A semiconductor ultraviolet laser

Abstract

The present invention provides a semiconductor ultraviolet laser, which relates to the technical field of semiconductor optoelectronic devices. It sequentially includes a substrate, a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, and an upper confinement layer from bottom to top. The active layer is a quantum well composed of a well layer and a barrier layer. By regulating the refractive index dispersion of carrier fluctuations, the laser confinement factor is improved, the mode gain is enhanced, and at the same time, the internal optical loss of non-ionized Mg acceptors is reduced, and the absorption loss of the optical waveguide is decreased. The Mg in the first upper confinement layer is distributed in an inverted V shape, the Mg in the second upper confinement layer is distributed in a U shape, the Mg in the third upper confinement layer is distributed linearly, and the Mg in the fourth upper confinement layer is distributed in an L shape, so as to form multiple two-dimensional electron gases in the upper confinement layer, reduce the ionization energy of Mg acceptors, improve the Mg ionization efficiency and the hole transport efficiency, thereby enhancing the efficiency of hole injection into the active layer and the symmetry and matching of electrons and holes in the active layer, and improving the peak gain and slope efficiency of the laser.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor optoelectronic devices, and more particularly, to a semiconductor ultraviolet laser. Background Art

[0002] Lasers are widely used in the fields of laser display, laser TV, laser projector, communication, medical treatment, weapons, guidance, ranging, spectral analysis, cutting, precision welding, high-density optical storage, etc. There are many types of lasers, and the classification methods are also diverse. The main types include solid-state, gas, liquid, semiconductor, and dye lasers; compared with other types of lasers, all-solid-state semiconductor lasers have the advantages of small size, high efficiency, light weight, good stability, long life, simple and compact structure, and miniaturization. There are significant differences between lasers and nitride semiconductor light-emitting diodes: 1) Laser is generated by stimulated emission of carriers, with a relatively small spectral full width at half maximum, high brightness, and the output power of a single laser can be in the watt level, while nitride semiconductor light-emitting diodes are spontaneous emission, and the output power of a single light-emitting diode is in the milliwatt level; 2) The operating current density of lasers reaches kA / cm², which is more than two orders of magnitude higher than that of nitride light-emitting diodes, resulting in stronger electron leakage, more serious Auger recombination, stronger polarization effect, and more serious electron-hole mismatch, leading to a more serious efficiency droop effect; 3) Light-emitting diodes undergo spontaneous transition radiation, and without external influence, the incoherent light jumps from a high energy level to a low energy level, while lasers are stimulated transition radiation, and the energy of the induced photon should be equal to the energy difference between the electron transitions, generating identical coherent light of photons and induced photons; 4) The principles are different: Light-emitting diodes generate radiative recombination light when electrons and holes jump to the active layer (103) or p-n junction under the action of an external voltage, while lasers can only lasing when the lasing conditions are met. It must satisfy the carrier population inversion distribution in the active region, and the stimulated emission light oscillates back and forth in the resonant cavity. The propagation in the gain medium amplifies the light, satisfies the threshold condition that the gain is greater than the loss, and finally outputs laser light. Nitride semiconductor lasers have the following problems: 1) The optical waveguide absorption loss is high. Intrinsic carbon impurities in p-type semiconductors will compensate for acceptors, destroy the p-type, etc. The ionization rate of p-type doping is low. A large number of un-ionized Mg acceptor impurities will cause an increase in internal optical loss, and the refractive index dispersion of the laser. The high-concentration carrier concentration fluctuation affects the refractive index of the active layer (103), and the confinement factor decreases with the increase of wavelength, resulting in a decrease in the mode gain of the laser; 2) The Mg acceptor activation energy in p-type semiconductors is large and the ionization efficiency is low. The hole concentration is much lower than the electron concentration, and the hole mobility is much smaller than the electron mobility. Moreover, the polarization electric field in the quantum well raises the hole injection barrier, and holes overflow from the active layer (103), etc. The hole injection is uneven and the efficiency is low, resulting in a serious asymmetry and mismatch of electrons and holes in the quantum well, electron leakage and carrier delocalization, and it is more difficult for holes to transport in the quantum well. The carrier injection is uneven, the gain is uneven. At the same time, the gain spectrum of the laser broadens and the peak gain decreases, resulting in an increase in the threshold current of the laser and a decrease in the slope efficiency. Summary of the Invention

[0003] The object of the present invention is to provide a semiconductor ultraviolet laser, which solves the problems existing in the prior art.

[0004] A semiconductor ultraviolet laser, which sequentially includes a substrate, a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, and an upper confinement layer from bottom to top. The active layer (103) is a quantum well composed of a well layer and a barrier layer; the band gaps of the quantum well, the upper waveguide layer, and the lower waveguide layer have specific band gap gradients and thickness gradients;

[0005] The active layer is a quantum well composed of a well layer and a barrier layer, and the quantum well period is w: 1 ≤ w ≤ 3; the well layer of the active layer is InGaN, the band gap is x: 2.9 eV ≤ x ≤ 3.5 eV, and the thickness is a: 5 ≤ a ≤ 20 angstroms; the barrier layer of the active layer is GaN, and the thickness is b: 10 ≤ b ≤ 150 angstroms; the emission wavelength of the quantum well is 360 - 420 nm;

[0006] As a preferred technical solution of the present invention, the lower waveguide layer includes a first lower waveguide layer and a second lower waveguide layer 102b; the first lower waveguide layer is GaN, and the thickness is c: 30 ≤ c ≤ 600 nm; the second lower waveguide layer 102b has a well layer of InGaN, the band gap is y: 3.0 eV ≤ y ≤ 3.6 eV, and the thickness is d: 50 ≤ d ≤ 800 nm;

[0007] As a preferred technical solution of the present invention, the upper waveguide layer is InGaN, the band gap is z: 3.1 eV ≤ z ≤ 3.7 eV, and the thickness is e: 20 ≤ e ≤ 500 nm;

[0008] As a preferred technical solution of the present invention, the quantum well, the upper waveguide layer 104, and the lower waveguide layer 102 have specific band gap gradients and thickness gradients, and have the following relationship: 0.5 ≤ a ≤ e ≤ c ≤ d ≤ 800 nm, 2.9 eV ≤ x < y < z ≤ 3.7 eV.

[0009] As a preferred technical solution of the present invention, the upper confinement layer includes a first upper confinement layer 105a, a second upper confinement layer, a third upper confinement layer, and a fourth upper confinement layer; the first upper confinement layer is made of AlGaN material, the band gap is k: 4.4 eV ≤ k ≤ 6.6 eV, and the thickness is f: 0.5 ≤ f ≤ 20 nm; the second upper confinement layer is made of AlGaN material, the band gap is l: 3.6 eV ≤ l ≤ 5.8 eV, and the thickness is g: 20 ≤ g ≤ 1000 nm; the third upper confinement layer is made of AlGaN material, the band gap is m: 3.6 eV ≤ m ≤ 5.8 eV, and the thickness is h: 20 ≤ h ≤ 1000 nm; the fourth upper confinement layer is made of GaN or InGaN material, the band gap is n: 2.8 eV ≤ n ≤ 3.6 eV, and the thickness is j: 0.5 ≤ j ≤ 800 nm;

[0010] As a preferred technical solution of the present invention, the upper confinement layer has a specific bandgap gradient and thickness gradient, and has the following relationship: 2.8 eV ≤ n < m = l < k ≤ 6.6 eV, j ≤ f ≤ g ≤ h.

[0011] As a preferred technical solution of the present invention, the bandgaps and thicknesses of the quantum well, the upper waveguide layer, the lower waveguide layer, and the upper confinement layer have the following relationship: x < y < z ≤ n < m = l < k, a ≤ j ≤ f ≤ e ≤ c ≤ d ≤ g ≤ h, regulating the refractive index dispersion of carrier fluctuations, enhancing the laser confinement factor, enhancing the mode gain, and at the same time, reducing the internal optical loss of non-ionized Mg acceptors and the absorption loss of the optical waveguide.

[0012] As a preferred technical solution of the present invention, the Mg in the first upper confinement layer is distributed in an inverted V shape, the Mg in the second upper confinement layer is distributed in a U shape, the Mg in the third upper confinement layer is distributed linearly, and the Mg in the fourth upper confinement layer is distributed in an L shape, thereby forming multiple two-dimensional electron gas layers in the upper confinement layer, reducing the ionization energy of Mg acceptors, enhancing the ionization efficiency of Mg and the transport efficiency of holes, thereby enhancing the efficiency of hole injection into the active layer and the symmetry and matching of electrons and holes in the active layer, enhancing the overlap probability of electron-hole wave functions, and enhancing the peak gain and slope efficiency of the laser.

[0013] As a preferred technical solution of the present invention, the lower confinement layer is any one or any combination of AlInGaN, AlInN, AlGaN, InGaN, and GaN, and the thickness is 10 angstroms to 9000 angstroms;

[0014] As a preferred technical solution of the present invention, the substrate includes any one of sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO2 composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, sapphire / SiO2 / SiNx composite substrate, magnesium aluminate spinel MgAl2O4, MgO, ZnO, ZrB2, LiAlO2, and LiGaO2 composite substrate.

[0015] Compared with the prior art, the beneficial effects of the present invention:

[0016] In the solution of the present invention:

[0017] Compared with the prior art, the lower waveguide layer includes a first lower waveguide layer and a second lower waveguide layer; the upper confinement layer includes a first upper confinement layer, a second upper confinement layer, a third upper confinement layer, and a fourth upper confinement layer; the band gaps and thicknesses of the quantum well, the upper waveguide layer, the lower waveguide layer, and the upper confinement layer have the following relationships: x < y < z ≤ n < m = l < k, a ≤ j ≤ f ≤ e ≤ c ≤ d ≤ g ≤ h, regulating the refractive index dispersion of carrier fluctuations, enhancing the laser confinement factor, enhancing the modal gain, and at the same time, reducing the internal optical loss of non-ionized Mg acceptors and the absorption loss of the optical waveguide; the Mg in the first upper confinement layer is distributed in an inverted V shape, the Mg in the second upper confinement layer is distributed in a U shape, the Mg in the third upper confinement layer is distributed linearly, and the Mg in the fourth upper confinement layer is distributed in an L shape, thereby forming multiple two-dimensional electron gas layers in the upper confinement layer, reducing the ionization energy of Mg acceptors, enhancing the ionization efficiency of Mg and the transport efficiency of holes, thereby enhancing the efficiency of hole injection into the active layer and the symmetry and matching of electrons and holes in the active layer, enhancing the overlap probability of electron-hole wave functions, and enhancing the peak gain and slope efficiency of the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic structural diagram of the present invention;

[0019] Figure 2 is a secondary ion mass spectrometry (SIMS) diagram of the structure of the present invention;

[0020] Figure 3 is a transmission electron microscopy (TEM) image of the structure of the present invention.

[0021] Labels in the figure:

[0022] 100: Substrate; 101: Lower confinement layer, 102: Lower waveguide layer, 102a: First lower waveguide layer, 102b: Second lower waveguide layer, 103: Active layer; 104: Upper waveguide layer, 105: Upper confinement layer, 105a: First upper confinement layer, 105b: Second upper confinement layer, 105c: Third upper confinement layer, 105d: Fourth upper confinement layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0024] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents some embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0025] It should be noted that, without conflict, the embodiments in the present invention and the features and technical solutions in the embodiments can be combined with each other.

[0026] Please refer to Figures 1 - 3 , this embodiment provides a technical solution: a semiconductor ultraviolet laser, which sequentially includes a substrate 100, a lower confinement layer 101, a lower waveguide layer 102, an active layer 103, an upper waveguide layer 104, and an upper confinement layer 105 from bottom to top. The active layer 103 is a quantum well composed of a well layer and a barrier layer, and the quantum well period is w: 1 ≤ w ≤ 3; the well layer of the active layer 103 is InGaN, the bandgap width is x: 2.9 eV ≤ x ≤ 3.5 eV, and the thickness is a: 5 ≤ a ≤ 20 angstroms; the barrier layer of the active layer 103 is GaN, and the thickness is b: 10 ≤ b ≤ 150 angstroms; the emission wavelength of the quantum well is 360 - 420 nm;

[0027] The lower waveguide layer 102 includes a first lower waveguide layer 102a and a second lower waveguide layer 102b; the first lower waveguide layer 102a is GaN, and the thickness is c: 30 ≤ c ≤ 600 nm; the second lower waveguide layer 102b has a well layer of InGaN, the bandgap width is y: 3.0 eV ≤ y ≤ 3.6 eV, and the thickness is d: 50 ≤ d ≤ 800 nm;

[0028] The upper waveguide layer 104 is InGaN, the bandgap width is z: 3.1 eV ≤ z ≤ 3.7 eV, and the thickness is e: 20 ≤ e ≤ 500 nm;

[0029] The bandgap widths and thicknesses of the quantum well, the upper waveguide layer 104, and the lower waveguide layer 102 have the following relationships: 0.5 ≤ a ≤ e ≤ c ≤ d ≤ 800 nm, 2.9 eV ≤ x < y < z ≤ 3.7 eV.

[0030] The upper confinement layer 105 includes a first upper confinement layer 105a, a second upper confinement layer 105b, a third upper confinement layer 105c, and a fourth upper confinement layer 105d; the first upper confinement layer 105a is made of AlGaN material, the bandgap width is k: 4.4 eV ≤ k ≤ 6.6 eV, and the thickness is f: 0.5 ≤ f ≤ 20 nm; the second upper confinement layer 105b is made of AlGaN material, the bandgap width is l: 3.6 eV ≤ l ≤ 5.8 eV, and the thickness is g: 20 ≤ g ≤ 1000 nm; the third upper confinement layer 105c is made of AlGaN material, the bandgap width is m: 3.6 eV ≤ m ≤ 5.8 eV, and the thickness is h: 20 ≤ h ≤ 1000 nm; the fourth upper confinement layer 105d is made of GaN or InGaN material, the bandgap width is n: 2.8 eV ≤ n ≤ 3.6 eV, and the thickness is j: 0.5 ≤ j ≤ 800 nm;

[0031] The bandgap width and thickness of the upper confinement layer 105 have the following relationship: 2.8 eV ≤ n < m = l < k ≤ 6.6 eV, j ≤ f ≤ g ≤ h.

[0032] The bandgap widths and thicknesses of the quantum well, the upper waveguide layer 104, the lower waveguide layer 102, and the upper confinement layer 105 have the following relationship: x < y < z ≤ n < m = l < k, a ≤ j ≤ f ≤ e ≤ c ≤ d ≤ g ≤ h. By regulating the refractive index dispersion of carrier fluctuations, the laser confinement factor is improved, the mode gain is enhanced, and at the same time, the internal optical loss of non-ionized Mg acceptors is reduced, and the absorption loss of the optical waveguide is decreased.

[0033] Mg in the first upper confinement layer 105a is distributed in an inverted V shape, Mg in the second upper confinement layer 105b is distributed in a U shape, Mg in the third upper confinement layer 105c is distributed linearly, and Mg in the fourth upper confinement layer 105d is distributed in an L shape. Thus, multiple two-dimensional electron gas layers are formed in the upper confinement layer 105, the ionization energy of Mg acceptors is reduced, the ionization efficiency of Mg and the transport efficiency of holes are improved, thereby enhancing the efficiency of hole injection into the active layer 103 and the symmetry and matching of electrons and holes in the active layer 103, increasing the overlap probability of electron-hole wave functions, and enhancing the peak gain and slope efficiency of the laser.

[0034] The lower confinement layer 101 is any one or any combination of AlInGaN, AlInN, AlGaN, InGaN, and GaN, and its thickness is 10 angstroms to 9000 angstroms;

[0035] The substrate 100 includes any one of sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO2 composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, sapphire / SiO2 / SiNx composite substrate, magnesium aluminate spinel MgAl2O4, MgO, ZnO, ZrB2, LiAlO2, and LiGaO2 composite substrate.

[0036] Experimental Example 1:

[0037] The ultraviolet laser experiment was carried out using the technical solution in this embodiment;

[0038] Comparative Example 1:

[0039] The ultraviolet laser experiment was carried out using the technical solution in the traditional laser;

[0040] The comparison data of each item in Experimental Examples 1 - 2 are as follows:

[0041] UV Laser - Project Comparative Example 1 Experimental Example 1 Amplitude of change <![CDATA[Beam quality factor M 2 > 3.7 1.72 115％ Slope efficiency (W / A) 0.34 0.76 124％ Confining factor 1.40％ 2.86％ 104％ <![CDATA[Internal optical loss (cm -1 )]]> 17.2 6.9 -60％

[0042] Taking an ultraviolet laser as an example, the beam quality factor of the laser of the present invention is improved from 3.7 to 1.72, an increase of about 115%; the confinement factor is improved from 1.4% to 2.86%, an increase of about 104%; the internal optical loss is decreased from 17.2 to 6.9 cm -1 , an increase of about 60%; the slope efficiency is improved from 0.34 W / A to 0.76 W / A, an increase of about 124%.

[0043] Compared with the prior art, the lower waveguide layer includes a first lower waveguide layer and a second lower waveguide layer; the upper confinement layer includes a first upper confinement layer, a second upper confinement layer, a third upper confinement layer, and a fourth upper confinement layer; the band gaps and thicknesses of the quantum well, the upper waveguide layer, the lower waveguide layer, and the upper confinement layer have the following relationships: x < y < z ≤ n < m = l < k, a ≤ j ≤ f ≤ e ≤ c ≤ d ≤ g ≤ h, regulating the refractive index dispersion of carrier fluctuations, improving the laser confinement factor, and improving the mode gain. At the same time, the internal optical loss of non-ionized Mg acceptors is reduced, and the absorption loss of the optical waveguide is reduced; the Mg in the first upper confinement layer is distributed in an inverted V shape, the Mg in the second upper confinement layer is distributed in a U shape, the Mg in the third upper confinement layer is distributed linearly, and the Mg in the fourth upper confinement layer is distributed in an L shape, thereby forming multiple two-dimensional electron gas layers in the upper confinement layer, reducing the ionization energy of Mg acceptors, improving the ionization efficiency of Mg and the transport efficiency of holes, thereby improving the efficiency of hole injection into the active layer and the symmetry and matching of electrons and holes in the active layer, increasing the overlap probability of electron-hole wave functions, and increasing the peak gain and slope efficiency of the laser.

[0044] The above embodiments are only used to illustrate the present invention and do not limit the technical solutions described in the present invention. Although this specification has described the present invention in detail with reference to the above embodiments, the present invention is not limited to the above specific embodiments. Therefore, any modification or equivalent replacement of the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the invention are covered by the scope of the claims of the present invention.

Claims

1. A semiconductor ultraviolet laser, which sequentially includes a substrate (100), a lower confinement layer (101), a lower waveguide layer (102), an active layer (103), an upper waveguide layer (104), and an upper confinement layer (105) from bottom to top. Characterized in that: The active layer (103) is a quantum well composed of a well layer and a barrier layer; the quantum well, the upper waveguide layer, and the lower waveguide layer have specific bandgap width gradients and thickness gradients, and the quantum well period is w: 1 ≤ w ≤ 3; the well layer of the active layer (103) is InGaN, with a bandgap width of x: 2.9 eV ≤ x ≤ 3.5 eV and a thickness of a: 5 ≤ a ≤ 20 angstroms; the barrier layer of the active layer (103) is GaN, with a thickness of b: 10 ≤ b ≤ 150 angstroms; the emission wavelength of the quantum well is 360 - 420 nm, and the lower waveguide layer (102) includes a first lower waveguide layer (102a) and a second lower waveguide layer (102b); the first lower waveguide layer (102a) is GaN, with a thickness of c: 30 ≤ c ≤ 600 nm; the second lower waveguide layer (102b) has a well layer of InGaN, with a bandgap width of y: 3.0 eV ≤ y ≤ 3.6 eV and a thickness of d: 50 ≤ d ≤ 800 nm; the upper waveguide layer (104) is InGaN, with a bandgap width of z: 3.1 eV ≤ z ≤ 3.7 eV and a thickness of e: 20 ≤ e ≤ 500 nm, and the upper confinement layer (105) includes a first upper confinement layer (105a), a second upper confinement layer (105b), a third upper confinement layer (105c), and a fourth upper confinement layer (105d); the first upper confinement layer (105a) is made of AlGaN material, with a bandgap width of k: 4.4 eV ≤ k ≤ 6.6 eV and a thickness of f: 0.5 ≤ f ≤ 20 nm; the second upper confinement layer (105b) is made of AlGaN material, with a bandgap width of l: 3.6 eV ≤ l ≤ 5.8 eV and a thickness of g: 20 ≤ g ≤ 1000 nm; the third upper confinement layer (105c) is made of AlGaN material, with a bandgap width of m: 3.6 eV ≤ m ≤ 5.8 eV and a thickness of h: 20 ≤ h ≤ 1000 nm; the fourth upper confinement layer (105d) is made of GaN or InGaN material, with a bandgap width of n: 2.8 eV ≤ n ≤ 3.6 eV and a thickness of j: 0.5 ≤ j ≤ 800 nm. The specific bandgap width gradients and thickness gradients of the quantum well, the upper waveguide layer (104), and the lower waveguide layer (102) have the following relationships: 0.5 ≤ a ≤ e ≤ c ≤ d ≤ 800 nm, 2.9 eV ≤ x < y < z ≤ 3.7 eV, and the upper confinement layer (105) has specific bandgap width gradients and thickness gradients for its bandgap width and thickness, with the relationship as follows: 2.8 eV ≤ n < m = l < k ≤ 6.6 eV, j ≤ f ≤ g ≤ h, the Mg in the first upper confinement layer (105a) has an inverted V-shaped distribution, the Mg in the second upper confinement layer (105b) has a U-shaped distribution, the Mg in the third upper confinement layer (105c) has a linear distribution, and the Mg in the fourth upper confinement layer (105d) has an L-shaped distribution, thereby forming a multi-layer two-dimensional electron gas in the upper confinement layer (105), reducing the acceptor ionization energy of Mg, improving the ionization efficiency of Mg and the hole transport efficiency, thereby improving the efficiency of hole injection into the active layer (103) and the symmetry and matching of electrons and holes in the active layer (103), increasing the overlap probability of electron-hole wave functions, and increasing the peak gain and slope efficiency of the laser.

2. For a semiconductor ultraviolet laser as described in claim 1, the specific bandgap gradient and thickness gradient of the quantum well, the upper waveguide layer (104), the lower waveguide layer (102), and the upper confinement layer (105) have the following relationships: x < y < z ≤ n < m = l < k, a ≤ j ≤ f ≤ e ≤ c ≤ d ≤ g ≤ h, regulating the refractive index dispersion of carrier fluctuations, enhancing the laser confinement factor, enhancing the mode gain, and at the same time, reducing the internal optical loss of non-ionized Mg acceptors and reducing the absorption loss of the optical waveguide.

3. For a semiconductor ultraviolet laser as described in claim 1, Characterized in that, The lower confinement layer (101) is any one or any combination of AlInGaN, AlInN, AlGaN, InGaN, and GaN, with a thickness of 10 angstroms to 9000 angstroms.

4. For a semiconductor ultraviolet laser as described in claim 1, Characterized in that, The substrate (100) includes any one of sapphire, silicon, Ge, SiC, AlN, GaN, GaAs, InP, sapphire / SiO2 composite substrate, sapphire / AlN composite substrate, sapphire / SiNx, sapphire / SiO2 / SiNx composite substrate, magnesium aluminate spinel MgAl2O4, MgO, ZnO, ZrB2, LiAlO2, and LiGaO2 composite substrate.

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