| Abstract Scope |
Lateral Diffusion Liquid Phase Epitaxy (LDLPE) is a new, modified LPE technology and it is a candidate technology for curf-free semiconductor substrate production. LDLPE shares the same advantages as conventional LPE technology: low cost, high growth rate, premium quality of grown crystal, feasibility of selective epitaxy and lateral growth with high aspect ratio. Furthermore, LDLPE enhances the lateral growth and increases the aspect ratio. If used with temperature gradient technology, LDLPE can achieve continuous epitaxial growth, making it possible to grow self-supported single crystalline semiconductor substrate for photovoltaic applications. As a demonstration, single crystalline silicon substrate is grown by LDLPE. A silicon dioxide layer is grown on an n-type <111> single crystalline silicon substrate. The SiO2 mask is formed by lithography and it is patterned with a set of parallel 100μm width opening windows as seed lines, which are aligned to <211> orientation. With conventional LPE technology, P-type silicon is epitaxially grown on seed lines. Two single crystalline silicon strips are formed on one single seed line, one strip on either side of the seed line. And there is a gap between these two strips. The typical dimensions of the silicon strip are 70μm x 40μm x 5mm (the length of the seed line). To achieve LDLPE, a special graphite slide boat is designed: a silicon bar (1mm-3mm width and entirely covered by SiO2) is placed 250μm ~ 750μm above the seed line. This bar can restrain the increasing of silicon strip thickness by blocking the diffusion pathway of silicon atoms from the bulk indium/silicon melt to the top surface of the silicon strip. Silicon atoms in the bulk indium/silicon melt can only access the silicon strip’s side wall. Therefore, under the continuous LDLPE growth condition (when temperature gradient technology is applied, Si source is supplied continuously), when the strip grows to a certain size, the strip does not increase its’ thickness anymore, but increase it’s width continuously, forming a single crystalline Si substrate. Both simulation and experiment results demonstrate that the new technology, LDLPE, can grow self supported single crystalline silicon strips with higher aspect ratio than that achieved by the conventional LPE technology. These silicon substrates can be peeled off from the substrate for low cost high efficiency silicon solar cells. |