Adsorption and decomposition of triethylindium (TEI: (C2H5)(3)In) on a GaP(0 0 1)-(2 x 1) surface have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). It is found from the TPD result that ethyl radical and ethylene are evolved at about 300-400 and 450-550 K, respectively, as decomposition products of TEI on the surface. This result is quite different from that on the GaP(0 0 1)-(2 x 4) surface. The activation energy of desorption of ethyl radical is estimated to be about 93 kJ/mol. It is suggested that TEI is adsorbed molecularly on the surface at 100 K and that some of TEI molecules are dissociated into C2H5 to form P-C2H5 bonds at 300 K. The vibration modes related to ethyl group are decreased in intensity at about 300-400 and 450-550 K, which is consistent with the TPD result. The TEI molecules (including mono- and di-ethylindium) are not evolved from the surface. Based on the TPD and HREELS results, the decomposition mechanism of TEI on the GaP(0 0 1)-(2 x 1) surface is discussed and compared with that on the (2 x 4) surface. (C) 2002 Elsevier Science B.V. All rights reserved.