Achieving a high internal quantum efficiency in GaAs∕AlGaAs based light-emitting diodes (LEDs) for room-temperature operation at low current-density injection is crucial for applications such as optical up-converters based on the integration of LEDs and photodetectros. We report the experimental results as well as the theoretical analyses of the internal quantum efficiency of GaAs∕AlGaAs LEDs as a function of the p-doping concentration of the active region for low current injection operation. By optimizing the doping concentration, we have achieved a close to 100% internal quantum efficiency for room-temperature operation of LEDs in the low injection current-density range, i.e., around 0.1A∕cm2. An optical up-converter was fabricated using wafer-fusion technology by integrating the optimized GaAs∕AlGaAs LED with an InGaAs∕InP photodetector. The internal up-conversion quantum efficiency was measured to be 76%.

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We report the direct determination of absorption losses in unstrained InGaAs/InGaAsP and InGaAs/InGaAlAs and strained InGaAs/InGaAsP layer multiple quantum well (MQW) laser structures. In the case of the unstrained structures we find a strong dependence of the absorption on carrier density indicating the presence of an intrinsic optical loss mechanism, the intervalence band absorption (IVBA). In the strained layer InGaAs/InGaAsP structures, IVBA is completely switched off. Our results explain the superiority of strained layer InGaAs MQW lasers.