Method of crystallizing amorphous material with a moving energy beam
AssigneeMassachusetts Institute of Technology
InventorsJohn C. C. Fan, Herbert J. Zieger
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Abstract
An improved method for crystallizing amorphous material with a moving beam of energy is disclosed. In this method, the energy beam is scanned in a manner to provide controlled, continuous motion of the crystallization front.
Claims34
A method of converting solid amorphous material to a more crystalline state comprising the steps of:
- (a) heating a portion of said material with energy from an energy beam to bring such portion to its crystallization temperature while maintaining the temperature below the melting temperature of the crystalline state of the material;
- and
- (b) moving said energy beam in relation to said material at a velocity V, which is less than or equal to V.sub.ac but fast enough to provide continuous controlled motion of the crystallization front;
- wherein V.sub.ac is the normalized boundary velocity of the transformation of the amorphous material to crystalline.
In the method of crystallizing an amorphous material by scanning it with an energy beam:
- providing continuous controlled motion of the crystallization front by (a) maintaining the background temperature of the amorphous material at a value which is between the temperature at which periodic structure occurs and the temperature which produces runaway crystallization and (b) modulating the beam and scanning a surface of the material with the beam at a rate less than or equal to the normalized boundary velocity of the crystallization front.
A method for producing a crystalline semiconductor film, comprising:
- a. forming an amorphous film of a semiconductor on a substrate;
- and,
- b. scanning said amorphous film to crystallize it with a laser beam, said laser beam being modulated to provide continuous, controlled motion of the crystallization front, the scanning rate being less than or equal to the velocity of the crystallization front and the modulation of the laser beam being at an energy level to crystallize the material without achieving a temperature equal to or greater than the crystalline melting point of the material.
A method of crystallizing an amorphous inorganic material in the solid phase comprising scanning said material with an energy beam sufficient to provide continuous, controlled motion of the crystallization front velocity but insufficient energy to reach the melting point of the crystalline material;
- the scanning rate being less than or equal to the crystallization front velocity.
A method of fabricating a photovoltaic cell, comprising:
- a. forming a conductive layer on a substrate;
- b. forming an amorphous semiconductor film on said conductive layer;
- c. scanning said amorphous semiconductor film with an energy beam at a rate which is less than or equal to the crystallization wavefront velocity and at an energy level high enough to provide continuous, controlled motion of the crystallization front to improve the crystallinity of said semiconductor film but below the melting temperature of the crystalline state of the film;
- and,
- d. forming a transparent rectifying contact with the scanned film.
A method of fabricated a photovoltaic cell, comprising:
- a. forming an amorphous semiconductor film on a transparent, conductive substrate;
- b. forming a rectifying contact between the amorphous semiconductor film and substrate;
- c. scanning said amorphous semiconductor film with an energy beam at a rate which is less than or equal to the crystallization wavefront velocity but at an energy level low enough to prevent reaching the crystalline melting point of the film to provide continuous, controlled motion of the crystallization front to improve the crystallinity of said semiconductor film;
- and,
- d. forming a conductive layer on the scanned film.
A method of fabricating a photovoltaic cell, comprising:
- a. depositing an amorphous semiconductor layer;
- b. scanning said amorphous semiconductor layer with an energy beam at a rate which is less than or equal to the crystallization wavefront velocity and at an energy level low enough to avoid the crystalline melting point of the layer thereby to provide a continuous, controlled motion of a crystallization front to form a crystalline semiconductor substrate;
- c. forming an active semiconductor film on said substrate;
- d. forming a p-n junction in said active film;
- and,
- e. forming an ohmic contact to said active semiconductor film.
In the fabrication of a shallow homojunction solar cell from a semiconductor layer:
- The improvement wherein said layer is formed from an amorphous semiconductor layer scanned with an energy beam at a rate which is less than or equal to the crystallization wavefront velocity and at an energy level low enough to prevent the temperature of the layer to reach its crystalline melting point thereby to provide continuous, controlled motion of the crystallization front to form a crystalline semiconductor layer for said shallow homojunction solar cell.
In the method of crystallizing an amorphous material with a moving energy beam:
- The improvement of modulating said energy beam in conjunction with heating said material to an elevated temperature at a rate which is less than or equal to the crystallization wavefront velocity and at an energy level low enough to prevent liquifying or vaporizing the material thereby to provide a controlled, continuous crystallization front.
Dependencies are inferred from the claim text.