Cryostat setup for measuring spectral and electrical properties of light-emitting diodes at junction temperatures from 81 K to 297 K.

Elvira Martikainen,Erkki Ikonen,Timo Dönsberg,Anna Vaskuri

doi:10.1063/1.5125319

Elvira Martikainen, Erkki Ikonen + Show 2 more

Open Access

https://doi.org/10.1063/1.5125319

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Abstract

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.

Highlights

Applications relying on opto-semiconductors cover, for example, light-emitting diodes (LEDs), lasers, optical detectors, and solar cells
Increasing forward voltages toward cryogenic temperatures have earlier been measured for InGaN LEDs by Meyaard et al.,27 and according to them, the effect is associated with the increment of series and contact resistances of an LED due to decreased mobility of the holes toward cryogenic temperatures
High temperature resolution of the data measured in this work allows for fitting and testing the theoretical models without the need of interpolation

Summary

INTRODUCTION

Applications relying on opto-semiconductors cover, for example, light-emitting diodes (LEDs), lasers, optical detectors, and solar cells. New ways to determine the junction temperature from LED spectra have been studied, for example, by Vaitonis et al., Chen and Narendran, He et al., Keppens et al., and Chou and Yang.. New ways to determine the junction temperature from LED spectra have been studied, for example, by Vaitonis et al., Chen and Narendran, He et al., Keppens et al., and Chou and Yang.12 These models either are empirical or can only model a narrow part of the spectrum as they neglect broadening of the joint density of states. Vaskuri et al. have proposed more accurate models to overcome the limitations of the simplified approaches These new models allow for estimating the junction temperature from electroluminescence spectra of red and blue LEDs with the standard uncertainty better than.

MEASUREMENT SETUP

JUNCTION TEMPERATURE ESTIMATION

RESULTS

CONCLUSIONS