Ultraviolet laser-assisted metalorganic chemical vapor deposition of GaAs

The growth of GaAs irradiated with ultraviolet laser light in a metalorganic chemical vapor deposition reactor has been investigated. Growth rate enhancements of up to 15% were observed at 450°C by illuminating the substrate with no more than 13 mJ/cm² of KrF laser (248 nm) radiation. For 5-eV photons, arsine is virtually transparent, while the trimethylgallium (TMG) photoabsorption cross section is approximately 10 ^-19 cm². Data acquired with and without the optical beam impinging on the substrate are well described by the Langmuir-Hinshelwood model, and the results point to photodissociation of adsorbed TMG as the origin of the growth rate enhancement. Nearly identical experiments carried out at 351 nm (XeF) corroborate this conclusion since no measurable increase in growth rate was observed at this wavelength, where both arsine and TMG photoabsorption is negligible. Conversely, significant improvement in surface morphology for samples grown below 700°C is observed with ultraviolet laser irradiation of the substrate at each of the wavelengths investigated (193, 248, and 351 nm). Smooth and specular surfaces are obtained with substrate temperatures as low as 550°C and at fluences well below those which induce a significant rise in the surface temperature.