MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Low-Frequency Noise and Lateral TransportLow-Frequency Noise and Lateral Transport

Studies of InStudies of In0.350.35GaGa0.650.65As/GaAsAs/GaAs

Quantum Dot HeterostructuresQuantum Dot Heterostructures

Vasyl P. KunetsVasyl P. Kunets, , T. Al. Morgan, Yu. I. Mazur, V. G. Dorogan, T. Al. Morgan, Yu. I. Mazur, V. G. Dorogan, P. M. Lytvyn,P. M. Lytvyn,

M. E. Ware, D. Guzun, J. L. Shultz, and G. J. Salamo M. E. Ware, D. Guzun, J. L. Shultz, and G. J. Salamo

Arkansas Institute for Nanoscale Materials Science and Engineering,Arkansas Institute for Nanoscale Materials Science and Engineering,

University of Arkansas, Fayetteville, Arkansas 72701University of Arkansas, Fayetteville, Arkansas 72701

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

OutlineOutline

Motivation Motivation (low-frequency noise from conductivity fluctuations : from bulk to QDs)(low-frequency noise from conductivity fluctuations : from bulk to QDs)

Sample growth (self-assembled quantum dots)elf-assembled quantum dots)

Electronic studies of QD heterostructuresElectronic studies of QD heterostructures

photoluminescence

temperature dependent Hall effect

low frequency noise spectroscopy

SummarySummary

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Origins of Low-Frequency Noise in Origins of Low-Frequency Noise in BulkBulk Semiconductors Semiconductors

motivationmotivation

n-typen-typeL

t W

V

-d Ee

Ej

ne

ne

ii

number of carriersnumber of carriersfluctuationfluctuation

mobility fluctuationsmobility fluctuations

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Low-Frequency Noise in Heterostructures with Low-Frequency Noise in Heterostructures with Quantum DotsQuantum Dots

motivationmotivation

multi-layer InGaAs QDsmulti-layer InGaAs QDs

E

x

E0

EF

GaAs

InGaAs WLEWL

B

tunneling

thermionic emission

InGaAs QDs

N(E)

E

0D QDs

2D WL

What conductivity mechanisms are important in the presence of QDs?What conductivity mechanisms are important in the presence of QDs?

• Carrier hopping random-telegraph noiseCarrier hopping random-telegraph noise

• Tunneling in-plane of QDs shot noiseTunneling in-plane of QDs shot noise

Self-assembled heteroepitaxy and the generation-recombination noiseSelf-assembled heteroepitaxy and the generation-recombination noise

What model (What model (nn or or ) is valid for ) is valid for 1/f1/f noise in heterostructures with QDs? noise in heterostructures with QDs?

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grantself-assembled quantum dotsself-assembled quantum dots

Growth of QD Heterostructures by Solid Source MBEGrowth of QD Heterostructures by Solid Source MBE

GaAs S.I. (001) substrateGaAs S.I. (001) substrate

500 nm GaAs buffer500 nm GaAs buffer

500 nm GaAs:Si, N500 nm GaAs:Si, Ndd = 7 = 710101616 cm cm-3-3

20 nm GaAs spacer20 nm GaAs spacer

20 nm GaAs spacer20 nm GaAs spacer

150 nm GaAs:Si, N150 nm GaAs:Si, Ndd = 7 = 710101616 cm cm-3-3

N ML InN ML In0.350.35GaGa0.650.65AsAs

RHEED Measurements for InRHEED Measurements for In0.350.35GaGa0.650.65AsAs

0 ML InGaAs – reference sample

6 ML InGaAs – QW sample

9 ML InGaAs – QD sample

11 ML InGaAs – QD sample

13 ML InGaAs – QD sample

FM

gro

wth

FM

gro

wth

SK

gro

wth

SK

gro

wth

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Correlation between AFM Statistical Analysis and PhotoluminescenceCorrelation between AFM Statistical Analysis and Photoluminescence

Electronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

NQD = 3.8 1010 cm-2

height = 34 Å

NQD = 8.4 1010 cm-2

height = 47 Å

NQD = 7.2 1010 cm-2

height = 54 Å

PL red shift with coverage PL line-shape correlates with

size distribution from AFM

higher density of quantum dots

BUT LOWER integral PL intensity

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 GrantElectronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

Transition from QW to QDs Examined by Temperature Dependent Hall EffectTransition from QW to QDs Examined by Temperature Dependent Hall Effect

Transition from bulk GaAs to quantum well and to QDs is observed in mobility vs. temperature trendsTransition from bulk GaAs to quantum well and to QDs is observed in mobility vs. temperature trends

Donor StatesDonor States2DEG2DEG

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 GrantElectronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

Deep Level DefectsDeep Level Defects

(Low Frequency Noise Spectroscopy)(Low Frequency Noise Spectroscopy)

LNALNA FFTFFT

Noise SpectrumNoise SpectrumAnalyzer SR785Analyzer SR785

GPIBGPIBLabViewLabView

SR560SR560

24 V24 VRRLL » R» Rsamplesample

i

B

i

inoiseV TRkf

Af

BS 4

21

12,

conductionconductionbandband

valencevalencebandband

NNSDSD

NNSASA

EE00

ccee

111 cei

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Evolution of Evolution of G-RG-R Signatures with Varying InGaAs Coverage Signatures with Varying InGaAs Coverage

Electronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

f f = 20 Hz= 20 HzDefect A, evolution with temperatureDefect A, evolution with temperature

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Deep Level EnergiesDeep Level Energies

Electronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

NNSDSD

EE00

ccee

EEFF

conductionconductionbandband

TAE tan

1

T

sE

tan

tan10

activationactivationenergyenergy

energy of theenergy of thelocal levellocal levelbelow Ebelow ECC

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Five Different Traps are Resolved and Quantitatively CharacterizedFive Different Traps are Resolved and Quantitatively Characterized

Electronic properties of self-assembled quantum dotsElectronic properties of self-assembled quantum dots

The activation energies of all traps, their densities and capture cross sections were obtainedThe activation energies of all traps, their densities and capture cross sections were obtained

MRS, 2008 Fall MeetingMRS, 2008 Fall MeetingSupported by DMR-0520550 GrantSupported by DMR-0520550 Grant

Summary, Outcome and AcknowledgementsSummary, Outcome and Acknowledgements

summarysummary

Lateral transport and noise characteristics of QW and QD heterostructures were studied and compared to

bulk GaAs material

Analysis of g-r noise temperature dependence in heterostructures allowed five different traps with activation

energies of 0.8 eV, 0.54 eV, 0.35 eV, 0.18 eV and 0.12 eV located in GaAs to be resolved

Trap with EA 0.12 eV located in GaAs spacer layer is caused by high deposition of InGaAs

The noise spectroscopy is a very sensitive technique applicable for characterization of nanostructures

This research resulted in the fabrication of infrared-photodetector (9 ML) that can be operated at room

temperature (B.S. Passmore, J. Wu, M.O. Manasreh, V.P. Kunets, P.M. Lytvyn, and G.J. Salamo, IEEE Electron Device Letters 29 224 (2008)B.S. Passmore, J. Wu, M.O. Manasreh, V.P. Kunets, P.M. Lytvyn, and G.J. Salamo, IEEE Electron Device Letters 29 224 (2008)))

Authors are grateful for the financial support of the National Science Foundation under Grant No. DMR-0520550