Porous semiconductive film and process for its production

• US 8,043,909 B2
• Filed: 03/21/2008
• Issued: 10/25/2011
• Est. Priority Date: 03/23/2007
• Status: Active Grant

• Current Assignee: Evonik Operations GmbH (Rag-Stiftung)
• Original Assignee: Evonik Degussa GmbH
• Inventors: Brandt, Martin S., Ebbers, André, Lechner, Robert, Wiggers, Hartmut, Stutzmann, Martin, Trocha, Martin
• Primary Examiner(s): MENZ, DOUGLAS M
• Application Number:
  US12/053,369
• Publication Number:
  US 20090026458A1
• Time in Patent Office: 1,313 Days
• Field of Search: 438/223, 438/409, 438/960
• US Class Current: 438/223
• CPC Class Codes: H01L 21/02376 Carbon, e.g. diamond-like carbon
• CPC Class Codes: H01L 21/0242 Crystalline insulating materials
• CPC Class Codes: H01L 21/02422 Non-crystalline insulating materials, e.g. glass, polymers
• CPC Class Codes: H01L 21/02532 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/0257 Doping during depositing
• CPC Class Codes: H01L 21/02581 Transition metal or rare earth elements
• CPC Class Codes: H01L 21/0259 Microstructure
• CPC Class Codes: H01L 21/02614 Transformation of metal, e.g. oxidation, nitridation
• CPC Class Codes: H01L 21/02628 using solutions
• CPC Class Codes: H01L 29/78 with field effect produced by an insulated gate H01L29/7725, H01L29/775, H01L29/778 take precedence
• CPC Class Codes: Y10S 438/96 Porous semiconductor

Abstract

The present invention provides a porous semiconductive structure, characterized in that the structure has an electrical conductivity of 5·10⁻⁸ S·cm⁻¹ to 10 S·cm⁻¹, and an activation energy of the electrical conductivity of 0.1 to 700 meV, and a solid fraction of 30 to 60% by volume, and a pore size of 1 nm to 500 nm, the solid fraction having at least partly crystalline doped constituents which are bonded to one another via sinter necks and have sizes of 5 nm to 500 nm and a spherical and/or ellipsoidal shape, which comprise the elements silicon, germanium or an alloy of these elements, and also a process for producing a porous semiconductive structure, characterized in that

• • A. doped semimetal particles are obtained, and then
  • B. a dispersion is obtained from the semimetal particles obtained after step A, and then
  • C. a substrate is coated with the dispersion obtained after step B, and then
  • D. the layer obtained after step C is treated by means of a solution of hydrogen fluoride in water, and then
  • E. the layer obtained after step D is treated thermally to obtain a porous semiconductive structure.

Claims

1. A process for producing a porous semiconductive structure, wherein

A. doped semimetal particles are obtained, and then

B. a dispersion is obtained from the semimetal particles obtained after step A, and then

C. a substrate is coated with the dispersion obtained after step B, and then

D. the layer obtained after step C is treated by means of a solution of hydrogen fluoride in water, and then

E. the layer obtained after step D is treated thermally to obtain a porous semiconductive structure.

2. A process according to claim 1, wherein, in step A, continuously,

(a) at least one vaporous or gaseous semimetal hydride selected from silane, germanium hydride and a mixture of these semimetal hydrides and at least one vaporous or gaseous dopant, and an inert gas are transferred into a reactor and mixed there, the proportion of the semimetal hydride being from 0.1% to 90% by weight based on the sum of semimetal hydride, dopant and inert gas, and then

(b) a plasma is obtained by energy input by means of electromagnetic radiation in the microwave range at a pressure of 10 to 1100 hPa, and then

(c) the reaction mixture is allowed to cool, and the reaction product is removed from gaseous substances in the form of a powder to obtain predominantly crystalline doped semimetal particles.

3. A process according to claim 2, wherein in step (a), a dopant is used which is selected from lithium metal and lithium metal amide (LiNH₂), from the group of hydrogen-containing compounds of phosphorus, arsenic, antimony, bismuth, boron, aluminium, gallium, indium, thallium, europium, erbium, cerium, praseodymium, neodymium, samarium, gadolinium, terbium, dysprosium, holmium, thulium, ytterbium, lutetium, lithium, germanium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, or from a mixture of these dopants.

4. A process according to any one of claims 1 to 3, wherein, in step B, doped semimetal particles are used with a proportion by mass of 1 to 60% by weight based on the total mass of the dispersion, and the doped semimetal particles are dispersed into a liquid phase which comprises water and/or at least one organic solvent to obtain a dispersion which, at 23°

C., has a viscosity of less than 100 mPas at 1000 s<sup>−

1</sup>.

5. A process according to claim 1, wherein, in step C, the dispersion is applied to the substrate by spin-coating, knife-coating, drip-coating, screen-printing, dip-coating or spray-coating, and then the liquid phase is driven out by introducing thermal energy to obtain a layer which has a conductivity of at most 10⁻

11 S·

cm<sup>−

1</sup>.

6. A process according to claim 5, wherein a substrate is used which is selected from organic material, inorganic material, and a composite comprising at least one organic and/or at least one inorganic material, the substrate being resistant to hydrofluoric acid.

7. A process according to claim 1, wherein, in step D, a solution of hydrogen fluoride in water in a concentration of the hydrogen fluoride of 0.01% by weight to 50% by weight, based on the total mass of the solution of hydrogen fluoride in water, is applied by dipping, drip-coating, spray-coating or flow-coating, and is applied at a temperature of 10°

C. to 70°

C. and over a period of 1 s to 1 hour to obtain a layer which has a conductivity of 5·

10<sup>−

11</sup> S·

cm<sup>−

1</sup> to 2·

10<sup>−

10</sup> S·

cm<sup>−

1</sup>.

8. A process according to claim 1, wherein the layer obtained after step D, in a further step before step E, is dipped or rinsed off in water and then blown with dry nitrogen, or then dried at a temperature of 60 to 200°

C.

9. A process according to claim 1, wherein the thermal treatment is effected in step E by introducing thermal energy with a power density of 10 kW·

cm<sup>−

2</sup> to 65 MW·

cm<sup>−

2</sup>, which at least partly sinters the particles of the layer obtained after step D.

10. A process according to claim 9, wherein the input of thermal energy is effected by laser light having a wavelength of 500 to 1100 nm, the thermal energy being introduced with an energy density of 1 mJ·

cm<sup>−

2</sup> to 500 mJ·

cm<sup>−

2</sup>, wherein the laser light is optionally pulsed laser light, said pulsed laser light being used with a pulse duration of 8 ns to 20 ns and a pulse frequency of 10 to 30 pulses at a pulse repetition rate of 0.01 to 10·

s<sup>−

1</sup>.

11. A porous semiconductor structure which is obtained according to claim 1.

12. A process according to claim 4, wherein said viscosity is less than 10 mPas at 1000 s⁻

1.

13. A process according to claim 10, wherein the laser light is pulsed laser light.