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-frequency noise of VPE-grown (vapour-phase epitaxy) GaAs epitaxial layers, which have been passivated by photo and plasma CVD (chemical-vapour deposition) of SiO2, using SiH4 and N2O as precursors. Generation-recombination (g-r) and 1/f-noise components have been separated from the obtained noise spectra by curve fitting. The g-r noise has been isolated, and 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 narrow temperature range close to room temperature, whereas plasma processes exhibit additional noise in a wide temperature range. Improved noise results with higher reproducibility are obtained using a modified plasma technique in a phosphorous ambient. The possible role of the interface and defects, which are located near to the surface and which were generated during the insulator deposition, is discussed. The 1/f-noise components were analysed according to Hooge's theory. The Hooge parameter and its temperature dependence for all analysed samples have been found to agree very well with values reported in the literature.