Quantitative parameters for the examination of InGaN QW multilayers by low-loss EELS

Abstract

We present a detailed examination of a multiple InxGa1-xN quantum well (QW) structure for optoelectronic applications. The characterization is carried out using scanning transmission electron microscopy (STEM), combining high-angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS). Fluctuations in the QW thickness and composition are observed in atomic resolution images. The impact of these small changes on the electronic properties of the semiconductor material is measured through spatially localized low-loss EELS, obtaining band gap and plasmon energy values. Because of the small size of the InGaN QW layers additional effects hinder the analysis. Hence, additional parameters were explored, which can be assessed using the same EELS data and give further information. For instance, plasmon width was studied using a model-based fit approach to the plasmon peak; observing a broadening of this peak can be related to the chemical and structural inhomogeneity in the InGaN QW layers. Additionally, Kramers-Kronig analysis (KKA) was used to calculate the complex dielectric function (CDF) from the EELS spectrum images (SIs). After this analysis, the electron effective mass and the sample absolute thickness were obtained, and an alternative method for the assessment of plasmon energy was demonstrated. Also after KKA, the normalization of the energy-loss spectrum allows us to analyze the Ga 3d transition, which provides additional chemical information at great spatial resolution. Each one of these methods is presented in this work together with a critical discussion of their advantages and drawbacks.

Electron effective mass in In0.33Ga0.67N determined by mid-infrared optical Hall effect

“…The determination of free charge carrier effective mass at room temperature or higher (under device operation condition) temperature is still a challenging task. There are only few reports which estimate experimentally the effective mass parameters in In x Ga 1−x N. 5,6 Eljar-rat et al estimated an isotropic average of the electron effective mass parameter between 0.14 m 0 and 0.16 m 0 (m 0 is the free electron mass) for multilayer quantum well structures of In 0.05 Ga 0.95 N and In 0.2 Ga 0.8 N layers using a numerical Kramers-Kronig extension of electron energy loss spectra. Yadav et al investigated polycrystalline In x Ga 1−x N layers and estimated isotropically averaged electron effective mass parameters for In contents from 0.4 to 1 combining parameters obtained from electrical Hall effect and optical reflectivity measurements.…”