| Luminescence refrigeration in semiconductors has recently attracted much interest and has developed into an active area of research. This dissertation focuses on understanding the fundamental mechanisms of luminescence refrigeration. To fulfill this task, the thermodynamic principles of luminescence refrigeration in semiconductors are investigated based on the balance equations for energy, entropy, and particle number. By taking background radiation into account, the output and input fluxes are examined using a thin-slab model in the steady state, through which the cooling efficiency and cooling power are obtained. The concept of radiation flux temperature is clarified and the origination of irreversible entropy generation during luminescence is investigated. The Eddington factor is also discussed.; High material quality is critical to the achievement of net cooling in luminescence refrigerators. To this end photoluminescence spectroscopy is utilized to characterize molecular beam epitaxy (MBE) grown samples; this information is then fed back to the growth of GaAs based luminescent devices to ensure the highest quality materials. The impact of Sb mediated growth on the performance of GaAs/AlGaAs materials is also studied. Moreover, the MBE system is precisely calibrated to ensure the accurate growth of device structures. The MBE calibration procedures using reflectance measurements and the growth rate calibration curves versus cell temperature for GaAs, AlAs, and InAs, the As/III overpressure versus As cell valve setting, and the dopant concentrations versus dopant cell temperatures are also presented.; Spontaneous emission quantum efficiency is one of the most important parameters in luminescence refrigeration. The injection and temperature dependence of the spontaneous emission quantum efficiency in GaAs/AlGaAs heterostructures and InGaAs/GaAs quantum wells is studied using photoluminescence measurements performed at temperatures from 50 to 320 K using a HeNe pump laser with power ranging from 0.6 to 35 mW. The quantum efficiency is inferred from the power law relations predicted by the rate equations that link pump power and integrated photoluminescence signal. For the GaAs/AlGaAs heterostructures, the use of Sb mediated growth improved the extrapolated peak spontaneous emission quantum efficiency from 0.970 to 0.977 at 300 K, with the best overall performance from 0.996 to 0.998 at 180 K. For the InGaAs/GaAs quantum well structure, the extrapolated peak spontaneous emission quantum efficiency is 0.941 at 300 K, with a best overall performance of 0.992 at 100 K. |
