Behavior of Cesium Oxide as a Low Work-Function Coating

Abstract

A detailed picture of the behavior of cesium oxide as a low work-function coating on III-V semiconductors and on silver has been obtained. Measurement of required cesium and oxygen exposure for optimum photoyield shows that the compound normally formed is close to CS2O, with variations in required exposure for very thin and very thick layers. By making simultaneous Kelvin work-function, photoyield-threshold, and thickness measurements, it was possible to establish that the CS2O, an n-type semiconductor, forms a heterojunction or Schottky barrier with its substrate. This provides a band bending which produces a gradual lowering of the vacuum level with increasing thickness to an ultimate work function of 0.6 eV. The photoyield and dark current from the substrate are limited by the interfacial barrier at the heterojunction. This barrier is 1.00±0.05 eV for a silver substrate and 1.23±0.03 eV for GaSb. The band-bending distance in the CS2O is about 50 Å and the hot electron scattering distance is 9 Å. These data have been used in an improved calculation of the maximum Γ escape probability and requisite CS2O thickness for electron emission from III-V semiconductors of different bandgaps. Electron emission from CS2O induced by an oxygen overpressure was also measured. CSOH is compared with CS2O as a work-function lowering coating.

The III-V Photocathode: A Major Detector Development

“…For the analogous system of Cs 2 0 on metallic silver, where the thermionic current from the substrate is more easily measured, it is observed experimentally that for a sufficiently high work fonction, the "metallic" (Richardson) value of thermionic emission is obtained. However, as the work function is reduced below the interface barrier value, the thermionic component from the metal saturates at a value determined by the barrier height (Uebbing and James 1970). Some experimental results on III-V/Cs 2 0 photoemitters (Klein 1969;Uebbing 1971) are shown in Figure 18.…”

“…(This is shown schematically in Fig. 11 evidence (James and Uebbing 1970;Uebbing and James 1970) indicates that die limiting factor is an interior barrier at the semiconductor-Cs-O interface (see Fig. 11).…”

Synthesis and characterization of Si/Cs/O nanocluster thin films with negative electron affinity

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] In most cases, only certain well prepared and highly oriented surfaces of some semiconductors or insulators ͓most notably: diamond ͑100͒ and ͑111͒, Si͑001͒, and GaAs ͑100͒ surfaces͔ exhibit NEA. The preparation of these surfaces usually requires etching and high-temperature annealing in an ultrahigh vacuum ͑UHV͒ chamber.…”

Strong interfacial dipole formation with thermal evaporation of lithium cobalt oxide for efficient electron injections

“…Alkali metal oxides could be more efficient EILs than original alkali metals because alkali metal oxides have even lower work functions than the original alkali metals. 12,13 However, evidence for the decomposition of LiCoO 2 has not yet been found. In addition, the detailed electronic structures at the interface of Al/LiCoO 2 /Alq 3 and the electron injection mechanism are still open problems.…”

“…At the final thickness (2.7 nm) of Li 2 O, the work function was decreased by 1.78 eV, which in agreement with a previous study on cesium oxide (Cs 2 O) on the semiconducting substrate. 12,13 In Fig. 2(b), the unique feature of the O 2p valence band of the Li 2 O layer emerged as it thickened.…”