Phosphorus doped diamond electrode with tunable low work function for emitter and collector applications

Patent metadata

Field	Value
Publication number	US-2018204702-A1
Application number	US-201815921225-A
Country	US
Kind code	A1
Filing date	Mar 14, 2018
Priority date	May 5, 2016
Publication date	Jul 19, 2018
Grant date	—

Abstract

An apparatus includes an emitter electrode including a phosphorus doped diamond layer with low work function. The apparatus further includes a collector electrode and a vacuum gap disposed between the emitter and the collector. The collector has a work function of 0.84 eV or less.

First claim

What is claimed is:

1 . A method for forming an electrode, comprising:
loading a substrate into a plasma enhanced chemical vapor deposition (PECVD) reactor and preparing a surface of the substrate for doped diamond growth; exposing the substrate to a pure hydrogen plasma for a preset duration; and depositing a phosphorus doped diamond layer on the substrate to form the electrode, wherein the electrode comprises a collector that has a work function of 0.84 eV or less.

2 . The method of claim 1 , wherein the wet-chemical cleaning procedure comprises:
boiling the substrate in H2SO4/H2O2/H2O at 220° C. for at least fifteen minutes; treating the substrate for at least five minutes using a solution comprising hydrofluoric acid; and boiling the substrate in NH4OH/H2O2/H2O at 75° C. for at least fifteen minutes.

3 . The method of claim 2 , wherein the wet-chemical cleaning procedure further comprises:
rinsing the substrate with deionized water after each step.

4 . The method of claim 1 , wherein exposing the substrate to the pure hydrogen plasma for the preset duration comprises:
exposing the substrate to the pure hydrogen plasma at a preset temperature range for at least fifteen minutes.

5 . The method of claim 4 , wherein the preset temperature range comprises a low temperature not greater than 800° C. and a high temperature of at least 900° C.

6 . The method of claim 1 , wherein depositing the phosphorus doped diamond layer on the substrate comprises:
depositing the phosphorus doped diamond layer using a methane flow rate of 2 sccm and a 200 ppm trimethylphosphine/hydrogen (the phosphorus source) flow rate between 10 sccm and 30 sccm with hydrogen as carrier gas.

7 . The method of claim 6 , wherein the methane flow rate is 0.5% of a total gas flow rate of 400 sccm.

8 . The method of claim 1 , wherein depositing the phosphorus doped diamond layer on the substrate comprises:
depositing the phosphorus doped layer at around 900° C.-1200° C. using a microwave power of at least 2500 W and a preset chamber pressure range.

9 . The method of claim 17 , wherein the preset chamber pressure range comprises a range of 75 to 85 Torr.

10 . The method of claim 1 , further comprising:
controlling impurities during layer deposition by using a water-cooled sample stage in the PECVD reactor.

11 . The method of claim 10 , further comprising:
timing a growth period of the doped diamond growth for less than or equal to seven minutes; terminating methane and TMP/H2 flow after the growth period; and inducing a negative electron affinity to the surface of the substrate using hydrogen plasma exposure.

Assignees

• Univ Arizona State

Inventors

• Koeck Franz A M
• Nemanich Robert J

Classifications

• H01J19/06

  characterised by the material · CPC title

• C30B29/04

  Diamond · CPC title

• C30B25/186

  being specially pre-treated by, e.g. chemical or physical means · CPC title

• H01J45/00

  Discharge tubes functioning as thermionic generators {(structural combination of fuel element with thermoelectric element G21C3/40; nuclear power plants using thermionic converters G21D7/04; structural combination of a radioactive source with a thermionic converter, e.g. radioisotope batteries G21H1/10; generators in which thermal or kinetic energy is converted into electrical energy by ionisation of a fluid and removal of the charge therefrom H02N3/00)} · CPC title

• H01J9/14

  of non-emitting electrodes · CPC title