Intersubband Transitions in Nonpolar m‐Plane AlGaN/GaN Heterostructures

Abstract

heterostructures have the potential to supplant polar heterostructures in infrared optoelectronic devices due to their theoretical advantages stemming from the absence of built-in polarization fields along nonpolar directions of the nitride wurtzite lattice. However, development of nonpolar m-plane infrared devices in a broad spectral range has been hampered, so far, by challenges to grow homogeneous high Al-composition AlGaN on m-plane GaN. Al x Ga 1-x N layers with 0.6< x <0.8 are found to be kinetically unstable under metal-rich growth conditions by plasma-assisted molecular-beam epitaxy. After reviewing recent progress in the field, this paper focuses on the effect of the structure of m-plane Al x Ga 1Àx N/GaN (x <0.6) superlattices on near-infrared intersubband absorption. Even at these intermediate Al-compositions, the effective growth rate of AlGaN is drastically reduced, and the AlGaN-GaN interface roughness is unexpectedly high. Consequently, accurate determination of layer thicknesses and alloy composition necessitates structural characterization by a combination of scanning transmission electron microscopy and high-resolution X-ray diffraction. The energy and linewidth of near-infrared intersubband transitions are also significantly affected by this unusual growth behavior. The experimental results for intersubband absorption of m-and c-plane superlattices are compared to each other and with numerical calculations, and the main reasons for discrepancies are discussed.

A Decade of Nonpolar and Semipolar III-Nitrides: A Review of Successes and Challenges

“…The relevant background and important physics are covered and perspectives on the successes, challenges, and future outlook for these materials and related devices are provided. For example, some successes include higher gain and lower transparency carrier density in laser diodes (LDs) enabled by larger optical matrix elements and lower effective mass, respectively; polarized light emission in LEDs and polarization pinning in vertical‐cavity surface‐emitting lasers (VCSELs) enabled by anisotropic optical gain; faster modulation speed in LEDs and more efficient intersubband transitions enabled by the lower carrier lifetime; and wavelength stability enabled by elimination of QCSE. On the other hand, nonpolar and semipolar orientations have failed to make a big impact on efficiency droop and the green gap.…”

Intersubband absorption in GaN nanowire heterostructures at mid-infrared wavelengths

“…The GaN/AlN material combination remains highly interesting due to the possibility to cover a broad range of the infrared spectrum [23][24][25][26][27], including the short-wavelength infrared (1-3 μm), mid-infrared (3-5 μm) and far-infrared (15-1000 μm). However, the observation of intersubband absorption in GaN/ AlN nanowire heterostructures is so far limited to 1.3-1.95 μm.…”

The Effect of the Ion Beam Energy on M-plane InGaN Layer Preparation for STEM

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Nonpolar AlGaN/InGaN superlattices are investigated as a strain balanced potential alternative for nonpolar high Al composition AlGaN/GaN for near infrared intersubband absorption [5]. Inhomogeneity and defects appearing during InGaN growth are still challenges to the realization of high performance nitride infrared optoelectronic devices.

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