University of Michigan

Ayush Pandey

Zetian Mi

Xudong Fan

Zhaohui Zhong

Xianhe Liu

Girish Kulkarni

Wenzhe Zang

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 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

Electrochemical sensors for the detection of select analytes are provided. The electrochemical sensors include a barrier layer having a substantially uniformed thickness disposed between a sensing layer and an ion exchange membrane. The barrier layer includes a two-dimensional nanomaterial. The barrier layer has a thickness of less than or equal to about 1 nm. The sensing layer has a thickness of less than or equal to about 10 nm. The sensing layer generates ions in response to select analytes. The barrier layer allows the generation ions to pass therethrough and travel into the ion exchange membrane. The barrier layer acts as a physical barrier to contaminants and larger molecules.

Growing community of inventors

Ann Arbor, MI, United States of America

Ayush Pandey