Fu-an Chu

Efficiency Droop Characteristics in InGaN-Based Near Ultraviolet-to-Blue Light-Emitting Diodes

In this study, we prepared InGaN-based light-emitting diodes (LEDs) with peak emissions ranging from 400 to 445 nm and investigated their efficiency droop characteristics at injection currents of up to 1 A. We found that the external quantum efficiencies (EQEs) changed dramatically when the critical current increased from 0 to 350 mA, but exhibited a similar negative slope upon increasing the current from 350 mA to 1 A. The effects of piezoelectric polarization and different localized states in the active layer of the near UV-to-blue LEDs influenced the peak EQEs and the dramatic decays of the EQE droops at lower injection currents.

Enhanced performance of InGaN-based light-emitting diodes grown on volcano-shaped patterned sapphire substrates with embedded SiO2

This paper describes highly efficient InGaN-based light-emitting diodes (LEDs) grown on volcano-shaped patterned sapphire substrates with embedded SiO2 (SVPSS). Raman spectroscopy and transmission electron microscopy revealed that the LEDs grown on the SVPSS had high internal quantum efficiency resulting from relaxed compressive strain and fewer threading dislocations in the GaN epitaxial layers. Experimentally measured data and ray-tracing simulations suggested that the enhancement in the light extraction efficiency was due to the light scattering effect arising from the conical air voids and the gradual refractive index matching resulting from the embedded SiO2. Compared with a conventional LEDs operated at an injection current of 350 mA, the light output power from our LED grown on SVPSS was increased by 72%.

Improved Device Performance of GaN/AlGaN High-Electron-Mobility Transistor Using PdO Gate Interlayer

We demonstrate significant improvements of GaN/AlGaN high-electron-mobility transistors (HEMTs) by employing a PdO gate interlayer, which exhibit device performance superior to that of Pd Schottky gate HEMTs. The PdO gate interlayer effectively reduces the gate leakage current by four orders of magnitude, and it also increases the ION/IOFF ratio to four orders of magnitude. The improved AlGaN/GaN/PdO HEMT shows a nearly ideal subthreshold slope of 66 mV/dec. The flicker noise characteristic is also observed to be lower in PdO-gate HEMTs than in Pd-Gate HEMTs. The high-work-function PdO layer and associated barrier height enhancement are the origins of the improved device performance.

Using Pre-TMIn Treatment to Improve the Optical Properties of Green Light Emitting Diodes

We investigated the effects of pre-TMIn treatment on the optical properties of green light emitting diodes (LEDs). Although pre-TMIn treatment did not affect the epitaxial structure of quantum wells, it significantly improved the quality of the surface morphology relative to that of the untreated sample. Indium cluster can be seen by high-resolution transmission electron microscopy (HR-TEM), which is the explanation for the red-shift of photoluminescence (PL). Time-resolved photoluminescence measurements indicated that the sample prepared with pre-TMIn treatment had a shorter radiative decay time. As a result, the light output power of the treated green LED was higher than that of the conventional untreated one. Thus, pre-TMIn treatment appears to be a simple and efficient means of improving the performance of green LEDs.

The analysis of nano-patterned sapphire substrates-induced compressive strain to enhance quantum-confined stark effect of InGaN-based light-emitting diodes

This paper demonstrates that the quantum-confined stark effect of InGaN-based light-emitting diodes can be enhanced by the means of using the hexagonal nano-post patterned sapphire substrates based on the increase of the post-duty cycle.

Investigation of nano-sized hole/post patterned sapphire substrates-induced strain-related quantum-confined stark effect of InGaN-based light-emitting diodes

This paper demonstrates that the efficiency of InGaN-based light-emitting diodes with nano-post patterned sapphire substrates is superior to that with nano-hole patterned sapphire substrates under the same nano-scale feature owing to reduced quantum-confined stark effect.

Impact of PdO Gate Interlayer on the DC Performance of GaN/AlGaN High Electron Mobility Transistor

We demonstrate significant improvements of GaN/AlGaN high-electronmobility-transistor (HEMT) by employing PdO gate interlayer which exhibit device performance superior to that of Pd Schottky gate HEMTs. The PdO gate interlayer effectively reduces the gate leakage current by four orders of magnitude and it also increases the ION/IOFF ratio to four orders of magnitude. The improved AlGaN/GaN/PdO HEMT shows a nearly ideal sub-threshold slope of 66 mV/dec. A lower flicker noise characteristic is also observed in the PdO-Gate HEMTs compared with Pd-Gate HEMT. The high work function PdO layer and associated barrier height enhancement is believed to be the origin of improved device performance.

Optimizing the multiple quantum well thickness of an InGaN blue light emitting diode

InGaN/GaN blue light emitting diodes with varied quantum well thickness from 2.4 nm to 3.6 nm are fabricated and characterized by atmosphere pressure metalorganic chemical vapor deposition (AP-MOCVD). Experimental results show that the exciton localization effect is enhanced from 21.76 to 23.48 by increasing the quantum well thickness from 2.4 nm to 2.7 nm. However, with the further increase of quantum well thickness, the exciton localization effect becomes weaker. Meanwhile, the peak wavelength of electroluminescence redshift with the increase of well thickness due to the larger quantum confined Stark effect (QCSE). In addition, the efficiency droop can be improved by increasing the well thickness.