Parijat Deb

High-reflectivity Al-Pt nanostructured Ohmic contact to p-GaN

The effect of nanoscale Pt islands on the electrical characteristics of contacts to p-type gallium nitride (GaN) has been investigated to explore the feasibility for the flip-chip configuration light-emitting diodes (LEDs) using an Al-based reflector. An as-deposited Al contact to p-GaN with a net hole concentration of 3times1017cm-3 was rectifying. However, an Al contact with nanoscale Pt islands at the interface exhibited ohmic behavior. A specific contact resistivity of 2.1times10-3Omegamiddotcm2 and a reflectance of 84% at 460 nm were measured for the Al contact with nanoscale Pt islands. Current-voltage temperature measurements revealed a Schottky barrier height reduction from 0.80 eV for the Al contact to 0.58 eV for the Al contact with nanoscale Pt islands. The barrier height reduction may be attributed to electric field enhancement and the enhanced tunneling due to the presence of the nanoscale Pt islands. This will offer an additional silver-free option for the p-type ohmic contact in flip-chip configuration LEDs. Theory suggests that the ohmic contact characteristics may be improved further with smaller Pt islands that will enhance tunneling across the interface with the GaN and in the vicinity of the Pt-Al interface

Field emission from GaN and (Al,Ga)N∕GaN nanorod heterostructures

Vacuum field emission from GaN and (Al,Ga)N∕GaN nanorods with pyramidal tips has been measured. The turn-on fields, defined at a current density of 0.1μA∕cm2, were found to be 38.7 and 19.3V∕μm, for unintentionally doped GaN and (Al,Ga)N∕GaN nanorods, respectively. The 5nm (Al,Ga)N layer reduced the electron affinity at the surface, thereby lowering the turn-on field and increasing the current density. The nanostructures exhibit a field enhancement factor of approximately 65 and the work function of the (Al,Ga)N∕GaN nanorod heterostructure was estimated to be 2.1eV. The stability of the emission characteristics and the simple fabrication method suggest that intentionally doped and optimized (Al,Ga)N∕GaN nanorod heterostructures may prove suitable for field-emission device.

Alpha-synuclein as a template for the synthesis of metallic nanowires

Exploiting the concepts learnt from nature to build new nanomaterials from the bottom up is critical for the efficient design of complex nanodevices. We demonstrate for the first time that the capacity of the α-synuclein protein to assemble into nanofibres can be used for the synthesis of metallic nanowires. Silver and platinum nanowires with controlled diameters, ranging from 15 to 125 nm, have been synthesized on an α-synuclein protein fibre scaffold.

Spatial and compositional dependence of deep-level defects in InGaN LEDs (Conference Presentation)

Efficiency droop and the green gap are challenges to InGaN/GaN light emitting diodes (LEDs). Defects have been suggested to contribute to both effects, so understanding the origin of defects and their impact on LED performance is important to improving efficiency. This talk describes the use of deep level optical spectroscopy (DLOS) to characterize deep level defects in quantum well (QW) and quantum barrier (QB) regions of InGaN LEDs. The spatial dependence of deep level defect density in the MQW region and the evolution of QW deep level defects with indium alloying will be discussed.

Metallic nanowires on a new protein template

Exploiting the concepts learnt from nature to build new nanomaterials from the bottom-up is critical for the efficient design of complex nanodevices. We demonstrate for the first time that the capacity of the &agr;-synuclein protein to assemble into nanofibers can be used for the synthesis of metallic nanowires. Silver and platinum nanowires with controlled diameters, ranging from 15 to 125nm, have been synthesized on an &agr;-synuclein protein fiber scaffold.