Electrical characterization of silicon nanocrystal films

Neema Rastgar, Dave Rowe, Lance M. Wheeler, Eray Aydil, Uwe Kortshagen

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Thin films of semiconductor nanocrystals continue to receive attention as potential materials for making light-emitting diodes, photodiodes and solar cells. This approach to making optoelectronic devices may be promising because semiconductor nanocrystals are inexpensive to synthesize and their optoelectronic properties can be tuned by changing their size. However, devices based on thin films of nanocrystals typically show high electrical resistivity, and establishing control over electronic properties is difficult. The understanding of electronic transport in these nanocrystal films is in its infancy compared to bulk semiconductors. To improve this understanding and to learn how to manipulate charge carrier transport in semiconductor nanocrystal films, we study electronic transport in thin films of intrinsic and doped silicon nanocrystals. Silicon nanocrystals with diameters ranging from 5-20 nm were synthesized through decomposition of silane in a radio-frequency plasma reactor. Thin films of these nanocrystals were deposited either through ballistic aerosol impaction onto substrates or through spin coating from colloidal dispersions of the nanocrystals. The former approach is in situ and the nanocrystals are deposited onto the substrate immediately after they leave the plasma. In the latter approach, the nanocrystals emerging from the plasma are collected, dispersed in a solvent and cast onto the substrate. In both cases, the nanocrystals are deposited between two 100 nm-thick thermally evaporated aluminum contacts to form thin films of randomly packed nanoparticles. Current-voltage characteristics of the nanocrystal films were measured as a function of doping and temperature between 100 and 300 K. Preliminary results show that the films exhibit space charge limited current above applied electric fields of 1000 V/cm, and Ohmic behavior at lower electric fields. The conductivity of annealed undoped films exhibits Arrhenius dependence on temperature, with an activation energy of 0.60 eV between room temperature and 225 K, indicative of conduction mediated by intrinsic carriers. Annealed boron-doped films, on the other hand, show moderate Arrhenius temperature dependence near room temperature, and weak temperature dependence below 225 K, characteristic of either dopant ionization or tunneling conduction. Many films also demonstrate hysteresis in the current-voltage characteristics, ranging from insignificant to severe. The hysteresis is thought to arise from a parasitic capacitance in the film due to charging and appears to be most significant in films made of nanocrystals with ligands such as hexene. Resistance-capacitance (RC) time constants on the order of seconds describe the hysteresis. Conduction is sensitive to the surface conditions of the nanocrystals. For example, the conductivity of nanocrystal films in vacuum increase by an order of magnitude when nitrogen, argon, and oxygen gases flow over the films and the chamber is purged continuously to reduce water partial pressure in the chamber. This change is reversible over a time scale of two hours and suggests that desorption of water from the film is the likely reason for improved conductivity.

Original languageEnglish (US)
Title of host publication11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings
StatePublished - Dec 1 2011
Event2011 AIChE Annual Meeting, 11AIChE - Minneapolis, MN, United States
Duration: Oct 16 2011Oct 21 2011

Other

Other2011 AIChE Annual Meeting, 11AIChE
CountryUnited States
CityMinneapolis, MN
Period10/16/1110/21/11

Fingerprint

Silicon
Nanocrystals
Thin films
Semiconductor materials
Hysteresis
Current voltage characteristics
Plasmas
Optoelectronic devices
Temperature
Capacitance
Substrates
Electric fields
Doping (additives)
Silanes
Boron
Carrier transport
Water
Argon
Spin coating
Ballistics

ASJC Scopus subject areas

  • Chemical Engineering(all)

Cite this

Rastgar, N., Rowe, D., Wheeler, L. M., Aydil, E., & Kortshagen, U. (2011). Electrical characterization of silicon nanocrystal films. In 11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings

Electrical characterization of silicon nanocrystal films. / Rastgar, Neema; Rowe, Dave; Wheeler, Lance M.; Aydil, Eray; Kortshagen, Uwe.

11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings. 2011.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Rastgar, N, Rowe, D, Wheeler, LM, Aydil, E & Kortshagen, U 2011, Electrical characterization of silicon nanocrystal films. in 11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings. 2011 AIChE Annual Meeting, 11AIChE, Minneapolis, MN, United States, 10/16/11.
Rastgar N, Rowe D, Wheeler LM, Aydil E, Kortshagen U. Electrical characterization of silicon nanocrystal films. In 11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings. 2011
Rastgar, Neema ; Rowe, Dave ; Wheeler, Lance M. ; Aydil, Eray ; Kortshagen, Uwe. / Electrical characterization of silicon nanocrystal films. 11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings. 2011.
@inproceedings{74915d09fa1c423a8dd07b74c6f79cc7,
title = "Electrical characterization of silicon nanocrystal films",
abstract = "Thin films of semiconductor nanocrystals continue to receive attention as potential materials for making light-emitting diodes, photodiodes and solar cells. This approach to making optoelectronic devices may be promising because semiconductor nanocrystals are inexpensive to synthesize and their optoelectronic properties can be tuned by changing their size. However, devices based on thin films of nanocrystals typically show high electrical resistivity, and establishing control over electronic properties is difficult. The understanding of electronic transport in these nanocrystal films is in its infancy compared to bulk semiconductors. To improve this understanding and to learn how to manipulate charge carrier transport in semiconductor nanocrystal films, we study electronic transport in thin films of intrinsic and doped silicon nanocrystals. Silicon nanocrystals with diameters ranging from 5-20 nm were synthesized through decomposition of silane in a radio-frequency plasma reactor. Thin films of these nanocrystals were deposited either through ballistic aerosol impaction onto substrates or through spin coating from colloidal dispersions of the nanocrystals. The former approach is in situ and the nanocrystals are deposited onto the substrate immediately after they leave the plasma. In the latter approach, the nanocrystals emerging from the plasma are collected, dispersed in a solvent and cast onto the substrate. In both cases, the nanocrystals are deposited between two 100 nm-thick thermally evaporated aluminum contacts to form thin films of randomly packed nanoparticles. Current-voltage characteristics of the nanocrystal films were measured as a function of doping and temperature between 100 and 300 K. Preliminary results show that the films exhibit space charge limited current above applied electric fields of 1000 V/cm, and Ohmic behavior at lower electric fields. The conductivity of annealed undoped films exhibits Arrhenius dependence on temperature, with an activation energy of 0.60 eV between room temperature and 225 K, indicative of conduction mediated by intrinsic carriers. Annealed boron-doped films, on the other hand, show moderate Arrhenius temperature dependence near room temperature, and weak temperature dependence below 225 K, characteristic of either dopant ionization or tunneling conduction. Many films also demonstrate hysteresis in the current-voltage characteristics, ranging from insignificant to severe. The hysteresis is thought to arise from a parasitic capacitance in the film due to charging and appears to be most significant in films made of nanocrystals with ligands such as hexene. Resistance-capacitance (RC) time constants on the order of seconds describe the hysteresis. Conduction is sensitive to the surface conditions of the nanocrystals. For example, the conductivity of nanocrystal films in vacuum increase by an order of magnitude when nitrogen, argon, and oxygen gases flow over the films and the chamber is purged continuously to reduce water partial pressure in the chamber. This change is reversible over a time scale of two hours and suggests that desorption of water from the film is the likely reason for improved conductivity.",
author = "Neema Rastgar and Dave Rowe and Wheeler, {Lance M.} and Eray Aydil and Uwe Kortshagen",
year = "2011",
month = "12",
day = "1",
language = "English (US)",
isbn = "9780816910700",
booktitle = "11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings",

}

TY - GEN

T1 - Electrical characterization of silicon nanocrystal films

AU - Rastgar, Neema

AU - Rowe, Dave

AU - Wheeler, Lance M.

AU - Aydil, Eray

AU - Kortshagen, Uwe

PY - 2011/12/1

Y1 - 2011/12/1

N2 - Thin films of semiconductor nanocrystals continue to receive attention as potential materials for making light-emitting diodes, photodiodes and solar cells. This approach to making optoelectronic devices may be promising because semiconductor nanocrystals are inexpensive to synthesize and their optoelectronic properties can be tuned by changing their size. However, devices based on thin films of nanocrystals typically show high electrical resistivity, and establishing control over electronic properties is difficult. The understanding of electronic transport in these nanocrystal films is in its infancy compared to bulk semiconductors. To improve this understanding and to learn how to manipulate charge carrier transport in semiconductor nanocrystal films, we study electronic transport in thin films of intrinsic and doped silicon nanocrystals. Silicon nanocrystals with diameters ranging from 5-20 nm were synthesized through decomposition of silane in a radio-frequency plasma reactor. Thin films of these nanocrystals were deposited either through ballistic aerosol impaction onto substrates or through spin coating from colloidal dispersions of the nanocrystals. The former approach is in situ and the nanocrystals are deposited onto the substrate immediately after they leave the plasma. In the latter approach, the nanocrystals emerging from the plasma are collected, dispersed in a solvent and cast onto the substrate. In both cases, the nanocrystals are deposited between two 100 nm-thick thermally evaporated aluminum contacts to form thin films of randomly packed nanoparticles. Current-voltage characteristics of the nanocrystal films were measured as a function of doping and temperature between 100 and 300 K. Preliminary results show that the films exhibit space charge limited current above applied electric fields of 1000 V/cm, and Ohmic behavior at lower electric fields. The conductivity of annealed undoped films exhibits Arrhenius dependence on temperature, with an activation energy of 0.60 eV between room temperature and 225 K, indicative of conduction mediated by intrinsic carriers. Annealed boron-doped films, on the other hand, show moderate Arrhenius temperature dependence near room temperature, and weak temperature dependence below 225 K, characteristic of either dopant ionization or tunneling conduction. Many films also demonstrate hysteresis in the current-voltage characteristics, ranging from insignificant to severe. The hysteresis is thought to arise from a parasitic capacitance in the film due to charging and appears to be most significant in films made of nanocrystals with ligands such as hexene. Resistance-capacitance (RC) time constants on the order of seconds describe the hysteresis. Conduction is sensitive to the surface conditions of the nanocrystals. For example, the conductivity of nanocrystal films in vacuum increase by an order of magnitude when nitrogen, argon, and oxygen gases flow over the films and the chamber is purged continuously to reduce water partial pressure in the chamber. This change is reversible over a time scale of two hours and suggests that desorption of water from the film is the likely reason for improved conductivity.

AB - Thin films of semiconductor nanocrystals continue to receive attention as potential materials for making light-emitting diodes, photodiodes and solar cells. This approach to making optoelectronic devices may be promising because semiconductor nanocrystals are inexpensive to synthesize and their optoelectronic properties can be tuned by changing their size. However, devices based on thin films of nanocrystals typically show high electrical resistivity, and establishing control over electronic properties is difficult. The understanding of electronic transport in these nanocrystal films is in its infancy compared to bulk semiconductors. To improve this understanding and to learn how to manipulate charge carrier transport in semiconductor nanocrystal films, we study electronic transport in thin films of intrinsic and doped silicon nanocrystals. Silicon nanocrystals with diameters ranging from 5-20 nm were synthesized through decomposition of silane in a radio-frequency plasma reactor. Thin films of these nanocrystals were deposited either through ballistic aerosol impaction onto substrates or through spin coating from colloidal dispersions of the nanocrystals. The former approach is in situ and the nanocrystals are deposited onto the substrate immediately after they leave the plasma. In the latter approach, the nanocrystals emerging from the plasma are collected, dispersed in a solvent and cast onto the substrate. In both cases, the nanocrystals are deposited between two 100 nm-thick thermally evaporated aluminum contacts to form thin films of randomly packed nanoparticles. Current-voltage characteristics of the nanocrystal films were measured as a function of doping and temperature between 100 and 300 K. Preliminary results show that the films exhibit space charge limited current above applied electric fields of 1000 V/cm, and Ohmic behavior at lower electric fields. The conductivity of annealed undoped films exhibits Arrhenius dependence on temperature, with an activation energy of 0.60 eV between room temperature and 225 K, indicative of conduction mediated by intrinsic carriers. Annealed boron-doped films, on the other hand, show moderate Arrhenius temperature dependence near room temperature, and weak temperature dependence below 225 K, characteristic of either dopant ionization or tunneling conduction. Many films also demonstrate hysteresis in the current-voltage characteristics, ranging from insignificant to severe. The hysteresis is thought to arise from a parasitic capacitance in the film due to charging and appears to be most significant in films made of nanocrystals with ligands such as hexene. Resistance-capacitance (RC) time constants on the order of seconds describe the hysteresis. Conduction is sensitive to the surface conditions of the nanocrystals. For example, the conductivity of nanocrystal films in vacuum increase by an order of magnitude when nitrogen, argon, and oxygen gases flow over the films and the chamber is purged continuously to reduce water partial pressure in the chamber. This change is reversible over a time scale of two hours and suggests that desorption of water from the film is the likely reason for improved conductivity.

UR - http://www.scopus.com/inward/record.url?scp=84857202840&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84857202840&partnerID=8YFLogxK

M3 - Conference contribution

SN - 9780816910700

BT - 11AIChE - 2011 AIChE Annual Meeting, Conference Proceedings

ER -