INTERNALLY DETECTED ELECTRON PHOTOEXCITATION SPECTROSCOPY ON HETEROSTRUCTURES

We applied an extension of the Internal Photoemission, the Internally Detected Photoexcitation Spectroscopy (IDEPS), to the direct observation of deep levels and band discontinuities at different semiconductor heterostructure interfaces. We studied Schottky barriers (Al/GaAs, Pd/n-GaAs, Ni-Au-Ge/n-GaAs) and heterojunctions (a-Ge/n-GaAs). The GaAs surface, before metal deposition, was treated in two different ways: chemical etching (CE samples) in air or argon ion sputtering (AIS samples) in vacuum. We found, for Al/GaAs, Pd/n-GaAs and Ni-Au-Ge/n-GaAs Schottky heterostructures, a barrier height of 0.78 eV, and for a-Ge/n-GaAs a valence band discontinuity of 0.42 eV. This results in a pinning of the Fermi-level at an average value of 0.76 +/- 0.03 eV above the top of the GaAs valence band. This pinning is probably due to the presence of oxygen at the semiconductor surface in the CE samples. In the AIS samples, where the metal was deposited without vacuum breaking, the PHI(b) results in a great value. Three onsets, due to transitions involving interfaces states, at 1.05 eV, 1.27 eV, and at 1.36 eV, were also evident in the Pd/n-GaAs heterostructure. Furthermore, we studied how a bombardment by hydrogen or hydrogen + nitrogen ions at low energy (approximately 100 eV) of this Schottky barrier modifies its interfacial states. In the case of Ni-Au-Ge/n-GaAs heterostructure we also determined the value of the energy gap at the interface, demonstrating that the thermal treatments could reduce such a value.