Photocathode with nanowires and method of manufacturing such a photocathode
The invention discloses a photocathode comprising an amorphous substrate such as a glass substrate ( 110 ) presenting an input face that will receive incident photons and a back face opposite the front face. Nanowires ( 120 ) made from at least one III-V semiconducting material are deposited on the back face of the substrate and extend from this face in a direction away from the front face. The invention also relates to a method for manufacturing such a photocathode by MBE.
1. Method of manufacturing a photocathode comprising a glass substrate transparent to the spectral working band of the photocathode and with a first face called the front face and a back face opposite the front face, a mat of nanowires made from at least one III-V semiconducting material deposited on said back face and extending from this face in a direction away from the front face, wherein, the nanowires are made to grow on said substrate by molecular beam epitaxy in a MBE frame, varying the fluxes of materials making up the III-V semiconductor material during the nanowire growth phase, so as to obtain a material exhibiting a radial variation in a ratio of the elements on the III-V material in order to have a band gap gradient in a direction from the core of the nanowires towards their periphery before the growth of the nanowires, a gold film is deposited on said substrate in the same MBE frame at a temperature from 0 to 1200° C. during a duration of 1 to 30 min and it is left to dewet at a temperature of between 400° C. and 700° C. for 1 to 30 min so as to create 5 to 50 nm diameter gold particles.
2. Method of manufacturing a photocathode according to claim 1 , wherein a colloidal solution of 5 to 50 nm diameter gold particles are dispersed on the surface of the substrate before the growth of the nanowires.
3. Method of manufacturing a photocathode according to claim 1 , wherein the temperature of the substrate during the nanowires growth phase is between 400° C. and 700° C. and in that the atomic fluxes are calibrated so as to obtain a growth rate of between 0.5 Å/s and 10 Å/s.
4. Method of manufacturing a photocathode according to claim 1 , wherein, at the end of the nanowires growth phase, an activation layer made of LiO, CsO or NF 3 is deposited within the same MBE frame or without breaking the vacuum.
5. Method of manufacturing a photocathode according to claim 2 , wherein the temperature of the substrate during the nanowires growth phase is between 400° C. and 700° C. and in that the atomic fluxes are calibrated so as to obtain a growth rate of between 0.5 Å/s and 10 Å/s.
6. Method of manufacturing a photocathode according to claim 2 , wherein, at the end of the nanowires growth phase, an activation layer made of LiO, CsO or NF 3 is deposited within the same MBE frame or without breaking the vacuum.
7. Method of manufacturing a photocathode according to claim 3 , wherein, at the end of the nanowires growth phase, an activation layer made of LiO, CsO or NF 3 is deposited within the same MBE frame or without breaking the vacuum.