High-power 980 nm edge-emitting semiconductor lasers (EELs) serve as the dominant pump sources for erbium-doped fiber amplifiers (EDFAs) and are crucial for various industrial, medical, and photonic integration applications. However, their performance severely degrades at elevated temperatures, primarily due to enhanced electron thermionic escape from the active region, leading to increased threshold current, reduced output power, and limited reliability. This work aims to address this fundamental challenge by strategically designing and optimizing an AlGaAs Electron Blocking Layer (EBL) within the P-side of the laser heterostructure. The core objective is to systematically investigate the influence of EBL aluminum (Al) composition on the carrier dynamics, recombination mechanisms, and resultant temperature-dependent electro-optical characteristics of 980 nm EELs, thereby identifying the optimal design paradigm for achieving superior high-temperature stability.
A comprehensive numerical simulation study was conducted using the commercial semiconductor device simulator PICS 3D, which self-consistently solves the coupled electrical, optical, and thermal equations. Three distinct epitaxial structures were designed and compared: 1) a Reference structure without an EBL; 2) a structure incorporating a 10 nm Al_0.3GaAs EBL; and 3) a structure incorporating a 10 nm Al_0.4GaAs EBL. The EBL was positioned between the undoped P-side waveguide and the barrier layer. The active region consisted of an 8 nm In_0.2Ga_0.3As single quantum well with GaAsP_0.03 barriers. The cladding layers employed a graded Al-composition AlGaAs design. Simulations were performed over a temperature range of 300 K to 360 K for devices with a 25 μm stripe width and a 2 mm cavity length. Key analyzed parameters included spatial carrier distributions (electron/hole concentrations), radiative and Auger recombination rates, power-current-voltage (P-I-V) characteristics, threshold current (I_th), characteristic temperature (T₀), and lasing wavelength shift.
Carrier Confinement and Injection Balance: The introduction of an AlGaAs EBL dramatically suppressed electron leakage into the P-cladding. At 360 K, the peak electron concentration in the P-cladding was reduced by 94.7% for the Al_0.3GaAs EBL and by 97.14% for the Al_0.4GaAs EBL, compared to the reference structure. However, the higher Al-content EBL (Al_0.4GaAs) introduced a significantly larger valence band barrier, severely impeding hole injection into the quantum well (QW). This imbalance caused an anomalous accumulation of electrons within the QW, reaching a density of 2.3×10¹⁸ cm^-3 at 360 K for the Al_0.4GaAs EBL, compared to 1.72×10¹⁸ cm^-3 for the Al_0.3GaAs EBL and 1.81×10¹⁸ cm^-3 for the reference structure.
Recombination Dynamics: The disparate carrier distributions led to distinct recombination pathways. The Al_0.4GaAs EBL structure exhibited the highest radiative recombination rate due to its high electron density but simultaneously suffered from the strongest Auger recombination—36.5% higher than the reference at 360 K. This is attributed to the cubic dependence of Auger recombination on carrier density. The Al_0.3GaAs EBL structure maintained a high radiative rate while effectively suppressing Auger recombination, achieving a more favorable balance.
Threshold and Spectral Characteristics: Despite its superior electron confinement, the Al_0.4GaAs EBL structure exhibited the highest threshold current across the temperature range, a direct consequence of the hole injection bottleneck and enhanced non-radiative losses. The Al_0.3GaAs EBL structure achieved the best temperature stability, characterized by the highest characteristic temperature T₀ = 280.9 K, compared to 271.7 K (reference) and 274.7 K (Al_0.4GaAs EBL). It also demonstrated the lowest wavelength temperature drift coefficient (0.346 nm/°C), enhancing spectral stability.
Power Output and Efficiency: The Al_0.3GaAs EBL structure delivered the highest continuous-wave output power across the entire temperature range. At 360 K, its maximum power was 3.592 W, representing an 6.90% improvement over the reference structure (3.360 W). The Al_0.4GaAs EBL structure showed a similar improvement (3.590 W) but at the cost of higher operating voltage at lower temperatures. The voltage-current relationship revealed a complex interplay between hole injection barrier and carrier recombination, with a crossover occurring above 350 K where the Al_0.4GaAs EBL voltage became lower, indicating a shift in the dominant mechanism to leakage and recombination dynamics.
This study elucidates the critical trade-off in EBL design for high-temperature 980 nm semiconductor lasers. While increasing the Al composition in the AlGaAs EBL strengthens electron confinement, an excessively high Al fraction (0.4) introduces a prohibitive hole injection barrier. This disrupts carrier balance in the active region, leading to electron pile-up, a dramatic increase in detrimental Auger recombination, and ultimately degrading threshold and power performance. The Al_0.3GaAs EBL emerges as the optimized design, successfully striking an optimal balance between effective electron blocking and efficient hole injection. It achieves a significant suppression of electron leakage (>94%) while minimizing parasitic non-radiative losses, resulting in the best overall performance: the highest T₀ (280.9 K), the lowest wavelength drift, and the greatest output power across the 300-360 K range. The findings underscore that the key to improving high-temperature laser characteristics lies not in merely maximizing the EBL barrier height but in globally optimizing the carrier confinement-injection equilibrium. This work provides essential guidelines and a theoretical foundation for the epitaxial design of temperature-stable, high-power 980 nm pump lasers.