Method for the controlled growth of crystal whiskers and application thereof to the making of tip microcathodes

A method for controlled growth of crystal whiskers, comprising the following steps:

• a first step of forming on a substrate a first layer of a first material on which neither growth nor nucleation of a second material to be grown occurs;
• a second step of forming at least one aperture in said first layer;
• a third step of selectively forming, in said at least one aperture, a third material which, in liquid form, is capable of dissolving and absorbing said second material;
• a fourth step of heating said third material and growing in vapor phase, in said at least one aperture, said second material in the form of said crystal whisker;
• and
• wherein the third material comprises a constituent that is volatile at a temperature of growth of the fourth step, and wherein the growth of the fourth step is achieved in the presence of a gas comprising said constituent that is volatile, thereby enabling the evaporation of this constituent to be controlled.

A method for the controlled growth of crystal whiskers, comprising:

• depositing a dielectric layer on a GaAs substrate;
• forming at least one aperture in said dielectric layer;
• heating said substrate to evaporate As from the substrate and forming localized droplets of Ga in the said apertures;
• growing GaAs whiskers in said apertures by absorption of a gas by said Ga droplets.

A method for controlled growth of a tapered crystal whisker, comprising the following steps:

• a first step of forming on a substrate a first layer of a first material on which neither growth nor nucleation of a second material occurs;
• a second step of forming at least one aperture in said first layer;
• a third step of selectively depositing, in said at least one aperture, a first quantity of a third material which in liquid form is capable of dissolving and absorbing said second material, wherein said third material has a high solubility in said second material;
• a fourth step of heating said third material to liquid form and growing in vapor phase in said at least one aperture, said second material to be grown in the form of said tapered crystal whisker, wherein said third material is incorporated in said second material during growth thereby continuously reducing the quantity of liquid third material available for absorbing and depositing said second material, thereby continuously decreasing a diameter of a growth surface of said whisker during growth resulting in a tapered pointed whisker.

A method for forming a plurality of insulated microtip cathode electrodes for a field-effect transistor, comprising the steps of:

• (a) forming, on a substrate, a first layer of a first material on which neither growth nor nucleation of a material to be grown occurs;
• (b) forming a plurality of apertures in said first layer;
• (c) selectively depositing, in each of said plurality of apertures, a second material which, in liquid form, is capable of dissolving and absorbing said material to be grown;
• (d) heating and growing in vapor phase, in each of said plurality of apertures, said material to be grown in the form of said plurality of insulated microtip cathode electrodes;
• and
• (e) decreasing a temperature of the growing microtip cathode electrodes during step (d) in such a way as to achieve a decrease of an upper width of each of the microtip cathode electrodes relative to a lower width of each of the microtip cathode electrodes in order to thereby form a plurality of insulated microtip cathode electrodes in the final field-effect transistor structure.

A method for forming a plurality of insulated microtip cathode electrodes of a field-effect transistor, comprising the steps of:

• (a) forming, on a substrate, a first layer of a first material on which neither growth nor nucleation of a second material to be grown occurs;
• (b) forming a plurality of apertures in said first layer;
• (c) selectively forming, in each of said plurality of apertures, a third material which, in liquid form, is capable of dissolving and absorbing said second material;
• (d) heating said third material and growing in vapor phase, in each of said plurality of apertures, said second material so as to form said plurality of insulated microtip cathode electrodes,
• wherein said third material comprises a constituent that is volatile at a temperature of growth in step (d), and wherein the growth in stp (d) is achieved in the presence of a gas comprising said constituent that is volatile, thereby enabling the evaporation of said constituent to be controlled, an wherein after step (d) said microtip cathode electrodes exist in a matrix form insulated from each other by said first layer.

A method for forming a plurality of insulated microtip cathode electrodes of a field-effect transistor, comprising the steps of:

• (a) forming, on a substrate, a first layer of a first material on which neither growth nor nucleation of a second material occurs;
• (b) forming a plurality of apertures in said first layer;
• (c) selectively forming, in each of said plurality of apertures, a first quantity of a third material which in liquid form is capable of dissolving and absorbing said second material, wherein said third material has a high solubility in said second material;
• (d) heating said third material to liquid form and growing in vapor phase in each of said plurality of apertures, said second material to be grown so as to form said plurality of insulated microtip cathode electrodes, wherein said third material is incorporated in said second material during growth, thereby continuously reducing the quantity of liquid third material available for absorbing and depositing said second material, and continuously decreasing a diameter of a growth surface of each of said microtip cathode electrodes during growth resulting in said plurality of insulated microtip cathode electrodes in the final field-effect transistor structure.