A design method to improve the reliability of semiconductor lasers
By optimizing the epitaxial layer thickness design, the reliability and performance issues of uncooled semiconductor lasers in high-temperature environments were resolved, resulting in reduced junction temperature and improved optical confinement, thus meeting the requirements of high-speed communication.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2026-04-21
- Publication Date
- 2026-07-31
AI Technical Summary
Existing technologies struggle to effectively reconcile epitaxial layer thickness design in uncooled mode, leading to junction temperature rise, power degradation, wavelength drift, and reliability issues in uncooled semiconductor lasers under high-temperature environments, thus failing to meet the requirements of high-speed communication and high reliability.
By comprehensively considering factors such as reducing junction temperature, ensuring optical confinement, and temperature characteristics, the epitaxial layer thickness design of semiconductor lasers is optimized. This includes reducing series resistance and thermal resistance, setting a minimum lateral optical confinement factor, and adjusting the waveguide layer thickness according to the zero-temperature drift characteristic current point to ensure that the operating point is in the high-current region.
It effectively reduces junction temperature, improves the optical confinement and temperature stability of the device, enhances the reliability and performance of the device in high-temperature environments, and meets the needs of high-speed communication.
Smart Images
Figure CN122490773A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor optoelectronics, and specifically relates to the design of epitaxial layer thickness suitable for improving the reliability of uncooled semiconductor lasers operating in high-temperature environments, belonging to the field of semiconductor laser structure design. Background Technology
[0002] Driven by the explosive growth of AI computing power and the high-speed interconnection of data centers, optical communication networks are evolving towards faster speeds, lower power consumption, and smaller size. Traditional laser solutions that rely on thermoelectric coolers (TECs) for active temperature control are struggling to meet the integration requirements of new architectures such as co-packaged optoelectronic (CPO) and pluggable optical modules due to bottlenecks such as large size, high power consumption, and numerous vulnerable components. Against this backdrop, uncooled lasers, with their core advantages of eliminating TECs, simplifying system thermal management, significantly reducing power consumption, and shrinking package size, are becoming the mainstream choice for scenarios such as data centers and 5G fronthaul.
[0003] Uncooled lasers lack active temperature control compensation, facing reliability challenges such as junction temperature rise, power degradation, wavelength drift, and catastrophic damage, directly hindering their large-scale application in high-reliability data center scenarios. Improving the temperature performance and reliability of uncooled lasers has become a key issue in the field of optical communication.
[0004] Epitaxial layer thickness is one of the key parameters determining the performance and reliability of uncooled semiconductor lasers, and existing technologies suffer from irreconcilable design contradictions:
[0005] An excessively thick waveguide layer increases the carrier transport distance, leading to a decrease in series resistance R. s Increase, Joule heat loss I 2 R s The thermal conductivity of the waveguide layer is significantly increased; at the same time, the thermal conductivity of the waveguide layer is much lower than that of the cladding layer, and an excessively thick waveguide layer will significantly increase the thermal resistance R of the device. th The formula for the junction temperature of a semiconductor laser is:
[0006]
[0007] Where T j T is the internal junction temperature of a semiconductor laser. case For the external casing temperature of the semiconductor laser; I op This represents the laser's operating current. As can be seen from the formula, the internal junction temperature is determined by the external case temperature T. case With operating current I op In the equivalent series resistance R s The Joule heat generated on the surface together determine that the combined increase in series resistance and thermal resistance will lead to a sharp rise in junction temperature, which will seriously degrade the performance of the uncooled device and its lifespan.
[0008] Furthermore, if the waveguide layer is too thick, it will excite higher-order modes, causing the laser spectrum to broaden and the mode to become unstable, which will not meet the requirements of high-speed communication.
[0009] Thin waveguide layers can lead to deterioration of optical confinement and mode distribution in semiconductor lasers: 1. The optical confinement factor Γ in the vertical direction is too low, and the optical field cannot be effectively confined in the active region, resulting in a large area of light leakage into the cladding; 2. Thin waveguides cause the optical field to spread in the vertical direction, which leads to an increase in the beam divergence angle, which is extremely detrimental to high-speed communication and focusing applications; 3. Due to the weak optical field confinement, the laser cavity is very sensitive to small changes in refractive index, which may lead to mode jumps or instabilities.
[0010] Thinning the waveguide layer can also lead to a sharp increase in the threshold current of the semiconductor laser and a decrease in device efficiency: 1. The decrease in optical confinement factor directly results in insufficient optical gain to overcome intracavity losses, and the threshold current density may increase by an order of magnitude; 2. Due to mode leakage to the high-absorption cladding, the laser efficiency decreases significantly, and the differential quantum efficiency deteriorates; 3. Optical field leakage to the doped cladding or absorption layer (such as a P-type waveguide layer) will increase free carrier absorption loss, thereby increasing the internal loss of the laser.
[0011] Most existing technologies rely on experience to design epitaxial layer thickness, lacking precise indicators related to epitaxial layer thickness design that are beneficial to improving laser reliability. Inappropriate epitaxial layer thickness design can seriously affect the reliability of uncooled semiconductor lasers, causing the devices to fail to meet the requirements for high-temperature uncooled operation. Summary of the Invention
[0012] To address the reliability issues of uncooled semiconductor lasers in high-temperature environments, this invention provides a semiconductor laser epitaxial layer thickness design method that comprehensively considers three aspects: reducing the internal junction temperature of the semiconductor laser, ensuring the optical confinement requirements of the device, and improving the temperature characteristics of the device.
[0013] The technical solution of the present invention is as follows:
[0014] A design method for improving the reliability of semiconductor lasers is proposed, which comprehensively considers three aspects: reducing the internal junction temperature of the semiconductor laser, ensuring the optical confinement requirements of the device, and improving the temperature characteristics of the device, to obtain a reasonable range for the design of the epitaxial layer thickness of the laser.
[0015] According to a preferred embodiment of the present invention, the design method for improving the reliability of a semiconductor laser includes the following specific steps:
[0016] The following methods can be used to improve the reliability of uncooled semiconductor lasers by reducing the junction temperature of the device:
[0017] According to the requirements, in order to improve the reliability of uncooled semiconductor lasers and reduce the negative impact of internal junction temperature on laser reliability, the series resistance R of the laser can be reduced. s With thermal resistance R th accomplish.
[0018] The formula for the series resistance of a semiconductor laser is:
[0019]
[0020] Where d i ρ is the thickness of the i-th layer in the epitaxial layer of the semiconductor laser. i Then it is the resistivity of the i-th layer.
[0021] The formula for the thermal resistance of a semiconductor laser is:
[0022]
[0023] Where d is the thickness of the epitaxial layer, k is the thermal conductivity of the layer, and A is the cross-sectional area of the layer.
[0024] The series resistance R of a semiconductor laser can be seen from the formulas for series resistance and thermal resistance. s Thermal resistance R th The thickness d of the epitaxial layer is directly proportional to the thickness of the epitaxial layer. In order to reduce the series resistance and thermal resistance of the device and reduce the impact of the internal junction temperature of the device on the reliability of the laser, the thickness d of the epitaxial layer of the semiconductor laser can be reduced.
[0025] However, the thickness d of the waveguide layer cannot be reduced indefinitely. If the waveguide layer is too thin, it will also have many adverse effects on the reliability of the device.
[0026] This invention sets a minimum value for the waveguide layer thickness from the perspective of the lateral light confinement factor of a semiconductor laser.
[0027] The transverse optical confinement factor of a semiconductor laser can be expressed as:
[0028]
[0029] Where D 2 Let be the normalized waveguide layer thickness, and:
[0030]
[0031] Where n a Let n be the refractive index of the active region. cl λ is the cladding refractive index, and λ is the laser lasing wavelength.
[0032] Conclusion:
[0033]
[0034] Conclusion:
[0035]
[0036] According to the requirements of the corresponding type of uncooled semiconductor laser, a minimum value of the transverse light confinement factor is set for the laser. Substituting this value into the formula in
[0026] will yield the minimum waveguide layer thickness that meets the transverse light confinement factor requirement.
[0037] The following methods can be used to improve the temperature characteristics of uncooled semiconductor lasers based on the zero-temperature-drift characteristic current design:
[0038] Zero temperature drift characteristic current (I ZTC : The intersection of the VI curves of a semiconductor laser at different temperatures.
[0039] The effect of temperature on the current-voltage characteristics of semiconductor lasers is influenced by two core mechanisms:
[0040] 1. According to Varshni's empirical formula, as temperature increases, the bandgap E of a semiconductor increases. g It will become narrower. This means that, at the same current density, a higher-temperature laser requires a lower voltage.
[0041] 2. Increased temperature leads to increased lattice vibrations (phonon scattering), thereby reducing the mobility μ of charge carriers (electrons and holes). This results in an increase in the resistivity ρ of epitaxial layers (especially heavily doped waveguide and confinement layers). At higher currents, the voltage drop across these resistors... It becomes dominant. At this point, high temperature will cause the pressure drop to increase.
[0042] Because the two trends described in
[0031] and
[0032] are opposite, the two VI curves of the semiconductor laser at different temperatures "chase each other" at a specific current density, thus intersecting. This specific current is defined as the zero-temperature-drift characteristic current (I0). ZTC ).
[0043] Low current region: Increased temperature leads to a decrease in forward voltage drop, therefore the high-temperature curve is in the I region. ZTC The left side (low current region) is usually located above the low temperature curve.
[0044] High current region: Increased temperature leads to increased ohmic voltage drop, therefore the high temperature curve at I... ZTC The right side (high current region) is usually located below the low temperature curve.
[0045] I ZTCLeft side (low current region): If the operating current of an uncooled semiconductor laser is in this region, the current value corresponding to the high-temperature VI curve will be larger under the same applied voltage. At this point, the laser's current and temperature exhibit positive feedback, which can easily affect the reliability of the device.
[0046] I ZTC Right side (high current region): If the operating current of an uncooled semiconductor laser is in this region, under the same applied voltage, the current value corresponding to the low-temperature VI curve is larger. At this time, the laser current and temperature exhibit negative feedback.
[0047] Therefore, in order to reduce the adverse effects of temperature rise on the reliability of uncooled semiconductor lasers, it is necessary to reduce the zero-temperature drift characteristic current point I. ZTC It is positioned to the left of the laser's operating point, allowing the device to operate in the high-current region.
[0048] Given that the operating point of an uncooled semiconductor laser is known, the series resistance can be changed by modulating the waveguide layer thickness d, thereby controlling the position of the zero-temperature drift characteristic current point in the device's VI curve.
[0049] If the waveguide layer thickness d increases, the series resistance of the semiconductor laser increases, and the voltage drop caused by the resistance becomes dominant in the voltage across the device, shifting the zero-temperature drift characteristic current point to the left (I). ZTC (Become smaller).
[0050] If the waveguide layer thickness d decreases, the series resistance of the semiconductor laser decreases, and the voltage drop generated by the resistance becomes less dominant in the voltage across the device, shifting the zero-temperature drift characteristic current point to the right (I0). ZTC (Get bigger).
[0051] Therefore, in order to enable uncooled semiconductor lasers to operate in the high-current region, it is necessary to determine the device's operating point and IL. ZTC The thickness of the waveguide layer of the device should be increased appropriately according to its position.
[0052] In summary, to improve the reliability of uncooled semiconductor lasers in high-temperature environments, the waveguide layer thickness needs to be reduced to lower the junction temperature; conversely, the waveguide layer thickness needs to be appropriately increased to ensure the device's operating point is to the right of the zero-temperature drift characteristic current. Furthermore, a minimum waveguide layer thickness can be set based on the transverse light confinement factor requirements of the device structure. According to these rules, a range can be set for the waveguide layer thickness of uncooled semiconductor lasers to facilitate improved high-temperature performance. Attached Figure Description
[0053] Figure 1 This is a schematic diagram of the VI curves of a semiconductor laser at different temperatures. In the figure, I ZTC This is the zero-temperature drift characteristic current point.
[0054] Figure 2 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is A.
[0055] Figure 3 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is B.
[0056] Figure 4 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is C.
[0057] Figure 5 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is D.
[0058] Figure 6 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is E.
[0059] Figure 7 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is F.
[0060] Figure 8 This is a schematic diagram of the VI curve of a semiconductor laser with a waveguide layer thickness of G.
[0061] Figure 9 This is a schematic diagram of the VI curve of a semiconductor laser when the waveguide layer thickness is H. Detailed Implementation
[0062] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All embodiments based on the present invention should fall within the scope of protection of the present invention.
[0063] I. Premise:
[0064] (1) The research object of this invention is an uncooled semiconductor laser, and it is assumed that the operating point specified during the use of the device is Q.
[0065] (2) Adjust the thickness of the laser waveguide layer without changing the epitaxial material system and doping factors, and test the VI curves of lasers with different waveguide layer thicknesses at different temperatures.
[0066] (3) Among the different waveguide layer thicknesses (A~H) of the laser, A<B<C<D<E<F<G<H.
[0067] II. Experimental Procedure:
[0068] 1. Determine the appropriate waveguide layer thickness range based on the laser's lateral confinement factor:
[0069] Because the relationship between the laser waveguide layer thickness and the lateral light confinement factor is:
[0070]
[0071] Substituting the minimum optical confinement factor that satisfies the minimum optical confinement requirement for the corresponding type of laser yields the minimum laser waveguide layer thickness d that satisfies the optical confinement requirement. min '.
[0072] Right now:
[0073]
[0074] III. Determining the appropriate waveguide layer thickness range based on the impact of device junction temperature on laser reliability:
[0075] The relationship between laser junction temperature and other parameters:
[0076]
[0077] It can be seen that the junction temperature of the laser is determined by the series resistance R of the device. s Thermal resistance R th Decision. Due to the series resistance R s Thermal resistance R th The thickness d of the waveguide layer of the semiconductor laser is directly proportional to the thickness of the epitaxial layer. From the perspective of the impact of the series resistance and thermal resistance of the device on the reliability of the laser, it is necessary to reduce the thickness d of the waveguide layer of the semiconductor laser.
[0078] IV. Determine the appropriate waveguide layer thickness range based on the relative position of the zero-temperature-drift characteristic current point and the operating point Q:
[0079] The VI curves of lasers with different waveguide layer thicknesses were tested at different temperatures.
[0080] Test Results: Among the test results of lasers with different thicknesses A to H, the zero-temperature drift characteristic current I of devices with waveguide layer thicknesses A to D is... ZTC > Current value corresponding to the device operating point Q; Temperature drift characteristic current I of devices with four waveguide layer thicknesses from E to H ZTC < The current value corresponding to the device's operating point Q.
[0081] To prevent positive feedback between laser current and temperature, the device needs to operate at the I specified in
[0038] . ZTC Right side (high current region).
[0082] That is, the current value corresponding to the laser's operating point Q needs to be ≥ I. ZTC .
[0083] Therefore, considering the zero-temperature drift characteristic current, in order to improve the reliability of uncooled semiconductor lasers, the waveguide layer thickness of the device needs to be ≥E.
[0084] Compare waveguide layer thickness E and d min The larger value of ' is taken as the lower limit d for the waveguide layer thickness of the uncooled semiconductor laser. min .
[0085] Considering the above design factors, in order to improve the reliability of uncooled semiconductor lasers, the waveguide layer thickness of the device needs to be set to be equal to or slightly greater than d. min .
Claims
1. A design method for improving the reliability of semiconductor lasers, characterized in that... The design of semiconductor laser epitaxial layer structures, taking into account three aspects—reducing the internal junction temperature of the semiconductor laser, ensuring the optical confinement requirements of the device, and improving the temperature characteristics of the device—includes the following steps: Step 1: Calculate the minimum waveguide layer thickness d based on the minimum optical confinement factor required by the specific device structure. min '; Step 2: Simulate or measure the VI curves of uncooled semiconductor lasers with different waveguide layer thicknesses at different temperatures to obtain the minimum waveguide layer thickness that ensures the device operating point is ≥ zero temperature drift characteristic current point; Step 3: Compare the minimum waveguide layer thickness obtained under the two conditions in Step 1 and Step 2, and take the maximum value of the two as the ideal waveguide layer thickness of the uncooled semiconductor laser; set a lower limit value for the waveguide layer thickness of the device, and the waveguide layer thickness needs to be equal to or greater than the ideal waveguide layer thickness in the subsequent laser structure design.
2. The design method for improving the reliability of semiconductor lasers according to claim 1, characterized in that, The derivation steps for the relationship between the optical confinement factor and the waveguide layer thickness mentioned in step 1 are as follows: The transverse light confinement factor of a semiconductor laser is expressed as: ； Where D 2 Let be the normalized waveguide layer thickness, and: ； Where n a Let n be the refractive index of the active region. cl λ is the cladding refractive index, and λ is the laser lasing wavelength. Based on the above formula, we can deduce that: ； and then: ； Depending on the specific requirements of the uncooled semiconductor laser, a minimum lateral optical confinement factor is set for the laser. Substituting this value into the above formula yields the minimum waveguide layer thickness d that satisfies the lateral optical confinement factor requirement. min ',Right now: 。 3. The design method for improving the reliability of semiconductor lasers according to claim 1, characterized in that, The zero-temperature-drift characteristic current point mentioned in step 2 is the intersection of the device's VI curves at different temperatures. At this point, the device's electrical characteristics are unaffected by temperature changes. In the device's VI curve, the region where the current is below the zero-temperature-drift characteristic current is defined as the low-current region, and the region where the current is above the zero-temperature-drift characteristic current is defined as the high-current region. In the low-current region, the device's current and temperature rise exhibit positive feedback under the same applied voltage, which is detrimental to the device's reliable operation. In the high-current region, the device's current and temperature rise exhibit negative feedback under the same applied voltage, which is more conducive to the device's reliable operation. When designing the waveguide layer thickness, it is necessary to ensure that the laser operates in the high-current region, i.e., the device's operating current ≥ the zero-temperature-drift characteristic current. As the waveguide layer thickness increases, the proportion of the voltage drop caused by the laser's series resistance to the total voltage drop increases, and the zero-temperature-drift characteristic current shifts to the left. To ensure that the device operates in the high-current region, a minimum waveguide layer thickness needs to be determined.
4. The design method for improving the reliability of semiconductor lasers according to claim 3, characterized in that, To determine the requirement for the laser to operate in the high current region, it is necessary to simulate or test the VI curves of uncooled semiconductor lasers with different waveguide layer thicknesses at different temperatures, and obtain the minimum waveguide layer thickness that satisfies the requirement that the operating point current is ≥ zero temperature drift characteristic current.
5. The design method for improving the reliability of semiconductor lasers according to claim 1, characterized in that, Step 3, which comprehensively considers three aspects—reducing the internal junction temperature of the semiconductor laser, ensuring the optical confinement requirements of the device, and improving the temperature characteristics of the device—involves the following specific steps to obtain the ideal waveguide layer thickness for the uncooled semiconductor laser: (1) From the perspective of reducing the junction temperature inside the semiconductor laser; The formula for the junction temperature of a semiconductor laser is: ； Where T j T is the internal junction temperature of a semiconductor laser. case For the external casing temperature of the semiconductor laser; I op This represents the laser's operating current; as can be seen from the formula, the internal junction temperature is determined by the external case temperature T. case With operating current I op In the equivalent series resistance R s The Joule heat generated on the surface together determine that the combined increase in series resistance and thermal resistance will lead to a sharp rise in junction temperature, which will seriously degrade the uncooled operating performance and device lifespan. The formula for the series resistance of a semiconductor laser is: ； Where d i ρ is the thickness of the i-th layer in the epitaxial layer of the semiconductor laser. i Then it is the resistivity of the i-th layer; The formula for the thermal resistance of a semiconductor laser is: ； Where d is the thickness of the epitaxial layer, k is the thermal conductivity of the layer, and A is the cross-sectional area of the layer; (2) From the perspective of ensuring the optical confinement requirements of the device; To ensure that the laser is effectively confined in the active region, there exists a minimum value for the transverse light confinement factor, which determines the lower limit for waveguide layer thinning; (3) From the perspective of improving the thermal properties of the device; By testing the VI characteristics of devices with different waveguide layer thicknesses at different temperatures, the minimum waveguide layer thickness that meets the thermal characteristics requirements of the device is obtained based on the relative position of the zero-temperature drift characteristic current and the device operating point. (4) The ideal value of the waveguide layer thickness of the uncooled semiconductor laser can be obtained by taking into account the three aspects.