Quantum dot electric absorption modulator and preparation method thereof

Abstract

The invention discloses a quantum dot electro-absorption modulator and a preparation method thereof. The electro-absorption modulator sequentially comprises an N contact electrode layer, an InP substrate, an InP buffer layer, an InGaAsP lower respective limiting layer, a multi-cycle InAs quantum dot active layer, an InGaAsP upper respective limiting layer, an InP spacer layer, an InP cover layer, an InGaAs contact layer and a P contact electrode layer from bottom to top. InP semi-insulating layers are distributed on the two sides of the InP buffer layer, the InGaAsP lower respective limiting layer and the multicycle InAs quantum dot active layer, InP barrier layers are distributed on the two sides of the InGaAsP upper respective limiting layer and the InP spacing layer, and BCB layers are distributed on the two sides of the P electrode. The electro-absorption modulator provided by the invention can have a larger extinction ratio under a lower bias voltage, and the bandwidth of the electro-absorption modulator is improved at the same time.

Description

Technical Field

[0001] The invention belongs to the field of electroabsorption modulators, and in particular relates to a quantum dot electroabsorption modulator and a preparation method thereof. Background Art

[0002] Electroabsorption modulators have the characteristics of simple structure, low power consumption and easy integration, and are widely used in signal modulation and coding in high-speed optical fiber communications.

[0003] Current InP-based electroabsorption modulators all use the quantum confined Stark effect of quantum well active region materials. Such active regions have very high requirements for the growth of quantum well materials, requiring uniform material growth, and adjusting the depth and width of the quantum wells during the growth process to change the absorption intensity of the electroabsorption modulator and the redshift speed of the absorption edge. However, quantum well materials only have a quantum confinement effect on carriers in one dimension along the epitaxial direction, so the modulation performance of electroabsorption modulators with quantum wells as active regions is limited.

[0004] Although quantum dots are semiconductor materials that bind excitons in three spatial directions and their quantum effects are more obvious, the performance of quantum dot modulators is also greatly limited due to problems with quantum dot materials and modulator design.

[0005] Based on this, a new type of electro-absorption modulator based on quantum dots is studied and designed to fully improve the performance of quantum dot modulators, that is, to make the modulator have a larger extinction ratio at a lower bias voltage while improving its bandwidth. Summary of the invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a quantum dot electro-absorption modulator and a preparation method thereof, so that the modulator has a larger extinction ratio at a lower bias voltage while improving its bandwidth.

[0007] Technical solution: The quantum dot electro-absorption modulator of the present invention comprises, from bottom to top, an N contact electrode layer, an InP substrate, an InP buffer layer, an InGaAsP lower limiting layer, a multi-period InAs quantum dot active layer, an InGaAsP upper limiting layer, an InP spacer layer, an InP cap layer, an InGaAs contact layer and a P contact electrode layer; wherein, InP semi-insulating layers are distributed on both sides of the InP buffer layer, the InGaAsP lower limiting layer and the multi-period InAs quantum dot active layer, InP barrier layers are distributed on both sides of the InGaAsP upper limiting layer and the InP spacer layer, and BCB layers are distributed on both sides of the P contact electrode layer.

[0008] The present invention adopts a modulator active region composed of multiple layers of InAs quantum dot potential well layers and InGaAsP potential barrier layers alternately, the potential well layers and the potential barrier layers jointly complete the restriction of carriers, due to the three-dimensional quantum confinement structure of the quantum dot material, the active region of the modulator is divided into many small volumes by the potential barrier layers, the linear dimensions of each small volume are close to or less than the de Broglie wavelength of the carriers in the three-dimensional direction, the quantum wells enhance the binding of electrons and holes, and the absorption coefficient of the modulator becomes larger. In addition, due to the small size characteristics of the quantum dots, the modulator can limit the carriers to the maximum extent under the thin potential well layers and potential barrier layers, and prevent the leakage of the carriers, the absorption edge red shift speed is large, so that the modulator has a larger extinction ratio under a lower bias voltage.

[0009] In addition, based on the active area structure of the modulator, the BCB filling of the top contact electrode and the InP semi-insulating layer burying on both sides of the active area of ​​the present invention can reduce the electrode parasitic capacitance and heterojunction capacitance of the modulator and effectively prevent lateral current diffusion, so that the modulator has a larger extinction ratio at a lower bias voltage while improving its bandwidth.

[0010] Furthermore, the period number of the multi-period InAs quantum dot active layer of the electro-absorption modulator of the present invention is 1-20, each layer is InAs quantum dots, and the quantum dots are covered with a 10-40 nm thick InGaAsP barrier layer.

[0011] Furthermore, the InP semi-insulating layer of the electroabsorption modulator of the present invention is doped with Ru, has a refractive index of 3.1-3.2, and a resistivity of 10 8 -10 9 Ω·m, and its width is 1-5μm.

[0012] Furthermore, the InP barrier layer of the electro-absorption modulator of the present invention is n-type doped, has a refractive index of 3.1-3.2, and has a width of 1-5 μm.

[0013] Furthermore, the thickness of the N-contact electrode layer of the electroabsorption modulator of the present invention is 1-5 μm, and the thickness of the InP substrate is 200-500 μm.

[0014] Furthermore, the thickness of the InP buffer layer of the electro-absorption modulator of the present invention is 280-320 nm, and the thickness of the respective limiting layer under InGaAsP is 300-340 nm.

[0015] Furthermore, the thickness of the limiting layer on the InGaAsP of the electro-absorption modulator of the present invention is 300-340nm, and the thickness of the InP spacer layer is 180-220nm.

[0016] Furthermore, the thickness of the InP cap layer of the electro-absorption modulator of the present invention is 580-620 nm, the thickness of the InGaAs contact layer is 180-220 nm, and the thickness of the P contact electrode layer is 1-5 μm.

[0017] The method for preparing the quantum dot electroabsorption modulator of the present invention comprises the following steps:

[0018] (1) sequentially growing an InP buffer layer, an InGaAsP lower limiting layer, a multi-period InAs quantum dot active layer, an InGaAsP upper limiting layer, and an InP spacer layer on an InP substrate;

[0019] (2) photolithographically exposing the multi-period InAs quantum dot active layer, the InGaAsP confinement layer and the two side regions of the InP spacer layer, and etching the two side regions to the InP substrate;

[0020] (3) epitaxially growing an InP semi-insulating layer, an InP barrier layer, an InP cap layer, and an InGaAs contact layer, respectively;

[0021] (4) An N contact electrode layer and a P contact electrode layer are grown on the InP substrate and the InGaAs contact layer, respectively, and a BCB layer is grown on both sides of the P contact electrode layer.

[0022] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: the electro-absorption modulator is designed to form a modulator active region composed of InAs quantum dots and InGaAsP barrier layers, and the energy band of the structure changes with the applied voltage to achieve absorption modulation of light; and the modulator can maximally restrict carriers under thinner potential well layers and barrier layers, and prevent carrier leakage, and the absorption edge red shift speed is large, so that the modulator has a larger extinction ratio at a lower bias. In addition, based on the active region, BCB filling is distributed on both sides of the top contact electrode and InP semi-insulating layer burial is performed on both sides of the active region, which can reduce the electrode parasitic capacitance and heterojunction capacitance of the modulator, and effectively prevent lateral current diffusion, so that the modulator has a larger extinction ratio at a lower bias while improving its bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a three-dimensional diagram of an electroabsorption modulator of the present invention;

[0024] Figure 2 It is a cross-sectional view of the electroabsorption modulator of the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings.

[0026] It should be noted that the materials used in the quantum dot electro-absorption modulator of the present invention, such as InP semiconductor materials, InGaAsP materials, InAs quantum dots, InGaAs materials and BCB materials, are all semiconductor materials known in the art. The process conditions for their growth can also be the conditions known in the art. The difference in the growth process lies in the difference in thickness caused by the growth time.

[0027] Specifically, the quantum dot electroabsorption modulator of the present invention has a structure as follows Figure 1 and Figure 2 As shown, it includes, from bottom to top, an N contact electrode layer 1, an InP substrate 2, an InP buffer layer 3, an InGaAsP lower limiting layer 4, a multi-periodic InAs quantum dot active layer 5, an InGaAsP upper limiting layer 6, an InP spacer layer 7, an InP cap layer 8, an InGaAs contact layer 9, and a P contact electrode layer 10. InP semi-insulating layers 11 are distributed on both sides of the InP buffer layer 3, the InGaAsP lower limiting layer 4, and the multi-periodic InAs quantum dot active layer 5. InP barrier layers 12 are distributed on both sides of the InGaAsP upper limiting layer 6 and the InP spacer layer 7, and BCB layers 13 are distributed on both sides of the P contact electrode layer 10.

[0028] The InP semi-insulating layer 11 is doped with Ru, and has a refractive index of 3.1-3.2 and a resistivity of 10 8 -10 9 Ω·m. The InP barrier layer 12 is n-type doped and has a refractive index of 3.1-3.2.

[0029] Example 1

[0030] The quantum dot electroabsorption modulator of Example 1 is prepared by the following steps:

[0031] (1) An InP buffer layer 3 with a thickness of 300 nm, an InGaAsP lower confinement layer 4 with a thickness of 320 nm, a multi-period InAs quantum dot active layer 5, an InGaAsP upper confinement layer 6 with a thickness of 320 nm, and an InP spacer layer 7 with a thickness of 200 nm are grown in sequence on an InP substrate 2 with a thickness of 300 μm; wherein the multi-period InAs quantum dot active layer 5 has a period number of 5, each layer is an InAs quantum dot, and the quantum dot is covered with a 30 nm thick InGaAsP barrier layer.

[0032] (2) Photolithography exposure of the multi-period InAs quantum dot active layer 5, the confinement layer 6 and the InP spacer layer 7 on the InGaAsP, and etching of the two side regions to the InP substrate 2 using 0.5-1% bromomethanol, with an etching width of 1.8 um.

[0033] (3) At 600° C., an InP semi-insulating layer 11, an InP barrier layer 12, an InP cap layer 8 with a thickness of 590 nm, and an InGaAs contact layer 9 with a thickness of 190 nm are epitaxially grown in sequence; wherein the thickness of the InP semi-insulating layer 11 is equal to the sum of the thicknesses of the InP buffer layer 3, the InGaAsP lower confinement layer 4, and the multi-period InAs quantum dot active layer 5; and the thickness of the InP barrier layer 12 is equal to the sum of the thicknesses of the InGaAsP upper confinement layer 6 and the InP spacer layer 7.

[0034] (4) An N contact electrode layer 1 with a thickness of 3 μm and a P contact electrode layer 10 with a thickness of 3 μm are grown on the InP substrate 2 and the InGaAs contact layer 9, respectively, and a BCB layer is grown on both sides of the P contact electrode layer 10. The width of the BCB depends on the width of the overall electro-absorption modulator (i.e., the width of the electro-absorption modulator minus the width of the middle P electrode).

[0035] Example 2

[0036] The quantum dot electroabsorption modulator of Example 2 is prepared by the following steps:

[0037] (1) An InP buffer layer 3 with a thickness of 290 nm, an InGaAsP lower confinement layer 4 with a thickness of 330 nm, a multi-period InAs quantum dot active layer 5, an InGaAsP upper confinement layer 6 with a thickness of 330 nm, and an InP spacer layer 7 with a thickness of 210 nm are grown in sequence on an InP substrate with a thickness of 350 μm; wherein the multi-period InAs quantum dot active layer 5 has a period number of 1, each layer is an InAs quantum dot, and the quantum dot is covered with a 10 nm thick InGaAsP barrier layer.

[0038] (2) Photolithography exposure of the multi-period InAs quantum dot active layer 5, the InGaAsP confinement layer 6 and the InP spacer layer 7 on both sides, and 0.5-1% bromomethanol is used to etch the two side areas to the InP substrate 2, and the etching width is 2.2 um.

[0039] (3) At 600° C., an InP semi-insulating layer 11, an InP barrier layer 12, an InP cap layer 8 with a thickness of 600 nm, and an InGaAs contact layer 9 with a thickness of 200 nm are epitaxially grown in sequence; wherein the thickness of the InP semi-insulating layer 11 is equal to the sum of the thicknesses of the InP buffer layer 3, the InGaAsP lower confinement layer 4, and the multi-period InAs quantum dot active layer 5; and the thickness of the InP barrier layer 12 is equal to the sum of the thicknesses of the InGaAsP upper confinement layer 6 and the InP spacer layer 7.

[0040] (4) An N contact electrode layer 1 with a thickness of 2 μm and a P contact electrode layer 10 with a thickness of 2 μm are grown on the InP substrate 2 and the InGaAs contact layer 9, respectively, and a BCB layer is grown on both sides of the P contact electrode layer 10. The width of the BCB depends on the width of the overall electro-absorption modulator (i.e., the width of the electro-absorption modulator minus the width of the middle P electrode).

[0041] Example 3

[0042] The quantum dot electroabsorption modulator of Example 3 is prepared by the following steps:

[0043] (1) An InP buffer layer 3 with a thickness of 280 nm, an InGaAsP lower confinement layer 4 with a thickness of 300 nm, a multi-period InAs quantum dot active layer 5, an InGaAsP upper confinement layer 6 with a thickness of 300 nm, and an InP spacer layer 7 with a thickness of 180 nm are grown in sequence on an InP substrate with a thickness of 200 μm; wherein the multi-period InAs quantum dot active layer 5 has 20 periods, each layer is an InAs quantum dot, and the quantum dots are covered with a 40 nm thick InGaAsP barrier layer.

[0044] (2) Photolithography exposure of the multi-period InAs quantum dot active layer 5, the InGaAsP confinement layer 6 and the InP spacer layer 7 on both sides, and 0.5-1% bromomethanol is used to etch the two side areas to the InP substrate 2, and the etching width is 1 um.

[0045] (3) At 600° C., an InP semi-insulating layer 11, an InP barrier layer 12, an InP cap layer 8 with a thickness of 580 nm, and an InGaAs contact layer 9 with a thickness of 180 nm are epitaxially grown in sequence; wherein the thickness of the InP semi-insulating layer 11 is equal to the sum of the thicknesses of the InP buffer layer 3, the InGaAsP lower confinement layer 4, and the multi-period InAs quantum dot active layer 5; and the thickness of the InP barrier layer 12 is equal to the sum of the thicknesses of the InGaAsP upper confinement layer 6 and the InP spacer layer 7.

[0046] (4) An N contact electrode layer 1 with a thickness of 1 μm and a P contact electrode layer 10 with a thickness of 1 μm are grown on the InP substrate 2 and the InGaAs contact layer 9, respectively, and a BCB layer is grown on both sides of the P contact electrode layer 10. The width of the BCB depends on the width of the overall electro-absorption modulator (i.e., the width of the electro-absorption modulator minus the width of the middle P electrode).

[0047] Example 4

[0048] The quantum dot electroabsorption modulator of Example 4 is prepared by the following steps:

[0049] (1) An InP buffer layer 3 with a thickness of 320 nm, an InGaAsP lower confinement layer 4 with a thickness of 340 nm, a multi-period InAs quantum dot active layer 5, an InGaAsP upper confinement layer 6 with a thickness of 340 nm, and an InP spacer layer 7 with a thickness of 220 nm are grown in sequence on an InP substrate with a thickness of 500 μm; wherein the multi-period InAs quantum dot active layer 5 has a period number of 10, each layer is an InAs quantum dot, and the quantum dots are covered with a 20 nm thick InGaAsP barrier layer.

[0050] (2) Photolithography exposure of the multi-period InAs quantum dot active layer 5, the limiting layer 6 and the InP spacer layer 7 on the InGaAsP are respectively performed, and the two side regions are etched to the InP substrate 2 using 0.5-1% bromomethanol, and the etching width is 3 um.

[0051] (3) At 600° C., an InP semi-insulating layer 11, an InP barrier layer 12, an InP cap layer 8 with a thickness of 620 nm, and an InGaAs contact layer 9 with a thickness of 220 nm are epitaxially grown in sequence; wherein the thickness of the InP semi-insulating layer 11 is equal to the sum of the thicknesses of the InP buffer layer 3, the InGaAsP lower confinement layer 4, and the multi-period InAs quantum dot active layer 5; and the thickness of the InP barrier layer 12 is equal to the sum of the thicknesses of the InGaAsP upper confinement layer 6 and the InP spacer layer 7.

[0052] (4) An N contact electrode layer 1 with a thickness of 5 μm and a P contact electrode layer 10 with a thickness of 5 μm are grown on the InP substrate 2 and the InGaAs contact layer 9, respectively, and a BCB layer is grown on both sides of the P contact electrode layer 10. The width of the BCB depends on the width of the overall electro-absorption modulator (i.e., the width of the electro-absorption modulator minus the width of the middle P electrode).

[0053] The quantum dot electroabsorption modulators prepared in Example 1 to Example 4 were respectively tested for electroabsorption performance, and the obtained results are shown in Table 1 below.

[0054] Table 1 Electroabsorption performance of quantum dot electroabsorption modulators of Examples 1 to 4

[0055]

[0056]

[0057] As shown in Table 1, the quantum dot electro-absorption modulator of the present invention has an extinction ratio of more than 20 dB, an insertion loss within 10 dB, and a 3dB bandwidth of approximately 22 GHz, achieving a higher extinction ratio at a lower bias voltage while having a high bandwidth.

Claims

1. A quantum dot electroabsorption modulator, characterized in that: The electroabsorption modulator comprises, from bottom to top, an N contact electrode layer (1), an InP substrate (2), an InP buffer layer (3), an InGaAsP lower limiting layer (4), a multi-period InAs quantum dot active layer (5), an InGaAsP upper limiting layer (6), an InP spacer layer (7), an InP cap layer (8), an InGaAs contact layer (9) and a P contact electrode layer (10); wherein an InP semi-insulating layer (11) is distributed on both sides of the InP buffer layer (3), the InGaAsP lower limiting layer (4) and the multi-period InAs quantum dot active layer (5), an InP barrier layer (12) is distributed on both sides of the InGaAsP upper limiting layer (6) and the InP spacer layer (7), and a BCB layer (13) is distributed on both sides of the P contact electrode layer (10).

2. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The period number of the multi-period InAs quantum dot active layer (5) is 1-20, each layer is an InAs quantum dot (14), and the quantum dot is covered with an InGaAsP barrier layer (15) with a thickness of 10-40 nm.

3. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The InP semi-insulating layer (11) is doped with Ru, has a refractive index of 3.1-3.2, and a resistivity of 10 8 -10 9 Ω·m, and its width is 1-5μm.

4. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The InP barrier layer (12) is n-type doped, has a refractive index of 3.1-3.2, and a width of 1-5 μm.

5. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The thickness of the N contact electrode layer (1) is 1-5 μm, and the thickness of the InP substrate (2) is 200-500 μm.

6. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The thickness of the InP buffer layer (3) is 280-320 nm, and the thickness of the InGaAsP lower limiting layer (4) is 300-340 nm.

7. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The thickness of the limiting layer (6) on the InGaAsP is 300-340nm, and the thickness of the InP spacer layer (7) is 180-220nm.

8. The quantum dot electroabsorption modulator according to claim 1, characterized in that: The thickness of the InP cap layer (8) is 580-620 nm, the thickness of the InGaAs contact layer (9) is 180-220 nm, and the thickness of the P contact electrode layer (10) is 1-5 μm.

9. A method for preparing the quantum dot electroabsorption modulator according to claim 1, characterized in that: The steps include: (1) sequentially growing an InP buffer layer (3), an InGaAsP lower limiting layer (4), a multi-periodic InAs quantum dot active layer (5), an InGaAsP upper limiting layer (6), and an InP spacer layer (7) on an InP substrate; (2) photolithographically exposing the multi-period InAs quantum dot active layer (5), the InGaAsP restriction layer (6) and the two side regions of the InP spacer layer (7) and etching the two side regions to the InP substrate (2); (3) epitaxially growing an InP semi-insulating layer (11), an InP barrier layer (12), an InP cap layer (8) and an InGaAs contact layer (9) in sequence; (4) An N contact electrode layer (1) and a P contact electrode layer (10) are grown on the InP substrate (2) and the InGaAs contact layer (9) respectively, and a BCB layer is grown on both sides of the P contact electrode layer (10).

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