Does Temperature Impact a Diode’s Performance?

Temperature has a significant and measurable impact on the performance of diodes, particularly semiconductor laser diodes and organic light-emitting diodes (OLEDs). This impact is primarily due to changes in the internal temperature of the diode package, which can affect the diode’s electrical characteristics, light output, and overall efficiency.

Semiconductor Laser Diodes

For semiconductor laser diodes, rapid temperature shifts can affect the laser’s internal temperature, leading to changes in its performance. The Newport application note [1] provides a detailed analysis of this phenomenon. Figure 2 in the application note shows the coldplate (case) temperature and the laser’s internal temperature as a function of time, with a 1.5W heat load enabled and disabled.

The data demonstrates that the laser’s internal temperature can rise significantly above the coldplate temperature when a heat load is applied, and it can take several minutes for the internal temperature to stabilize. This temperature rise can affect the laser’s performance in several ways:

1. Wavelength Shift: The laser’s output wavelength is highly sensitive to temperature changes. A 1°C increase in junction temperature can cause a wavelength shift of 0.3 to 0.6 nm, depending on the laser’s design.
2. Output Power: The laser’s output power can decrease by 2-3% per 1°C increase in junction temperature, due to changes in the gain and threshold current.
3. Beam Quality: Temperature-induced changes in the refractive index and thermal lensing can degrade the laser’s beam quality, leading to increased divergence and astigmatism.
4. Lifetime: Elevated temperatures can accelerate the degradation of the laser’s active region, reducing its lifetime.

To ensure stable and reliable performance, it is crucial to maintain temperature stability during laser diode characterization and operation. The application note recommends thermalization between current ramp steps to ensure that the laser’s internal temperature has stabilized before measurements are taken.

Organic Light-Emitting Diodes (OLEDs)

Similar to semiconductor laser diodes, the performance of OLEDs is also heavily influenced by temperature. The Wiley Online Library paper [2] reports on the effects of sample size, forward current, and temperature on the performance of red OLEDs.

The key findings from the OLED study include:

1. Luminous Efficiency: The luminous efficiency of the OLEDs decreased as the operating temperature increased, due to enhanced non-radiative recombination and reduced charge carrier mobility.
2. Thermal Resistance: The thermal resistance between the case and internal components of the OLED package can significantly affect the time required for internal temperature stabilization. This thermal resistance can be reduced by using a larger OLED sample size.
3. Thermal Quenching: At higher temperatures, the radiative recombination rate of the OLED’s emissive layer can be reduced, leading to a decrease in light output and efficiency.

To mitigate the impact of temperature on OLED performance, it is essential to carefully control the operating temperature and minimize the thermal resistance within the OLED package.

Theoretical Models

In addition to the experimental studies, theoretical models have also been developed to describe the impact of temperature on diode performance. One such model is Shockley’s equation, which can be used to manipulate the relationship between diode current, voltage, and temperature.

The Electronics Stack Exchange post [3] provides a detailed explanation of Shockley’s equation and its implications:

I = I_s * (e^(V/n*V_T) - 1)
Where:
I = Diode current
I_s = Saturation current
V = Voltage across the diode
n = Ideality factor (typically between 1 and 2)
V_T = Thermal voltage = k*T/q
k = Boltzmann constant
T = Absolute temperature (in Kelvin)
q = Electron charge

This equation demonstrates that temperature (T) is directly proportional to the thermal voltage (V_T), which in turn affects the voltage across the diode (V). As the temperature increases, the voltage across the diode decreases, indicating that changes in temperature can significantly impact the diode’s electrical characteristics.

Junction Temperature Measurement

Accurately measuring the junction temperature of diodes, particularly LEDs, is crucial for understanding their performance and reliability. The NCBI article [4] provides a critical review of junction temperature measurement techniques for light-emitting diodes (LEDs).

The key points from the NCBI article include:

1. Importance of Junction Temperature: The junction temperature of an LED is a critical parameter that affects its luminous efficacy, color stability, and lifetime.
2. Measurement Techniques: Various techniques have been developed to measure the junction temperature, including forward voltage method, thermal resistance method, and optical method.
3. Factors Affecting Measurement: Factors such as self-heating, thermal coupling, and measurement errors can introduce uncertainties in the junction temperature measurement.
4. Challenges and Improvements: Ongoing research is focused on improving the accuracy and reliability of junction temperature measurement techniques, particularly for high-power and high-brightness LEDs.

Understanding the junction temperature and its impact on diode performance is essential for optimizing the design, operation, and reliability of diode-based devices.

Conclusion

In summary, temperature has a significant and measurable impact on the performance of diodes, particularly semiconductor laser diodes and organic light-emitting diodes (OLEDs). This impact is primarily due to changes in the internal temperature of the diode package, which can affect the diode’s electrical characteristics, light output, and overall efficiency.

Experimental studies have demonstrated the effects of temperature on parameters such as wavelength shift, output power, beam quality, and lifetime for laser diodes, as well as luminous efficiency and thermal quenching for OLEDs. Theoretical models, such as Shockley’s equation, have also been developed to describe the relationship between temperature, current, and voltage in diodes.

Accurate measurement of the junction temperature is crucial for understanding and optimizing the performance and reliability of diode-based devices. Ongoing research is focused on improving the accuracy and reliability of junction temperature measurement techniques, particularly for high-power and high-brightness diodes.

Overall, the impact of temperature on diode performance is a critical consideration in the design, characterization, and operation of diode-based systems, and it is an active area of research and development in the field of electronics and photonics.

References

1. Newport. (2016). 21 High Performance Temperature Control in Laser Diode Test Applications. Retrieved from https://www.newport.com/medias/sys_master/images/images/h46/h2b/8797049880606/AN21-High-Performance-Temperature-Control-in-Laser-Diode-Test-Applications.pdf
2. Wiley Online Library. (2014). Temperature and emitting area dependence of red organic light-emitting diodes. Retrieved from https://onlinelibrary.wiley.com/doi/10.1002/pssa.201330437
3. Electronics Stack Exchange. (2021). Temperature vs diode voltage in Shockley’s equation. Retrieved from https://electronics.stackexchange.com/questions/585225/temperature-vs-diode-voltage-in-shockleys-equation
4. NCBI. (2022). A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9611508/
5. ResearchGate. (2020). The Impact of Temperature on the Performance of Semiconductor Laser Diode. Retrieved from https://www.researchgate.net/publication/342707254_The_Impact_of_Temperature_on_the_Performance_of_Semiconductor_Laser_Diode