AES, LEELS AND XPS STUDIES ON THE INTERFACE FORMATION BETWEEN LAYERED SEMICONDUCTORS GASE AND INSE

The interface formation at the initial stage of hetero-epitaxy of GaSe and InSe, and InSe on GaSe has been studied by means of AES (Auger electron spectroscopy), LEELS (low-energy electron loss spectroscopy) and XPS (X-ray photoemission spectroscopy). GaSe (InSe) was deposited onto the cleaved substrate by using a W filament. The growth mode was determined by measuring the decrease in the AES signal intensity from the substrate and the evolution of the LEELS spectrum upon deposition, which revealed that the GaSe deposited on InSe (or InSe on GaSe) grows layer by layer with the unit thickness of a primitive layer consisting of four atomic planes in the sequence Se-M-M-Se (M = Ga, In). The crystal quality of the grown layers was characterized by LEELS and XPS. The results indicate that the deposited layers at elevated substrate temperatures (approximately 300-degrees-C) grow in a single crystal in spite of the large lattice mismatch of about 7% between GaSe and InSe. The XPS measurements showed that the interface is abrupt for both depositions of GaSe on InSe and of InSe on GaSe at 300-degrees-C. The valence band discontinuity between GaSe and InSe estimated by XPS was 0.30 +/- 0.05 eV, irrespective of the growth sequence, where the top of valence band of InSe lies above that of GaSe.