[0033] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features, and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are described below with reference to the accompanying drawings. Give further details.
[0034] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, or it can be a communication between two components, which can be It is directly connected or indirectly connected through an intermediary. For those of ordinary skill in the art, the specific meaning of the above-mentioned terms can be understood according to specific circumstances.
[0035] See figure 1 , Is a schematic structural diagram of an embodiment of a semiconductor laser with a built-in grating of the present invention. The built-in grating semiconductor laser may include a substrate 110, a lower cladding layer 120, a lower waveguide layer 130, an active layer 140, an upper waveguide layer 150, an upper cladding layer 160, and a top layer 170 arranged sequentially from bottom to top, wherein the upper waveguide The layer 150 may include a first upper waveguide layer 151 and a second upper waveguide layer 152. The first upper waveguide layer 151 is the upper layer of the active layer 140, and the second upper waveguide layer 152 is the upper layer. A layer below the cladding layer 160, and a grating layer 180 is provided between the first upper waveguide layer 151 and the second upper waveguide layer 152.
[0036] In this embodiment, since the grating has the mode selectivity, the grating layer is arranged between the first upper waveguide layer and the second upper waveguide layer, which can improve the consistency of the center wavelength of the semiconductor laser pump source; at the same time, due to the grating The period and the refractive index of the material change very little with temperature. Therefore, the wavelength drift coefficient of the semiconductor laser pump source with temperature will be greatly reduced after the grating is adopted. The built-in grating laser diode pump source designed by the present invention has a wavelength drift coefficient of about 0.09nm/℃, the half-width of the spectrum is about 0.5nm, its half-width of the spectrum is less than 1/4 of the (FP) structure high-power laser, and the temperature drift coefficient is lower than 1/3 of the (FP) structure high-power laser. The narrow half-width of the spectrum and better wavelength stability not only greatly reduce the power consumption and volume of the pumping system, but also greatly improve the adaptability of engineering applications. It can be seen that the present invention can greatly improve the spectral quality and temperature stability of the semiconductor laser by providing a grating layer between the first upper waveguide layer and the second upper waveguide layer, and can reduce the power consumption and volume of the laser.
[0037] When designing the active layer, GaAlAs compound materials are generally used to make the active layer 140 at present, but the use of GaAlAs compound materials to make the active layer 140 has the following disadvantages: The oxidation of GaAlAs makes further growth and device production become Difficult, high growth temperature is not suitable for monolithic integration; the migration of dark line defects and faults degrades device performance. Research has found that these problems are due to the presence of Al element. The quaternary InGaAsP lattice matches with GaAs, which is a very attractive alternative to GaAlAs/GaAs. They have higher reliability. InGaAsP acts as an active layer, which effectively prevents the formation of defects. InGaAsP/GaAs lasers are at least one to two orders of magnitude higher than the DLD (dark line defects) of GaAlAs/GaAs lasers. Since InGaAsP has a significantly lower recombination rate than GaAlAs, the laser cavity surface temperature is significantly reduced. InGaAsP as an active layer device, its catastrophic damage power density is at least twice that of GaAlAs as an active layer device. In other words, with the same geometric structure, the stable working power of the laser made of InGaAsP as the active layer is twice that of the GaAlAs active layer, thereby greatly improving the laser cavity surface damage threshold. It can be seen that the present invention uses Al-free InGaAsP compound materials to make the active layer, avoiding device degradation caused by Al oxidation in the Al-containing active layer, thereby increasing the working life of the laser and making the laser more reliable .
[0038] In addition, according to the wavelength calculation formula (1), the equivalent band gap E eff Calculation formula (2) and linear interpolation method are used to calculate, the thickness of the active layer 140 can be The molar fractions of the components In and Ga range from 0 to 0.25 and 0.75 to 1, respectively. The molar fractions of As and P range from 0.7 to 0.9 and 0.1 to 0.3. Because the emission wavelength is The mole fraction of the active layer material component is related to the well width (that is, the thickness of the active layer), the wavelength is constant, and the two are in a one-to-one correspondence. In this embodiment, the thickness of the active layer 140 is taken as The available mole fractions of In, Ga, As and P are: 0.14, 0.86, 0.78, 0.22, respectively. It should be noted that: since In and Ga are group III atoms, As and P are group V atoms, so when calculating the mole fraction of components, the mole fractions are calculated with the same group of atoms as the unit, such as the group III atoms of In and Ga. The mole fractions are 0.14 and 0.86 respectively, and the sum of the two is equal to 1.
[0039] Wavelength calculation formula:
[0040] λ=hc/hv≈1.24/E eff (1)
[0041] In the formula, h is Planck's constant, c is the speed of light in vacuum, and ν is the photon frequency.
[0042] Equivalent band gap E eff Calculation formula:
[0043]
[0044] Where E g For In1-XGaXAsYP 1-Y Body material forbidden width, Is Planck's constant, m e , M hh Are the effective masses of electrons and holes, d W Is the thickness of the well layer. Therefore, the present invention can optimize the efficiency of laser transmission by designing the thickness of the active layer and the molar fraction of each component, and can avoid the waste of preparation materials when the active layer is too thick.
[0045] When designing the waveguide layer, theoretically, increase the energy gap difference ΔE between the active layer 140 and the waveguide layer 150 c , Which can reduce the leakage of carriers, thereby improving quantum efficiency and lowering the threshold, but the energy gap difference ΔE is too high c , Will inevitably cause the heterogeneous crystal lattice mismatch between the active region and the waveguide region to form more interface states, thereby affecting the internal quantum efficiency η i In addition, AIGaAs compound materials are usually used to make the waveguide layer at present, but as the waveguide widens, the series resistance and thermal resistance will increase. In the wide waveguide structure, the waveguide doping is often used, but this will bring light The problem of increased absorption and decreased electro-optical conversion. Research has found that InGaP has better thermal and electrical conductivity than AIGaAs, and its internal loss coefficient is α i Can be approximated as:
[0046] α i =α fc Γ+α fc.x (1-Γ) (3)
[0047] Where Г is the light field limiting factor, α fc Is the free carrier absorption loss, α fc.x Absorption loss for free carriers outside the well layer. α fc It has the following approximate relationship with the initial carrier concentration N (doped to GaAs materials):
[0048] α fc =0.5×10 -17 N (4)
[0049] When the active area doping concentration is 10 18 cm -3 Below, α fc Constantly unchanged at 10cm -1 , And reach 10 18 cm -3 When the absorption coefficient increases with the doping concentration according to equation (4). Right α fc.x With the above and α fc In the same relationship, since the laser in the present invention adopts a quantum well structure, the active layer 140 is very thin, even if the active layer 140 and the waveguide layer 150 are not doped, injecting less current into the active layer can also achieve the number of particles. Reverse. Therefore, the present invention can avoid doping the waveguide layer and the active layer by using the InGaP compound material to make the waveguide layer, thereby solving the problems of increased light absorption and decreased electro-optical conversion.
[0050] In addition, in this embodiment, the first upper waveguide layer 151, the second upper waveguide layer 152, and the lower waveguide layer 130 are all made of undoped InGaP compound materials, and the mole fractions of In and Ga are all They are 0.49 and 0.51 in turn, and the thickness of the three is 0.2-0.4 μm, which can ensure the energy gap difference ΔE between the active layer 140 and the waveguide layer 150 c Moderate, not only can reduce the leakage of carriers, thereby improve the quantum efficiency and lower the threshold, but can also avoid the mismatch of the heterogeneous crystal lattice between the active layer and the waveguide layer, forming more interface states, thereby affecting the internal quantum efficiency η i. In an optional implementation manner, the thickness of the first upper waveguide layer 151, the second upper waveguide layer 152, and the lower waveguide layer 130 may be 0.4 μm, which can effectively increase the laser output power and reduce the vertical divergence angle; The grating layer 180 may be located in the middle of the first waveguide layer 151 and the second waveguide layer 152, thereby facilitating the switching between InGaP and GaAs during material growth.
[0051] When designing the cladding, in order to ensure that the cladding has a good limit on the optical field and prevent carrier leakage, it is necessary to ensure that there is an energy gap difference ΔE between the cladding and the waveguide area. c. Studies have found that InGaAlP is more suitable as a cladding layer for InGaP materials than GaAlAs. InGaAlP is a direct band gap material when the Al component mole fraction of InGaAlP is lower than 0.3. Therefore, it has lower resistance than GaAlAs, and higher than 0.3 is an indirect band. The resistance of the gap will increase significantly, so the value is generally not more than 0.3, but this will make the conduction band energy difference between the waveguide layer and the waveguide layer smaller, which will lead to carrier leakage in the waveguide region, resulting in quantum efficiency and characteristic temperature To reduce, the present invention uses three upper cladding layers to solve this problem. In this embodiment, the upper cladding layer 160 includes a first upper cladding layer 161, a second upper cladding layer 162, and a third upper cladding layer 163 that are sequentially arranged from bottom to top, wherein the first upper cladding layer 161 is the first The upper layer of the second waveguide layer 152, the third upper cladding layer 163 is the lower layer of the top layer 170, and the first upper cladding layer 161, the third upper cladding layer 163 and the lower cladding layer 120 can all be InGaAlP Made of compound material, the second upper cladding layer 162 may be made of GaAlAs compound material.
[0052] Generally, the carrier diffusion length is about 1 μm, so the cladding layer should not be too thick; at the same time, reducing the cladding layer thickness can also reduce the thermal resistance. Therefore, the thickness of the lower cladding layer 120 can be 1.25 μm. The mole fractions of Ga and Al are 0.5, 0.25, and 0.25, respectively; the first upper cladding layer 161 has the same mole fraction of In, Ga, and Al as the lower cladding layer 120, and the thickness is 0.1 μm, so that the second upper cladding layer 162 can be quite close to the waveguide area to effectively confine carriers; the Al composition of the second upper cladding layer 162 is set to 0.85, which is to provide an effective conduction band energy compensation, but due to its large resistance, we choose its thickness The band gap energy of the third upper cladding layer 163 is lower than that of the first upper cladding layer 161, the In, Ga, and Al component mol fractions are 0.5, 0.45, and 0.05, respectively, and the thickness is 1.25 μm. In the present invention, by making the band gap energy of the third upper cladding layer lower than that of the first upper cladding layer, the Al composition content of the third upper cladding layer can be lower than that of the first upper cladding layer, and the thermal resistance and series resistance can be reduced. Ensure that the third upper cladding layer has good thermal and electrical conductivity to stably output the laser to the top layer. Therefore, the present invention uses InGaAlP, which has good material matching with the waveguide layer InGaP, as the cladding layer. We add a GaAlAs cladding layer with high Al content between the two InGaAlP cladding layers to form a three-clad structure to compensate The conduction band energy difference between InGaP and InGaAlP is small, which leads to the problem of carrier leakage in the waveguide region.
[0053] Since the first upper cladding layer 161 and the third upper cladding layer 163 are made of InGaAlP, the second upper cladding layer 162 located between the first upper cladding layer 161 and the third upper cladding layer 163 is made of GaAlAs , InGaAlP and GaAlAs materials are obviously different, and the imperfect growth interface between them will adversely affect the performance of the device. Therefore, in this embodiment, a first transition layer 191 is provided between the first over cladding layer 161 and the second over cladding layer 162, and the second over cladding layer 162 and the third over cladding layer A second transition layer 192 is arranged between the layers 163, and both the first transition layer 191 and the second transition layer 192 are made of GaAlAs compound material. In the present invention, a transition layer made of GaAlAs compound is added between the first upper cladding layer and the second upper cladding layer, and between the second upper cladding layer and the third upper cladding layer. The growth interface has an adverse effect on device performance. In addition, in order to make the materials of the first upper cladding layer and the second upper cladding layer and the second upper cladding layer and the first upper cladding layer more compatible, the Al composition in the transition layer should be as low as possible, and in order to reduce the transition layer Influence, the thickness of the transition layer should be as thin as possible. In this embodiment, the mole fraction of Al component in the first transition layer and the second transition layer are both 0.1, and the thickness is both
[0054] When designing the top layer, it is known from the theory of metal-semiconductor (MS) contact that MS contact is generally similar to an ideal Schottky contact. The barrier height between them is related to the nature of the metal and the doping of the semiconductor surface. The metal-semiconductor contact The quality is usually the characteristic resistivity R c Said. Theoretical calculation results show that as the doping concentration increases, the width of the space charge region in the semiconductor can be reduced. For heavily doped semiconductors, if the doping concentration is large (N>10 19 cm -3 ), the barrier width of M-S contact becomes very thin, and the tunneling probability of electrons is greatly increased. R c It strongly depends on the doping level and the effective quality of tunneling electrons. In the actual device production, in addition to choosing a metal with low contact barrier as the contact metal, it is more important to prepare a layer of uniform degeneration (ie, heavy Doped) semiconductor. In order to ensure that the M-S contact is a low-resistance ohmic contact, rather than a Schottky barrier of rectification characteristics. The present invention designs top doping concentration greater than 10 19 cm -3 , The thickness of the top layer of InGaAsP/GaAs laser is 0.2μm.
[0055] When designing the grating layer, through theoretical calculations and LASTIP software for light field simulation, the value conditions are as follows: the cavity length is 4mm, and the injection current density is 30A/mm 2 , Equivalent to 0.1×4mm 2 The injection current in the area is 12A (the working current of the chip and the area of the injection area), and the reflectivity of the front and rear surfaces are respectively 0.001 and 0.95. The simulation results found that when and only when KL (L is the grating layer cavity length) is 0.25 and 1.5 Obtain a better convergence light field map, that is, wavelength locking can be achieved, and the light field distribution is as figure 2 with 3 Shown. It can be seen from the figure that when kL is 0.25, the light field distribution changes uniformly, and there is no protrusion in the middle, and the value is reasonable; when KL is 1.5, wavelength locking can also be quickly achieved, but the light field distribution changes unevenly, and there is Protrusions, the value is too high, the "hole burning" effect is likely to occur in the middle, and the KL should be in the range of 0.2-0.3 for high injection current working conditions. We use a first-order grating with a KL of 0.25, taking the laser cavity length of 4mm, and K should be 0.0625/mm.
[0056] We use Rsoft Beamprop software to simulate and obtain the coupling coefficients of gratings with different thicknesses such as Figure 4 As shown, it can be seen from the figure: when the thickness of the grating layer is 20nm, K is about 0.0625/mm, we use the thickness of the grating layer to be 20nm, and the distance to the active layer is 0.2μm. Through calculation, the grating The period is 113.2nm, and the duty ratio is 1:1.
[0057] among them, figure 1 The material parameters of each layer shown in are as follows:
[0058] Substrate: GaAs<100>Si doping concentration is 1~4×10 18 cm -3 , Thickness 100±5μm, EPD<500cm -2;
[0059] First layer: In 0.5 (Ga 0.5 Al 0.5 ) 0.5 P under cladding, n (Si) doping concentration is 1~3×10 18 cm -3 ,1.25μm;
[0060] The second layer: In 0.49 Ga 0.51 Waveguide layer under P, undoped, 0.4μm
[0061] The third layer: In 0.14 Ga 0.86 As 0.78 P 0.22 Active layer, undoped,
[0062] Fourth layer: In 0.49 Ga 0.51 P first upper waveguide layer, undoped, 0.2μm;
[0063] The fifth layer: GaAs grating layer, undoped, 20nm;
[0064] Sixth layer: In 0.49 Ga 0.51 P second upper waveguide layer, undoped, 0.2μm;
[0065] Seventh floor: In 0.5 (Ga 0.5 Al 0.5 ) 0.5 P first upper cladding layer, p(Zn) doping concentration is 2×10 17 cm -3 , 0.1μm;
[0066] Eighth layer: Ga 0.9 Al 0.1 As the first transition layer, p(Zn) doping concentration is 2×10 17 cm -3 ,
[0067] Ninth layer: Ga 0.15 Al 0.85 As the second upper cladding layer, p(Zn) doping concentration is 2×10 17 cm -3 , 0.1μm;
[0068] Tenth layer: Ga 0.9 Al 0.1 As the second transition layer, p(Zn) doping concentration is 2×10 17 cm -3 ,
[0069] The eleventh layer: In 0.5 (Ga 0.9 Al 0.1 ) 0.5 P third upper cladding layer, p(Zn) doping concentration is 2×10 17 cm -3 ,1.25μm;
[0070] The twelfth layer: GaAs top layer, heavily doped with p(Zn), the concentration is> 1×10 19 cm -3 , 0.2μm;
[0071] The width of the light-emitting strip is designed to be 100 μm.
[0072] In addition, the schematic diagram of the 808nm multi-clad structure high-power semiconductor laser die designed by this invention is as follows: Figure 5 Shown. Through testing, the main optoelectronic performance parameters of the high-power semiconductor laser with this structure are: central wavelength: 808±1nm; spectral half-width: ≤0.5nm; temperature drift coefficient of central wavelength: ≤0.1nm/℃; output power: ≥12W; luminescence Strip width: 100μm, the laser PI and electro-optical conversion efficiency curve are as follows Image 6 As shown, the spectral characteristic curve of the laser is as Figure 7 Shown. Although the invention designs a single-emitting-point laser, the structure is completely applicable to the laser array bar, but the array bar is composed of several single-emitting-point lasers with the same structure.
[0073] Those skilled in the art will easily think of other embodiments of the present invention after considering the description and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptive changes of the present invention. These variations, uses, or adaptive changes follow the general principles of the present invention and include common knowledge or conventional technical means in the technical field not disclosed by the present invention. . The description and the embodiments are to be regarded as exemplary only, and the true scope and spirit of the present invention are pointed out by the following claims.
[0074] It should be understood that the present invention is not limited to the precise structure described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims.
