Effect of Cu Deposition and Annealing upon a GaSe/Si(111) Heterojunction

Single crystal substrates of GaSe, a layered semiconductor with a 2 eV band gap, were epitaxially grown by MBE onto a Si(111)(1 x 1)-H substrate, forming a perfectly abrupt heterojunction. Controlled amounts of Cu were sequentially deposited onto the clean passive surface of GaSe from a few tenths to several hundred monolayers (1 ML refers to the GaSe surface: 8 x 10(14) at/cm(2)). After given Cu depositions, the effect of UHV annealings at increasing temperatures was studied, until GaSe removal. The system was characterized as a function of either Cu deposit or annealing temperature using low energy electron diffraction, Auger electron spectroscopy and photoemission yield spectroscopy. The room temperature interaction starts as an apparent intercalation process until Cu islands begin to form, beyond about 50 ML. Upon annealings as low as 250 degrees C, several ML of Cu disappear into the bulk of an apparently recovered GaSe, towards the GaSe/Si interface.