Organic-Inorganic Hybrid nanostructured devices

         This research goal is to investigate the (In)GaN/organic semiconductor hybrid heterojunction device as a part of ongoing efforts to improve the performance of (In)GaN-based optoelectronic devices and to explore novel materials.

The research direction has been focused on the charge injection and transport studies for understanding the organic/inorganic interface, especially focusing on the photocurrent response at the reverse or photovoltaic regime. Our ultimate goal is to create synergy as combining high performance wide-bandgap III-nitides and organic semiconductors, for device applications which reach beyond lighting and photovoltaics, such as bio/chemical detector photosensor. Furthermore, we would like to pursue enhanced performance of nanostructured device (such as Si nanowires or GaN nano-pillars) using soft organic materials as an electron or hole transport layer by conformal deposition onto the nano-structured inorganic materials, which will have increased contact area and better light extraction through nano-structure.

CuPc/GaN Hybrid Structure
Fig.1.
(a) CuPc/GaN hybrid device structure: Al(80nm)/Ti(10nm)/n-GaN/CuPc(80nm)/Au(80nm) was fabricated for photo-detector application

(b) Photocurrent spectrum: Efficient photocurrent (EQE=4%) was generated from absorption of InGaN at 380nm.

 

GaN/Organic Hybrid LED Fabrication

Fig.2.
(a) GaN/organic hybrid LED fabrication: CuPc was used as an hole injector for InGaN LED structure and uniform electroluminescence was observed at 460nm.

(b) GaN nanorod fabrication: GaN nanorod structure was fabricated for hybrid nanostructure photo-detector application using Au as an etching mask.

 

 Ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) were performed. For as-grown GaN samples, 0.6 eV and 0.13 eV upward bend bending was observed for Ga-polar and N-polar GaN, respectively and the mechanism of band bending was explained by spontaneous polarization field. Furthermore the band alignments between CuPc and Ga- vs. N-polar GaN show contrasting results. No indication of additional band bending or charge displacement was observed from Ga-polar GaN. On the other hand, 0.54 eV additional upward band bending was observed from N-polar GaN and HOMO energy level of CuPc shifted upward with increased thickness, indicating the displacement of electrons from GaN toward CuPc.

 Band alignment of GaN and CuPc 

Ultraviolet photoemission spectroscopy(UPS) and X ray photoemission spectroscopy (XPS) were performed. For as grown GaN samples, 0.6 eV and 0.13 eV upward band bendig was observed for Ga-polar and N-polar GaN, respectively and the mechanism of band bending was explained by spontaneous polarization fields. Furthermore the band alighment between CuPc and Ga -vs. N polar GaN shw contrasting results. No indication of  additional band bending or charge displacement was observed from Ga polar GaN. On the other hand, 0.54eV additional upward band bending was observed from N polar GaN and HOMO energy level of CuPc shhifted upwrad with increased thickness, indicating the displacement of electrons from GaN toward CuPc.

 
Random Lasing

 
A new demonstration of random lasing in a boundary-free system has shown new avenues to create random lasers in disordered systems. For most lasers, scattering is an undesired effect leading to losses. Random lasers, on the other hand, depend on multiple scattering events to achieve their effects. Instead of a cavity that contains photons, random lasers use the scattering process as a mode of containment, providing enough time for a pump source to create inversion.
 
This research is in collaboration with A.Kahn in Princeton U.V and Jung Han in Yale U.V

 

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