<p>The role of electron–phonon interactions in the performance of optoelectronic devices is crucial for designing optimal structures. Here, we examined temperature-dependent photoluminescence spectra for three InGaAs photodetector samples with varying absorber and window layer thicknesses over a temperature range of 20–300 K. Using theoretical equations and a fitting procedure, we evaluated variations in the peak position to determine electron–phonon coupling strengths and average phonon energies in the photodetectors. Subsequently, we simulated the entropy of the samples across a temperature range of 150–300 K. The results reveal a strong correlation between electron–phonon interactions in the detectors and previously reported performance metrics, particularly quantum efficiency and photoluminescence efficiency of these samples. As the absorber and window layer thicknesses increase, electron–phonon coupling weakens, and phonon energy decreases. Finally, the results show that the entropy of the samples decreases with increasing thicknesses. This relationship between electron–phonon interactions and the optical efficiencies of the samples offers a straightforward approach to characterizing and optimizing other optoelectronic structures.</p>