Laser removal of defects in a dielectric for modulating an adjoining atomically two-dimensional material
A method removes defects in a dielectric layer, such as during fabrication of a device that emits light from hot electrons injected into an atomically two-dimensional material. An atomically two-dimensional material and the dielectric layer are adjoined. The dielectric layer is adapted to convey a variable electric field for modulating a wavelength of photons electronically emitted across a band structure of the atomically two-dimensional material. Laser pulses are strobed into the dielectric layer with sufficient cumulative energy to remove a majority of the defects in the dielectric layer without altering the atomically two-dimensional material.
1. A method for removing a plurality of defects in a dielectric layer, the method comprising:
adjoining an atomically two-dimensional material to a first side of the dielectric layer having the defects, wherein the dielectric layer is adapted to convey a variable electric field for modulating a wavelength of photons electronically emitted across a band structure of the atomically two-dimensional material; and
strobing a plurality of laser pulses into a second side opposite the first side of the dielectric layer with sufficient cumulative energy to remove a majority of the defects in the dielectric layer without altering the atomically two-dimensional material, where the dielectric layer is not a two-dimensional material, where the defects consist of oxygen vacancies or oxygen interstitials, and where the dielectric layer is amorphous.
2. The method of claim 1 , further comprising:
applying the variable electric field conveyed through the dielectric layer for modulating the band structure of the atomically two dimensional material;
injecting a plurality of hot electrons into the atomically two dimensional material; and
emitting the photons within the atomically two dimensional material in response to the hot electrons transitioning across the band structure modified by the variable electric field, wherein the variable electric field modulates the wavelength of the photons because the variable electric field modulates the band structure of the atomically two dimensional material.
3. The method of claim 1 , further comprising:
illuminating the atomically two-dimensional material and the dielectric layer with an excitation beam after the adjoining and the strobing, wherein the excitation beam illuminates an entirety of the atomically two-dimensional material or a focused region of the atomically two-dimensional material; and
measuring an intensity of a photoluminescence excited by the excitation beam, wherein the photoluminescence includes a defect luminescence from the defects in the dielectric layer and a desired luminescence emitted from the atomically two dimensional material, and because the strobing removes the majority of the defects, the defect luminescence from the dielectric layer is less than the desired luminescence from the atomically two dimensional material.
4. The method of claim 1 , wherein the adjoining includes adjoining to convey the variable electric field that modulates the band structure of the atomically two dimensional material and thereby modulates allowed direct transitions across the band structure for hot electrons emitting the photons during the allowed direct transitions, with the wavelength of the photons corresponding to an energy of the allowed direct transitions.
5. The method of claim 4 , wherein the atomically two dimensional material is graphene or a transition metal dichalcogenide.
6. The method of claim 1 , wherein the dielectric layer is composed of a metal oxide incorporating the defects, which include oxygen vacancies and oxygen interstitials, and wherein the strobing combines certain of the oxygen vacancies and certain of the oxygen interstitials, thereby removing the certain of the oxygen vacancies and the certain of the oxygen interstitials from the metal oxide of the dielectric layer.
7. The method of claim 6 , wherein the strobing of the laser pulses into the dielectric layer includes the strobing of the laser pulses through an atmosphere including oxygen and then into the metal oxide of the dielectric layer.
8. The method of claim 6 , wherein the strobing of the laser pulses into the dielectric layer includes the strobing of the laser pulses through an atmosphere not including any oxygen and then into the metal oxide of the dielectric layer.
9. The method of claim 6 , wherein the metal oxide of the dielectric layer is selected from the group consisting of HfO2 and Al2O3.
10. The method of claim 9 , wherein the atomically two dimensional material is graphene or a transition metal dichalcogenide.
11. The method of claim 1 , wherein the adjoining the atomically two-dimensional material and the dielectric layer includes adjoining such that bonding between the atomically two dimensional material and the dielectric layer consists essentially of van der Waals bonding.
12. The method of claim 1 , wherein the adjoining includes adjoining a first surface of the atomically two-dimensional material and the dielectric layer, the atomically two dimensional material also having a second surface opposite the first surface, and wherein the atomically two dimensional material does not have any dangling atomic bonds at the first and second surfaces.
13. The method of claim 12 , wherein the atomically two dimensional material is a two dimensional crystal having one to five molecular layers, with bonding within the molecular layers primarily being covalent bonding or ionic bonding, and with bonding between the molecular layers consisting essentially of van der Waals bonding.
14. The method of claim 1 , wherein the adjoining includes depositing the dielectric layer onto the atomically two-dimensional material, wherein the defects are introduced into the dielectric layer during the depositing.
15. The method of claim 14 , wherein the depositing the dielectric layer includes repeated atomic layer deposition of a metal oxide onto the atomically two dimensional material, resulting in the dielectric layer that is amorphous and includes the defects within the metal oxide.
16. The method of claim 1 , wherein the adjoining includes adjoining the atomically two dimensional material, which is graphene, and the dielectric layer, which is adapted to convey the variable electric field for modulating a Fermi level in the graphene and thereby modulating allowed direct transitions into holes at or above the Fermi level for hot electrons emitting the photons during the allowed direct transitions within the graphene.
17. The method of claim 1 , wherein the adjoining includes adjoining the atomically two dimensional material, which is a transition metal dichalcogenide having the band structure including a direct bandgap, and the dielectric layer, which is adapted to convey the variable electric field for modulating the direct bandgap via the Stark effect and thereby modulating allowed direct transitions across the direct bandgap for hot electrons emitting the photons during the allowed direct transitions within the transition metal dichalcogenide.
18. The method of claim 1 where the wavelength of the laser pulses substantially matches a thickness of the dielectric layer so that the laser pulses do not appreciably reach the underlying atomically two-dimensional material.
19. The method of claim 18 where the wavelength is at or about 193 nm.
20. The method of claim 1 where the laser illuminates the dielectric layer with a cumulative energy of at or about 4 mJ/cm 2 .
21. A method for fabricating a device emitting light from hot electrons, the method comprising:
providing a conductive layer that is a supply of a plurality of electrons;
adjoining the conductive layer and an insulating layer, which presents a thin barrier allowing only the hot electrons out of the plurality of electrons to tunnel from the conductive layer through the thin barrier;
adjoining the insulating layer and an atomically two dimensional material having a band structure;
adjoining the atomically two-dimensional material and a dielectric layer that is not a two-dimensional material having a plurality of defects, wherein the dielectric layer is adapted to convey a variable electric field for modulating a wavelength of photons electronically emitted across the band structure of the atomically two dimensional material;
strobing a plurality of laser pulses into the dielectric layer with sufficient cumulative energy to remove a majority of the defects in the dielectric layer without altering the atomically two dimensional material; and
adjoining the dielectric layer and an electrode layer, which is adapted to apply the variable electric field via the dielectric layer to modulate the wavelength of the photons emitted when the hot electrons transition across the band structure of the atomically two-dimensional material, where the dielectric layer is amorphous, and where the defects consist of oxygen vacancies or oxygen interstitials.
22. The method of claim 21 , wherein the adjoining of the atomically two-dimensional material and the dielectric layer includes adjoining to convey the variable electric field that modulates the band structure of the atomically two dimensional material and thereby modulates allowed direct transitions across the band structure for the hot electrons emitting the photons during the allowed direct transitions, with the wavelength of the photons corresponding to an energy of the allowed direct transitions.
23. The method of claim 21 , wherein the dielectric layer is composed of a HfO2 or Al2O3 incorporating the defects, which include oxygen vacancies and oxygen interstitials, and wherein the strobing combines certain of the oxygen vacancies and certain of the oxygen interstitials, thereby removing the certain of the oxygen vacancies and the certain of the oxygen interstitials from the HfO2 or Al2O3 of the dielectric layer.