INFLUENCE OF THE DOPANT CONCENTRATION ON THE PHOTOEMISSION IN NEA GAAS PHOTOCATHODES

The influence of impurity concentration on the photoemission from Nega tive Electron Affinity (NEA) GaAs photocathodes has been investigated. Experimental curves of photoemission spectral sensitivity are obtaine d for several dopant concentrations and when normalized to their peak value their spectral response shows three zones of well differentiated behaviour, in good agreement with theoretical predictions derived in this work. For illumination with wavelengths below approximate to 800 nm, photoemission is dominated by the escape probability. Higher conce ntration leads to higher normalized photoemission sensitivity. For wav elengths between approximate to 800 and 910 nm, the dominant role is p layed by the diffusion length of electrons in the bulk. Higher normali zed sensitivity is obtained for lower concentration. For wavelengths a bove approximate to 910 nm, photoemission is dominated by the absorpti on coefficient, which depends on concentration through the value of th e gap energy. The behaviour of sensitivity with concentration in this spectral zone is similar to that of wavelength shorter than 800 nm. (C ) 1997 Elsevier Science Ltd.