Systematic experimental and theoretical investigation of intersubband absorption inGaN∕AlNquantum wells

Abstract

We have studied the electronic confinement in hexagonal ͑0001͒ GaN / AlN multiple quantum wells by means of structural ͑high-resolution x-ray diffraction and transmission electron microscopy͒ as well as optical characterizations, namely intersubband absorption and interband photoluminescence spectroscopies. Intense intersubband absorptions covering the 1.33-1.91 m wavelength range have been measured on a series of samples with well thicknesses varying from 1 to 2.5 nm. The absorption line shape exhibits either a pure Lorentzian shape or multiple peaks. In the first case the broadening is homogeneous with a state-of-the-art low value of 67 meV. We deduce a dephasing time of the electrons in the excited subband T 2 of about 20 fs. For structured spectra the absorption can be perfectly reproduced with a sum of several Lorentzian curves; the individual peaks originate from absorption in quantum well regions with thickness equal to an integer number of monolayers. We have also carried out simulations of the electronic structure which point out the relevance of the nonparabolicity and many-body corrections on the intersubband absorption energy. The intersubband absorption exhibits a blue shift with doping as a result of many-body effects dominated by the exchange interaction. An excellent agreement with the experimental data is demonstrated. The best fit is achieved using a conduction band offset at the GaN / AlN heterointerfaces of 1.7± 0.05 eV and a polarization discontinuity ⌬P / ͑⑀ 0 ⑀ r ͒ of 10±1 MV/cm.

Long-lived excitons in GaN/AlN nanowire heterostructures

“…In NW geometries, the 3D elastic strain relaxation via the surface in the form of plane bending [15] permits a wider range of quantum dot sizes and compositions before forming misfit dislocations, i.e., plastic relaxation [15,16]. In the case of GaN/AlN quantum dots or nanodisks, the large band offsets (∼1.8 eV in the conduction band [17]) provide efficient exciton confinement, so that the observed long (microsecond) photoluminescence (PL) decay times [9,12] can persist up to room temperature [18].…”

Polarization-balanced design of heterostructures: Application to AlN/GaN double-barrier structures

“…This demand arises because the large band offset and heavy conduction electron mass ∼(0.2-0.3) m 0 weaken the coupling between states in adjacent quantum wells. The wide depletion regions and two-dimensional electron gases (2DEGs) forming at the two sides of an active region 2,4,[15][16][17] exacerbates this challenge for devices based on perpendicular quantum transport. For instance, in resonant-tunneling diodes and QC lasers, the depletion regions make it difficult to simultaneously obtain efficient current injection and control over the alignment of levels and transitions in the structure.…”

“…14,[18][19][20][21][22][23] A related issue exists for structures operating at zero bias (like absorption structures), especially those of only a few layers: As electrons accumulate in the 2DEG, the active region is depleted. 2,4,16,17 To tackle some of the design problems, we here introduce the two related concepts of polarization balance and polarization-balanced design. A structure is polarization balanced when the unscreened field vanishes in the cladding layers (buffer and cap) layers.…”

Crack Free GaInN/AlInN Multiple Quantum Wells Grown on GaN with Strong Intersubband Absorption at 1.55μm

“…New materials with a higher conduction band discontinuity are required. One of the candidates is nitride system, where intensive research works brought to successful fabrication by plasma-assisted molecular beam epitaxy (PAMBE) GaN/AlN IS structures, which absorb light at the telecommunication wavelength region [1][2][3][4][5][6][7].…”