Wednesday, November 4, 2009: 3:50 PM
Charolais (Camino Real Hotel)
Unexpected discovery of a very narrow band gap in InN (0.7 eV, previously thought it was 2 eV) has extended the range of energy gaps for group III-nitride alloys from the deep ultraviolet to near infrared spectral region. The band gap energy of InxGa1-xN alloys can thus be continuously varied from 0.7 eV to 3.4 eV. This spectral range covers the most useful part of solar spectrum, offering a unique opportunity to design multi junction (MJ) solar cells using a single material system (current technologies combine different material systems such as group III-V and group IV into MJ solar cells). Furthermore, it has been observed that alloying significantly reduces thermal conductivity in solids with very little deterioration in electrical properties, making these alloys high-quality thermometric (TE) materials which can convert heat energy directly into electrical energy without any moving parts. We found that the thermoelectric properties of In0.36Ga0.64N are as good as those of SiGe alloys, which are currently the prime choice for deep space based TE materials. Growth with photovoltaic and thermoelectric characteristics of InxGa1-xN alloys in the energy range from 1.8 to 1.0 eV (which corresponds to x = 0.4 to 0.7) will be presented. InxGa1-xN alloys were synthesized by metal organic chemical vapor deposition (MOCVD). Issues such as phase separation suppression and improvement of material quality in the above mentioned composition range will be discussed.