results have shown that emission energies have a minor dependence on small variations of device dimensions. Studies based on device simulation have shown that it could be possible to increase InGaN/GaN LED efficiency using band gap engineering, especially for green LEDs. Photovoltaics The ability to perform bandgap engineering with InGaN over a range that provides a good spectral match to sunlight, makes InGaN suitable for solar photovoltaic cells. It is possible to grow multiple layers with different bandgaps, as the material is relatively insensitive to defects introduced by a lattice mismatch between the layers. A two-layer multijunction cell with bandgaps of 1.1 eV and 1.7 eV can attain a theoretical 50% maximum efficiency, and by depositing multiple layers tuned to a wide range of bandgaps an efficiency up to 70% is theoretically expected. Significant photoresponse was obtained from experimental InGaN single-junction devices. In addition to controlling the optical properties, which results in band gap engineering, photovoltaic device performance can be improved by engineering the microstructure of the material to increase the optical path length and provide light trapping. Growing nanocolumns on the device can further result in resonant interaction with light, and InGaN nanocolumns have been successfully deposited on using plasma enhanced evaporation. Nanorod growth may also be advantageous in the reduction of treading dislocations which may act as charge traps reducing solar cell efficiency Metal-modulated epitaxy allows controlled atomic layer-by-layer growth of thin films with almost ideal characteristics enabled by strain relaxation at the first atomic layer. The crystal's lattice structures match up, resembling a perfect crystal, with corresponding luminosity. The crystal had indium content ranging from x ∼ 0.22 to 0.67. Significant improvement in the crystalline quality and optical properties began at x ∼ 0.6. Films were grown at ∼400 °C to facilitate indium incorporation and with precursor modulation to enhance surface morphology and metal adlayer diffusion. These findings should contribute to the development of growth techniques for nitride semiconductors under high lattice misfit conditions. Quantum heterostructures Quantum heterostructures are often built from GaN with InGaN active layers. InGaN can be combined with other materials, e.g. GaN, AlGaN, on SiC, sapphire and even silicon. Nanorods InGaN nanorod LEDs are three-dimensional structures with a larger emitting surface, better efficiency and greater light emission compared to planar LEDs. Safety and toxicity The toxicology of InGaN has not been fully investigated. The dust is an irritant to skin, eyes and lungs.