Suppressed power saturation due to optimized optical confinement in 9xx nm high-power diode lasers that use extreme double asymmetric vertical designs

Abstract

Broad area lasers with novel extreme double asymmetric structure (EDAS) vertical designs featuring increased optical confinement in the quantum well, Γ, are shown to have improved temperature stability without compromising series resistance, internal efficiency or losses. Specifically, we present here vertical design considerations for the improved continuous wave (CW) performance of devices operating at 940 nm, based on systematically increasing Γ from 0.26% to 1.1%, and discuss the impact on power saturation mechanisms. The results indicate that key power saturation mechanisms at high temperatures originate in high threshold carrier densities, which arise in the quantum well at low Γ. The characteristic temperatures, T 0 and T 1 , are determined under short pulse conditions and are used to clarify the thermal contribution to power limiting mechanisms. Although increased Γ reduces thermal power saturation, it is accompanied by increased optical absorption losses in the active region, which has a significant impact on the differential external quantum efficiency, h diff . To quantify the impact of internal optical losses contributed by the quantum well, a resonator length-dependent simulation of h diff is performed and compared to the experiment, which also allows the estimation of experimental values for the light absorption cross sections of electrons and holes inside the quantum well. Overall, the analysis enables vertical designs to be developed, for devices with maximized power conversion efficiency at high CW optical power and high temperatures, in a trade-off between absorption in the well and power saturation. The best balance to date is achieved in devices using EDAS designs with G = 0.54%, which deliver efficiencies of 50% at 14 W optical output power at an elevated junction temperature of 105 °C.

Optimizing Vertical and Lateral Waveguides of kW-Class Laser Bars for Higher Peak Power, Efficiency and Lateral Beam Quality

“…Fig. 1 shows the length dependence of the differential quantum efficiency η d and threshold current density J thr of the uncoated BA lasers, with the length analysis for the ETAS design corresponding to a repeat growth and fabrication run, to the same epitaxy design used in [10], confirming reproducibility. The extracted internal parameters, i.e., internal differential quantum efficiency η int , optical loss α int , modal gain factor Γ g 0 and transparency current density J tr are listed in Table . I.…”

“…First, we present the internal parameters of the investigated ETAS structure. The ETAS structure, described in detail in [10] (structure with 0.54% confinement) and previously used in [11], is designed for an efficient emission at λ ∼ 940 nm at T HS = 25 °C. As a reference, we have chosen a recent efficiency optimized (unpublished) ASLOC vertical design which enabled a bar peak power over 1 kW.…”

Extreme Double/Triple Asymmetric Epitaxial Structure Based Diode Lasers for High Powers and High Efficiencies

“…For the top p-type contact, we assume it to be connected to a thermal conductor with a specified thermal conductance, the value of which is fitted from the experiment results in Refs [25], [26]. The extracted T 0 and T 1 characteristic temperatures of 4 mm length ETAS-based BALs are 183.5K and 572.8K for t n = 70 nm, and 223.5K and 813.1K for t n = 350 nm, respectively, which show good agreement with the experimental results reported in [24], [26] that the epitaxial structures with higher confinement factors show relatively higher T 0 and T 1 values. The effect of thermal lensing is considered in the LASTIP simulation by using 2.5e−4 K −1 as the temperature dependence of the thermal index change n/T for AlGaAs [27].…”

Optimization of a New GaN-Based Blue Laser Diode with a Quadruple Asymmetric Waveguide for High Efficiency Performance

“…Moreover, a higher junction temperature results in a significant index drop, that causes to decrease confinement and may also lead to a further reduced modal gain. Thus, for the highest efficiencies at high operating temperature and power, it is vital to stop this cycle in the quantum well using a high confinement factor [19]. Here, the composition of Al in the AlxGa1-xN n-cladding layer is fixed at 8%; furthermore, considering experimental reports, the aluminium composition in the AlxGa1-xN p-cladding layer varies from 2% to 10% [18].…”