Compositional analysis of AlInGaN quaternary layers grown by metalorganic vapour phase epitaxy

Abstract

PACS 68.37. Hk, 78.55.Cr, 78.66.Fd Using wavelength dispersive X-ray spectrometers on an Electron Probe Micro-Analyser we have accurately quantified the elemental composition of a series of homogeneous AlInGaN epitaxial layers. The thickness of the quaternary layer (~100 nm) necessitates the combination of data measured at a number of different electron beam energies and an analytical model based on a layered structure. The samples studied have aluminium fractions in the range 0.03-0.12 and indium fractions in the region of 0.01. Photoluminescence data from the samples are used to plot the dependency of the luminescence energy, linewidth and intensity on the composition. WDX mapping was employed to investigate spatial variations in the elemental compositions and the films were found to be uniform with no evidence for clustering of In or Al on a >100 nm scale. IntroductionThe ternary nitride semiconductors InGaN and AlGaN have proved to be highly successful active layers in GaN-based devices, including light emitters and transistors. However, lattice mismatch in ternary heterostructures imposes serious limitations for the design and operation of certain devices. In addition the efficiency of InGaN light emitters is severely degraded by the incorporation of too much, or too little, indium. Use of quaternary AlInGaN layers offers potential for the fabrication of lattice matched III-N heterostructures and improvement of the quantum efficiency of light emitters [1,2], particularly in the UV region with its host of important applications. The growth of high quality AlInGaN layers requires a balance between the high temperatures suited for Al-containing layers and the low temperatures necessary for incorporation of indium. Measuring the composition of AlInGaN layers using standard X-ray diffraction is complicated by the lack of a unique solution for the quaternary system and further by overlapping diffraction peaks in the case of lattice-match to the underlying GaN. In this paper we describe the compositional analysis of a series of AlInGaN layers using an Electron Probe Micro-Analyser (EPMA) equipped with wavelength dispersive X-ray (WDX) spectrometers, allowing the elemental composition to be determined with high accuracy and sub-micron spatial resolution. The compositional data are then correlated with the light emitting properties of the layers.

Determination of Ga auto-incorporation in nominal InAlN epilayers grown by MOCVD

“…Assuming the layer to be both fully strained and Ga free an initial estimate of the InAlN composition was made, as shown in Figure 1a. A [10][11][12][13][14][15] reciprocal space map confirmed the InAlN layers to be fully strained to the GaN buffer to within experimental error. While the c-plane lattice parameter and knowledge of the strain state of a layer can give an accurate estimate of the composition of ternary compound such as InAlN, it cannot unequivocally estimate the composition of a quaternary like InAlGaN as for fully strained layers a range of compositions will allow fitting.…”

Спектры Люминесценции Мощных Светодиодов На Основе Нитрида Галлия В Ультрафиолетовой И Фиолетовой Областях Спектра

“…Кристаллы были предоставлены фирмой SemiLEDs (Тайвань) и имели размеры 1.07 × 1.07 мм (размеры активной области 0.97 × 0.97 мм). Они были выращены методом газофазной эпитаксии из металлоорганических соединений на сапфировых подложках [6,7], отделены от этих подложек с использованием технологии " lift-off" и смонтированы на медную пластину, обладающую высокой теплопроводностью. Такая технология позволяет повысить внешний квантовый выход излучения, уменьшив концентрацию дефектов в слое GaN Форма спектров была описана в рамках модели, учитывающей двумерную плотность состояний и флуктуации потенциала в активной области рекомбинации, с характерным экспоненциальным спадом (энергия E 0 ) в длинноволновой области, а также функцию заполнения состояний с экспоненциальным наклоном (энергия E 1 ) в коротковолновой области [8].…”

Composition and luminescence of AlInGaN layers grown by plasma-assisted molecular beam epitaxy

“…5͑a͒, which shows data measured from two different spots on each of the "center region" samples from both series along with those from Ref. 17. For comparison the wavelengths corresponding to estimated energy gaps are plotted in Fig.…”

“…Earlier AlInGaN epilayers grown by metalorganic vapor phase epitaxy at Sheffield University follow the same tendencies. 17 The FWHM depends on a complex interplay of many factors, including the effects of electric fields, composition inhomogeneities, and dislocation/defect densities and there is no single trend with emission wavelength. An earlier investigation of AlInGaN epilayers grown by MBE on sapphire with a GaN buffer layer demonstrated a decrease in FWHM and increase in luminescence intensity as the Al/In composition ratio brought the layers closer to the lattice-match point.…”