Fabrication and characterization of 785 nm laser grown by metalorganic chemical vapor deposition
Mähönen, Mika (2023)
Mähönen, Mika
2023
Teknis-luonnontieteellinen DI-ohjelma - Master's Programme in Science and Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-05-24
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202304264585
https://urn.fi/URN:NBN:fi:tuni-202304264585
Tiivistelmä
Due to their compact size, power efficiency, and low price semiconductor lasers are applied in many fields ranging from optical communication to different sensing applications. Moreover, they have enabled the development of modern consumer electronics.
Lasers operating in the spectral range of 760-790 nm can be utilized in biomedical to quantum computing applications. Semiconductor lasers are a good candidates to replace the more complex laser systems already used in the fields. The goal of this thesis was to fabricate a 785 nm wavelength broad area laser using metalorganic chemical vapor deposition and investigate how quantum well thickness and undoped region width affect the laser performance. The laser structure was calibrated using in-situ metrology, X-ray diffraction, electrochemical-capacitance voltage and photoluminescence measurement.
The AlGaAs layers were measured using X-ray diffraction and the Al-compositions were determined by fitting the recorded X-ray rocking curves to simulations. The Al-compositions were found to linearly follow the nominal compositions. Furthermore, X-ray diffraction mapping over a 4’’ wafer shows good uniformity and there was no measurable shift in the layer compositions (±0.1%). Photoluminescence measurements were used to adjust the GaAsxP1−x quantum well thicknesses and compositions. Additionally, the effect of growth temperature for enhancing the phosphine pyrolysis was studied using photoluminescence measurements. Different doping levels were calibrated using electrochemical capacitance-voltage depth profiling. The attained AlGaAs doping levels with SiH4 ranged from 4 × 10^17 to 5 × 10^18, and similarly from 5 × 10^17 to 1 × 10^20 with CBr4.
After the completed calibrations, two laser structures were grown. Version A had a thicker quantum well than version B. Additionally, laser version B had 250 nm undoped regions around the quantum well, while in laser version A the doping started from the active region. The laser performance was evaluated using uncoated and coated devices at three different cavity lengths. For version A, the 1 mm device had an output power of 0.69 W at 1.5 A, threshold current of 310 mA, and a slope was 0.57 W/A. The 1 mm device from the version B had an output power of 0.63 W at 1.5 A, the threshold current of 327 mA, and the slope was 0.53 W/A. In all merit - threshold current, slope, and operation voltage - version A showed a better performance than version B. These results can be attributed to higher carrier confinement and strain of version A quantum well and shorter undoped layer in the active region. Both devices performed well in the lifetime tests and did not show significant degradation after 1,300 h at 1.5 and 1.9 A currents confirming the high epitaxial quality of lasers. Moreover, the performance of both lasers (version A and B) were in the same level as in the scientific publications and commercially available devices.
Lasers operating in the spectral range of 760-790 nm can be utilized in biomedical to quantum computing applications. Semiconductor lasers are a good candidates to replace the more complex laser systems already used in the fields. The goal of this thesis was to fabricate a 785 nm wavelength broad area laser using metalorganic chemical vapor deposition and investigate how quantum well thickness and undoped region width affect the laser performance. The laser structure was calibrated using in-situ metrology, X-ray diffraction, electrochemical-capacitance voltage and photoluminescence measurement.
The AlGaAs layers were measured using X-ray diffraction and the Al-compositions were determined by fitting the recorded X-ray rocking curves to simulations. The Al-compositions were found to linearly follow the nominal compositions. Furthermore, X-ray diffraction mapping over a 4’’ wafer shows good uniformity and there was no measurable shift in the layer compositions (±0.1%). Photoluminescence measurements were used to adjust the GaAsxP1−x quantum well thicknesses and compositions. Additionally, the effect of growth temperature for enhancing the phosphine pyrolysis was studied using photoluminescence measurements. Different doping levels were calibrated using electrochemical capacitance-voltage depth profiling. The attained AlGaAs doping levels with SiH4 ranged from 4 × 10^17 to 5 × 10^18, and similarly from 5 × 10^17 to 1 × 10^20 with CBr4.
After the completed calibrations, two laser structures were grown. Version A had a thicker quantum well than version B. Additionally, laser version B had 250 nm undoped regions around the quantum well, while in laser version A the doping started from the active region. The laser performance was evaluated using uncoated and coated devices at three different cavity lengths. For version A, the 1 mm device had an output power of 0.69 W at 1.5 A, threshold current of 310 mA, and a slope was 0.57 W/A. The 1 mm device from the version B had an output power of 0.63 W at 1.5 A, the threshold current of 327 mA, and the slope was 0.53 W/A. In all merit - threshold current, slope, and operation voltage - version A showed a better performance than version B. These results can be attributed to higher carrier confinement and strain of version A quantum well and shorter undoped layer in the active region. Both devices performed well in the lifetime tests and did not show significant degradation after 1,300 h at 1.5 and 1.9 A currents confirming the high epitaxial quality of lasers. Moreover, the performance of both lasers (version A and B) were in the same level as in the scientific publications and commercially available devices.