Excimer laser-induced electron emission from diamond films

Abstract

Diamond films with a thickness from submicron to a few microns were the choice to study the electron emission induced by UV laser pulses and by electric fields. One of the goals of the research was to compare photoelectron emission behaviour under irradiation with XeCl (λ=308 nm) and KrCl (λ=222 nm) laser pulses, i.e. with a photon energy being respectively smaller (4.02 eV) and larger (5.58 eV) than the diamond band gap. The effects of the film thickness (grain size) and post-growth plasma treatments on the photoelectron yield were also studied. In addition, the results on the field electron emission from these diamond films are presented. A correlation between the photoemission and field electron emission is discussed based on an analysis of deep level distribution in the films examined with a charge-based deep level transient spectroscopy (Q-DLTS). The role of defect states in the gap is shown to be important in the processes of electron emission from thin diamond films. It is pronounced in the wavelength-dependent photoemission behaviour and, especially, in the negative effect on photocurrent of the plasma treatments. The reduction of the photocurrent signals from both the H and Ar plasma-treated films was interpreted with the help of Q-DLTS spectra which give information on the parameters of electrically active defects (concentration, activation energy, capture cross-section). The field electron emission behaviour is shown to depend on the film thickness, and the lowest turn-on field of 25 V μm −1 was obtained for the thinnest diamond film.