The Influence of Pressure on the Roughness of InGaP Layers

Today, the technology of typical silicon-solar cells is fully developed and mature. In spite of its continuous improvements, the record efficiencies of 25.0% are approaching theoretical solar conversion limits of around 33.7%. Values much beyond this limit are likely to be achieved using III-V semiconductor compounds, electrical and optical properties are more suitable for solar energy conversion. They are the most promising candidates for realizing solar cells, which can achieve efficiencies of 50% and more. In this paper we studied the influence of pressure in the reactor chamber on the roughness of an InGaP "nucleation layer" grown on Ge. The growth of the layers was performed in a metalorganic vapour phase epitaxy reactor AIX 200/4. The source gases were trimethylgallium, trimethylindium and $AsH_3$. The rate of pressure in the reactor was raised from 100 mbar to 400 mbar by 50 mbar. The InGaP layers with the lowest roughness were achieved at the pressure of 400 mbar. The layers were characterized by very low roughness (RMS < 0.3) measured by atomic force microscopy. The quality of the surface was perfect enough to be applied in a solar cell structure.