This work presents an in-depth investigationof the characteristics and challenges of visible InGaN laser diodes (LDs) equipped with top cladding constructed from graded AlGaN polarization-doped p-type layers. Our research demonstrates the successful achievement of highly efficient electrical conductivity within the p-type layers, along with a high slope efficiency of laser diodes reaching up to around 1.5 W/A.We attribute this value to the relatively low optical losses of 5–7 cm−1, resulting from both the optimized structural design and reduced overlap of Mg containing layers with optical mode. Furthermore, we provide compelling evidence indicating that the utilization of a single slope AlGaN profile yields enhanced electrical properties when compared to a multiple gradient approach. Our preliminary findings underscore the indispensability of thin layers of Mg-doped materials, serving as both the electron-blocking layer and the subcontact layer.
The names of the individual files correspond to the numbering of the figures in the paper Muhammed Aktas, Anna Kafar, Szymon Stanczyk, Łucja Marona, Dario Schiavon,Szymon Grzanka, Przemysław Wiśniewski, Piotr Perlin; Optimization of p-cladding layer utilizing polarization doping for Blue-Violet InGaN laser diodes - https://doi.org/10.1016/j.optlastec.2024.111144
Files included in this collection:
Fig. 1. (a) Scheme of the standard InGaN laser structure emitting visible light, and (b) structure adapted to incorporate polarization doping in the upper cladding layer. On the right side of the structures, a schematic diagram of the conduction band profile is shown (internal electric fields are disregarded for simplicity of representation).
Fig. 2. (a) Comparison of an Al concentration profile and SIMS measurement result from test LED of the same profile (the inserted graph explains the main parameters of the profile), (b) Carrier concentration calculated using Equation (9) for different composition gradients in the AlGaN layer. ΔAl represents the disparity between the highest and lowest Al concentrations within the graded layer.
Fig. 3. (a) Gen_v1′s structure and (b) simulated optical mode distribution.
Fig. 4. (a) Valance band profiles are calculated under zero bias by SiLENSe software for various doping levels of the interface between the two graded AlGaN layers. A doping level of approximately 1019 cm−3 is necessary to achieve a reasonable barrier level. (b) Comparison of the I-V characteristics between a Mg-doped laser and polarization-doped laser diodes at 293 K.
Fig. 5. (a) Gen_v1′s EL spectra, (b) gain spectra, and (c) maximum value of gain as a function of current.
Fig. 6. (a) Gen_v1′s L-I-V measurement, as well as threshold current and (b) slope efficiency estimated from the initial linear part of the LI dependence.
Fig. 7. (a) EL spectra below and above threshold current of coated Gen_v1 laser at 20 °C. (b) Near field measurement of Gen_v1 below and above threshold current. The figure shows the vertical (fast axis) cross-section of the near field pattern.
Fig. 8. (a) Gen_v2′s structure and Gen_v1 structure gave in gray color to show difference between structure and (b) simulated optical mode distribution.
Fig. 9. (a) Gen_v2′s L-I measurement, threshold current, and slope efficiencies with various mirror coating. The threshold current of uncoated, coated(A), and coated(B) lasers are 284 mA, 200 mA, and 66 mA, respectively. Please note that for uncoated laser, only half of the optical power is emitted through the front facet, so the total efficiency is closer to 1.6 W/A. (b) EL spectra above threshold current of uncoated and coated Gen_v2 laser at 20 °C. (c) Longitudinal modes of a coated (7 % / 80 %) Gen_v2 laser. (d) Free spectral range (FSR) of the same laser Gen_v2 (7 % / 80 %).
Fig. 10. (a) Gen_v2′s L-I-V measurement, (b) threshold current and slope efficiencies.
Fig. 11. Near field measurement of Gen_v2 below and above threshold current. The figure shows (a) the vertical (fast axis) cross-section of the near field pattern, and (b) an overexposed near-field pattern at lasing.
Fig. 12. Gain spectra of uncoated Gen_v2.
Fig. 13. (a) The maximum value of gain as a function of current and (b) EL spectra of uncoated Gen_v2 laser.
Fig. 14. (a) Gen_v3′s structure and (b) simulated optical mode distribution. Gen_v2 structure gave in gray color to show difference between structures and main difference zooms in insert graph. (c) Valance band profiles calculated under zero bias by SiLENSe software for various doping levels of 5% AlGaN layer marked by the dotted lines.
Fig. 15. Gen_v3′s L-I measurement, threshold current, and slope efficiencies. Please note that for uncoated laser only half of the optical power is emitted through the front facet, so the total efficiency is close to 1.4 W/A. The threshold current of uncoated and coated lasers are 122 mA and 56 mA, respectively. (b) EL spectra above threshold current of uncoated and coated Gen_v3 laser at 20 °C.
Fig. 16. (a) Gen_v3′s L-I-V measurement, (b) threshold current and slope efficiencies.
Fig. 17. Near field measurement of Gen_v3 below and above threshold current. The figure shows the vertical (fast axis) cross-section of the near field pattern.
Fig. 18. (a) Maximum value of gain as a function of current, (b) EL spectra of uncoated Gen_v3 laser.
