CVD nanocrystalline silicon thermoelectric material

Patent metadata

Field	Value
Publication number	US-9577174-B2
Application number	US-201615256764-A
Country	US
Kind code	B2
Filing date	Sep 6, 2016
Priority date	Feb 20, 2015
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

A process for forming a doped nc-Si thin film thermoelectric material. A nc-Si thin film is slowly deposited on a substrate, either by hot-wire CVD (HWCVD) with a controlled H 2 :SiH 4 ratio R=6-10 or by plasma-enhanced (PECVD) with a controlled R=80-100, followed by ion implantation of an n- or p-type dopant and a final annealing step to activate the implanted dopants and to remove amorphous regions. A doped nc-Si thin film thermoelectric material so formed has both a controllable grain size of from a few tens of nm to 3 nm and a controllable dopant distribution and thus can be configured to provide a thermoelectric material having predetermined desired thermal and/or electrical properties. A final annealing step is used to activate the dopants and remove any residual amorphous regions.

First claim

What is claimed is:

1. A process for forming a germanium-free doped nanocrystalline silicon (nc-Si) thermoelectric material having a high electrical conductivity and a low thermal conductivity, comprising the steps of:
(1) providing a deposition mixture comprising H 2 and SiH 4 having a controlled H 2 :SiH 4 ratio R of between 80 and 100, the deposition mixture being free of any added germanium;
(2) controllably depositing the deposition mixture on a substrate by means of plasma-enhanced chemical vapor deposition (PECVD) at a growth rate of about 0.01-0.03 nm/s to form an nc-Si thin film material having a controlled grain size of about 10 nm to about 3 nm and a predetermined thermal conductivity κ, wherein the grain size is controlled by controlling the H 2 :SiH 4 ratio R of the deposition mixture;
(3) controllably doping the nc-Si thin film material by implanting dopant ions into the material to a concentration of about 10 21 cm −3 to form a doped nc-Si thin film material having a controlled dopant profile and controlled electrical conductivity; and
(4) annealing the doped nc-Si thin film material by first subjecting the material to a furnace annealing at a temperature between about 600 and about 800° C. for at least about 2 hours and then subjecting the material to a cycle of rapid thermal annealing at a temperature of about 800 to about 1000° C. for at least 1 minute.

2. The process according to claim 1 , wherein the nc-Si thin film is doped with an n-type dopant.

3. The process according to claim 1 , wherein the nc-Si thin film is doped with a p-type dopant.

4. The process according to claim 1 ,
wherein R=100 with H 2 flow rate of 100 sccm;
wherein the nc-Si thin film is deposited on a substrate having a temperature of 250° C. using a plasma power of 90 W with a frequency of 13.56 Mhz and a chamber pressure 700 mTorr; and
wherein the nc-Si film has a growth rate of about 0.02 nm/s.

5. The process according to claim 1 , further comprising depositing multiple layers of nc-Si on the substrate to produce an engineered multi-layered nc-Si thin film material having a predetermined overall thermal conductivity κ, wherein each layer is deposited using a deposition mixture of H 2 and SiH 4 having a controlled R to produce a layer of nc-Si having a predetermined grain size, wherein the grain sizes of the layers of the nc-Si thin film are configured to obtain the predetermined overall thermal conductivity κ.

6. The process according to claim 5 , wherein the nc-Si thin film material is doped and annealed after all layers have been deposited.

7. The process according to claim 5 , wherein the nc-Si thin film material is doped and annealed after deposition of less than all of the layers have been deposited, the deposition, doping, and annealing steps being repeated until all layers have been deposited, doped, and annealed.

Assignees

• Us Navy

Inventors

• Liu Xiao
• Metcalf Thomas H
• Queen Daniel R
• Jugdersuren Battogtokh
• Wang Qi
• Nemeth William

Classifications

• H01L35/22

  Electricity · mapped topic

• H01L35/34 Primary

  Electricity · mapped topic

• H10N10/8556

  comprising compounds containing germanium or silicon · CPC title

• H10N10/01 Primary

  Manufacture or treatment · CPC title