows that the responsivity of Example 2 is significantly improved compared with that of the symmetric structure, which is due to less carrier recombination;

[0039] Figure 4 In Example 1, the germanium absorber 04 is close to the N lightly doped region 03c. In Example 2, the position of the germanium absorber 04 is close to the P lightly doped region 03b. In the symmetric structure, the distance between the germanium absorber 04 and the P lightly doped region 03b is equal to the distance between the germanium absorber 04 and the N lightly doped region 03c. It can be seen from the frequency response curve in the figure that the bandwidth of Example 1 is significantly improved compared with that of the symmetric structure, which is due to the reduction of the photo-generated electron transit time;

[0040] In the present invention, a silicon substrate layer 01, a buried silicon oxide layer 02, a waveguide layer, a silicon oxide upper cladding layer 05, and an electrode layer 06 are sequentially stacked in a first direction; the waveguide layer includes a germanium absorber 04 and a thin silicon layer 03e, the germanium absorber 04 is located between the thin silicon layer 03e and the silicon oxide upper cladding layer 05, and the position of the germanium absorber 04 is asymmetric; the silicon oxide upper cladding layer 05 includes a metal via structure 06a, and the electrode layer 06 is connected through the via structure 06a, effectively improving the bandwidth of the optical waveguide detector. Specifically, it includes: being compatible with the mature CMOS process, and compared with the ordinary transverse optical waveguide detector, there is no need to use a more complex process; the electron lifetime is greater than the hole lifetime. Compared with the symmetric structure where the distances between the germanium absorber 04 and the two electrodes are equal, in the asymmetric structure where the germanium absorber 04 is closer to the P electrode, the transit distance of the photo-generated holes is reduced, and the transit distance of the photo-generated electrons is increased. Therefore, fewer carriers are recombined in this structure, and the photocurrent is larger, improving the responsivity of the optical waveguide detector; the mobility of electrons is greater than the mobility of holes, and the drift speed is faster. Compared with the symmetric structure where the distances between the germanium absorber 04 and the two electrodes are equal, in the asymmetric structure where the germanium absorber 04 is closer to the N electrode, the distance for the photo-generated electrons in the germanium absorber to be transmitted to the N electrode is shorter, thereby reducing the transit time of electrons and improving the bandwidth of the optical waveguide detector.

[0041] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An asymmetric germanium optical waveguide detector, comprising: A silicon substrate layer (01), a buried silicon oxide layer (02), a waveguide layer, a silicon oxide upper cladding layer (05), and an electrode layer (06) stacked in sequence along a first direction, wherein: the waveguide layer includes a germanium absorber (04) and a thin silicon layer (03), and the germanium absorber (04) is located between the thin silicon layer (03) and the silicon oxide upper cladding layer (05); The silicon oxide upper cladding layer (05) includes a metal via structure (06a), and the metal via structure (06a) connects the thin silicon layer (03) and the electrode layer (06).

2. The asymmetric germanium optical waveguide detector according to claim 1, wherein The thin silicon layer (03) includes a P-type heavily doped silicon region (03a), a P-type lightly doped silicon region (03b), an N-type lightly doped silicon region (03c), and an N-type heavily doped silicon region (03d), and an intrinsic region is between the P-type lightly doped region (03b) and the N-type lightly doped region (03c).

3. The asymmetric germanium optical waveguide detector according to claim 2, wherein The lower surface of the germanium absorber (04) along the first direction overlaps with the intrinsic region between the P-type lightly doped region (03b) and the N-type lightly doped region (03c), and the distance between the germanium absorber (04) and the N-type lightly doped region (03c) is not equal to the distance between the germanium absorber (04) and the P-type lightly doped region (03b).

4. The asymmetric germanium optical waveguide detector according to claim 3, characterized in that, The light is coupled and injected through the thin silicon layer (03e) at a position below the germanium absorber (03).

5. An asymmetric germanium optical waveguide detector according to claim 4, wherein The via structure (06a) connects the metal electrode (06) and the P-type heavily doped region (03a), the N-type heavily doped region (03d); The metal electrode 06 connected to the P-type heavily doped region 03a is a P electrode, and the metal electrode (06) connected to the N-type heavily doped region (03d) is an N electrode, wherein a reverse bias is applied to the P electrode and the N electrode is grounded.

6. The asymmetric germanium optical waveguide detector according to claim 1, wherein The germanium absorber (04) is grown and prepared using a low-temperature buffer layer technique.

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