Combined multi-quantum well active region, light-emitting device and preparation method of combined multi-quantum well active region

Abstract

The invention discloses a combined multi-quantum well active region, a light-emitting device and a preparation method of the light-emitting device, and relates to the field of semiconductor light-emitting devices. The combined multi-quantum well active region is formed by repeating M periods by taking a barrier layer, a quantum well layer and a barrier layer as repeating units, two adjacent periods share the same barrier layer, each quantum well layer comprises N well sub-layers and N-1 interlayers, the interlayers are arranged between the adjacent well sub-layers, and M and N are positive integers not less than 2; the energy band gap of the barrier layer is larger than that of the well sub-layer, and the difference between the two energy band gaps is not smaller than 0.15 eV; the energy band gap of the interlayer is larger than the energy band gap of the well sub-layer, and the difference between the two energy band gaps is not smaller than 0.1 eV. The combined multi-quantum well active region can effectively broaden the gain spectrum.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor light-emitting devices, and in particular to a combined multi-quantum well active region, a light-emitting device and a preparation method thereof. Background Art

[0002] In semiconductor light-emitting devices (such as semiconductor lasers and light-emitting diodes), the active region serves as the core active area for carrier injection and recombination, and its structural design directly determines the device's optoelectronic performance. The quantum well active region, based on the quantum confinement effect, forms a multi-quantum well structure by periodically alternating narrow-bandgap well layers and wide-bandgap barrier layers. This creates a strong confinement effect on electrons and holes perpendicular to the well layers, significantly increasing the carrier concentration and radiative recombination probability within the active region.

[0003] Conventional strained quantum well active region designs typically form a single isolated energy level on the conduction band side of the well, while multiple isolated energy levels, including heavy-hole and light-hole, are formed on the valence band side. When a certain degree of in-plane biaxial tensile strain is introduced into the well layer material, the light-hole energy level is positioned above the heavy-hole energy level. In other cases (including small tensile strain, no strain, and compressive strain), the heavy-hole energy level is positioned above the light-hole energy level. In the former case, transitions primarily occur between the isolated conduction band energy level within the well and the light-hole energy level in the valence band, with the gain contribution to the perpendicular-to-well (TM) mode being 75% and to the parallel-to-well (TE) mode being 25%. In the latter case, transitions primarily occur between the isolated conduction band energy level within the well and the heavy-hole energy level in the valence band, with the gain contribution to the parallel-to-well (TE) mode being 100% and to the perpendicular-to-well (TM) mode being 0%. In this case, the gain spectrum coverage is determined by the transition energy level spacing (corresponding to the longest wavelength) to the quasi-Fermi level difference (corresponding to the shortest wavelength) between the carriers filling the energy band. Exciton and collision effects between carriers, as well as collision effects between carriers and the lattice, can further broaden the gain spectrum coverage. However, considering all these factors, the full width at half maximum (FWHM) of the gain spectrum for typical InP- or GaAs-based III-V compound semiconductor materials is generally around 60nm. Although increasing the energy level difference between the barrier and the conduction band edge of the quantum well material (i.e., increasing the barrier height) can introduce more discrete energy levels on the conduction band side of the well, thereby broadening the gain spectrum through multiple transitions between conduction band energy levels and valence band energy levels, this approach, due to the limited number of material and structural parameters that can be manipulated, makes it difficult to precisely control both the spacing between the transition energy levels and the contribution of each transition energy level to the gain magnitude. Therefore, the gain spectrum obtained using this approach generally does not meet the desired shape. Alternatively, the transition energy level spacing within each quantum well can be adjusted by varying the thickness of each quantum well in the active region multi-quantum well structure, thereby expanding the gain spectrum. However, the main problem with this approach is that the transition energy levels within each well are located at different positions, resulting in differences in the filling of the transition energy levels in each well during carrier injection. Furthermore, the carrier wave functions at energy levels at different positions within each well differ, leading to differences in their overlap integrals. Consequently, the electron-hole pair dipole radiative recombination transition matrix elements between energy levels within different wells differ. These factors cause the transitions in each well to contribute unevenly to the gain. In severe cases, individual wells may be insufficiently filled, resulting in quasi-Fermi energy levels that are even lower than their transition energy level spacing, leading to absorption. Furthermore, the lack of overall periodicity in this quantum well structure also presents certain difficulties in precise control and calibration of the growth process (for example, when characterizing the grown material and structure using X-ray diffraction techniques).

[0004] Therefore, the prior art lacks a quantum well active region that can effectively broaden the gain spectrum. Summary of the Invention

[0005] The purpose of the present invention is to provide a combined multi-quantum well active region, which can effectively broaden the gain spectrum.

[0006] In order to achieve the above-mentioned object, the present invention provides a combined multi-quantum well active region, which is composed of M periods of repeating units of a barrier layer, a quantum well layer and a barrier layer, and two adjacent periods share the same barrier layer, wherein the quantum well layer includes N well sub-layers and N-1 spacer layers, and the spacer layers are arranged between adjacent well sub-layers, wherein M and N are positive integers not less than 2; the energy band gap of the barrier layer is greater than the energy band gap of the well sub-layer, and the difference between the two is not less than 0.15eV; the energy band gap of the spacer layer is greater than the energy band gap of the well sub-layer, and the difference between the two is not less than 0.1eV.

[0007] Optionally, the thickness of the well sublayer is 2 nm to 10 nm, and the thickness of the barrier layer is not less than 6 nm.

[0008] Optionally, the thickness of the spacer is 1 nm to 5 nm.

[0009] Optionally, the material of the combined multi-quantum well active region is AlGaInAs or InGaAsP.

[0010] The present invention also provides a light-emitting device, which includes the combined multi-quantum well active region as described above.

[0011] Optionally, the material of the spacer matches the lattice of the substrate of the light-emitting device.

[0012] Optionally, the light emitting device is one of a semiconductor laser, a light emitting diode, a superluminescent diode and a semiconductor optical amplifier.

[0013] Optionally, the light-emitting device is a semiconductor laser, which includes, from bottom to top, a bottom N-side electrode, an N-type substrate, an N-type buffer layer, an N-side confinement layer, the combined multi-quantum well active region, a P-side confinement layer, a P-type isolation layer, a grating layer, a wetting layer, a P-type cladding layer, a P-side ohmic contact layer and a top P-side electrode.

[0014] The present invention also provides a method for preparing the combined multi-quantum well active region as described above, the preparation method comprising: repeating epitaxial growth of M cycles with a barrier layer, a quantum well layer and a barrier layer as repeating units, wherein two adjacent cycles share the same barrier layer, wherein the quantum well layer comprises N well sub-layers and N-1 spacers, and the spacers are arranged between adjacent well sub-layers, wherein M and N are positive integers not less than 2.

[0015] The beneficial effects of the present invention are that the combined multi-quantum well active region proposed in the present invention can be used to form an effectively broadened gain spectrum. For example, the full width at half maximum of the gain spectrum can be widened to above 100 nm, making it suitable for use in tuned or arrayed light-emitting devices requiring a broadband continuous gain spectrum, dense wavelength division multiplexing light-emitting devices, as well as superluminescent diodes and semiconductor optical amplifiers with broadband requirements. In addition, the combined multi-quantum well active region proposed in the present invention can also be used to form a continuously and smoothly broadened gain spectrum. For example, within the range between two adjacent broadened gain peaks, the gain fluctuation, that is, the change in each gain relative to the mean gain within this range, is within ±1 dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic cross-sectional view of a semiconductor laser based on a combined multi-quantum well active region proposed by the present invention; Figure 2 is a schematic cross-sectional view of a combined multi-quantum well active region; Figure 3 1 is the intensity normalized gain graph of Example 1 and Comparative Example 1; Figure 4 2 is the intensity normalized gain diagram of Example 2 and Comparative Example 2. DETAILED DESCRIPTION

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0018] The present invention utilizes the fact that when two separate well sublayers are sufficiently close, their original energy levels will be split due to the coupling of their wave functions, thereby simultaneously generating a pair of separate energy levels in both well sublayers. At this point, the energy levels in the two well sublayers are completely identical, so the contributions of the same energy levels in each well sublayer to the gain are the same. In this pair of well sublayers, the lower energy level on the conduction band side has a symmetric wave function, while the higher energy level has an antisymmetric wave function; the higher energy level on the valence band side has a symmetric wave function, while the lower energy level has an antisymmetric wave function. Because the matrix element of the dipole radiative recombination transition from a conduction band electron to a valence band hole is proportional to the overlap integral of their wave functions, in the above structure, radiative transitions can only occur between pairs of lower energy electrons on the conduction band side and higher energy holes on the valence band side that both have symmetric wave functions, or between pairs of higher energy electrons on the conduction band side and lower energy holes on the valence band side that both have antisymmetric wave functions. The former has a relatively long wavelength, while the latter has a relatively short wavelength. The wavelength separation between them, as well as their respective contributions to the gain, can be precisely controlled by selecting the composition and thickness of the interlayer between the two well sublayers. This design principle can be further extended to utilize the coupling between more well sublayers to generate more discrete energy levels, further expanding or modifying the gain spectrum to meet different practical application requirements. Generally speaking, N coupled well sublayers separated by N-1 interlayers can produce N discrete energy levels. The N energy levels in each well sublayer are identical, so the contribution of each well sublayer to the gain at the same energy level is consistent. In other words, for a single electron-hole pair, there is no unevenness between well sublayers. Due to the orthogonality of the carrier wave functions at each energy level and the properties of the dipole radiative recombination transitions between energy levels, all radiative transitions can only occur between N discrete conduction-to-valence band energy level pairs. The corresponding gain spectrum will have N independent gain peaks, whose separation wavelengths correspond to the wavelengths of the transition energy level pairs. By adjusting the material composition and thickness of the N-1 spacers between each well sub-layer, the spacing and size of these independent gain peaks can be adjusted so that the coverage and shape of the entire gain spectrum reach certain predetermined targets.

[0019] Based on the above mechanism, the present invention provides a combined multi-quantum well active region and a light-emitting device based on the combined multi-quantum well active region. In one embodiment, the light-emitting device is a semiconductor laser. However, it should be understood that the combined multi-quantum well active region proposed in the present invention is not limited to use in semiconductor lasers and can also be used in light-emitting diodes, superluminescent diodes, semiconductor optical amplifiers, etc. Below, the invention content of the present invention is introduced using the semiconductor laser based on the combined multi-quantum well active region proposed in the present invention as an example.

[0020] Figure 1 It is a two-dimensional structure defined along the growth direction X of the semiconductor laser and the light propagation direction Z. Figure 1 As shown, the semiconductor laser includes, from bottom to top, a bottom N-side electrode 101, an N-type substrate 102, an N-type buffer layer 103, an N-side confinement layer 104, a combined multi-quantum well active region 105, a P-side confinement layer 106, a P-type isolation layer 107, a grating layer 108, a wetting layer 109, a P-type cladding layer 110, a P-side ohmic contact layer 111, and a top P-side electrode 112.

[0021] Among them, the function of the bottom N-side electrode 101 and the top P-side electrode 112 is to connect an external power supply to provide a bias voltage to the semiconductor laser. The function of the N-type substrate 102 is to provide support for the semiconductor laser. The N-type buffer layer 103 and the N-side confinement layer 104 not only provide vertical confinement for the light field, but also provide a channel for the injection of conduction band electrons into the active area. The P-side confinement layer 106 and the P-side cladding 110 not only limit the light field in the vertical direction, but also provide a channel for the injection of valence band holes into the active area. The combined multi-quantum well active area 105 is used to provide wide-spectrum gain for the entire active area. The function of the grating layer 108 is to select the longitudinal mode of light. The P-side ohmic contact layer 111 is to ensure that the Schottky barrier between the electrode metal and the P-type semiconductor is eliminated to form an ohmic contact. It is worth mentioning that, Figure 1 The semiconductor laser structure shown in the figure is only an example. The combined multi-quantum well active region structure provided by the present invention can be applied to any other semiconductor laser, and the present invention is not limited to this.

[0022] The combined multi-quantum well active region 105 is composed of M cycles of a barrier layer, a quantum well layer, and a barrier layer as a repeating unit. Adjacent cycles share the same barrier layer. The quantum well layer includes N well sublayers and N-1 spacer layers, with the spacer layers positioned between adjacent well sublayers. M and N are positive integers not less than 2. The energy band gap (Eg_B) of the barrier layer is greater than the energy band gap (Eg_W) of the well sublayer, satisfying Eg_B - Eg_W ≥ 0.15 eV. For example, the thickness of the well sublayer is 2 nm to 10 nm, and the thickness of the barrier layer is not less than 6 nm. The spacer layer is made of a material lattice-matched to the substrate. For example, if the substrate is InP, the spacer layer can be InGaAsP or AlGaInAs. The energy band gap (Eg_S) of the spacer layer is wider than the energy band gap of the well sublayer, satisfying Eg_S - Eg_W ≥ 0.1 eV. For example, the thickness of the spacer layer is 1 nm to 5 nm. The thickness and energy band gap of the spacer are the main parameters that control the energy level splitting, that is, the separation wavelength distance. Thinner spacers and appropriate energy band gaps are beneficial to increasing the coupling of the well sublayers on both sides of the spacer.

[0023] This active region structure generates N coupled, separate energy levels within the well sublayers on both the conduction and valence band sides, resulting in N pairs of separate transitions (the orthogonality of the wave functions between the energy levels precludes further transitions). These transitions produce N corresponding, separate peaks in the gain spectrum, each at the wavelength corresponding to the transition energy level. By adjusting the parameters (composition and thickness) of the potential barrier, well sublayer, and spacer layers, these peaks can be connected and smoothly transitioned, significantly extending the width of the continuous gain spectrum, facilitating the gain requirements of broadband, multi-wavelength array lasers or other light-emitting devices.

[0024] like Figure 2 As shown, in one embodiment, the combined multi-quantum well active region 105 is composed of a barrier layer 201, a quantum well layer, and a barrier layer 201 as a unit, repeated for two periods. Two adjacent periods share the same barrier layer 201, wherein the quantum well layer is composed of a stacked well sub-layer 202, a spacer 203, and a well sub-layer 202. In one period, by controlling the composition and thickness of the spacer between a pair of well sub-layers, a pair of coupled separated transition energy levels is generated in the two well sub-layers. The electrons on the lower energy level on the conduction band side and the holes on the higher energy level on the valence band side have symmetric wave functions, while the electrons on the higher energy level on the conduction band side and the holes on the lower energy level on the valence band side have antisymmetric wave functions. Therefore, transitions can and can only occur between the two pairs of energy levels with symmetric wave functions and antisymmetric wave functions. As a result, such a gain spectrum will produce two peaks, corresponding to the wavelength between the two transition energy levels. By adjusting the composition and thickness of the potential barrier, well sublayer, and spacer, the wavelength interval and the magnitude of the respective intensities of the two gain peaks can be controlled according to design requirements, thereby broadening the gain peak.

[0025] The semiconductor laser in the present invention can be a ridge waveguide structure or a buried heterojunction structure, which is not limited in the present invention. The semiconductor laser in the present invention also has no special restrictions on the growth material system.

[0026] 1. Example 1 The semiconductor laser in this embodiment has a ridge waveguide structure and is based on the InP-AlGaInAs-InGaAsP material system. The two-dimensional structure defined by its growth direction X and light propagation direction Z is as follows: Figure 1 The combined multi-quantum well active region comprises two repeating units, each of which includes two well sublayers and one spacer layer. The structure of the combined multi-quantum well active region is barrier layer-well sublayer-spacer-well sublayer-barrier layer-well sublayer-spacer-well sublayer-barrier layer-well sublayer-barrier layer. The specific materials and structural parameters of the combined multi-quantum well active region are shown in Table 1.

[0027] Table 1 shows the specific materials and structural parameters of the combined multi-quantum well active region

[0028] like Figure 3 As shown, in Comparative Example 1, which does not adopt the combined multi-quantum well active region of the present invention but adopts the multi-quantum well active region formed by alternately growing narrow-bandgap well layers and wide-bandgap barrier layers commonly used in the prior art, the full width at half maximum (FWHM1) of the gain spectrum is 75nm; while in this embodiment, the full width at half maximum (FWHM2) of the gain spectrum is 130nm, that is, the gain spectrum is broadened by 73.3%. At the same time, Figure 3 It can be seen from the figure that the gain spectrum in this embodiment is continuously and smoothly broadened, and the gain fluctuation within the interval between the two gain peaks formed by the broadening is within ±0.4 dB.

[0029] 2. Example 2 The difference between this embodiment and embodiment 1 is that the semiconductor laser in this embodiment is based on the GaAs-InGaAsP-AlGaInP material system. The specific materials and structural parameters of the combined multi-quantum well active region in this embodiment are shown in Table 2.

[0030] Table 2 shows the specific materials and structural parameters of the combined multi-quantum well active region

[0031] like Figure 4 As shown, in Comparative Example 2, which does not adopt the combined multi-quantum well active region of the present invention but adopts the multi-quantum well active region formed by alternately growing narrow-bandgap well layers and wide-bandgap barrier layers commonly used in the prior art, the full width at half maximum (FWHM3) of the gain spectrum is 70nm; while in this embodiment, the full width at half maximum (FWHM4) of the gain spectrum is 115nm, that is, the gain spectrum is broadened by 64.3%. At the same time, Figure 4 It can be seen from the figure that the gain spectrum in this embodiment is continuously and smoothly broadened, and the gain fluctuation within the interval between the two gain peaks formed by the broadening is within ±0.4 dB.

[0032] The present invention also provides a method for preparing a semiconductor laser comprising a combined multi-quantum well active region, comprising: S1. Epitaxially grow an N-type buffer layer, N-side confinement layer, combined multi-quantum well active region, P-side confinement layer, P-type isolation layer, grating layer, and wetting layer on the substrate. The substrate is typically made of InP or GaAs. When using a GaAs substrate, a low-refractive-index buffer layer is required to isolate the high-refractive-index GaAs.

[0033] The preparation method of the combined multi-quantum well active region includes: S11, repeat epitaxial growth for M periods with a barrier layer, a quantum well layer, and a barrier layer as repeating units, wherein two adjacent periods share the same barrier layer, wherein the quantum well layer includes N well sub-layers and N-1 spacers, and the spacers are arranged between adjacent well sub-layers, wherein M and N are positive integers not less than 2.

[0034] S2, fabricating a grating structure on the grating layer. When fabricating the grating structure, the grating can be written by electron beam exposure, or any other technology in the prior art can be used to fabricate the grating structure.

[0035] S3, epitaxially growing a P-type cladding layer and a P-side ohmic contact layer.

[0036] S4, prepare ridge waveguide, open electrical contact window, make P-side pattern electrode, thin the back side and make N-side electrode.

[0037] Existing crystal growth technologies based on MOCVD or MBE can precisely control the growth of large-area III-V semiconductor material layers as thin as 2 nm, so the structure involved in the present invention can be easily realized based on the current process manufacturing level.

[0038] In summary, the combined multi-quantum well active region proposed in the present invention can be used to form an effectively broadened gain spectrum, for example, the full width at half maximum of the gain spectrum can be broadened to more than 100 nm. In addition, the combined multi-quantum well active region can also be used to form a continuously and smoothly broadened gain spectrum, for example, within the range of the interval between two adjacent gain peaks that are expanded, the gain fluctuation, that is, the change in the mean value of each gain relative to the gain within this range, is within ±1 dB; in some embodiments, the gain fluctuation can be controlled within ±0.4 dB. In the present invention, the range between two adjacent gain peaks refers to the range between the vertices of the two gain peaks.

[0039] It is worth mentioning that the combined multi-quantum well active region proposed in the present invention can be applied not only to various types of semiconductor lasers, but also to various types of semiconductor light-emitting diodes and superluminescent diodes, as well as various types of semiconductor optical amplifiers, so that its light-emitting wavelength coverage range can be greatly expanded through array, tuning and other means.

[0040] The present invention has been described above with reference to specific embodiments. These descriptions are intended only to illustrate the present invention and are not to be construed in any way as limiting the scope of protection of the present invention. Based on the explanations herein, those skilled in the art will be able to conceive of other specific embodiments of the present invention without inventive effort, and such embodiments will fall within the scope of protection of the present invention.

Claims

1. A combined multi-quantum well active region, characterized in that: The combined multi-quantum well active region is composed of M periods of repeating units of a barrier layer, a quantum well layer and a barrier layer, and two adjacent periods share the same barrier layer, wherein the quantum well layer includes N well sub-layers and N-1 spacer layers, and the spacer layers are arranged between adjacent well sub-layers, wherein M and N are positive integers not less than 2; the energy band gap of the barrier layer is greater than the energy band gap of the well sub-layer, and the difference between the two is not less than 0.15eV; the energy band gap of the spacer layer is greater than the energy band gap of the well sub-layer, and the difference between the two is not less than 0.1eV.

2. The combined multi-quantum well active region according to claim 1, wherein: The thickness of the well sublayer is 2nm-10nm, and the thickness of the barrier layer is not less than 6nm.

3. The combined multi-quantum well active region according to claim 1, wherein: The thickness of the interlayer is 1 nm to 5 nm.

4. The combined multi-quantum well active region according to claim 1, wherein: The material of the combined multi-quantum well active region is AlGaInAs or InGaAsP.

5. A method for preparing a combined multi-quantum well active region according to any one of claims 1 to 4, characterized in that: The preparation method includes: repeating epitaxial growth for M periods with a barrier layer, a quantum well layer and a barrier layer as repeating units, wherein two adjacent periods share the same barrier layer, wherein the quantum well layer includes N well sublayers and N-1 spacers, and the spacers are arranged between adjacent well sublayers, wherein M and N are positive integers not less than 2.

6. A light emitting device, characterized in that: The light-emitting device comprises the combined multi-quantum well active region according to any one of claims 1 to 4.

7. The light emitting device according to claim 6, wherein The material of the spacer matches the crystal lattice of the substrate of the light emitting device.

8. The light emitting device according to claim 6, wherein The light emitting device is one of a semiconductor laser, a light emitting diode, a superluminescent diode and a semiconductor optical amplifier.

9. The light emitting device according to claim 6, wherein: The light-emitting device is a semiconductor laser, which includes, from bottom to top, a bottom N-side electrode, an N-type substrate, an N-type buffer layer, an N-side confinement layer, the combined multi-quantum well active region, a P-side confinement layer, a P-type isolation layer, a grating layer, a wetting layer, a P-type cladding layer, a P-side ohmic contact layer and a top P-side electrode.

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