Quantum wells produce multi-color LED arrays

A new monolithic LED device that emits four colors of light in the mid-IR range has been developed by investigators at the University of Glasgow. Details about the construction of the device and tests of its function are reported in Applied Physics Letters by AIP Publishing.

Four wavelengths will prove useful in infrared spectrometers and could be used for the detection of different molecular substances in the same sample. By combining the four-color LED array with device switching technology developed by this same group of investigators, multi-color infrared cameras also become possible.

The researchers produced the four light frequencies by stacking quantum well (QW) structures in a vertical arrangement on a semi-insulating GaAs substrate. Previous work had demonstrated two tunable LEDs, but on a substrate not available in large formats. The QWs used here are thin layers of low band gap material (InSb) sandwiched between thicker layers of high band gap material (Al_xIn_1-xSb).

The QWs are created using epitaxial growth that enables various semiconductors to grow in layers and provides tight control over the thickness of each layer. The thickness of the layer (2 nm, 4 nm or 6 nm in this device) determines the width of the QW, which, in turn, determines the wavelength of light emitted by the device.

The investigators used numerical simulations with commercially-available software, SiLENSe, to help design their device and found good agreement between simulation and experimental observations. In the conclusion of their paper, the authors say the combined approach using theory and experiment has yielded a good understanding of the role of QW width fluctuations, heat generation and other curve-broadening processes. According to lead author Mohsin Aziz, future work will explore the development of an electronically-controlled multispectral IR source or detector, as well as applications to biological systems.

Source: “Multispectral mid-infrared light emitting diodes on a GaAs substrate,” by Mohsin Aziz, Chengzhi Xie, Vincenzo Pusino, Ata Khalid, Matthew Steer, Iain G. Thayne, and David R.S. Cumming, Applied Physics Letters (2017). The article can be accessed at https://doi.org/10.1063/1.4986396 .