Abstract
We report an experimental investigation of 16 different mid-infrared diode laser samples with type-II “W” active regions. A number of design modifications were employed to study effects on the I–V characteristics, lasing threshold, and wallplug efficiency. Contrary to expectations, the threshold current density at low temperatures did not vary significantly with the number of active quantum-well periods, nor was there any clear correlation between lasing threshold and photoluminescence intensity. A shorter-wavelength device (3.2–3.6 µm) produced >500 mW of cw power at 80 K, and a second device displayed a wallplug efficiency >10%. The maximum lasing temperature was 317 K for pulsed operation and 218 K for cw operation. At T=100 K, cavity-length studies indicated an internal loss of 7 cm−1 and nominal internal efficiency of 96%. Hakki-Paoli measurements of the gain spectrum implied an intrinsic linewidth enhancement factor of ∼1.3, which slightly exceeds the theoretical prediction. Longer-wavelength devices (λ ≈ 3.8–4.5 µm) showed similarly low threshold current densities at T=80 K but degraded more rapidly with increasing temperature.
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