Tzveta Apostolova
(Institute for Nuclear Research and Nuclear Energy (INRNE))
3D diamond detectors are at present investigated as they offer a superior radiation hardness with respect to planar detectors, promising to be the radiation hardest detector ever. Conductive channels are fabricated in the material by means of induced pulsed laser graphitization. The best characteristics are obtained by employing pulse durations as short as tens of femtoseconds. However a number of issues still remains open at the actual state of the art. The composition of the conductive phase is not well assessed as well as the optimal process parameters necessary to obtain low resistivity material, comparable to that of amorphous graphite, without damaging the diamond lattice. A thorough understanding of the graphitization process is still lacking. A better insight of the physics involved could greatly help to tune the parameters, e.g. pulse width, wavelength, field intensity, etc. to achieve an optimal device.
In this work we report on a theoretical simulation of the processes involved in laser irradiation under the experimental condition used to obtain high efficiency 3D detectors on monocrystalline diamond material.
A quantum kinetic approach based on the Boltzmann equation is employed to describe the response of diamond material to high excitation laser irradiation during and after the pulse duration. The different processes of excitation and rapid thermalization through electron-electron scattering to the final heat up by electron-phonon coupling are taken into account. The energy exchange between the electrons and phonons are given by a separate equation for the lattice temperature where the rate of energy transfer per unit volume from the electrons to the lattice is defined quantum mechanically.
As a result of our calculations the electron energy distribution function, average kinetic energy of the electron system and electron density are obtained as a function of laser intensity, laser photon energy (wavelength) and laser pulse duration. Furthermore we obtain the change of lattice temperature caused by irradiation..
Our calculations are intended as the first step of studying the response of diamond to laser excitation below the laser graphitization threshold, with theoretical predictions that can be validated experimentally with charge collection measurements at different laser intensities.
Summary
A quantum kinetic approach based on the Boltzmann equation is employed to describe the response of diamond material to high excitation laser irradiation during and after the pulse duration. The input parameters are derived from the experimental condition used to fabricate 3D diamond detectors on monocrystalline CVD diamond: pulse width of the order of tens of femtometers, wavelength peaked at 800 nm, different field inetnsityaround the graphitization threshold.
The different processes of excitation and rapid thermalization through electron-electron scattering to the final heat up by electron-phonon coupling are taken into account. The energy exchange between the electrons and phonons are given by a separate equation for the lattice temperature where the rate of energy transfer per unit volume from the electrons to the lattice are defined quantum mechanically.
As a result of our calculations the electron energy distribution function, average kinetic energy of the electron system and electron density are obtained as a function of laser intensity, laser photon energy (wavelength) and laser pulse duration. Furthermore we obtain the change of lattice temperature.
