New production process results in efficient lasers and LEDs

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A new process by scientists from North Carolina State University (State of North Carolina) exploits current industry standard techniques to produce III-nitride semiconductor materials, but results in layered materials that can improve efficiency levels of lasers and LEDs.

Electroluminescence measurements of (a) blue LED on GaN, (b) green LED on InGaN model, (c) almost yellow LED on InGaN model. The insets in Figure 1 (b) and Figure 1 (c) show the image of the emission at an injection current of 1.5 mA. Image credit: North Carolina State University.

Wide bandgap semiconductors such as III-nitride semiconductor materials are of particular interest in photonic and optical applications because they can be used to fabricate LEDs and lasers that create light in the range of visible bandwidth.

Regarding mass production, III-nitride semiconductor materials can be produced using a process known as metal-organic chemical vapor deposition (MOCVD).

Semiconductor equipment needs two materials, a “p-type” and an “n-type”. Electrons move from n-type material to p-type material, which is made possible by developing a p-type material that contains “holes” or spaces in which electrons can travel.

One difficulty faced by those who make lasers and LEDs was that there was a restriction on the number of holes that could be made in a p III-type nitride semiconductor material that was produced in the past. help from MOCVD. However, this restriction has recently increased.

We have developed a process that produces the highest concentration of holes in a p-type material in any III-Nitride semiconductor made using MOCVD. And this is a high quality material – very few flaws – which makes it suitable for use in a variety of devices.

Salah Bedair, study co-author and Emeritus Professor of Electrical and Computer Engineering, State of North Carolina

In real terms, this translates into the fact that more of the energy absorbed by LEDs is turned into light. For lasers, this results in a decrease in the energy input in the form of heat by reducing the contact resistance of the metal.

LEDs consist of three key layers: an n-type layer where electrons are created; the so-called “active” zone, which comprises numerous quantum wells of indium gallium nitride and of gallium nitride; and a p-type layer, where the holes are created.

To fabricate semiconductor materials for use in laser diodes or LEDs, the NC State team used a growth technique called “semi-bulk growth” to create models of indium nitride and gallium. The jig is made up of dozens of layers of gallium nitride and indium gallium nitride.

Scientists use these models for the n-type region to minimize complications due to the growth of quantum wells. Forcing the gallium nitride layer between the semi-bulk indium gallium nitride layers decreases imperfections due to the lattice offset between the semi-bulk jig and the gallium nitride substrate, as well as the filling the pits that develop on the surface.

In their new study, the team showed that the semi-bulk growth method can be applied for the p-type layer in LEDs to increase the number of holes. This new method is economical from a manufacturing point of view since the III nitride based LED devices can be manufactured in a single growth via MOCVD, without a significant processing time in between.

Using this method, scientists were able to achieve a hole density of 5 × 1019 cm-3 in p-type material. Previously, the highest hole concentration achieved in Type III nitride materials using MOCVD was approximately an order of magnitude lower.

These models of indium gallium nitride were also used by the team as substrates for LED structures in order to solve a long-standing problem known as “green space”, where the LED output weakens during operation. of the discharge in the green and yellow parts of the spectrum.

One of the main reasons for the green space is the large network disparity between the light emitting part of the material and the quantum well when gallium nitride substrates are used. Scientists have shown that replacing gallium nitride substrates with indium gallium nitride models results in better LED performance.

The team compared the emission spectrum of LEDs for the same quantum well discharging blue when grown on a gallium nitride substrate and producing green or yellow when grown on various nitride models. indium and gallium. A 100 nm change in the emission wavelength was achieved due to the application of the indium gallium nitride matrices.

Efficiency improvement article, “P-type InxGa1-xN semi-bulk models (0.02 -3 and the morphology of the surface of the device quality ”, was reported in the journal Letters of Applied Physics.

The first two authors of the article are Evyn Routh and Mostafa Abdelhamid, both doctoral students at NC State. The article was co-authored by Peter Colter, postdoctoral researcher at NC State and Nadia El-Masry of the National Science Foundation and NC State.

The article describing the resolution of the green gap in LEDs was published in Super-networks and Microstructures titled “Shifting the LED emission from blue to the spectral range of green space using relaxed models In0.12Ga0.88N.” “

The first two authors of the article are Routh and Abdelhamid. The article was co-authored by Ahmed Shaker, visiting scholar at NC State at EinShams University in Egypt.

Journal references:

  • Routh, EL, et al. (2021) InxGa1-xN type P semi-bulk models (0.02 Letters of Applied Physics. doi.org/10.1063/5.0065194.
  • Abdelhamid, M., et al. (2021) Shift of the LED emission from blue to the spectral domain of green space using relaxed models In0.12Ga0.88N. Superlattices and microstructures. doi.org/10.1016/j.spmi.2021.107065.

Source: https://ncsu.edu

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