Selective area growth and characterization of InGaN nano-disks implemented in GaN nanocolumns with different top morphologies

This work reports on the morphology control of the selective area growth of GaN-based nanostructures on c-plane GaN templates. By decreasing the substrate temperature, the nanostructures morphology changes from pyramidal islands (no vertical m-planes), to GaN nanocolumns with top semipolar r-planes, and further to GaN nanocolumns with top polar c-planes. When growing InGaN nano-disks embedded into the GaN nanocolumns, the different morphologies mentioned lead to different optical properties, due to the semi-polar and polar nature of the r-planes and c-planes involved. These differences are assessed by photoluminescence measurements at low temperature and correlated to the specific nano-disk geometry

Origin of faceted surface hillocks on semi-polar (1 1 2 ¯ 2) GaN templates grown on pre-structured sapphire

The microstructure of semi-polar (1 1 2 2) GaN templates grown on pre-structured r-plane sapphire by metal–organic vapor phase epitaxy (MOVPE) followed by hydride vapor phase epitaxy (HVPE) has been characterised by transmission electron microscopy (TEM). It is found that dislocations originating from the inclined c-plane-like GaN/sapphire interface bend and then terminate either at the coalescence regions of the adjacent GaN stripes or at the SiO2 mask. However, the regions associated with the coalescence event during the MOVPE growth act as a source of dislocations and stacking faults in the subsequent growth process. More importantly, a direct link between the formation of a surface hillock, the presence of an inversion domain, and the preferential nucleation of randomly oriented GaN particles at a region containing a dislocation bundle originating from coalescence has been established. It is suggested that controlling the surface conditions of the MOVPE GaN layer before HVPE and optimising the HVPE nucleation process are important to avoid the surface hillocks.This work was financially supported by the European Commission (FP7) within the framework of the project “AlGaInN materials on semi-polar templates for yellow emission in solid state lighting applications” (ALIGHT) (Project no.: 280587) and by the Deutsche Forschungsgemeinschaft (DFG) within the framework of the project “Polarization Field Control in Nitride Light Emitters” (PolarCoN).This is the accepted manuscript for a paper published in Journal of Crystal Growth Volume 415, 1 April 2015, Pages 170–175, doi: 10.1016/j.jcrysgro.2014.12.04

Brief review on the physics of solid-state lighting device

In this review, the chronological advances of solid state lighting (SSL) alongside the theoretical predictions was examined. The discussion includes its crystallographic orientations, substrate growth, colour rendering, misfit dislocations, quantum well fabrication, stacking fault and energy efficiency. It has been discovered that the challenges confronting the potential of SSL devices may not just be ambient temperature of the operating environment or the safe limits of the blue/white-light hazard. This paper sheds lighter on the physics responsible for the SSL white lighting, wave function lapping at different crystallographic orientations and stress relaxation limits of quantum well (QW) heterointerface

Brief review on the physics of solid-state lighting device

In this review, the chronological advances of solid state lighting (SSL) alongside the theoretical predictions was examined. The discussion includes its crystallographic orientations, substrate growth, colour rendering, misfit dislocations, quantum well fabrication, stacking fault and energy efficiency. It has been discovered that the challenges confronting the potential of SSL devices may not just be ambient temperature of the operating environment or the safe limits of the blue/white-light hazard. This paper sheds lighter on the physics responsible for the SSL white lighting, wave function lapping at different crystallographic orientations and stress relaxation limits of quantum well (QW) heterointerface

Brief review on the physics of solid-state lighting device

In this review, the chronological advances of solid state lighting (SSL) alongside the theoretical predictions was examined. The discussion includes its crystallographic orientations, substrate growth, colour rendering, misfit dislocations, quantum well fabrication, stacking fault and energy efficiency. It has been discovered that the challenges confronting the potential of SSL devices may not just be ambient temperature of the operating environment or the safe limits of the blue/white-light hazard. This paper sheds lighter on the physics responsible for the SSL white lighting, wave function lapping at different crystallographic orientations and stress relaxation limits of quantum well (QW) heterointerfaces

Deep-Ultraviolet AlGaN/AlN Core-Shell Multiple Quantum Wells on AlN Nanorods via Lithography-Free Method

We report deep ultraviolet (UVC) emitting core-shell-type AlGaN/AlN multiple quantum wells (MQWs) on the AlN nanorods which are prepared by catalyst/lithography free process. The MQWs are grown on AlN nanorods on a sapphire substrate by polarity-selective epitaxy and etching (PSEE) using high-temperature metal organic chemical vapor deposition. The AlN nanorods prepared through PSEE have a low dislocation density because edge dislocations are bent toward neighboring N-polar AlN domains. The core–shell-type MQWs grown on AlN nanorods have three crystallographic orientations, and the final shape of the grown structure is explained by a ball-and-stick model. The photoluminescence (PL) intensity of MQWs grown on AlN nanorods is approximately 40 times higher than that of MQWs simultaneously grown on a planar structure. This result can be explained by increased internal quantum efficiency, large active volume, and increase in light extraction efficiency based on the examination in this study. Among those effects, the increase of active volume on AlN nanorods is considered to be the main reason for the enhancement of the PL intensity

Heterostructures of III-Nitride Semiconductors for Optical and Electronic Applications

III-Nitride-based heterostructures are well suited for the fabrication of various optoelectronic devices such as light-emitting diodes (LEDs), laser diodes (LDs), high-power/high-frequency field-effect transistors (FETs), and tandem solar cells because of their inherent properties. However, the heterostructures grown along polar direction are affected by the presence of internal electric field induced by the existence of intrinsic spontaneous and piezoelectric polarizations. The internal electric field is deleterious for optoelectronic devices as it causes a spatial separation of electron and hole wave functions in the quantum wells, which thereby decreases the emission efficiency. The growth of III-nitride heterostructures in nonpolar or semipolar directions is an alternative option to minimize the piezoelectric polarization. The heterostructures grown on these orientations are receiving a lot of focus due to their potential improvement on the efficiency of optoelectronic devices. In the present chapter, the growth of polar and nonpolar III-nitride heterostructures using molecular beam epitaxy (MBE) system and their characterizations are discussed. The transport properties of the III-nitride heterostructure-based Schottky junctions are also included. In addition, their applications toward UV and IR detectors are discussed

Controlled facet growth of GaN and the overgrowth with ZnO

Ph.DDOCTOR OF PHILOSOPH

Structural and optical emission uniformity of m-plane InGaN single quantum wells in core-shell nanorods

Controlling the long-range homogeneity of core-shell InGaN/GaN layers is essential for their use in light-emitting devices. This paper demonstrates variations in optical emission energy as low as ~7 meV.µm-1 along the m-plane facets from core-shell InGaN/GaN single quantum wells as measured through high-resolution cathodoluminescence hyperspectral imaging. The layers were grown by metal organic vapor phase epitaxy on etched GaN nanorod arrays with a pitch of 2 µm. High-resolution transmission electron microscopy and spatially-resolved energy-dispersive X-ray spectroscopy measurements demonstrate a long-range InN-content and thickness homogeneity along the entire 1.2 μm length of the m-plane. Such homogeneous emission was found on the m-plane despite the observation of short range compositional fluctuations in the InGaN single quantum well. The ability to achieve this uniform optical emission from InGaN/GaN core-shell layers is critical to enable them to compete with and replace conventional planar light-emitting devices