INVESTIGATION OF POROUS SILICON MORPHOLOGY FOR ELECTRON-EMISSION APPLICATIONS

The morphology and composition of porous silicon (PS) of high porosity (80%), realized on flat and on emitter covered surfaces, were investi gated in order to establish the optimal preparation conditions for ele ctron emission applications. Scanning force microscopy (SFM) images re veal a variable number of hillocks of different sizes, depending on si licon type, randomly distributed on the Si surface. A great number of cracks are present on the high porosity PS layers thicker than 2-3 mu m realized on flat Si surfaces, but the average hillocks size is more uniform compared to the case of PS on emitters. A higher density of hi llocks was observed on PS/p-Si comparatively to the case of PS/n-Si. A good correlation between the PS morphology and field emission charact eristics was obtained. A maximum value of 2.5 mu A of the emission cur rent was measured on PS layers prepared on p-type Si Bat surface for a pplied voltage V-a = 100 V. Secondary ion mass spectrometry (SIMS) ana lyses indicate a high degree of PS oxidation when kept in atmospheric conditions after preparation. The Fowler-Nordheim behavior of the emis sion characteristics occurs only after native oxide breakdown. (C) 199 8 Elsevier Science B.V. All rights reserved.