Martikainen Elvira, Vaskuri Anna, Dönsberg Timo, Ikonen Erkki
Metrology Research Institute, Aalto University, P.O. Box 15500, 00076 Aalto, Finland.
Rev Sci Instrum. 2020 Jan 1;91(1):015106. doi: 10.1063/1.5125319.
We introduce a cryostat setup for measuring fundamental optical and electrical properties of light-emitting diodes (LEDs). With the setup, the cryostat pressure and the LED properties of the forward voltage, junction temperature, and electroluminescence spectrum are monitored with temperature steps less than 1.5 K, over the junction temperature range of 81-297 K. We applied the setup to commercial yellow AlGaInP and blue InGaN LEDs. At cryogenic temperatures, the fine structure of the electroluminescence spectra became resolved. For the yellow LED, we observed the phonon replica at 2.094 eV that was located 87 meV below the peak energy at the junction temperature of 81 K. For the blue LED, we observed the cascade phonon replicas at 2.599 eV, 2.510 eV, and 2.422 eV with the energy interval of 89 meV. For both LED types, the forward voltage increased sharply toward the lower temperatures due to the increased resistivity of materials in the LED components. We found significant differences between the temperature dependent behaviors of the forward voltages, spectral peak energies, and bandgap energies of LEDs obtained from the Varshni formula. We also noted a sharp pressure peak at 180-185 K arising from the solid-vapor phase transition of water when the base level of the cryostat pressure was approximately 0.4 mPa.
我们介绍了一种用于测量发光二极管（LED）基本光学和电学特性的低温恒温器装置。利用该装置，在81 - 297 K的结温范围内，以小于1.5 K的温度步长监测低温恒温器压力以及正向电压、结温和电致发光光谱等LED特性。我们将该装置应用于商用黄色AlGaInP和蓝色InGaN LED。在低温下，电致发光光谱的精细结构得以分辨。对于黄色LED，我们在81 K的结温下观察到位于峰值能量以下87 meV处、能量为2.094 eV的声子复制品。对于蓝色LED，我们观察到能量分别为2.599 eV、2.510 eV和2.422 eV、能量间隔为89 meV的级联声子复制品。对于这两种类型的LED，由于LED组件中材料电阻率的增加，正向电压在较低温度下急剧上升。我们发现从瓦尔什尼公式获得的LED正向电压、光谱峰值能量和带隙能量的温度依赖性行为之间存在显著差异。我们还注意到，当低温恒温器压力的基线约为0.4 mPa时，在180 - 185 K处出现由水的固 - 气相变引起的尖锐压力峰值。
