GaSb-Based Type-I Quantum Well 3–3.5- $\mu$ m Cascade Light Emitting Diodes

Mid-infrared light emitting diodes based on cascade pumping of the type-I quantum wells were designed and fabricated. The 500- $\mu \text{m}$ -diameter mesa ten-stage devices emitted more than 2 mW of continuous wave power in a wide spectrum peaking at $3.1~\mu \text{m}$ at room temperature. More than 6 mW was obtained at 77 K. The above-mentioned output power levels were measured from an uncoated window in the substrate-side contact metallization of epi-side-down mounted emitters. The maximum output power and the device operating voltage are roughly scaled with the number of cascades in the device heterostructure. The low-current device slope efficiency per stage decreased with increasing the acceptor doping level in the layers adjacent to the active quantum wells. Increase of the number of quantum wells in each stage from one to three led to about 25% improvement of the output power at 300 K.