Published online by Cambridge University Press: 25 February 2011
We compare three approaches to excimer laser assisted growth of GaAs: 1) Film growth is dominated by gas phase photolysis of deposition precursor gases at 193 nm under low pressure metal organic chemical vapor deposition (MOCVD) conditions. This approach leads to rapid deposition at low substrate temperature, but with very low spatial resolution (∼1 cm). 2) Growth is controlled by laser induced pyrolysis of adsorbed triethylgallium (TEGa) at 193 nm under metal organic molecular beam epitaxy (MOMBE) conditions. Films grown under these conditions have the potential for high spatial resolution (i.e. submicron), but geometric constraints in MBE conflict with the requirement of a short working distance between the lens and substrate, making it difficult to attain this limit. 3) Areaselective growth is controlled by laser induced pyrolysis of adsorbed TEGa at 351 nm (XeF excimer laser) under low pressure MOCVD conditions. This approach combines the advantage of laser controlled surface chemistry with the potential for much shorter working distances.
Selected area growth of GaAs occurs in this latter mode because TEGa dissociatively chemisorbs at 400°C to form a stable layer which decomposes further under laser irradiation to liberate hydrocarbon products. The Ga left behind on the surface reacts with As2 and As4 (formed by pyrolysis of trimethlyarsine or triethylarsine in a side tube) to grow GaAs in irradiated areas. Since the gas does not absorb at 351 nm the process is highly areaselective. Patterned films with feature sizes of ∼70µm (limited by the mask dimensions) were grown by this method. Interference between the incident beam and light scattered along the surface also causes a substructure of parallel lines to form on the features with a line spacing about equal to the laser wavelength 0.35µm. This indicates that the ultimate spatial resolution is comparable to that predicted by thermal diffusion calculations (∼0.3µm).