Metalorganic molecular‐beam epitaxy (MOMBE) combines many important advantages of molecular‐beam epitaxy and metalorganic chemical vapor deposition. One of the most important features of MOMBE is that photochemical reaction can be used and we can call this new technique ‘‘photo‐MOMBE.’’ Triisobutylaluminum (TIBA) has been used in photo‐MOMBE instead of triethylaluminum (TEA) as a new aluminum source in order to enhance the photodecomposition. The optical absorption coefficient of TIBA for 193 nm was found to be three times greater than that of TEA. Selective deposition of Al, AlAs, and GaAlAs was carried out by using an ArF excimer laser. The Al mole fraction of GaAlAs ternary alloy grown with the excimer laser irradiation was greater than that of the film grown without the laser irradiation.