A small array structure of vertical cavity surface-emitting laser

Abstract

This invention discloses a small array structure for a vertical-cavity surface-emitting laser (VCSEL), comprising, from bottom to top, a negative electrode layer, an N-type GaAs substrate, a lower N-type diode-controlled laser (DBR), an active region layer, an electron blocking layer, an aperture oxide confinement layer, an upper P-type DBR, a small array structure, and a polymer lens layer. The active region layer includes two sets of chirped quantum wells, each with a narrow-domain steep-change SCH layer on both sides. The two sets of chirped quantum wells are connected by a tunnel junction to form a double-junction structure. The small array structure includes multiple independent small-aperture VCSEL units. This invention enhances thermal stability and expands the device's wide-temperature-range output capability through four sets of quantum wells; it significantly improves differential gain and optical gain bandwidth by cascading multiple quantum wells through the double-junction structure; it broadens the gain spectrum, enhances mode stability, and expands the gain control range through chirped quantum wells; and it achieves single-mode high-power output through the small array structure, resolving the performance contradiction between penetration and accuracy.

Description

Technical Field

[0001] This invention relates to the field of semiconductor laser technology, and more particularly to a small array structure for a vertical cavity surface-emitting laser. Background Technology

[0002] The 760nm wavelength is an important and relatively strong absorption line for oxygen molecules in the near-infrared band. This makes 760nm lasers the core light source for tunable diode laser absorption spectroscopy (TDLAS), currently the mainstream method for high-performance, high-precision, and fast-response gas concentration measurement. Compared to traditional oxygen sensors, which suffer from short lifespan, slow response, and susceptibility to interference, the inherent advantages of vertical-cavity surface-emitting lasers (VCSELs) perfectly meet the needs of TDLAS sensors. Today, 760nm VCSELs have become the preferred light source for high-performance, miniaturized, and low-power oxygen sensors, and are widely used in medical, industrial process control, environmental monitoring, automotive, and aerospace fields.

[0003] As oxygen sensors, the impact of temperature on VCSEL performance directly affects the breadth of their applications. Traditional oxygen sensors are extremely sensitive to temperature, making them unstable in environments with large temperature variations, such as automotive, outdoor, and industrial settings, or requiring expensive and bulky temperature control systems. Furthermore, when addressing industrial safety monitoring challenges, traditional oxygen sensors suffer from insufficient output power for long-range open-path monitoring, limiting their application scope. Summary of the Invention

[0004] The purpose of this invention is to provide a small array structure for a vertical cavity surface-emitting laser to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides a small array structure for a vertical cavity surface-emitting laser, comprising, from bottom to top, a negative electrode layer, an N-type GaAs substrate, a lower N-type DBR, an active region layer, an electron blocking layer, an aperture oxide confinement layer, an upper P-type DBR, a small array structure, and a polymer lens layer;

[0006] The active region layer includes two sets of chirped quantum wells, each set of chirped quantum wells has a narrow-domain steep-change SCH layer on both sides, and the two sets of chirped quantum wells are connected by a tunnel junction to form a double-junction structure.

[0007] The small array structure includes multiple independent small-aperture VCSEL units integrated on the same chip, and the oxide confinement holes on the aperture oxide confinement layer are adapted to the small-aperture VCSEL units.

[0008] Preferably, each group of chirped quantum wells includes multiple four-component material layers, each of which has a different material composition, and a barrier layer is disposed between two adjacent four-component material layers.

[0009] Preferably, the four-component material layer has four layers.

[0010] Preferably, the above-mentioned vertical cavity surface-emitting laser small array structure is applied to a 760nm vertical cavity surface-emitting laser, and the materials of the four component material layers are all In(1-xy)GaxAlyAs material, where x is 0.57-0.88 and y is 0.11-0.23.

[0011] Preferably, the four-component material layers in each group of chirped quantum wells are, from top to bottom, a first four-component material layer, a second four-component material layer, a third four-component material layer, and a fourth four-component material layer; wherein, the first four-component material layer is In0.13Ga0.69Al0.18As, the second four-component material layer is In0.14Ga0.67Al0.19As, the third four-component material layer is In0.15Ga0.65Al0.2As, and the fourth four-component material layer is In0.16Ga0.64Al0.21As.

[0012] Compared with the prior art, the present invention has the following advantages and technical effects:

[0013] The vertical-cavity surface-emitting laser (VCSEL) small array structure provided by this invention enhances thermal stability and expands the device's wide-temperature-range output capability through four-component quantum wells; it significantly improves differential gain and optical gain bandwidth by achieving multi-quantum-well cascading through a double-junction structure; it broadens the gain spectrum, enhances mode stability, and expands the gain control range through chirped quantum wells; it constructs a steep bandgap, strong local optical field, and a highly repulsive built-in electric field through narrow-domain steep-change SCH, effectively suppressing high-configuration carrier overflow; it reduces sensor size and adapts to complex environments by utilizing polymer lenses based on micron-level processes; and it achieves single-mode high-power output through the small array structure, resolving the performance contradiction between penetration and accuracy. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a cross-sectional view of the small array structure of the vertical cavity surface-emitting laser of the present invention;

[0016] Figure 2 This is a schematic diagram of the SCH of the present invention;

[0017] Figure 3 This is a schematic diagram of the small array structure of the present invention;

[0018] Figure 4 This is a schematic diagram of the double-junction structure of the present invention.

[0019] In the figure: 1. Negative electrode layer; 2. N-type GaAs substrate; 3. Lower N-type DBR; 4. Active region layer; 5. Electron blocking layer; 6. Aperture oxide confinement layer; 7. Upper P-type DBR; 8. Small array structure; 9. Polymer lens layer; 401. Narrow-domain steep-change SCH layer; 402. First layer four-component material; 403. Second layer four-component material; 404. Third layer four-component material; 405. Fourth layer four-component material; 406. Barrier layer; 407. Tunnel junction. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. The described embodiments are merely some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] like Figures 1 to 4 As shown, the present invention provides a small array structure for a vertical cavity surface-emitting laser, comprising, from bottom to top, a negative electrode layer 1, an N-type GaAs substrate 2, a lower N-type DBR 3, an active region layer 4, an electron blocking layer 5, an aperture oxide confinement layer 6, an upper P-type DBR 7, a small array structure 8, and a polymer lens layer 9.

[0022] The active region layer 4 includes two sets of chirped quantum wells. Narrow-domain steep-change SCH layers 401 are provided on both sides of the chirped quantum wells. The two sets of chirped quantum wells are connected by a tunnel junction 407 to form a double-junction structure.

[0023] The small array structure 8 includes multiple independent small-aperture VCSEL units integrated on the same chip, and the oxide confinement pores on the pore oxide confinement layer 6 are adapted to the small-aperture VCSEL units.

[0024] In a further optimized scheme, each group of chirped quantum wells includes multiple four-component material layers, each with a different material composition, and a barrier layer 406 is set between two adjacent four-component material layers.

[0025] The scheme was further optimized so that the number of material layers in the four-component system is four.

[0026] The vertical-cavity surface-emitting laser (VCSEL) array structure provided by this invention achieves advantages in thermal stability and high gain by using a four-component InAlGaAs quantum well material instead of the traditional three-component AlGaAs quantum well material, thereby changing the quantum well composition. The InAlGaAs quantum well, by introducing In elements to modulate the band structure, forms a deeper potential well, significantly improving the confinement of electrons and holes. This stronger quantum confinement reduces the escape of charge carriers at high temperatures, thereby reducing the sensitivity of the threshold current to temperature increases and improving the high-temperature stability of the device. Furthermore, the deeper potential well and optimized band structure reduce the Auger recombination probability, minimizing nonradiative recombination losses at high temperatures, thus maintaining high internal quantum efficiency and mitigating efficiency degradation with increasing temperature. Simultaneously, the flexible compositional adjustment capability of the quaternary material allows for strain engineering to optimize the mobility matching of electrons and holes, increasing the radiative recombination probability and further enhancing optical gain. Furthermore, chirped quantum wells are used in the quantum well structure. Through band gradient optimization, carrier dynamics optimization, and optical field manipulation, chirped quantum wells significantly outperform conventional quantum wells in terms of frequency chirp suppression, temperature stability, modulation bandwidth, and gain characteristics. Conventional quantum wells are prone to carrier leakage at high temperatures, leading to increased threshold current and decreased efficiency. Chirped quantum wells, through deep barrier design and band gradient, enhance carrier confinement and reduce leakage. In addition, conventional quantum wells have narrow gain spectra and poor symmetry, while chirped quantum wells form multi-peak or extended gain spectra through band gradients, supporting optical amplification over a wider wavelength range and facilitating gain spectrum flattening. Simultaneously, designing the quantum well as a double-junction structure, through multi-quantum-well gain superposition, oxidation confinement optimization, and gain-cavity mode mismatch design, achieves significantly better thermal stability and high gain than single-junction structures.

[0027] Furthermore, this invention optimizes the SCH layer design, using a narrow-domain steep-change SCH with a small thickness range, significant refractive index abrupt change, and highly concentrated light field. The refractive index of this narrow-domain steep-change SCH is 3.0-3.5, without a gradient layer, and it is connected to the low-refractive-index layer of the DBR. The thickness of the narrow-domain steep-change SCH is 10nm-15nm, resulting in a cavity length of 0.5 wavelengths. This effectively suppresses high-configuration carrier overflow and is more suitable for high-temperature, high-power operating scenarios compared to general SCH structures. For the light-emitting aperture design, a small array structure 8 is chosen. Compared to traditional single large-aperture structures, the small array structure 8 overcomes the contradiction between single-mode operation and high power. Single-mode operation requires a small aperture, but small apertures have low power handling capacity. While large apertures can increase power, they are prone to multimode operation. The small array densely integrates multiple independent small-aperture VCSEL units on the same chip, forming a parallel light-emitting array. This not only maintains single-mode operation but also doubles the total power. Therefore, the small array structure 8 for the light-emitting aperture has significant advantages in oxygen sensor applications. Meanwhile, this structure uses polymer lenses, which, compared with traditional glass / silicon lenses, have advantages such as low-cost mass production, millimeter-level integration, customized optical correction, and environmental weather resistance, which are beneficial for the miniaturization of oxygen sensors.

[0028] In summary, this invention improves the thermal stability of the laser by using four-component quantum wells, thereby reducing the impact of temperature on the device; it achieves multiple quantum well cascades through a double-junction structure, thus realizing gain superposition and significantly improving differential gain and optical gain bandwidth; it broadens the gain spectrum and enhances mode stability through chirped quantum wells, achieving greater gain flexibility; it achieves a steep band gradient, strong local optical field, and high-repulsion built-in electric field through narrow-domain steep transition (SCH), effectively suppressing high-configuration carrier overflow; it achieves micron-level fabrication through polymer lenses, reducing sensor size and adapting to complex environments; and it achieves single-mode, high-power light output through a small array structure, resolving the current contradiction between laser penetration and accuracy.

[0029] Example 1

[0030] This invention provides a novel method for fabricating a vertical-cavity surface-emitting laser, as follows:

[0031] Quantum wells (QWs) are grown using metal-organic chemical vapor deposition (MOCVD). During MOCVD growth, the In / Ga source gas flow rate is linearly varied to achieve a gradual bandgap and subband level broadening, resulting in component chirping. A gradient mask is fabricated using photolithography and reactive ion etching (RIE). Combined with selective growth in MOCVD, the quantum well thickness is gradually varied, and the coupling strength distribution between the optical field and charge carriers is controlled to achieve thickness chirping, thus realizing a four-component chirped quantum well. Furthermore, an ultrathin, heavily doped layer is grown using MOCVD. Heavy doping reduces tunneling resistance, ensuring efficient carrier tunneling. Simultaneously, the number, composition, and thickness of the quantum wells in the upper and lower active regions are strictly matched. Photoluminescence spectroscopy is used to calibrate the gain spectrum consistency of the two active regions, avoiding carrier distribution imbalance and achieving a double-junction structure. A narrow-domain confinement layer is grown using MOCVD to achieve efficient carrier confinement in the chirped quantum well (SCH). Furthermore, wet oxidation is used to form oxide-confined vias in each VCSEL cell to suppress higher-order modes and ensure single-mode output. The array is fabricated using photolithography and dicing, and a multi-channel driving ASIC chip is employed to independently control the injection current of each VCSEL cell, achieving power superposition. This structure solves the problem of traditional VCSEL performance being susceptible to temperature variations in applications, thus improving device reliability.

[0032] Example 2

[0033] The aforementioned vertical cavity surface-emitting laser (VCSEL) small array structure is applied to a 760nm VCSEL. The four material layers are all made of In(1-xy)GaxAlyAs material, where x is 0.57-0.88 and y is 0.11-0.23.

[0034] The four-component material layers within each chirped quantum well, from top to bottom, are: a first layer of four-component material 402, a second layer of four-component material 403, a third layer of four-component material 404, and a fourth layer of four-component material 405. Specifically, the first layer of four-component material 402 is In0.13Ga0.69Al0.18As, the second layer of four-component material 403 is In0.14Ga0.67Al0.19As, the third layer of four-component material 404 is In0.15Ga0.65Al0.2As, and the fourth layer of four-component material 405 is In0.16Ga0.64Al0.21As.

[0035] Because the gain medium redshifts with increasing temperature, and the cavity mode wavelength also drifts with temperature, it is necessary to introduce gain mode difference to optimize the temperature stability performance of the device. For example, in a 760nm laser, a 5-10nm offset can be introduced to fix the lasing wavelength. The bandgap of In(1-xy)GaxAlyAs is 1.643eV. When x is from 0.88-0.55 and y is from 0.11-0.24, the strain exceeds 1.5%. The maximum material gain and its corresponding optimal In(1-xy)GaxAlyAs composition are screened from the range of x and y.

[0036] Specifically, the In0.15Ga0.65Al0.2As strain is -1.09%, and the lasing wavelength is 755nm, which meets the quantum well design requirements of a 760nm laser and can provide high gain to achieve high power output.

[0037] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A small array structure for a vertical-cavity surface-emitting laser, applied to a 760nm vertical-cavity surface-emitting laser, characterized in that, It includes, from bottom to top, a negative electrode layer (1), an N-type GaAs substrate (2), a lower N-type DBR (3), an active region layer (4), an electron blocking layer (5), a pore size oxide confinement layer (6), an upper P-type DBR (7), a small array structure (8), and a polymer lens layer (9). The active region layer (4) includes two sets of chirped quantum wells. Each set of chirped quantum wells has a narrow-domain steep-change SCH layer (401) on both sides. The refractive index of the narrow-domain steep-change SCH layer (401) is 3.0-3.

5. No gradient layer is added. It is connected to the low refractive index layer of the DBR. The thickness of the narrow-domain steep-change SCH layer is 10nm-15nm. The two sets of chirped quantum wells are connected by a tunnel junction (407) to form a double junction structure. The small array structure (8) includes multiple independent small aperture VCSEL units integrated on the same chip, and the oxide confinement holes on the aperture oxide confinement layer (6) are adapted to the small aperture VCSEL units; Each set of chirped quantum wells includes multiple four-component material layers, each of which has a different material composition, and a barrier layer (406) is provided between two adjacent four-component material layers. The four-component material layer has four layers. The four-component material layers are all made of In(1-xy)GaxAlyAs material, where x is 0.57-0.88 and y is 0.11-0.23.

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