COMPARISON OF PHOTO-ASSISTED AND PLASMA-ASSISTED PASSIVATING PROCESS EFFECTS ON GAAS DEVICES BY MEANS OF LOW-FREQUENCY NOISE MEASUREMENTS

We report on measurement results of temperature-dependent low-frequenc y noise of VPE-grown (vapour-phase epitaxy) GaAs epitaxial layers, whi ch have been passivated by photo and plasma CVD (chemical-vapour depos ition) of SiO2, using SiH4 and N2O as precursors. Generation-recombina tion (g-r) and 1/f-noise components have been separated from the obtai ned noise spectra by curve fitting. The g-r noise has been isolated, a nd it has been shown to be the main additional noise component to the 1/f noise in our case and to depend strongly on the deposition process . In the case of photo CVD, the additional noise was observed in a nar row temperature range close to room temperature, whereas plasma proces ses exhibit additional noise in a wide temperature range. Improved noi se results with higher reproducibility are obtained using a modified p lasma technique in a phosphorous ambient. The possible role of the int erface and defects, which are located near to the surface and which we re generated during the insulator deposition, is discussed. The 1/f-no ise components were analysed according to Hooge's theory. The Hooge pa rameter and its temperature dependence for all analysed samples have b een found to agree very well with values reported in the literature.