A vertical cavity surface emitting semiconductor laser and a manufacturing method thereof

Abstract

The application relates to the technical field of semiconductor lasers, in particular to a vertical cavity surface emitting semiconductor laser and a manufacturing method thereof, which comprises, from bottom to top, a substrate, an N-type DBR layer, an active region, an oxidation layer, a P-type DBR layer, a P contact layer and a P metal layer, the oxidation layer is provided with an oxidation hole, the P contact layer is provided with a carbon substitution modulation structure layer, the lower end of the carbon substitution modulation structure layer is located in the P-type DBR layer, the carbon substitution modulation structure layer is opposite to the oxidation hole, and the material of the carbon substitution modulation structure layer is GaAs doped with carbon atoms. The application realizes the high-frequency characteristics, single-mode performance, super-long life, wide-temperature working and extreme environment resistance which cannot be achieved by the traditional simple oxidation limiting scheme and the traditional diffusion process plus oxidation limiting VCSEL scheme through the cooperation of the accurate control of the SEG process and the ultra-low diffusion characteristics of carbon.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor lasers, in particular to a vertical cavity surface emitting semiconductor laser and a manufacturing method thereof. BACKGROUND

[0002] With the upgrading of the performance requirements of optoelectronic devices in scenarios such as high-speed optical interconnection of data centers, industrial-grade wide-temperature control, and aerospace anti-extreme environment, the market urgently needs single-mode vertical cavity surface emitting lasers (VCSELs) that meet the requirements of “high-frequency modulation of more than 100 Gbps, stable operation in a wide temperature range of -55°C to 125°C, long service life of 100,000 hours, anti-radiation, and anti-aging”. The current mainstream VCSEL preparation schemes (traditional oxidation limiting type, Zn / Be / Mg diffusion type) can realize basic single-mode and high-frequency characteristics, but there are significant technical bottlenecks in the coordinated optimization of “long-term reliability, high-frequency stability, and mass production safety”. The specific problems and scheme comparisons are as follows:

[0003] Traditional oxidation limiting type VCSEL: both reliability and performance are insufficient. Key technical bottlenecks:

[0004] 1. Low current control precision, high-frequency performance limited: the oxidation process is affected by water vapor partial pressure and crystal direction difference, the oxidation aperture edge is irregular (deviation ±0.5um), and the longitudinal oxidation depth is uneven (deviation ±10nm), resulting in a current lateral diffusion ratio of 3% to 5%, accumulation of edge carriers in the active region, significant SHB effect, and a 3dB bandwidth of less than 20GHz;

[0005] 2. Poor long-term reliability, serious aging attenuation: there are a large number of dangling bonds (interface state density ≥1×10 11 cm -2 ) at the Al2O3 and GaAs interface, which easily adsorb water vapor to form oxidation defects under long-term high temperature (125°C), and Al atoms diffuse to the active region, resulting in a power attenuation of ≥10% and a threshold current increase of ≥8% after 1000 hours of aging;

[0006] 3. Weak ability to resist extreme environments: the oxidation layer edge is rough (roughness ≥5nm), and mode competition easily occurs in a radiation environment, 1×10 6 radγ radiation causes RIN to deteriorate to -125dB / Hz, which cannot meet the aerospace anti-radiation requirements.

[0007] Zn / Be / Mg diffusion type VCSEL: diffusion uncontrollability leads to insufficient stability. Key technical bottlenecks:

[0008] 1. Lateral diffusion is uncontrollable, and the current channel precision is low. The diffusion coefficient of Zn atoms in GaAs is high, and the lateral diffusion is 1-2 um during the diffusion process, which leads to that the actual current channel (4-6 um) is larger than the design value, the matching degree with the high-intensity area of the light field is reduced, the SHB effect is not completely inhibited, and the bandwidth attenuation is greater than or equal to 5% after long-term work of high-speed modulation;

[0009] 2. The concentration gradient is uneven, and the carrier transport efficiency is low: the diffusion coefficient of Zn in high-Al component AlGaAs (such as Al 0.93 Ga 0.07 As) is only 1 / 100 of that in low-Al component, the Zn concentration gradient in the DBR layer reaches 10 4 cm -3 / nm, and there is a “high resistance area” in the current transmission path, and the series resistance is 20% higher than the target value;

[0010] 3. High-temperature diffusion damage and lattice quality deterioration: the diffusion temperature of 620 DEG C is close to the thermal decomposition temperature of GaAs, which easily leads to the mixing of interfaces between DBR layers (interdiffusion of Al components between high-Al layers and low-Al layers), and the reflectivity decreases from 99.5% to 98.5%, and the optical gain efficiency decreases by 8%-10%. SUMMARY

[0011] In order to solve the above problems, the application provides a vertical cavity surface emitting semiconductor laser and a manufacturing method thereof.

[0012] One of the purposes of the application is to provide a vertical cavity surface emitting semiconductor laser, which adopts the following technical scheme:

[0013] A vertical cavity surface emitting semiconductor laser comprises, from bottom to top, a substrate, an N-type DBR layer, an active region, an oxidation layer, a P-type DBR layer, a P-contact layer and a P-metal layer, the oxidation layer is provided with an oxidation hole, the P-contact layer is provided with a carbon substitution modulation structure layer, the lower end of the carbon substitution modulation structure layer is located in the P-type DBR layer, the carbon substitution modulation structure layer is opposite to the oxidation hole, and the material of the carbon substitution modulation structure layer is GaAs doped with carbon atoms.

[0014] By adopting the above technical scheme, the application forms double current limitation through the nesting cooperation of “SEG carbon doped aperture and oxidation aperture”:

[0015] Primary current limiting: SEG carbon substitution modulation structure layer: only carbon doped GaAs carbon substitution modulation structure layer (low resistance area, 1.2*10 -3 -1.5*10 -3 Ω·cm) is grown in the window, and the window is covered with a high resistance area (resistivity is greater than or equal to 1*10 3 Ω·cm), and the current is preliminarily limited in the carbon substitution modulation structure layer;

[0016] Secondary current limiting: Oxidation aperture: After the growth of the carbon substitution modulation structure layer, the underlying AlGaAs layer is oxidized with wet oxygen to form an oxidation aperture, further limiting the injection current.

[0017] Limiting current precision advantage: The diameter of the carbon substitution modulation structure layer is determined by the photolithography precision (±0.1um), and the oxidation aperture achieves ±0.2um precision by controlling the oxidation time (such as 30min), and the nesting deviation of the two is ≤0.3um, and the current limiting is more accurate.

[0018] Inhibition of spatial hole burning effect (SHB):

[0019] Precise matching of current injection and light field: The light field of the VCSEL active region is in a Gaussian distribution, with 80% of the light intensity concentrated in the central region, high photon density in the center (fast carrier consumption) and low in the edge (slow carrier consumption); The SEG carbon substitution modulation structure layer is directly aligned with the center of the light field, and the current is only injected into the center area where the carrier consumption is the fastest, and the uniformity of the carbon substitution modulation structure layer is ≤7%, and the current is uniformly distributed in the center area——Avoiding the problem of "current injection area large leading to edge carrier accumulation" in traditional scheme, the carrier injection rate is completely matched with the center area photon consumption rate; The low-frequency roll-off (≤1GHz) caused by SHB is due to the "supplementary delay" after the center carrier is depleted, and the current-light field matching degree of the present application is ≥95%, the low-frequency modulation response flatness is improved by 15%, and the RIN is stable at -149dB / Hz.

[0020] Flattening of light field distribution: Oxidation hole and carbon substitution modulation structure layer work together to make the light field distribution more flat. The oxidation aperture limits the light field in the oxidation aperture by the difference in refractive index (Al2O3 refractive index 1.7, GaAs refractive index 3.6), avoiding light field leakage to the edge; The carbon substitution modulation structure layer (high carrier concentration) has slight absorption to the light field, which can weaken the local high intensity in the center of the light field, so that the gradient of the light field intensity from the center to the edge is reduced from 20% to 10%, and the difference in photon density is reduced——The carrier consumption is more uniform, and there is no local "burning hole", which provides support for a wide bandwidth of more than 30GHz.

[0021] Double-aperture light field synergistic reduction, mode selection more stable, realize single-mode output:

[0022] The application realizes more stable single-mode output by "preliminarily restricting the aperture of oxidation and further reducing the light field by carbon substitution modulation structure layer": accurate control of the lateral size of the light field, primary light field restriction: oxidation aperture: the oxidation aperture limits the light field within the oxidation aperture range through total reflection, preliminarily suppressing large-size high-order modes; secondary light field reduction: carbon substitution modulation structure layer: the high carrier concentration of the carbon substitution modulation structure layer has a "mode filtering" effect on the light field - only the fundamental mode can stably transmit in the narrow channel of the carbon substitution modulation structure layer, and the high-order modes will be absorbed or leaked by the carbon substitution modulation structure layer (high-order mode loss ≥ 20 dB / cm, fundamental mode loss ≤ 5 dB / cm); when the lateral size of the light field is 3.5-4.7 times the working wavelength, the mode gain of the high-order mode is lower than the threshold gain (fundamental mode gain ≥ 15 dB, high-order mode gain ≤ 8 dB), and only the fundamental mode realizes resonant output.

[0023] Single-mode stability advantage:

[0024] No mode shift: the low diffusion characteristics of carbon ensure that the diameter of the carbon substitution modulation structure layer is stable for a long time (deviation ≤ 0.1 um after 1000 hours of work), and the light field restriction has no shift; while the Zn diffusion scheme has a diffusion aperture shift ≥ 0.3 um due to Zn atom migration, and the single-mode characteristics deteriorate;

[0025] High SMSR output: the scheme cooperates with double apertures, and the fundamental mode suppression ratio (SMSR) is stably maintained at 38-40 dB, and the vertical divergence angle is ≤ 14°, so that the single-mode output is more stable.

[0026] Preferably, the concentration of carbon atoms in the carbon substitution modulation structure layer is 1×10 19 -1×10 20 cm -3 .

[0027] Preferably, the diameter of the carbon substitution modulation structure layer is smaller than the aperture of the oxidation hole.

[0028] By adopting the above technical scheme, the oxidation aperture covers the diameter of the carbon substitution modulation structure layer, further blocking the leakage current outside the carbon substitution modulation structure layer.

[0029] Another object of the application is to provide a manufacturing method of a vertical cavity surface emitting semiconductor laser, which adopts the following technical scheme:

[0030] A manufacturing method of a vertical cavity surface emitting semiconductor laser, for preparing the vertical cavity surface emitting semiconductor laser described above, comprising the following steps,

[0031] S1, epitaxial growth, growing an epitaxial layer on a substrate, the epitaxial layer comprising an N-type DBR layer, an active region, an oxidation layer, a P-type DBR layer, a P-contact layer and a P-metal layer;

[0032] S2, preparing a carbon-substituted modulation structure layer; S2 includes the following steps,

[0033] S221, depositing a layer of SiN on the P-contact layer X ,

[0034] S222, photoetching and dry etching a circular window in the SiN X center that matches the high-intensity area of the Gaussian distribution of the light field, the circular window etching through the P-contact layer;

[0035] S223, using the MOCVD method to perform carbon atom doping, using CCl4 as a doping source to provide carbon atoms to dope on the P-contact layer within the circular window, forming a carbon-substituted modulation structure layer.

[0036] By adopting the above technical solution, the SiN X mask window size is precisely controlled by photoetching, the carbon-substituted modulation structure layer only grows within the window, the lateral boundary is absolutely clear (without the problem of oxidized edge blur), and the current lateral diffusion ratio is ≤0.5%. C atoms form acceptor energy levels (ionization energy 26 meV) by "replacing Ga sites", providing hole conduction. The synergistic effect of high V / III ratio and high temperature - As atoms occupy surface adsorption sites, reducing C atom aggregation, while high temperature promotes the migration of C atoms in the lattice, dispersing local high concentration areas; the solid solubility limit of carbon results in a doping concentration (8×10 18 ) lower than Zn (1×10 19 ), the resistivity is slightly higher, the total resistance is kept consistent by increasing the thickness by 50 nm (resistance is proportional to thickness), which does not affect the bandwidth.

[0037] As a preferred, in S223, the growth temperature is 600-610℃; the growth pressure is 200 mTorr; and the As / Ga ratio is 60.

[0038] By adopting the above technical solution, the replacement rate of carbon atoms is ≥90% at around 600℃; but no more than 610℃ to avoid GaAs decomposition.

[0039] As a preferred, S2 further includes a step before S221,

[0040] S211, using a two-step method of diamond grinding and colloidal silica fine polishing to control the surface roughness of the P-contact layer to Ra≤0.3 nm, and ensuring that the protrusions in a 5×5um 2 area are ≤1 nm through AFM full-scan;

[0041] S212, cleaning with acetone ultrasonic and isopropyl alcohol ultrasonic for 10 minutes respectively;

[0042] S213, after soaking for 5 minutes with diluted HF, rinse with DIW;

[0043] S214, ashing with O2 / Ar plasma, and detecting the surface carbon content by XPS to be ≤0.05%.

[0044] By adopting the above technical solution, the subsequent carbon-doped epitaxial temperature reaches 600℃, the SiN X The mask can enhance the high-temperature resistance, avoid the shrinkage of the mask at high temperature, and cause the deformation of the window (diameter deviation ≤0.1um); the residue at the edge of the window can block the diffusion of C atoms, causing the local doping concentration to decrease by 20%, and the BOE treatment can ensure the edge doping uniformity.

[0045] As preferred, in the process of S223, the intensity of the C-C bond characteristic peak is monitored in real time by in-situ infrared spectrum.

[0046] As preferred, it further includes a step after S223,

[0047] S231, rapid thermal annealing under N2 atmosphere, temperature 400℃, time 30 seconds;

[0048] S232, dry etching with Cl2 / BCl3 mixed gas to remove the 5-10nm high protrusions at the edge of the SEG epitaxial layer window, so that the epitaxial layer surface is flush with the SiN X The surface of the mask is flush.

[0049] By adopting the above technical solution, a small amount of "C interstitial atoms" (shallow level defects, causing carrier traps) may exist in the carbon substitution modulation structure layer, and the 400℃ annealing can promote the interstitial C to migrate to the Ga vacancy (substitution site), and the activation rate is increased from 90% to 95%.

[0050] As preferred, in step S222, after etching a circular window, the SiN X Residue.

[0051] By adopting the above technical solution, the GaAs surface is completely exposed, and the carbon doping shadow effect is avoided.

[0052] In summary, the present application includes at least one of the following beneficial technical effects:

[0053] 1. Higher current limiting accuracy, high frequency performance (bandwidth) improved by more than 20%.

[0054] 2. SiN X The window size of the mask is precisely controlled by photolithography, the carbon substitution modulation structure layer only grows in the window, the lateral boundary is absolutely clear (without the problem of edge blur due to oxidation), and the proportion of current lateral diffusion is ≤0.5%.

[0055] 3. Resistivity uniformity of carbon substitution modulation structure layer ≤ 7% (resistivity uniformity of traditional oxidation layer ≥ 15%), current density distribution is more concentrated (overlap rate with high intensity area of light field ≥ 95%), SHB effect is extremely suppressed (RIN ≤ -149 dB / Hz, traditional scheme is -135 dB / Hz), carrier consumption and replenishment are more balanced during high-frequency modulation, and bandwidth is improved.

[0056] 4. Long-term reliability is improved by more than 30%, and service life is extended to 100,000 hours.

[0057] 5. The current limiting area is composed of "SiN X masking and carbon-doped GaAs", SiN X has strong chemical inertness (does not react with water vapor) and low interface state density (≤ 5 × 10 10 cm -2 ) with GaAs (≤ 5 × 10

[0058] 6. Carbon has extremely low diffusion coefficient, only 1 / 100 of Al, and almost no migration of carbon atoms during high-temperature aging (diffusion distance ≤ 0.1 nm / 1000 hours), stable doping distribution, and current channel resistance change ≤ 1%, avoiding threshold current increase due to resistance increase.

[0059] 7. Long-term doping stability is optimal, suitable for extreme environments (-55°C to 125°C). After wide temperature cycling (-55°C to 125°C, 1000 cycles), the carrier concentration change of the carbon substitution modulation structure layer is ≤ 2%. The diffusion coefficient of carbon is much lower than that of Zn, Be and Mg, which means that when the temperature fluctuates, carbon atoms almost do not leave the lattice position (replace Ga position), and the carrier concentration is stable.

[0060] 8. Electrical performance decay is minimal at high temperatures, suitable for industrial-grade wide-temperature applications. At high temperatures, the "ionization energy" of the doping atoms determines the stability of the carrier concentration: the ionization energy of carbon in GaAs is only 26 meV, and the ionization rate is higher at high temperatures;

[0061] 9. Carbon has higher lattice matching degree with GaAs (carbon atom radius 0.077 nm, Ga 0.126 nm, lattice distortion ≤ 0.5% after substitution), and is less likely to produce lattice relaxation at high temperatures, with smaller carrier mobility decay.

[0062] 10. Excellent radiation resistance, suitable for aerospace and nuclear industry scenarios. In 1 × 10 6The power attenuation of the carbon-doped VCSEL is less than or equal to 8% after radγ ray irradiation. Irradiation can generate "vacancy-interstitial atom pairs" (defects) in the semiconductor, which can scatter carriers or become non-radiative recombination centers. The carbon atom has a high binding energy with the GaAs lattice, which can "pin" the defects generated by irradiation (reduce defect migration) and reduce the impact on carrier transport, so the performance is more robust in the radiation environment. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 is a schematic diagram of the overall structure of embodiment one.

[0064] REFERENCE SIGNS:

[0065] 1, substrate; 2, N-type DBR layer; 3, active region; 4, oxidation layer; 5, P-type DBR layer; 6, P-contact layer; 7, P-metal layer; 8, oxidation hole; 9, carbon substitution modulation structure layer. DETAILED DESCRIPTION

[0066] The application will be further described in detail below in combination with all the drawings.

[0067] Embodiment one

[0068] The embodiments of the application disclose a vertical cavity surface emitting semiconductor laser, referring to Figure 1 , comprising a substrate 1, an N-type DBR layer 2, an active region 3, an oxidation layer 4, a P-type DBR layer 5, a P-contact layer 6 and a P-metal layer 7 arranged in sequence from bottom to top, the oxidation layer 4 is provided with an oxidation hole 8, the P-contact layer 6 is provided with a carbon substitution modulation structure layer 9, the lower end of the carbon substitution modulation structure layer 9 is located in the P-type DBR layer 5, the carbon substitution modulation structure layer 9 is opposite to the oxidation hole 8, and the material of the carbon substitution modulation structure layer 9 is GaAs doped with carbon atoms.

[0069] The parameters of the carbon substitution modulation structure layer 9 are a substitution aperture Wz=3-4um (±0.1um) and a substitution growth depth d of 0.5um; the carbon atom concentration is 1×10 19 -1×10 20 cm -3 The aperture Wo of the oxidation hole 8 is 6-7um (±0.2um).

[0070] Embodiment two

[0071] The embodiments of the application disclose a manufacturing method of a vertical cavity surface emitting semiconductor laser, which is used for manufacturing the vertical cavity surface emitting semiconductor laser in the above embodiments and comprises the following steps,

[0072] S1, epitaxial growth;

[0073] The specific technical solutions are as follows:

[0074] S11, N-type GaAs substrate crystal orientation (<100>, off-angle 2°, Si-doped, concentration 1 x 10 18 cm -3 ) pre-treatment, to ensure epitaxial growth on a "clean substrate".

[0075] Process steps: sequentially clean with acetone and isopropyl alcohol for 10 minutes (remove organic contaminants), rinse with deionized water, then immerse in 10% HF solution for 30 seconds (remove surface native oxide layer), and finally dry with nitrogen. Place the substrate in the MOCVD reaction chamber and anneal at 800°C for 10 minutes in a H2atmosphere to further remove surface residual oxides and adsorbed impurities.

[0076] Purpose of substrate pre-treatment: a clean substrate surface can reduce the dislocation density of the epitaxial layer (target <10 4 cm -2 ), to ensure lattice matching of subsequent semiconductor layers (lattice mismatch rate of GaAs substrate and AlGaAs <0.1%).

[0077] S12, growth of N-type DBR layer;

[0078] Process steps: use metal organic chemical vapor deposition (MOCVD), growth temperature: 700°C (high temperature is conducive to reducing interface roughness), pressure maintained at 200 Torr, carrier gas is H2. Use reaction gases group III source (TMGa, TMAl) and group V source (AsH3), doping source SiH4, introduce trimethylaluminum (TMAl, Al source) and TMGa, control the Al component to 0.9 by adjusting the TMAl / TMGa flow ratio (set to 9:1) to form Al 0.93 Ga 0.07 As (high Al layer) with a refractive index of about 3.0; turn off TMAl and only introduce TMGa to form Al 0.15 Ga 0.85 As (low Al layer) with a refractive index of about 3.6; alternately grow 39±1 pairs of periods, with each layer thickness strictly controlled to be 1 / 4 of the laser wavelength (when λ=850nm, Al 0.93 Ga 0.07 As layer thickness about 70nm, Al 0.15 Ga 0.85 As layer thickness about 58nm), error <1nm; form N-type doping (Si concentration about 5 x 10 17 ±10%cm -3 ) to ensure good electrical conductivity.

[0079] Role of N-type DBR: the refractive index difference between high Al component and low Al component can maximize the reflectivity; the thickness of each layer is λ / 4n (n is the material refractive index) to ensure that the reflected light phases of each interface are superimposed to form a high-reflectivity "optical mirror".

[0080] S13, lower spacer layer growth;

[0081] Process step: using metal organic chemical vapor deposition (MOCVD), the temperature is reduced to 680°C, and the pressure is 200 Torr. TMAl, TMGa and AsH3 are introduced, and the TMAl / TMGa flow ratio is set to 9:1 (consistent with the high Al layer of the N-type DBR) to form Al 0.93 Ga 0.07 As, the doping source is diethyl beryllium (DEBe, P-type doping source), the flow rate is 8 sccm, and a P-type high Al component AlGaAs with a Be doping concentration of about 1×10 18 cm -3 is formed. The thickness is 80 nm (error ±2 nm).

[0082] Lower spacer layer function: the lower spacer layer is located between the N-type DBR and the active region, and functions to isolate the active region from the N-type DBR, while assisting in light field confinement. The wide bandgap characteristics of the high Al component material can reduce the absorption of photons by the active region, and low P-type doping can reduce the non-radiative recombination of carriers in the spacer layer.

[0083] S14, active region (multiple quantum wells) growth;

[0084] Process step: using metal organic chemical vapor deposition (MOCVD), the growth temperature is reduced to 600°C (low temperature can inhibit In atom diffusion, ensuring quantum well interface flatness), and the pressure is reduced to 100 Torr (reducing gas phase reaction, improving layer thickness uniformity); trimethylindium (TMIn, In source), TMGa and AsH3 are introduced, and the In component is controlled to 0.15 (adjusted by TMIn / (TMIn plus TMGa) flow ratio), to form In 0.07 Ga 0.93 As (well layer) / , with a bandgap width corresponding to 850 nm wavelength; then TMIn is turned off, and only TMGa and AsH3 are introduced, to form Al 0.3 Ga 0.7 As (barrier layer); 4±1 periods of quantum wells (MQWs) are grown; the well layer thickness is 8±0.5 nm, and the In component is 7±0.3%; the barrier layer thickness is 20±1 nm, and the Al component is 30±0.5%.

[0085] Active region (multiple quantum wells) function: the active region is the core area of laser generation, composed of InGaAs quantum wells and GaAs barriers, and generates optical gain through carrier recombination. The well width and In component need to be strictly controlled to match the laser wavelength. The quantum confinement effect of quantum wells quantizes the carrier energy, and only photons of a specific energy (corresponding to 850 nm) can be amplified; thin well width (8 nm) can enhance quantum confinement and improve the gain coefficient.

[0086] S15, upper isolation layer growth;

[0087] Process step: using metal organic chemical vapor deposition (MOCVD), the growth temperature is raised to 680°C, the pressure is 200 Torr; TMAl, TMGa and AsH3 are input, the TMAl / TMGa flow ratio is set to 3:7, Al 0.3 Ga 0.7 As (low Al component, reducing absorption of photons) is formed; DEBe (flow rate 8 sccm) is input, the Be doping concentration is about 1×10 18 cm -3 (P type); 80 nm (error ±2 nm) is grown, which is symmetrical with the lower isolation layer, to ensure that the light field is symmetrically distributed in the active region.

[0088] Upper isolation layer function: the upper isolation layer is located between the active region and the P type DBR, which functions to isolate the active region and the P type DBR, and reduce non-radiative recombination of holes in the DBR. The refractive index of the low Al component material is closer to the active region InGaAs, which can reduce interface reflection loss and improve the overlap of the light field and the active region.

[0089] S16, P type DBR growth;

[0090] Process step: using metal organic chemical vapor deposition (MOCVD), the growth temperature is 700°C (consistent with the N type DBR growth), the pressure is 200 Torr; DEBe (flow rate 10 sccm) is input, to form a P type layer with a Be doping concentration of about 5×10 17 ±10%cm -3 (P type layer with high doping ensures efficient transmission of holes). Al 0.93 Ga 0.07 As (high Al layer) / Al 0.15 Ga 0.85 As (low Al layer) is alternately grown, 24±1 pairs of periods are grown, and the total thickness of each pair is =λ / 4; the Be doping concentration is 5×10 17 ±10%cm -3 P type DBR layer.

[0091] Function: the P type DBR and the N type DBR structure are symmetrical, and together form a vertical resonant cavity. The high reflectivity of the P type DBR and the N type DBR (total >99.9%) forms a closed resonant cavity, so that the photons are reflected back and forth in the active region, continuously obtaining gain until forming a laser.

[0092] S17, P type contact layer growth;

[0093] Process steps: Metal-organic chemical vapor deposition (MOCVD) was used at a growth temperature of 650℃ and a pressure of 200 Torr, with only TMGa and AsH3 introduced to form GaAs; the Be doping concentration was approximately 1×10⁻⁶. 19 ±10%cm -3 Heavy doping of P + Layer; thickness approximately 200±5nm.

[0094] Function of P-type contact layer: Heavily doped P + The layer can eliminate the Schottky barrier at the metal-semiconductor contact, forming a low-resistance ohmic contact (contact resistance < 1 × 10⁻⁶). -4 Ω·cm 2 ).

[0095] S2, preparation of carbon substitution modulation structure layer;

[0096] The specific technical solution is as follows:

[0097] S21. Pre-treatment: Ultra-high cleanliness substrate pretreatment (inhibiting carbon cluster nucleation sites).

[0098] Process steps:

[0099] S211. Using a two-step method of "diamond grinding (0.1um) followed by colloidal silica polishing", P + The surface roughness of the contact layer (GaAs, 200nm) is controlled to Ra≤0.3nm, and AFM full-sheet scanning (5×5um² area) is used to ensure that there are no protrusions ≥1nm (to avoid becoming the nucleation center of carbon clusters).

[0100] S212, Deep Cleaning: Organic Cleaning: Acetone (99.9%) ultrasonic (300W, 10 minutes), followed by isopropanol ultrasonic cleaning (same power, 10 minutes) (extend the time to remove micron-sized organic residues).

[0101] S213, Oxide layer removal: Soak in diluted HF (1:100, concentration 0.4%) for 5 minutes (low concentration, slow corrosion, avoid surface damage), then rinse 5 times with DIW.

[0102] S214. Ultimate removal of carbon pollution: O2 / Ar plasma ashing (power 200W, O2:Ar=1:1, flow rate 100sccm, 5 minutes), surface carbon content detected by XPS is ≤0.05% (conventional solution is 0.1%).

[0103] Action and principle: nucleation of carbon clusters depends on "surface defects or impurity sites", an ultra-smooth surface with Ra≤0.3nm can reduce 90% of nucleation centers; residual carbon impurities (such as surface adsorbed CO2) will combine with C atoms decomposed from CCl4 to form clusters, deep cleaning will reduce the cluster density from 1×10 6 cm -2 to 1×10 4 cm -2 .

[0104] S22, carbon replacement modulation structure layer preparation.

[0105] Medium mask preparation process steps:

[0106] S221, PECVD deposition of 200nm SiN X (50nm thicker than conventional, too thin to be easily etched by epitaxial gas, too thick to cause stress concentration at the window edge), parameters: SiH4 / NH3=1:6, temperature 350℃ (higher temperature to improve film density), stress control ≤8MPa (to avoid cracking when high temperature epitaxial).

[0107] S222, dry etching (power 120W, 10mTorr), photolithography and dry etching define a 3-4um diameter circular window (fully matched with the high intensity area of the Gaussian distribution of the light field, lateral accuracy ±0.1um, no lateral expansion problem of zinc diffusion); after etching, soak in BOE (buffered oxide etching liquid) for 10 seconds to remove SiN X residue at the window edge (to ensure complete exposure of the GaAs surface and avoid carbon doping shadow effect).

[0108] Action and principle: subsequent carbon-doped epitaxial temperature up to 600℃, thickening SiN X mask can enhance the high temperature resistance, avoid mask shrinkage at high temperature leading to window deformation (diameter deviation ≤0.1um); window edge residue will block the diffusion of C atoms, resulting in a 20% decrease in local doping concentration, BOE treatment can ensure the uniformity of edge doping.

[0109] Carbon-doped selective epitaxial growth (MOCVD parameter optimization).

[0110] Process steps:

[0111] S223, using metal organic chemical vapor deposition (MOCVD), growth temperature: 600°C (±1°C) (high temperature promotes the diffusion of C atoms in the GaAs lattice, reduces local enrichment (cluster density is reduced by 50%), but not more than 610°C (to avoid GaAs decomposition)). Growth pressure: 200 mTorr (±10 mTorr) (high pressure prolongs the residence time of gas phase precursors in the reaction chamber (from 0.5 s to 1 s), making the distribution of C atoms more uniform (in-die doping uniformity ≤7%)). V / III ratio (As / Ga): 60 (±2) (high As atmosphere can inhibit Ga atom surface migration, reduce "Ga vacancies" (C atoms are prone to occupy Ga vacancies to form clusters), and reduce cluster size from 5 nm to below 2 nm). Doping source flow: CCl4 (CCl4 is decomposed into CCl2 + and Cl - , CCl2 + provides C atoms). Corresponding doping concentration 5×10 18 -8×10 18 cm -3 , avoid exceeding the solid solubility. Growth thickness: 350-550 nm (±5 nm) (increase 50 nm redundancy: carbon substitution modulation structure layer resistivity is slightly higher (1.5×10 -3 Ω·cm), thickening compensates for resistance loss);

[0112] Real-time monitoring:

[0113] 1, in-situ infrared spectrum (IR) monitoring: 1500 cm -1 C-C bond characteristic peak intensity (threshold value: ≤0.1 a.u., exceed immediately reduce CCl4 flow);

[0114] 2, laser interferometer thickness measurement: ensure thickness deviation ≤5 nm (avoid resistance difference caused by uneven thickness).

[0115] Action and principle: C atoms form acceptor levels (ionization energy 26 meV) by "replacing Ga sites", providing hole conduction, replacement rate ≥90% at 600°C (higher than 70% at low temperature); The synergistic effect of high V / III ratio and high temperature - As atoms occupy surface adsorption sites, reducing C atom clustering, while high temperature promotes C atom migration in the lattice, dispersing local high concentration areas; The solid solubility limit of carbon results in a lower doping concentration than Zn, and the resistivity is slightly higher. By increasing the thickness by 50 nm (resistance is proportional to thickness), the total resistance remains consistent, and the bandwidth is not affected.

[0116] S23, post-processing optimization (for defect control of carbon substitution modulation structure layer);

[0117] Low-temperature annealing to eliminate shallow level defects, process steps:

[0118] S231, Rapid thermal annealing (RTA) under N2 atmosphere, temperature 400℃, time 30s (ramp rate 50℃ / s).

[0119] Action and principle: There may be a small amount of "C interstitial atoms" (shallow level defects, leading to carrier traps) in the carbon substitution modulation structure layer. Annealing at 400℃ can promote the migration of interstitial C to Ga vacancies (substitution sites), and the activation rate increases from 90% to 95%.

[0120] Epitaxial layer edge flattening etching process steps:

[0121] S232, Dry etching with Cl2 / BCl3 mixed gas (volume ratio 3:1), etching power 50W, pressure 10mTorr, flow rate 30sccm, etching depth 5-10nm (monitored by a step meter), removing the small protrusions (height ≤10nm) at the edge of the SEG epitaxial layer window, making the epitaxial layer surface flat with the SiN X mask surface flush (step height ≤5nm).

[0122] Action and principle: During SEG growth, small protrusions (height 5-10nm) may form at the edge of the window due to "vapor phase supersaturation". If not treated, it will cause "edge electrode over-thickness" during subsequent electrode evaporation (current concentrated at the edge), causing local carrier accumulation. By slight dry etching (only 5-10nm is removed), a "stepless" surface can be achieved, ensuring uniform electrode contact (current density deviation ≤5%).

[0123] Design principle of carbon substitution modulation structure layer: Selective epitaxial growth with carbon substitution doping, through "physical mask definition of epitaxial area and precise lattice occupation of carbon atoms", realizing current limitation, SHB suppression and single-mode output three major core functions. The following is a detailed design principle explanation:

[0124] This patent scheme forms a double current limitation through the nesting and synergy of "SEG carbon doped aperture and oxidation aperture":

[0125] First-order current limiting: SEG carbon doped aperture (Wc=3-4um): through SiN X mask lithography and etching 3-4um circular window, only carbon doped GaAs epitaxial layer (low resistance area, 1.2×10 -3 -1.5×10 -3 Ω·cm) is grown in the window, and SiN X covered high resistance area (resistivity ≥1×10 3 Ω·cm) outside the window, the current is preliminarily limited in the 3-4um carbon substitution modulation structure layer;

[0126] Secondary current limiting: Oxidation aperture (Wo=6-7um): After the growth of the carbon substitution modulation structure layer, the underlying AlGaAs layer (such as Al 0.98 Ga 0.02 As) is subjected to wet oxygen oxidation to form an oxidation aperture of 6-7um (Al2O3 insulating region) - the oxidation aperture covers the carbon-doped aperture (3-4um), further limiting the injected current;

[0127] Limiting current precision advantage: The carbon-doped aperture is determined by the precision of photolithography (±0.1um), and the oxidation aperture achieves a precision of ±0.2um by controlling the oxidation time (such as 30min), and the nesting deviation of the two is ≤0.3um, making the current limiting more precise.

[0128] Inhibition of spatial hole burning effect (SHB):

[0129] Precise matching of current injection and light field: The light field of the VCSEL active region is Gaussian distributed, with 80% of the light intensity concentrated in the central region of 3-4um (within the oxidation aperture of 6-7um), with high central photon density (fast carrier consumption) and low edge (slow carrier consumption); The SEG carbon-doped aperture (3-4um) is directly aligned with the central region of the light field, and the current is only injected into the central region where the carrier consumption is the fastest, and the carrier concentration uniformity of the carbon substitution modulation structure layer is ≤7%, and the current is uniformly distributed in the central region - avoiding the problem of "current injection area large leading to edge carrier accumulation" in traditional schemes, and the carrier injection rate is completely matched with the central photon consumption rate; The low-frequency roll-off (≤1GHz) caused by SHB is due to the "supplementary delay" after the central carrier is depleted, and the scheme has a current-light field matching degree ≥95%, the modulation response flatness in the low-frequency band is improved by 15%, and the RIN is stabilized at -149dB / Hz.

[0130] Flattening of light field distribution: The synergistic effect of the oxidation aperture (6-7um) and the carbon-doped aperture (3-4um) makes the light field distribution more flat. The oxidation aperture of 6-7um limits the light field within the oxidation aperture by refractive index difference (Al2O3 refractive index 1.7, GaAs refractive index 3.6), avoiding light field leakage to the edge; The carbon substitution modulation structure layer (high carrier concentration) of 3-4um slightly absorbs the light field, which can weaken the local high intensity of the light field in the center, making the gradient of the light field intensity from the center to the edge decrease from 20% to 10%, and the photon density difference decreases - the carrier consumption is more uniform, and there is no local "burning hole", providing support for a wide bandwidth of more than 30GHz.

[0131] Double-aperture light field synergistic reduction, mode selection more stable, single-mode output is realized:

[0132] The scheme realizes more stable single-mode output by "preliminary restriction of oxidation aperture and further reduction of carbon-doped aperture": precise control of the lateral size of the optical field, primary optical field restriction: oxidation aperture (6-7 um): the oxidation aperture limits the optical field in the range of 6-7 um through total reflection, preliminarily suppressing large-size high-order modes (such as TEM 20 , TEM 11 ); secondary optical field reduction: carbon-doped aperture (3-4 um): the high carrier concentration of the carbon substitution modulation structure layer has a "mode filtering" effect on the optical field - only the fundamental mode (TEM 00 ) can stably transmit in the narrow channel of 3-4 um, and high-order modes (such as TEM 01 , TEM 10 ) will be absorbed or leaked by the carbon substitution modulation structure layer (high-order mode loss ≥ 20 dB / cm, fundamental mode loss ≤ 5 dB / cm); when the lateral size of the optical field (3-4 um) is 3.5-4.7 times the working wavelength (850 nm), the mode gain of the high-order mode is lower than the threshold gain (fundamental mode gain ≥ 15 dB, high-order mode gain ≤ 8 dB), and only the fundamental mode realizes resonant output.

[0133] Single-mode stability advantages:

[0134] No mode shift: the low diffusion characteristics of carbon ensure that the size of the carbon-doped aperture is stable for a long time (deviation ≤ 0.1 um after 1000 hours of work), and the optical field restriction does not shift; while the Zn diffusion scheme has a diffusion aperture shift ≥ 0.3 um due to Zn atom migration, and the single-mode characteristics deteriorate;

[0135] High SMSR output: the scheme stabilizes the fundamental mode suppression ratio at 38-40 dB through the cooperation of the double apertures, and the vertical divergence angle ≤ 14°, so that the single-mode output is more stable.

[0136] The remaining preparation procedures are the same as the traditional laser preparation process, and therefore are not described in detail.

[0137] S3, a layer of SiN X is grown by a plasma-enhanced chemical vapor deposition (PECVD) process, and a low-stress SiN X passivation protection film is covered on the surface of the device for passivation protection and optical regulation;

[0138] S4, the dielectric film above the current injection area in step 4 is removed by a dry etching process, and a P-type metal contact layer (seed gold) is prepared by magnetic sputtering (Sputtering);

[0139] S5, the etching of the oxidation trench is completed by dry etching, and then wet oxidation is used for oxidation, and the oxidation aperture size is controlled to be 6-7 um;

[0140] S6, using benzocyclobutene as a medium material to fill the positive and negative electrode regions of the chip, and reducing the parasitic parameters of the chip itself;

[0141] S7, using ALD process to passivate the chip device region, protect the internal structure of the chip, and improve the reliability of the chip;

[0142] S8, using evaporation process to grow the front N-type electrode;

[0143] S9, grinding and thinning;

[0144] S10, RTA treatment (annealing).

[0145] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, therefore: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A vertical-cavity surface-emitting semiconductor laser, comprising, from bottom to top, a substrate (1), an N-type DBR layer (2), an active region (3), an oxide layer (4), a P-type DBR layer (5), a P-contact layer (6), and a P-metal layer (7), wherein oxide holes (8) are formed on the oxide layer (4), characterized in that: The P contact layer (6) is provided with a carbon substitution modulation structure layer (9). The lower end of the carbon substitution modulation structure layer (9) is located in the P-type DBR layer (5). The carbon substitution modulation structure layer (9) is directly opposite the oxide hole (8). The material of the carbon substitution modulation structure layer (9) is GaAs doped with carbon atoms. The diameter of the carbon substitution modulation structure layer (9) is smaller than the pore size of the oxide hole (8).

2. A vertical-cavity surface-emitting semiconductor laser according to claim 1, characterized in that: The carbon atom concentration in the carbon substitution modulation structure layer (9) is 1×10¹ 9 -1×10 20 cm⁻³.

3. A method for manufacturing a vertical-cavity surface-emitting semiconductor laser, characterized in that: The method for fabricating a vertical-cavity surface-emitting semiconductor laser as described in any one of claims 1-2 includes the following steps: S1. Epitaxial growth: An epitaxial layer is grown on the substrate. The epitaxial layer includes an N-type DBR layer, an active region, an oxide layer, a P-type DBR layer, a P-contact layer, and a P-metal layer. S2, Preparation of carbon substitution modulation structure layer; S2 Includes the following steps, S221, Deposit a SiN layer on the P contact layer. X , S222, Photolithography plus dry etching in SiN X A circular window matching the high-intensity region of the Gaussian distribution of the light field is etched out at the center; S223. Carbon atom doping is performed using MOCVD, with CCl4 as the dopant source to provide carbon atoms for growth within the circular window of the P contact layer, forming a carbon substitution modulation structure layer.

4. The method for manufacturing a vertical-cavity surface-emitting semiconductor laser according to claim 3, characterized in that: In S223, the growth temperature is 600-610℃; the growth pressure is 200 mTorr; and the As / Ga ratio is 60.

5. The method for manufacturing a vertical-cavity surface-emitting semiconductor laser according to claim 3, characterized in that: S2 also includes the steps preceding S221. S211. A two-step method of diamond grinding and colloidal silica polishing is adopted to control the surface roughness of the p contact layer to Ra≤0.3nm. AFM full-wafer scanning is used to ensure that the protrusions in the 5×5um² area are ≤1nm. S212. Clean with acetone and isopropanol for 10 minutes each. S213. Soak in diluted HF for 5 minutes, then rinse with DIW. S214. Ashing was performed using O2 / Ar plasma, and the surface carbon content was determined by XPS to be ≤0.05%.

6. The method for manufacturing a vertical-cavity surface-emitting semiconductor laser according to claim 3, characterized in that: During the S223 process, the intensity of the C-C bond characteristic peaks was monitored in real time using in-situ infrared spectroscopy.

7. The method for manufacturing a vertical-cavity surface-emitting semiconductor laser according to claim 3, characterized in that: It also includes the steps following S223. S231. Rapid thermal annealing in a N2 atmosphere at 400°C for 30 seconds; S232. Dry etching is performed using a Cl2 / BCl3 mixed gas to remove the 5-10nm high protrusions at the edge of the SEG epitaxial layer window, making the epitaxial layer surface flush with the SiN. X The mask surface is flush.

8. A method for manufacturing a vertical-cavity surface-emitting semiconductor laser according to claim 3, characterized in that: In step S222, after etching out the circular window, it is immersed in BOE to remove the SiN at the edge of the circular window. X Residue.

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