Long wavelength red to green emissions from {11 2¯ 2} semipolar multi-quantum wells on fully relaxed InGaN underlayer

Abstract

In this study, we report a high In composition {11-22} InGaN underlayer grown on an m-plane sapphire substrate and the multi-quantum wells (MQWs) grown on it. The InGaN template with high In composition (In:~18%) was fully relaxed. The MQWs photoluminescence (PL) spectrum on the InGaN underlayer exhibited a higher emission intensity and a longer emission wavelength compared with that on a GaN template. Additionally, when the InGaN underlayer was adopted, an InGaN barrier was more suitable than a GaN barrier for the long-wavelength (red) region; the PL spectrum of InGaN/InGaN MQWs was twice as high as that of InGaN/GaN MQWs in the red emission region. Finally, we investigated the optical polarization of the MQWs on {11-22} InGaN underlayers and discussed its characteristics using theoretical equations.

Growth and Microstructure Analyses of Semipolar AlInN Epitaxial Layers on a Fully Relaxed Semipolar {112¯2} GaInN/GaN/m‐plane Sapphire Template

“…The three samples showed almost the same surface morphologies with streak‐shape lines parallel to the [] direction, which probably represent the surface morphology of the underlying semipolar GaInN layer. [ 23 ] The lower images in Figure 2 are surface morphologies obtained by the AFM observation for the same samples as in the upper images, in which their root‐mean‐square (RMS) roughness values are also shown. The results showed that a granular morphology was formed for all the samples and that their RMS values were as relatively small as less than 1.5 nm.…”

“…Figure 1 schematically shows a typical sample structure investigated in this study. The AlInN layers were grown on a semipolar {} GaInN template [ 23 ] using a horizontal‐type MOCVD system (Taiyo Nippon Sanso, SR‐2000). The semipolar GaInN template consisted of a 1.6 μm‐thick GaInN layer and a 1.4 μm‐thick GaN layer on an m ‐plane sapphire substrate, which was prepared via another MOCVD process.…”

“…[ 21,22 ] Recently, Tawarazako et al [ 23 ] reported that fully relaxed GaInN layers with high InN mole fractions can be grown on the semipolar {} GaN layers formed on m ‐plane sapphire substrates and that they were surely effective for improving the luminescence efficiency in long‐wavelength GaInN QW light emitters. [ 23 ] In addition to this, if thick and flat‐surface AlInN layers can be formed on the fully relaxed semipolar GaInN layers, they will become highly promising structural components for long‐wavelength visible GaN LDs. On the other hand, although some researchers have reported the growth of nonpolar [ 7,8,24–27 ] and semipolar [ 26–29 ] AlInN layers, there have been no reports focusing on the growth of thick and flat‐surface AlInN epitaxial layers with high‐InN mole fraction.…”

“…This is because they can suppress the quantum confined Stark effect (QCSE) occurring at QWs in polar nitride structures and thereby promote the radiative carrier recombination. [ 21,22 ] Recently, Tawarazako et al [ 23 ] reported that fully relaxed GaInN layers with high InN mole fractions can be grown on the semipolar {} GaN layers formed on m ‐plane sapphire substrates and that they were surely effective for improving the luminescence efficiency in long‐wavelength GaInN QW light emitters. [ 23 ] In addition to this, if thick and flat‐surface AlInN layers can be formed on the fully relaxed semipolar GaInN layers, they will become highly promising structural components for long‐wavelength visible GaN LDs.…”

“…[21,22] Recently, Tawarazako et al [23] reported that fully relaxed GaInN layers with high InN mole fractions can be grown on the semipolar {1122} GaN layers formed on m-plane sapphire substrates and that they were surely effective for improving the luminescence efficiency in long-wavelength GaInN QW light emitters. [23] In addition to this, if thick and flat-surface AlInN…”