Characteristics of InGaN Designed for Photovoltaic Applications

This work addresses the required properties and device structures for an InGaN solar cell. Homojunction InGaN solar cells with a bandgap greater than 2.0 eV are specifically targeted due to material limitations. These devices are attractive because over half the available power in the solar spectrum is above 2.0 eV. Using high growth rates, InGaN films with indium compositions ranging from 1 to 32% have been grown by Molecular Beam Epitaxy with negligible phase separation according to X-ray diffraction analysis, and better than 190 arc-sec ω-2θ FWHM for ≃0.6 μm thick In_0.32Ga _0.68N film. Using measured transmission data, the adsorption coefficient of InGaN at 2.4 eV was calculated as α ≅ 2×10 ⁵ cm^-1 near the band edge. This results in the optimal solar cell thickness of less than a micron and may lead to high open circuit voltage while reducing the constraints on limited minority carrier lifetimes.