Holod O. Improvement of technology for making contacts to porous layer of semiconductors

The thesis is devoted to solving the actual scientific task to improve technology for making ohmic contacts to porous semiconductors. To achieve a goal the mathematical model describing dependence the general resistance of system “metal contact – porous layer of gallium arsenide – gallium arsenide substrate” from porosity of the film is improved; it is shown that by increasing porous film thickness general resistance increases. Assessment of the offered model adequacy showed compliance between results of the general resistance modeling and between experimental data at the level of 20 %. It is determined that contact resistance of metal to a porous gallium arsenide is depended on the Schottky barrier height. Change the film of a por-GaAs porosity leads to change of the contact resistance. It is shown that the general resistance of a metal-to-por-GaAs can be considered as system of parallel consistently connected resistance. To improve a porous layer morphology the approach for receiving porous layer by anode etching using pulse current with amplitude of 10 mA and period of 0,14 s is developed. Parameters of the impulse porosity that have value of 40 ms “switch off” and of 100 ms “switch on” are determined. That allowed receiving porous films with the maximum homogeneity of porosity. The automated system of determination contacts with Schottky barrier parameters by measurement of current-voltage characteristics (I–V curves), which allows to measure in one cycle direct and return branches I–V curves and equipped with the thermostat for carrying out measurement I–V curves at the set temperature conditions, is developed. The system allows receiving characteristics both concerning vol-tage, and concerning current. On the end of I–V curves measurement the possibility of calculation such parameters contacts with Schottky barrier exists: ideality factor, Schottky barrier height, contact resistance, too. While carrying out experiments dependence between porous layer morphology and electric parameters of Schottky contact is determined. It is shown that this dependence has linear character. Increasing porous layer thickness leads to deterioration in parameters of Schottky contact that is shown by increasing ideality coefficient which by growth of the film thickness increases from 1,24 to 1,7. The approach of making contacts with Schottky barrier to porous semiconductors, which differs from others by application of chemical method to draw Pd on porous GaAs with the subsequent sputtering of Ge and Ag layers and annealing, is improved. Annealing temperature of 350 °C and time of annealing of 20 min. are determined. The advanced approach allowed to reduce the Schottky barrier contact non-ideality coefficient from 1,7 to 1,2. A hydrogen sensor based on porous gallium arsenide with Schottky contact has been developed, and it is observed that the porosity of sensitive to hydrogen contact of Pd-to-por-GaAs Schottky diode influences speed and sensitivity of a hydrogen sensor. It is determined that sensor has response time less than 1 s and sensitivity to relative hydrogen concentration of 93,5 %. It is demonstrated that porous GaAs is applicable to measure hydrogen concentration and can be easily integrated on a chip as intelligent sensor.