Abstract
Atom probe tomography and quantitative scanning transmission electron microscopy are used to assess the composition of non-polar a-plane (11-20) InGaN quantum wells for applications in optoelectronics. The average quantum well composition measured by atom probe tomography and quantitative scanning transmission electron microscopy quantitatively agrees with measurements by X-ray diffraction. Atom probe tomography is further applied to study the distribution of indium atoms in non-polar a-plane (11-20) InGaN quantum wells. An inhomogeneous indium distribution is observed by frequency distribution analysis of the atom probe tomography measurements. The optical properties of non-polar (11-20) InGaN quantum wells with indium compositions varying from 7.9% to 20.6% are studied. In contrast to non-polar m-plane (1-100) InGaN quantum wells, the non-polar a-plane (11-20) InGaN quantum wells emit at longer emission wavelengths at the equivalent indium composition. The non-polar a-plane (11-20) quantum wells also show broader spectral linewidths. The longer emission wavelengths and broader spectral linewidths may be related to the observed inhomogeneous indium distribution.
Highlights
Blue InxGa(1Àx)N quantum well (QW) based light emitting diodes (LEDs) exhibit high efficiencies compared to traditional lighting sources.[1,2] the efficiency of nitride devices rapidly decreases at longer emission wavelengths, which extend into the green spectrum.[3–6] Emission over the green spectral region is important for lighting and display technologies since it is where the response of the human eye is greatest
quantitative scanning transmission electron microscopy are used to assess the composition of non-polar a-plane
The average quantum well composition measured by atom probe tomography
Summary
Blue InxGa(1Àx)N quantum well (QW) based light emitting diodes (LEDs) exhibit high efficiencies compared to traditional lighting sources.[1,2] the efficiency of nitride devices rapidly decreases at longer emission wavelengths, which extend into the green spectrum.[3–6] Emission over the green spectral region is important for lighting and display technologies since it is where the response of the human eye is greatest. Growth along non-polar orientations suppresses the internal electric field along the growth axis[12,13] and may aid in the development of high efficiency longer wavelength emission devices. It has been widely reported that polar (0001) InGaN QW structures exhibit a random indium distribution,[20,21] which has been observed by Riley et al in non-polar m-plane (1–100) InGaN QWs.[22]. Tang et al have recently suggested that non-polar a-plane (11–20) QWs may exhibit an inhomogeneous distribution of indium.[23]. APT is applied to study non-uniformities in the indium distribution in the QWs. We proceed to measure the photoluminescence (PL) spectral properties of the non-polar a-plane (11–20) QWs over a range of indium compositions, and compare with QWs grown on the perpendicular non-polar m-plane (1–100)
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