Differential Carrier Lifetime Measurements of InGaN Light-Emitting Diodes
Department: Electrical and Computer Engineering / Physics
Advisor: Jonathan Wierer
The efficiencies of light-emitting diodes (LEDs) are partially determined by carrier lifetimes which are a function of light-producing radiative and heat-producing non-radiative lifetimes. Determining these lifetimes will allow us to not only understand the physics within the active region of the LEDs, but also allow us to design more efficient LEDs. Carrier lifetimes of LEDs are typically measured through electrical excitation of the p-n junction of the LED, wherein the delay in phase between a radio-frequency (RF) electrical input signal and the resulting output light signal determines the lifetimes. Such a measurement is difficult because of competing carrier injection and transport processes within the LED and can potentially lead to incorrect results. The solution to this dilemma is to implement an all-optical differential carrier lifetime method where the carrier injection is provided by a 405 nm blue laser diode. In this experiment the input signal is produced by the combination of a small and variable RF signal from a vector network analyzer (VNA) and a constant DC current that is then emitted from the laser diode onto the the LED. This input light is then absorbed and creates electron-hole pairs directly within the InGaN LEDs active layers. Using an avalanche photodiode, one is able to analyze the phase-shift of the resulting light signal produced by the LED and therefore determine its recombination lifetimes. We will show the differential carrier lifetime setup and preliminary measurements of InGaN-based LED structures produced in the epitaxy facilities of Lehigh’s Center for Photonics and Nanoelectronics.
About Rebecca Lentz:
Rebecca Lentz is a third-year electrical engineering student with a focus in semiconductor materials. She began research the summer after her sophomore year and hopes to continue past receiving her bachelors by pursuing a PhD in the field. In the fall of 2017, she received a research scholarship from the Clare Boothe Luce Foundation in the hopes to strengthen her current and future projects under the guidance of Professor Jonathan Wierer.
Outside of the lab, she is the president of the women’s club volleyball team and the professional and alumni relations chair for Alpha Omega Epsilon. Other organizations that she is a part of include Eta Kappa Nu and IEEE.