The quantum-confined Stark effect in single cadmium selenide (CdSe) nanocrystallite quantum dots was studied. The electric field dependence of the single-dot spectrum is characterized by a highly polarizable excited state (∼10 5 cubic angstroms, compared to typical molecular values of order 10 to 100 cubic angstroms), in the presence of randomly oriented local electric fields that change over time. These local fields result in spontaneous spectral diffusion and contribute to ensemble inhomogeneous broadening. Stark shifts of the lowest excited state more than two orders of magnitude larger than the linewidth were observed, suggesting the potential use of these dots in electro-optic modulation devices.

Quantum Confined Stark Effect in Single CdSe Nanocrystallite Quantum Dots

https://www.repository.cam.ac.uk/bitstream/1810/264501/1/Fu_et_al-2017-Progress_in_Material_Science-VoR.pdf

Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Recent technological advances in nanomaterials have driven the development of high‐performance light‐emitting devices with flexible and stretchable form factors. Deformability in such devices is mainly achieved by replacing the rigid materials in the device components with flex...

Flexible and Stretchable Smart Display: Materials, Fabrication, Device Design, and System Integration

GaN and related III-nitrides have attracted considerable attention as promising materials for application in optoelectronic devices, in particular, light-emitting diodes (LEDs). At present, sapphire is still the most popular commercial substrate for epitaxial growth of GaN-based LEDs. However, due to its relatively large lattice mismatch with GaN and low thermal conductivity, sapphire is not the most ideal substrate for GaN-based LEDs. Therefore, in order to obtain high-performance and high-power LEDs with relatively low cost, unconventional substrates, which are of low lattice mismatch with GaN, high thermal conductivity and low cost, have been tried as substitutes for sapphire. As a matter of fact, it is not easy to obtain high-quality III-nitride films on those substrates for various reasons. However, by developing a variety of techniques, distincts progress has been made during the past decade, with high-performance LEDs being successfully achieved on these unconventional substrates. This review focuses on state-of-the-art high-performance GaN-based LED materials and devices on unconventional substrates. The issues involved in the growth of GaN-based LED structures on each type of unconventional substrate are outlined, and the fundamental physics behind these issues is detailed. The corresponding solutions for III-nitride growth, defect control, and chip processing for each type of unconventional substrate are discussed in depth, together with a brief introduction to some newly developed techniques in order to realize LED structures on unconventional substrates. This is very useful for understanding the progress in this field of physics. In this review, we also speculate on the prospects for LEDs on unconventional substrates.

https://iopscience.iop.org/article/10.1088/0034-4885/79/5/056501/pdf

GaN-based light-emitting diodes on various substrates: a critical review.

The application of gas discharge plasmas has assumed an important place in many manufacturing processes. Plasma methods contribute significantly to the economic prosperity of industrialized societies. However, plasma is mainly an enabling method and therefore its role remains often hidden. Hence the success of plasma technologies is described for different examples and commercial areas. From these examples and emerging applications, the potential of plasma technologies is discussed. Economic trends are anticipated together with research needs. The community of plasma scientists strongly believes that more exciting advances will continue to foster innovations and discoveries in the first decades of the 21st century, if research and education will be properly funded and sustained by public bodies and industrial investors.

The future for plasma science and technology

Epitaxial growth of group III-nitride films by pulsed laser deposition and their use in the development of LED devices

High-quality GaN epitaxial films have been grown on Si substrates with Al buffer layer by the combination of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD) technologies. MBE is used to grow Al buffer layer at first and then PLD is deployed to grow GaN epitaxial films on the Al buffer layer. The surface morphology, crystalline quality and interfacial property of as-grown GaN epitaxial films on Si substrates are studied systematically. The as-grown ~300 nm-thick GaN epitaxial films grown at 850 °C with ~30 nm-thick Al buffer layer on Si substrates show high crystalline quality with the full-width at half-maximum (FWHM) for GaN(0002) and GaN(102) X-ray rocking curves of 0.45° and 0.61°, respectively; very flat GaN surface with the root-mean-square surface roughness of 2.5 nm; as well as the sharp and abrupt GaN/AlGaN/Al/Si hetero-interfaces. Furthermore, the corresponding growth mechanism of GaN epitaxial films grown on Si substrates with Al buffer layer by the combination of MBE and PLD is hence studied in depth. This work provides a novel and simple approach for the epitaxial growth of high-quality GaN epitaxial films on Si substrates.

A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD

AlN (0001) epitaxial films have been grown on Al (111) substrates with an in-plane epitaxial relationship of AlN[110]//Al[10] by pulsed laser deposition. The as-grown AlN films grown at 450 °C exhibited a very smooth and flat surface with a surface root-mean-square roughness less than 1.1 nm. There is no interfacial layer existing between AlN films and Al substrates, indicating an abrupt interface. The as-grown ~302 nm thick AlN films are almost fully relaxed only with an in-plane compressive strain of 0.16%. With the increase in growth temperature, the interfacial layer thickness increases, resulting in the degradation in the crystalline quality of the as-grown AlN films. These AlN films are of great interest for the commercial development of AlN-based devices.

Epitaxial growth of high quality AlN films on metallic aluminum substrates

GaN is a unique material with outstanding optoelectronic properties and is suitable for application in light-emitting diodes (LEDs), laser diodes (LDs), high electron mobility transistors (HEMTs), etc. Usually, GaN films are grown on sapphire substrates. However, due to the relatively large lattice and thermal expansion coefficient mismatches between GaN and sapphire, to obtain high-performance and high-power GaN-based devices is still highly desired. In this regard, many researchers have tried hard to grow GaN films on unconventional oxide substrates other than sapphire, which share relatively small lattice and thermal expansion coefficient mismatches with GaN. This review focuses on the recent progress of the epitaxial growth of GaN films on unconventional oxide substrates. The perspectives for the epitaxial growth of GaN films on unconventional oxide substrates are also discussed.

Weijia Yang

Papers

GaN-based light-emitting diodes on various substrates: a critical review.

Epitaxial growth of group III-nitride films by pulsed laser deposition and their use in the development of LED devices

A new approach to epitaxially grow high-quality GaN films on Si substrates: the combination of MBE and PLD

Epitaxial growth of high quality AlN films on metallic aluminum substrates

Epitaxial growth of GaN films on unconventional oxide substrates