The Novel Investigation and Fabrication of High Quality III-Nitride-Based Light-Emitting Diodes Grown by Metal Organic Vapor Phase Epitaxy

  • 顏 政雄

學生論文: Doctoral Thesis

摘要

There are two main approaches to enhance output efficiency of GaN-based LEDs 1) internal quantum efficiency (IQE) and light extraction efficiency (LEE) Therefore in this dissertation we propose some solutions which were focused on improvement of material quality and light extraction efficiency for realizing highly efficient GaN-based LEDs The main focus of this dissertation can be dividing into three parts First we demonstrate GaN-based blue and UV LEDs with ex-situ sputtered AlN nucleation layers The effects of the sputtered AlN nucleation layer on the electrical and optical properties of the GaN-based blue and UV LEDs are discussed For the blue LEDs replacing the in-situ AlN nucleation layer with the sputtered AlN nucleation layer reduced the (002) and (102) X-ray rocking curve widths of the GaN layer from 318 0 to 201 1 and 412 5 to 225 0 arcsec respectively The –20 V reverse leakage current of the LEDs with the sputtered AlN nucleation layer is about 3 orders less than that of the LEDs with the in-situ AlN nucleation layer In addition the LEDs with sputtered AlN nucleation layer could sustain more than 60% passing yield on the ESD test of under a –600 V machine mode whereas the LEDs with the in-situ AlN nucleation layer sustained less than 40% passing yield Moreover the 20-A/cm^2 output power of the LEDs with the sputtered AlN nucleation layer also improved by approximately 5 6%compared with that of the LEDs with the in-situ AlN nucleation layer Furthermore for the UV LEDs the introduction of the ex-situ sputtered AlN nucleation layer also improved the crystal quality of the GaN and the n-AlGaN layer of the GaN-based UV LEDs Hence the 20-mA output power of UV LEDs with ex-situ AlN nucleation layers is higher than that of UV LEDs with GaN nucleation layers In addition the enhanced power output of UV LEDs with ex-situ AlN nucleation could reach around 52% in magnitude at peak emission wavelengths of 370 nm compared with power outputs of UV LEDs with GaN nucleation layers Furthermore UV LEDs with ex-situ AlN nucleation show improved reliability The UV LEDs with ex-situ AlN nucleation layer revealed a power output drop of around 9% within 168 hours which is less than the around 14% power drop of UV LEDs with GaN nucleation layer The second part we report the use of digital InN/GaN growth structure to replace the thick InGaN well layers in the InGaN/GaN multiquantum well (MQW) and the fabrication of GaN-based green light-emitting diodes (LEDs) Using this method it was found that we could achieve InGaN “well layers” with high crystal quality due to the enhanced migration of adatoms during the growth It was also found that indium composition in the InGaN “well layers” and the thickness of the InGaN “well layers” both depend strongly on the growth time of InN and GaN It was also found that we could achieve stronger electroluminescence (EL) intensities with narrower full-width-half-maxima (FWHMs) from the LEDs with digital InN/GaN growth InGaN “well layers” Thick InGaN wells with digital InN/GaN growth growth exhibit superior optical properties than conventional growth thin InGaN wells The activation energy of thick InGaN wells by digital InN/GaN growth (48 meV) from temperature-dependent integrated photoluminescence intensity is larger than that of conventional growth thin InGaN wells (25 meV) Moreover thick InGaN wells with digital InN/GaN growth exhibit less σ value (degree of localization effects) of 19 meV than conventional growth thin InGaN wells (23 meV) The 20 A/cm^2 output power improvement of light-emitting diodes (LEDs) with digital InN/GaN growth thick InGaN wells is approximately 22% as compared to that of green LEDs with conventional thin InGaN wells Furthermore it was found that we could achieve better ideality factors and smaller reverse leakage currents from the proposed devices In the third part we report the fabrication of GaN-based blue LEDs with embedded reshaped ellipsoidal voids by using an electrochemically etched n(-)-GaN template It was found that the size of the reshaped ellipsoidal voids is strongly related to the initial diameter of the horizontal/tree-branch-like pores in the n(-)-GaN and the bias of electrochemical etching It was also found that the forward voltage of the LEDs on such templates did not increase drastically Furthermore it was found that light output power at 20 A/cm^2 is 50% higher for such LEDs as compared to conventional LEDs
獎項日期2014 一月 22
原文English
監督員Wei-Chi Lai (Supervisor)

引用此文

The Novel Investigation and Fabrication of High Quality III-Nitride-Based Light-Emitting Diodes Grown by Metal Organic Vapor Phase Epitaxy
政雄, 顏. (Author). 2014 一月 22

學生論文: Doctoral Thesis