Surface control of light‐emitting structures based on III‐nitrides

Abstract

The results on surface control of light-emitting structures (LES) based on MQW InGaN/GaN grown by MOCVD on (0001) sapphire substrates have been presented. For these purposes, the treatment of atomicforce-microscopy data by multifractal analyses has been applied. It was shown, that multifractal parameter (the degree of order of mosaic structure, ∆) reflects the peculiarities of the extended defect system (EDS), including mosaic structure and high density of dislocations, and correlates with the volume structural, electrical and optical properties of LES. Depending on ∆, EDS relaxes with formation of either the domain dilatation boundaries or numerous domain dislocation boundaries and these structural peculiarities influence essentially the shape of photo-and electroluminescence spectra, delayed spectra and the values of external quantum efficency. The surface control using ∆ can be applied to optimize the properties of LES and the process of their creation.

Degradation of blue LEDs related to structural disorder

“…It is well known from material science that the migration of dislocations in such system is practically impossible. Resent experimental data for GaN-based blue LEDs confirmed this conclusion [2].Our previous results of structural, optical and electrical properties studies [6,7] allow to suppose that structural disorder determined by the extended defect system relaxation and related with peculiarities of domains coalescence can be one of the degradation reason.…”

Comparative study of quantum efficiency of blue LED with different nanostructural arrangement

“…For the well-ordered mosaic structures the defect relaxation occurs via the coherent concordance of mosaic structure domains with a formation of dilatation boundaries, while for the less-ordered mosaic structures the defect system relaxation occurs via the formation of numerous dislocated domain boundaries, the edge dislocation density in which exceeds essentially that of screw threading dislocations [1]. As shown in [2,3], the close correlation between mosaic structure ordering and the surface roughness allows the quantitative characterization of mosaic structure ordering by the multifractal analysis based on the atomic force microscopy data. However, in spite of essential ordering effect on the electrical and optical properties of hexagonal III-nitrides, the detail study of QE dependence in the III-nitride based LEDs on the nanostructural arrangement (NA) determined by the extended defect system relaxation was not carried out up to now.…”

Failure mechanisms in blue InGaN/GaN LEDs for high power operation

“…NA becomes apparent in surface and in surface morphology of LED structures. The different NA forms can be characterized quantitatively using such multifractal parameters as degree of order (or degree of disorder) [5]. Correlation between values of degree of disorder values and properties of EDS such as leakage current values at biases U < 2 V had been clarified earlier [7].…”

“…NA determines the properties of EDS, including a high density of threading dislocations, screw, their accumulations, dilatation and dislocation boundaries [5,6]. NA becomes apparent in surface and in surface morphology of LED structures.…”

“…In order to solve these problems, the approach taking into account numerous forms of NA of LED structures has been used [5]. NA determines the properties of EDS, including a high density of threading dislocations, screw, their accumulations, dilatation and dislocation boundaries [5,6].…”