We report the interplay between In incorporation and strain relaxation kinetics in high-In-content InxGa1-xN (x = 0.3) layers grown by plasma-assisted molecular-beam epitaxy. For In mole fractions x = 0.13–0.48, best structural and morphological qualities are obtained under In excess conditions, at In accumulation limit, and at a growth temperature where InGaN decomposition is active. Under such conditions, in situ and ex situ analyses of the evolution of the crystalline structure with the layer thickness point to an onset of misfit relaxation after the growth of 40 nm, and a gradual relaxation during more than 200 nm, which results in an inhomogeneous strain distribution along the growth axis. This process is associated with a compositional pulling effect, i.e., indium incorporation is partially inhibited in presence of compressive strain, resulting in a compositional gradient with increasing In mole fraction towards the surface.

The structural, morphological, electrical and optical properties of In-rich Al _x In _{1− x} N (0 < x < 0.39) layers grown by reactive radio-frequency (RF) sputtering on sapphire are investigated as a function of the deposition parameters. The RF power applied to the aluminum target (0 W–150 W) and substrate temperature (300 °C–550 °C) are varied. X-ray diffraction measurements reveal that all samples have a wurtzite crystallographic structure oriented with the c -axis along the growth direction. The aluminum composition is tuned by changing the power applied to the aluminum target while keeping the power applied to the indium target fixed at 40 W. When increasing the Al content from 0 to 0.39, the room-temperature optical band gap is observed to blue-shift from 1.76 eV to 2.0 eV, strongly influenced by the Burstein–Moss effect. Increasing the substrate temperature, results in an evolution of the morphology from closely-packed columnar to compact. For a substrate temperature of 500 °C and RF power for Al of 150 W, compact Al _0.39 In _0.61 N films with a smooth surface (root-mean-square surface roughness below 1 nm) are produced.

The impact of the barrier thickness on the performance of In _0.17 Ga _0.83 N multiple-quantum-well (MQW) solar cells is studied. When the barrier thickness is reduced from 9.0 to 3.7 nm, the effect of the internal polarization fields on the MQW band structure results in a blueshift of the cell photoresponse. At the same time, the overlap of the fundamental electron and hole wave-functions in the quantum wells increases and the carrier extraction by field-assisted tunneling is enhanced, impacting the external quantum efficiency and fill-factor of the cells. The experimental results show that the performance of the thinner-barrier cells studied in this work is superior, or at least comparable to the performance of their thicker-barrier counterparts, in spite of the smaller total thickness of their absorbing region. This is due to their higher external quantum efficiency (37% at 370 nm) and improved fill-factor (62%), which result in a conversion efficiency of η = 0.82%.

In this work, we investigate the effects of deposition conditions on the structural and morphological properties of AlInN thin films deposited on p-doped Si(111) substrates by reactive radio-frequency sputtering. The aluminum composition can be tuned in the 0 to 0.36 range by changing the power applied to the aluminum target. Al incorporation leads to a change in the layer morphology and improvement of the rms surface roughness of the layers. The compact Al_0.36In_0.64N sample grown at 550 °C exhibits intense room-temperature photoluminescence centered at 1.75 eV.