BALLISTIC-ELECTRON-EMISSION MICROSCOPY SPECTROSCOPY STUDY OF ALSB ANDINAS ALSB SUPERLATTICE BARRIERS/

Due to its large band gap, AlSb is often used as a barrier in antimoni de heterostructure devices. However, its transport characteristics are not totally clear. We have employed ballistic electron emission micro scopy (BEEM) to directly probe AlSb barriers as well as more complicat ed structures such as selectively doped n-type InAs/AlSb superlattices . The aforementioned structures were grown by molecular beam epitaxy o n GaSb substrates. A 100 Angstrom InAs or 50 Angstrom GaSb capping lay er was used to prevent surface oxidation from ex situ processing. Diff erent substrate and capping layer combinations were explored to suppre ss background current and maximize transport of BEEM current. The samp les were finished with a sputter deposited 100 Angstrom metal layer so that the final BEEM structure was of the form of a metal/capping laye r/semiconductor Of note is that we have found that hole current contri buted significantly to BEEM noise due to type II band alignment in the antimonide system. BEEM data revealed that the electron barrier heigh t of Al/AlSb centered around 1.17 eV, which was attributed to transpor t through the conduction band minimum near the AlSb X point. Variation in the BEEM threshold indicated unevenness at the Al/AlSb interface. The metal on semiconductor barrier height was too low for the superlat tice to allow consistent probing by BEEM spectroscopy. However, the su perlattice BEEM signal was elevated above the background noise after r epeated stressing Of the metal surface. A BEEM threshold of 0.8 eV was observed for the Au/24 Angstrom period superlattice system after the stress treatment. (C) 1998 American Vacuum Society.