Electron accumulation layer at the Cs-covered GaN(0001) n-type surface

Abstract

We report on the observation of photoemission from the Cs∕GaN(0001) n-type interface by excitation of visible light in the transparency region of GaN. Under Cs adsorption, sharp decrease in photoemission threshold up to 1.3eV at 0.5 monolayer of Cs is found and shown to be due to formation of a charge accumulation layer in the near-interface region. An interesting phenomenon is revealed, namely, the appearance of an oscillation structure in spectra of photoyield. A model conception taking into account both the formation of charge accumulation layer and occurrence of multiple-beam interference in parallel-sided GaN epilayer is suggested.

Anti-Fowler Temperature Regime in Photoemission from <i>n</i>-Type Semiconductors with Surface Accumulation Layer

“…However, the authors of Ref [10] [11] [12] do not report on the exact value of QE, but only report that the maximal QE of the Cs/n-GaN system is comparable and even exceeds the QE for highly-efficient source of electron GaAs photo-cathodes, which can reach 50% [14]. Therefore, we assume that the QE for the Cs/n-GaN system is also not less than 50% at room temperature for photon energy 3.1 eV (5) shows that in the conventional Fowler regime for a temperature range from 300 to 500 K the QE value increases by only on 0.7%.…”

“…Therefore, the exact value of the Fermi and vacuum energy levels is a crucial parameter in the calculation of the threshold energy for photoemission. For a clean n-GaN (0001) surface the reported room temperature work function Φ and electron affinity χ are 3.9 and 3.35 eV respectively [10]. In this case the Fermi energy is ( ) ( ) 300 0.55 eV,…”

“…The reported value of photoemission threshold from surface AL at room temperature, induced by cesium coverage with thickness of 0.5 ML is 1.4 eV, which corresponds to the infrared range with wavelength 885 nm AL th λ = . The theory for photoemission from 2D metallic-like AL in semiconductor was considered in [10] [11] within the framework of the Urbakh-Brodsky theory for photoemission from metal surfaces [13].…”

10.1007/s11448-008-2010-8

“…The method is based on the separation of the bulk and surface photoemission, as well as on the effect of the near-thresh- We have earlier revealed that the electron properties of the n -GaN(0001) surface change radically during the process of the formation of ultrathin Cs/ n -GaN(0001) and Ba/ n -GaN(0001) interfaces at the initial adsorption stage at the submonolayer Cs and Ba coatings. In this case, the main effect is the appearance of a 2D electron channel, which is a charge accumulation layer (CAL) on the GaN surface [14]. We recorded for the first time this phenomenon in the wide-bandgap semiconductors.…”

Effects of Potassium Adsorption and Potassium–Water Coadsorption on the Chemical and Electronic Properties of n-Type GaN(0001) Surfaces

“…The surface properties of polar and nonpolar GaN surfaces as well as adsorption and interaction processes have been studied to a relatively broad extent . However, there are still unanswered or only recently addressed scientific questions related to surface adsorption kinetics − and how they can be used for generation of novel functionality or for the manipulation of the electronic properties. , As an example, the adsorption of alkali and alkaline earth metal atoms at polar GaN surfaces has also been studied for the cases of cesium (Cs) and barium (Ba). − For both alkali metals, a deposition time-dependent modification of the surface electronic properties was observed, with a strong reduction of the work function induced by formation of an adatom-induced surface dipole, which lowers the surface barrier for electron emission. At the same time, the adatoms induce changes in surface band bending and surface/adatom states within the fundamental band gap of GaN.…”