A quantum dot electroabsorption modulator and its preparation method

Abstract

The present invention discloses a quantum dot electro-absorption modulator and its fabrication method. The electro-absorption modulator comprises, from bottom to top, an N-contact electrode layer, an InP substrate, an InP buffer layer, an InGaAsP lower confinement layer, a multi-periodic InAs quantum dot active layer, an InGaAsP upper confinement layer, an InP spacer layer, an InP cap layer, an InGaAs contact layer, and a P-contact electrode layer. InP semi-insulating layers are disposed on either side of the InP buffer layer, the InGaAsP lower confinement layer, and the multi-periodic InAs quantum dot active layer; InP barrier layers are disposed on either side of the InGaAsP upper confinement layer and the InP spacer layer; and BCB layers are disposed on either side of the P electrode. The electro-absorption modulator of the present invention can achieve a higher extinction ratio at a lower bias voltage while increasing its bandwidth.

Description

Technical Field

[0001] The present 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 (EBMs) utilize the quantum-confined Stark effect in their quantum well active region. These active regions place high demands on the growth of the quantum well material, requiring uniform growth and adjusting the depth and width of the quantum well during growth to alter the EBM's absorption intensity and the redshift rate of the absorption edge. However, the quantum well material only quantum-confines carriers in one dimension, along the epitaxial direction. Therefore, the modulation performance of EBMs using quantum wells as their active region 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, we are now studying a new type of electro-absorption modulator based on quantum dots to fully improve the performance of the quantum dot modulator, that is, to enable the modulator to have a larger extinction ratio at a lower bias voltage while increasing 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 confinement layer, a multi-period InAs quantum dot active layer, an InGaAsP upper confinement 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 confinement layer and the multi-period InAs quantum dot active layer, InP barrier layers are distributed on both sides of the InGaAsP upper confinement layer and the InP spacer layer, and BCB layers are distributed on both sides of the P contact electrode layer.

[0008] The present invention employs a modulator active region composed of alternating layers of InAs quantum dot potential well layers and InGaAsP barrier layers. The potential well layers and barrier layers jointly confine carriers. Due to the three-dimensional quantum confinement structure of the quantum dot material, the modulator active region is divided into many small volumes by the barrier layers. The linear dimensions of each small volume in the three-dimensional direction are close to or less than the de Broglie wavelength of the carriers. This enhances the quantum well's confinement of electrons and holes, increasing the modulator's absorption coefficient. Furthermore, due to the small size of the quantum dots, the modulator can maximize carrier confinement and prevent carrier leakage under thin potential well and barrier layers, resulting in a large absorption edge redshift velocity, thus enabling the modulator to achieve a higher extinction ratio at lower bias voltages.

[0009] In addition, based on the active area structure of the modulator, the BCB filling of the top contact electrode of the present invention and the InP semi-insulating layer burying on both sides of the active area 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 an InGaAsP barrier layer with a thickness of 10-40 nm.

[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 a width of 1-5 μm.

[0013] Furthermore, the thickness of the N-contact electrode layer of the electro-absorption 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 InGaAsP lower confinement layer is 300-340 nm.

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

[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 confinement layer, a multi-period InAs quantum dot active layer, an InGaAsP upper confinement layer, and an InP spacer layer on an InP substrate;

[0019] (2) photolithographically exposing the multi-period InAs quantum dot active layer, the confinement layer on InGaAsP, and the regions on both sides of the InP spacer layer, and etching the regions on both sides 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. The energy band of this structure changes with the applied voltage, achieving absorption modulation of light; and the modulator can maximally confine carriers under thinner potential well layers and barrier layers and prevent carrier leakage. The absorption edge redshift rate is large, thereby enabling the modulator to have a larger extinction ratio at a lower bias voltage. In addition, based on the active region, BCB filling is distributed on both sides of the top contact electrode and InP semi-insulating layer is buried on both sides of the active region. This 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a perspective view of an electroabsorption modulator of the present invention;

[0024] Figure 2 2 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 with reference to 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 well-known semiconductor materials in the art. Furthermore, the growth process conditions used can also be those known in the art. The only difference in thickness due to the growth time is the difference in growth process.

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

[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 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 on an InP substrate 2 with a thickness of 300 μm, respectively. The multi-period InAs quantum dot active layer 5 has 5 periods, each layer is an InAs quantum dot, and the quantum dots are covered with a 30 nm thick InGaAsP barrier layer.

[0032] (2) Photolithographically expose the multi-period InAs quantum dot active layer 5, the confinement layer 6 and the InP spacer layer 7 on the InGaAsP, and etch the two side regions to the InP substrate 2 using 0.5-1% bromomethanol. The etching width is 1.8 μm.

[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 on an InP substrate with a thickness of 350 μm, respectively. 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 dots are covered with a 10 nm thick InGaAsP barrier layer.

[0038] (2) Photolithographically expose the multi-period InAs quantum dot active layer 5, the confinement layer 6 and the InP spacer layer 7 on the InGaAsP, and etch the two side regions to the InP substrate 2 using 0.5-1% bromomethanol. The etching width is 2.2 μm.

[0039] (3) 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 at 600°C; 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 P electrode in the middle).

[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 on an InP substrate with a thickness of 200 μm, respectively. 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) Photolithographically expose the multi-period InAs quantum dot active layer 5, the confinement layer 6 and the InP spacer layer 7 on the InGaAsP, and etch the two side regions to the InP substrate 2 using 0.5-1% bromomethanol. The etching width is 1 μm.

[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 P electrode in the middle).

[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 on an InP substrate with a thickness of 500 μm, respectively. The multi-period InAs quantum dot active layer 5 has 10 periods, each layer is an InAs quantum dot, and the quantum dots are covered with a 20 nm thick InGaAsP barrier layer.

[0050] (2) Photolithographically expose the multi-period InAs quantum dot active layer 5, the confinement layer 6 and the InP spacer layer 7 on the InGaAsP, and etch the two side regions to the InP substrate 2 using 0.5-1% bromomethanol. The etching width is 3 μm.

[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 P electrode in the middle).

[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 3 dB bandwidth of approximately 22 GHz, achieving a larger 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-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); 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-periodic 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); The period number of the multi-periodic 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; 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, whose width is 1-5 μm; 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.

2. 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.

3. 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.

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

5. 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.

6. A method for preparing the quantum dot electroabsorption modulator according to claim 1, characterized in that: The steps include: (1) An InP buffer layer (3), an InGaAsP lower confinement layer (4), a multi-periodic InAs quantum dot active layer (5), an InGaAsP upper confinement layer (6), and an InP spacer layer (7) are sequentially grown on an InP substrate; the number of periods of the multi-periodic 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; (2) photolithographically exposing the multi-period InAs quantum dot active layer (5), the confinement layer (6) on the InGaAsP 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) Growing an N contact electrode layer (1) and a P contact electrode layer (10) on the InP substrate (2) and the InGaAs contact layer (9), respectively, and growing a BCB layer on both sides of the P contact electrode layer (10).

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