An inexpensive up-gradation of scanning tunneling microscope for ballistic electron emission microscopy and spectroscopy

Ballistic electron emission microscopy (BEEM) and Ballistic electron emission spectroscopy (BEES) have become highly useful tools for studying the transport property of electrons and holes across metals, metal-semiconductor interfaces and in semiconductors. Although the techniques are developed, but there is hardly any detailed description of experimental set-ups in this regard. We have carried out an inexpensive upgradation of commercial STM (model STM635 of RHK Technologies) for BEEM and BEES studies on metal-semiconductor interfaces. Along with the associated electronics and a suitable sample holder, we have also developed a technique to produce high quality STM tips necessary for these studies. We have carried out BEEM studies on gold-silicon interface and the results are in conformity with those reported earlier. The minimum threshold of obtaining ballistic current is found to be 0.7 V for Au-n-Si interface whereas it may rise up to 4 V if a layer of oxide is permitted to grow on silicon before deposition of gold film. In the case of a 100 Angstrom gold film over n-Si(100), the BEEM current is more intense at the grain boundaries and relatively less over the grains of greater heights. (C) 2000 Elsevier Science B.V. All rights reserved.