The Royal Institution for the Advancement of Learning / Mcgill University

University of Michigan

Mcgill University

Bandar Alotaibi

Shizhao Fan

Zetian Mi

Renjie Wang

Songrui Zhao

Yong-Ho Ra

Md Golam Kibria

Xianhe Liu

Roksana Tonny Rashid

Mohammad Faqrul Alam Chowdhury

Ayush Pandey

Jun Song

Hieu Pham Trung Nguyen

Pengfei Ou

Baowen Zhou

Thomas Szkopek

Sharif Sadaf

Kai Cui

GaN-based nanowire heterostructures have been intensively studied for applications in light emitting diodes (LEDs), lasers, solar cells and solar fuel devices. Surface charge properties play a dominant role on the device performance and have been addressed within the prior art by use of a relatively thick large bandgap AlGaN shell covering the surfaces of axial InGaN nanowire LED heterostructures has been explored and shown substantial promise in reducing surface recombination leading to improved carrier injection efficiency and output power. However, these lead to increased complexity in device design, growth and fabrication processes thereby reducing yield/performance and increasing costs for devices. Accordingly, there are taught self-organising InGaN/AlGaN core-shell quaternary nanowire heterostructures wherein the In-rich core and Al-rich shell spontaneously form during the growth process.

High efficiency visible and ultraviolet nanowire emitters

An all-epitaxial, electrically injected surface-emitting green laser operates in a range of about 520-560 nanometers (nm). At 523 nm, for example, the device exhibits a threshold current density of approximately 0.4 kilo-amperes per square centimeter (kA/cm), which is over one order of magnitude lower than that of previously reported blue laser diodes.

Nanowire light emitting devices

The presented devices and methods are directed to efficient and effective photon emission. In one embodiment, high-performance tunnel junction deep ultraviolet (UV) light-emitting diodes (LEDs) are created using plasma-assisted molecular beam epitaxy. The device heterostructure was grown under slightly Ga-rich conditions to promote the formation of nanoscale clusters in the active region. The nanoscale clusters can act as charge containment configurations. In one exemplary implementation, a device operates at approximately 255 nm light emission with a maximum external quantum efficiency (EPE) of 7.2% and wall-plug efficiency (WPE) of 4%, which are nearly one to two orders of magnitude higher than previously reported tunnel junction devices operating at this wavelength. The devices exhibit highly stable emission originating from highly localized carriers in Ga-rich regions formed in the active region, with nearly constant emission peak with increasing current density up to 200 A/cm, due to the strong charge carrier confinement related to the presence of nanoclusters (e.g., Ga-rich) and radiative emission originating from highly localized carriers in Ga-rich regions formed in the active region.

Light emitting device

An electrode of a chemical cell includes a substrate having a surface, an array of conductive projections supported by the substrate and extending outward from the surface of the substrate, each conductive projection of the array of conductive projections having a semiconductor composition for reduction of carbon dioxide (CO) in the chemical cell, and a catalyst arrangement disposed along each conductive projection of the array of conductive projections, the catalyst arrangement including a copper-based catalyst and an iron-based catalyst for the reduction of carbon dioxide (CO) in the chemical cell.

COreduction toward methane

Nanocrystal surface-emitting lasers

An epitaxial growth process, referred to as metal-semiconductor junction assisted epitaxy, of ultrawide bandgap aluminum gallium nitride (AlGaN) is disclosed. The epitaxy of AlGaN is performed in metal-rich (e.g., Ga-rich) conditions using plasma-assisted molecular beam epitaxy. The excess Ga layer leads to the formation of a metal-semiconductor junction during the epitaxy of magnesium (Mg)-doped AlGaN, which pins the Fermi level away from the valence band at the growth front. The Fermi level position is decoupled from Mg-dopant incorporation; that is, the surface band bending allows the formation of a nearly n-type growth front despite p-type dopant incorporation. With controlled tuning of the Fermi level by an in-situ metal-semiconductor junction during epitaxy, efficient p-type conduction can be achieved for large bandgap AlGaN.

Enhanced doping efficiency of ultrawide bandgap semiconductors by metal-semiconductor assisted epitaxy

InGaN/GaN quantum layer nanowire light emitting diodes are fabricated into a single cluster capable of exhibiting a wide spectral output range. The nanowires having InGaN/GaN quantum layers formed of quantum dots are tuned to different output wavelengths using different nanowire diameters, for example, to achieve a full spectral output range covering the entire visible spectrum for display applications. The entire cluster is formed using a monolithically integrated fabrication technique that employs a single-step selective area epitaxy growth.

Monolithically integrated InGaN/GaN quantum nanowire devices

A nanowire can include a first semiconductor portion, a second portion including a quantum structure disposed on the first portion, and a second semiconductor portion disposed on the second portion opposite the first portion. The quantum structure can include one or more quantum core structures and a quantum core shell disposed about the one or more quantum core structures. The one or more quantum core structures can include one or more quantum disks, quantum arch-shaped forms, quantum wells, quantum dots within quantum wells or combinations thereof.

Core-shell InGaN/AlGaN quantum nanowire photonic structures

Solid state sources offers potential advantages including high brightness, electricity savings, long lifetime, and higher color rendering capability, when compared to incandescent and fluorescent light sources. To date however, many of these advantages, however, have not been borne out in providing white LED lamps for general lighting applications. The inventors have established that surface recombination through non-radiative processes results in highly inefficient electrical injection. Exploiting in-situ grown shells in combination with dot-in-a-wire LED structures to overcome this limitation through the effective lateral confinement offered by the shell the inventors have demonstrated core-shell dot-in-a-wire LEDs, with significantly improved electrical injection efficiency and output power, providing phosphor-free InGaN/GaN nanowire white LEDs operating with milliwatt output power and color rendering indices of 95-98. Additionally, the inventors demonstrate efficient UV nanowire LEDs for medical applications as well as the non-degraded growth of nanowire LEDs on amorphous substrates.

Methods and devices for solid state nanowire devices

InGaN offers a route to high efficiency overall water splitting under one-step photo-excitation. Further, the chemical stability of metal-nitrides supports their use as an alternative photocatalyst. However, the efficiency of overall water splitting using InGaN and other visible light responsive photocatalysts has remained extremely low despite prior art work addressing optical absorption through band gap engineering. Within this prior art the detrimental effects of unbalanced charge carrier extraction/collection on the efficiency of the four electron-hole water splitting reaction have remained largely unaddressed. To address this growth processes are presented that allow for controlled adjustment and establishment of the appropriate Fermi level and/or band bending in order to allow the photochemical water splitting to proceed at high rate and high efficiency. Beneficially, establishing such material surface charge properties also reduces photo-corrosion and instability under harsh photocatalysis conditions.

Growing community of inventors

Ann Arbor, MI, United States of America

Zetian Mi