Enhanced Mode Stability and Reduced Beam Divergence in Inverted Junction Oxide Vertical‐Cavity Surface‐Emitting Laser Arrays by Employing Tunnel Junction

We report inverted n‐p junction vertical‐cavity surface‐emitting lasers (VCSEL) arrays grown on an n‐type GaAs substrate to mitigate current‐crowding at the oxide aperture rim that degrades transverse mode stability and increases beam divergence in conventional p‐n oxide‐confined devices. This design incorporates a tunnel junction between the substrate and the bottom distributed Bragg reflector (DBR) to achieve junction polarity inversion. The n‐type top DBR provides higher lateral conductivity, promoting uniform carrier injection and enhanced current confinement. Arrays of 875 devices exhibit threshold currents of ∼0.4 A, slope efficiencies of ∼0.98 W/A, and peak power conversion efficiencies of ∼43%, comparable to those of conventional VCSELs. Near‐field imaging confirms that the inverted n‐p VCSEL sustains a compact, centrally peaked emission profile dominated by the LP ₀₁ mode up to ∼1.0 A, whereas conventional p‐n devices with LP ₀₂ dominance as early as 0.7 A. Corresponding far‐field measurements reveal divergence increasing gradually from 14.3° at 0.7 A to 24.1° at 5.0 A—on average ∼18% narrower (13.9%–23.1%)—compared with 16.6° to 27.8° for p‐n devices. This extended single‐mode operating range and consistent divergence reduction demonstrate the n‐p architecture's superior modal control, making it highly promising for scalable, high‐brightness VCSEL arrays in light detection and ranging, 3D sensing, and optical communication systems.