(Negative) Electron Affinity of AlN and AlGaN Alloys

Abstract

The electron affinity of a semiconductor defines the relationship of the vacuum level and the semiconductor band structure. It is dependent on the atomic orbitals of the material and the surface termination. We report experimental and theoretical results that support the presence of a negative electron affinity on AlN and the Al rich AlGaN alloys. The GaN surface is found to exhibit a (positive) electron affinity of 3.3eV. The experimental measurements employ UV-photoemission spectroscopy on in situ gas-source MBE samples and on CVD samples. Theoretical results indicate that the (negative) electron affinity of AlN depends sensitively on the surface reconstruction and adatom termination. The experimental dependence of the electron affinity on alloy concentration is presented. The results indicate that AlGaN alloys with band gap similar or greater than that of diamond will exhibit a negative electron affinity. Field emission results are reported, and the characteristics are similar to those obtained from a diamond film. Issues related to cold cathode electronic devices based on NEA surfaces are noted.

Synthesis and field emission properties of triangular-shaped GaN nanowires on Si(100) substrates

“…Compared to single-walled carbon nanotubes and ZnO nanowires, whose work functions are about 4.9 and 5.3 eV, respectively [5,6], GaN has a lower work function of 4.1 eV, stronger thermal stability, mechanical hardness, chemical stability, and a lower electron affinity of 2.7-3.3 eV [7]. Therefore, GaN cold cathodes probably obtain high electron emission current densities and low operation voltages.…”

Fabrication of field emitters using GaN particles

“…This results in a very low potential barrier for the electron conduction from n-Si to PEDOT for the case of the ideal interface. On the other hand, from the electron affinity of 2.7-3.3 eV reported for GaN [13,14], the potential barrier of electrons from PE-DOT to GaN can be estimated to be around 2 eV. Although it causes the increase in applied voltage depending on the carrier concentration of GaN particles, this effect was not taken into consideration in the analysis of this study, which is described in the next section.…”

Field emission study of gated GaN and Al0.1Ga0.9N/GaN pyramidal field emitter arrays

“…Recently, the electron affinities of III nitrides were studied by using the ultraviolet photoemission spectroscopy ͑UPS͒. 2,13 Nemanich et al 2 showed that the surfaces of GaN and Al 0.13 Ga 0.87 N exhibit the electron affinities of 3.3 and 2.9 eV, respectively. The lower electron affinity of Al 0.1 Ga 0.9 N than that of GaN accounts for enhancement of the emission current, as observed in the present results.…”