researchers at the u.s. department of energy national renewable energy laboratory (nrel) have demonstrated that it is possible to use dissimilar semiconductors in a heterostructure by using ultraviolet (uv) light to modify the interface between the two layers.
nrel postdoctoral researcher kwangwook park, left, and scientist kirstin alberi
work on the molecular beam epitaxy system at the solar energy research facility at nrel.
(national renewable energy lab)
according to a report from the nrel, “typically, the semiconductor materials used in electronic devices are chosen based on such factors as having a similar crystal structure, lattice constant, and thermal expansion coefficients. the close match creates a flawless interface between layers and results in a high-performance device.”
being able to combine different classes of semiconductors in a single device creates new possibilities for highly-efficient devices.
“the researchers explored this approach in a model system consisting of a layer of zinc selenide (znse) grown on top of a layer of gallium arsenide (gaas),” the article explained. “using a 150-watt xenon lamp to illuminate the growth surface, they determined the mechanisms of light-stimulated interface formation by varying the light intensity and interface initiation conditions.”
the uv light altered the chemical bonds at the interface through “photo-induced desorption” of arsenic atoms on the gaas surface. this meant a greater percentage of bonds between the gallium and selenium and also allowed the znse to tbe grown at a lower temperature.
the research was recently published in scientific reports. the abstract read:
“integrating different semiconductor materials into an epitaxial device structure offers additional degrees of freedom to select for optimal material properties in each layer. however, interfaces between materials with different valences (i.e. iii-v, ii-vi and iv semiconductors) can be difficult to form with high quality.
“using znse/gaas as a model system, we explore the use of ultraviolet (uv) illumination during heterovalent interface growth by molecular beam epitaxy as a way to modify the interface properties. we find that uv illumination alters the mixture of chemical bonds at the interface, permitting the formation of ga-se bonds that help to passivate the underlying gaas layer. illumination also helps to reduce defects in the znse epilayer.
“these results suggest that moderate uv illumination during growth may be used as a way to improve the optical properties of both the gaas and znse layers on either side of the interface.”