RF magnetron sputtering of LaS thin films on InP substrates

摘要

Recently, we have proposed that rare-earth sulfides on various III-V semiconductor surfaces [1, 2] are attractive materials to reach Negative Electron Affinity (NEA) [3] at various III-V semiconductor surfaces [1, 2]. These compounds are chemically more stable than the cesiated surfaces [4] used hitherto in such applications. Of particular interest is the fact that the work function (WF) of rare-earth sulfides at room temperature, when extrapolated from high-temperature measurements, is quite mall (between 1 and 1.5 eV). It is therefore expected that these materials can be used to reach NEA when deposited on p-type doped semiconductors. For instance, LaS has a lattice constant (5.854 A) very close to the lattice constant of InP (5.8688 A). Since the room temperature WF of LaS (1.14 eV) is below the band gap of InP (1.35 eV), NEA can therefore be realized at InP/LaS interface using heavily p-type doped semiconductor substrate [1, 2]. Two other important features of the fcc cubic form of LaS are its fairly large melting temperature (about 2200 °C) and its metallic character (its electrical resistivity has been measured as low as 25 μΩ cm [5]).