Unexpected current lowering by a low work-function metal contact: Mg/SI–GaAs

The work functions of Au/Mg decorated Au(100), Mg(001), and AuMg alloy surfaces: A theoretical study

“…that the work functions are Mg dominated (lie below Φ avg ) and typically approach the work function of pure Mg. Nonideality/disorder further lowers Φ. Based on the reported results, we theorize that the work function of an amorphous AuMg is similar to the pure Mg, a conclusion in agreement with the experimental observations [8] and expectations [5].…”

“…The AuMg surface energies γ (in the limit of T → 0), that determine the stability, were estimated from thermodynamic considerations [19][20][21] assuming limiting cases of Au-(γ Au-rich ) and Mg-rich (γ Mg-rich ) atmospheres. The Au-rich limit is relevant to the experimental conditions of the GaAs/Mg/Au contact preparation that is of our interest [5]. We neglect pV terms and zeropoint vibrations [19] and the Gibbs free energies are approximated by the total energies (E) from the zerotemperature DFT calculations [21].…”

“…Since the XPS analysis of the formed contact suggests a presence of a non-ideal disordered AuMg alloy [7] with the changing composition instead of distinct Au/Mg phases, the question remains to be answered: what is the work function of the alloy right at the alloy/GaAs interface? This value would be decisive for further understanding of the non-trivial transport phenomena observed [5].…”

“…Further improvement of these devices with a promising application potential in sensorics, γ/X-ray detection and medical imaging [6], relies on the properties of the interfaces between the reactive low work function metal layers and surface passivisation metals. In one of the most striking cases [5], the Mg overlayer on GaAs was passivated by the Au. Since the XPS analysis of the formed contact suggests a presence of a non-ideal disordered AuMg alloy [7] with the changing composition instead of distinct Au/Mg phases, the question remains to be answered: what is the work function of the alloy right at the alloy/GaAs interface?…”

“…Recent progress in planar GaAs Schottky barrier diodes, primarily developed for the X-ray detection applications, stimulated interest in the low work function M/S contacts, since the diodes possessing them revealed unexpectedly and favorably low leakage current [3][4][5]. Further improvement of these devices with a promising application potential in sensorics, γ/X-ray detection and medical imaging [6], relies on the properties of the interfaces between the reactive low work function metal layers and surface passivisation metals.…”