Abstract
Intersubband (intraband) transitions allow absorption of photons in the infrared spectral regime, which is essential for IR-photodetector and optical communication applications. Among various technologies, nanodisks embedded in nanowires offer a unique opportunity to be utilized in intraband devices due to the ease of tuning the fundamental parameters such as strain distribution, band energy, and confinement of the active region. Here, we show the transverse electric polarized intraband absorption using InGaN/GaN nanodisks cladded by AlGaN. Fourier transform infrared reflection (FTIR) measurement confirms absorption of normal incident in-plane transverse electric polarized photons in the mid-IR regime (wavelength of ~ 15 μm) at room temperature. The momentum matrix of the nanodisk energy states indicates electron transition from the ground state s into the px or py orbital-like excited states. Furthermore, the absorption characteristics depending on the indium composition and nanowire diameter exhibits tunability of the intraband absorption spectra within the nanodisks. We believe nanodisks embedded nanowires is a promising technology for achieving tunable detection of photons in the IR spectrum.
Highlights
Intersubband transitions allow absorption of photons in the infrared spectral regime, which is essential for IR-photodetector and optical communication applications
The intraband absorption has been confirmed in the near- to mid-infrared spectrum using GaN/AlGaN multiple quantum well (MQWs)[12–18], coupled double quantum well[19], and GaN/AlN quantum dot (QD)[20–23] material systems
The intraband absorption energy as a function of indium composition and the radius of the nanowire indicates that higher indium concentration induces a stronger internal electrical field, leading to a deeper potential in the nanodisk, which leads to a blue-shift in the absorption energy, whereas an increase in nanowire radius reduce the absorption energy due to a relaxed quantum confinement
Summary
Intersubband (intraband) transitions allow absorption of photons in the infrared spectral regime, which is essential for IR-photodetector and optical communication applications. Fourier transform infrared reflection (FTIR) measurement confirms absorption of normal incident in-plane transverse electric polarized photons in the mid-IR regime (wavelength of ~ 15 μm) at room temperature. Intraband absorption of transverse electric (TE) polarized light can be hardly achieved using quantum well based structures; a consequence of intraband selection rules. This imposes limitations for application of quantum well systems for intraband transition since normal incidence absorption is forbidden. This limitation can be eliminated using quantum wire, disk, and dot structures alternative to the planar quantum well devices. The intraband absorption energy as a function of indium composition and the radius of the nanowire indicates that higher indium concentration induces a stronger internal electrical field, leading to a deeper potential in the nanodisk, which leads to a blue-shift in the absorption energy, whereas an increase in nanowire radius reduce the absorption energy due to a relaxed quantum confinement
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