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 investigated in order to establish the optimal preparation conditions for electron emission applications. Scanning force microscopy (SFM) images reveal a variable number of hillocks of different sizes, depending on silicon 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 hillocks was observed on PS/p-Si comparatively to the case of PS/n-Si. A good correlation between the PS morphology and field emission characteristics was obtained. A maximum value of 2.5 mu A of the emission current was measured on PS layers prepared on p-type Si Bat surface for applied voltage V-a = 100 V. Secondary ion mass spectrometry (SIMS) analyses indicate a high degree of PS oxidation when kept in atmospheric conditions after preparation. The Fowler-Nordheim behavior of the emission characteristics occurs only after native oxide breakdown. (C) 1998 Elsevier Science B.V. All rights reserved.