A new method to measure optical absorption in semiconductor crystals

October 29, 2020

Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

"Our findings confirm the accuracy of ODPL measurements and show the possibility to measure optical absorption of crystals by the ODPL method, making the process much easier," says Tohoku University materials scientist Kazunobu Kojima.

Huge strides have been made in the development of highly efficient electronic and optical devices, e.g. ultraviolet, blue, and white light-emitting diodes (LEDs) as well as high-frequency transistors, that use nitride semiconductors--specifically aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and gallium nitride (GaN).

GaN is a suitable material for power devices on account of its large bandgap energy, high breakdown field and high saturation electron velocity.

There is a strong need for manufacturers to be able to detect crystal defects and test their efficiency. Within such high quality crystals, the concentration of nonradiative recombination centers (NRC) serves as a good predictor of the crystals quality.

Annihilation spectroscopy, deep-level transient spectroscopy and photoluminescence (PL) spectroscopy are among the estimation techniques for detecting point defects which are the source of NRCs. PL spectroscopy is attractive because it requires no electrodes and contacts.

First proposed by Kojima and his research team in 2016, ODPL is a novel form of PL spectroscopy that measures PL intensity by using an integrating sphere to quantify the quantum efficiency of radiation in sample semiconductor crystals. It is non-touching, non-destructive and good for large-sized GaN wafers for room-lighting LEDs and transistors for electric vehicles. Yet, the origin of the two-peak structure formed in ODPL had remained elusive until now.

Kojima and his team combined ODPL and standard PL (SPL) spectroscopy experiments on a GaN crystal at various temperatures (T) between 12 K and 300 K. The intensity ratio (r) of the ODPL spectra to SPL spectra for the NBE emission of GaN showed a linearly decreasing slope for photon energy (E) below a fundamental absorption edge energy (Eabs).The slope obtained in r corresponded to the so-called Urbach-Martienssen (U-M) absorption tail, which is observed in many semiconductor crystals.

Therefore, the origin of the two-peak structure in the ODPL spectra around the NBE emission of the GaN crystal exists because of the U-M tail.
-end-


Tohoku University

Related Spectroscopy Articles from Brightsurf:

Perspectives of infrared spectroscopy in quantitative estimation of proteins
The present review describes the basic principle and the instrumentation of IR spectroscopy along with its advancements.

A new method to measure optical absorption in semiconductor crystals
Tohoku University researchers have revealed more details about omnidirectional photoluminescence (ODPL) spectroscopy - a method for probing semiconducting crystals with light to detect defects and impurities.

Properties of catalysts studied with gamma ray resonance
Steam-assisted oil extraction methods for heavy deposits have long been the focus of attention at Kazan Federal University.

Researchers demonstrate record speed with advanced spectroscopy technique
Researchers have developed an advanced spectrometer that can acquire data with exceptionally high speed.

Spectroscopy approach poised to improve treatment for serious heart arrhythmia
Researchers have demonstrated that a new mapping approach based on near infrared spectroscopy can distinguish between fat and muscle tissue in the heart.

Late blight research pairs spectroscopy with classic plant pathology diagnostics
Gold and colleagues at the University of Wisconsin-Madison recently published research showing how they used contact spectroscopy to non-destructively sense how plant pathogens differentially damage, impair, and alter plant traits during the course of infection.

Doing more with terahertz: Simplifying near-infrared spectroscopy systems
Researchers from Beihang University, China, and Tokushima University, Japan, have developed a terahertz spectroscopy scheme that offers outstanding resolution using a single laser.

A new horizon for vibrational circular dichroism spectroscopy
(1) The development of solid state and time-step VCD methods opened a new horizon to reveal the mechanism of chirality amplification from microscopic to supramolecular scales.

Unraveling the optical parameters: New method to optimize plasmon enhanced spectroscopy
Plasmon enhanced spectroscopies allow to reach single molecule sensitivity and a lateral resolution even down to sub-molecular resolution.

Nanoscale spectroscopy review showcases a bright future
A new review authored by international leaders in their field, and published in Nature, focuses on the luminescent nanoparticles at the heart of many advances and the opportunities and challenges for these technologies to reach their full potential.

Read More: Spectroscopy News and Spectroscopy Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.