In
this work, we study the thermal degradation of In-rich In
x
Ga1–x
N
quantum wells (QWs) and propose explanation of its origin based on
the diffusion of metal vacancies. The structural transformation of
the In
x
Ga1–x
N QWs is initiated by the formation of small initial voids
created due to agglomeration of metal vacancies diffusing from the
layers beneath the QW. The presence of voids in the QW relaxes the
mismatch stress in the vicinity of the void and drives In atoms to
diffuse to the relaxed void surroundings. The void walls enriched
in In atoms are prone for thermal decomposition, what leads to a subsequent
disintegration of the surrounding lattice. The phases observed in
the degraded areas of QWs contain voids partly filled with crystalline
In and amorphous material, surrounded by the rim of high In-content
In
x
Ga1–x
N or pure InN; the remaining QW between the voids contains residual
amount of In. In the case of the In
x
Ga1–x
N QWs deposited on the GaN layer
doped to n-type or on unintentionally doped GaN, we observe a preferential
degradation of the first grown QW, while doping of the underlying
GaN layer with Mg prevents the degradation of the closest In
x
Ga1–x
N QW. The
reduction in the metal vacancy concentration in the In
x
Ga1–x
N QWs and
their surroundings is crucial for making them more resistant to thermal
degradation.
The SiO 2 /CaCl 2 hybrid porous materials were obtained by the two-step hydrolysis and condensation of tetraethoxysilane with (a) replacement of ethanol from alcogel by supercritical CO 2 to obtain aerogel morphology and (b) drying alcogel at ambient to obtain xerogel structures. Aerogels and xerogels containing ∼17 and ∼30 wt % of CaCl 2 (dry matter) were prepared and investigated for adsorptivity of water vapor to obtain sorption capacities in excess of 1 kg of water/kg of adsorbate. The adsorbates obtained can be dried and reused. No notable loss in adsorption capacity was observed during 50 cycles.
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