Electron Spectroscopies of InN grown by HPCVD

Department of Physics and AstronomyGeorgia State University

Atlanta, Georgia

Rudra P. BhattaSolid State Physics (Physics - 8510)

Fall 2005

Motivation: InN and its application InN sample grown by HPCVD Auger Electron Spectroscopy

Data Analysis to Determine Composition

Composition vs. Treatment and Position Low energy electron diffraction High Resolution Electron Energy Loss Spectroscopy

Surface Structure and Bonding

Film Polarity Summary Future work

Outline

High-efficient energy conversion system solid state lighting (high-efficient light emitting diodes)   High speed opto-electronics for optical communication systems

 Solid state lasers operating in the blue and ultraviolet regions

 Terahertz device structures (emitters and detectors)

  Nonlinear optical switching elements. Spintronic device structures.

Application of InN & In rich group III-Nitides

Motivation for studying indium nitride

Research on indium nitride growth and characterizarion has increased tremendously in recent years.

Controversy in the measurement of fundamental properties

such as band gap, lattice constant, and effective mass.

Difficulty of InN growth due to its low dissociation temperature

and the high vapor pressure of nitrogen over InN.

Potential of high pressure chemical vapor deposition (HPCVD): - stabilizes InN to higher temperature, and - allows growth of InN, GaN, and AlN at similar conditions.

Flow Direction

Reactor pressure15 bar

Gas flow velocity41 cm /s

Ammonia:TMI ratio 240

SubstrateHPCVD GaN buffer

on sapphire (0001)

HPCVD grown Indium Nitride

HPCVD Growth: N. Dietz and coworkers, JVST B 23, 1790 (2005) or phys. stat. sol. latest issue

Auger Electron Spectroscopy (AES)

AES is a surface-sensitive spectroscopic technique used for elemental analysis of surfaces; it offers:

High sensitivity (nearly 1% monolayer) for all elements except H and He.

Quantitative compositional analysis of the surface region.

A means of monitoring surface cleanliness of samples.

Auger electrons are the secondary ionized electrons

Nitrogen and Indium AES peaks (dN/dE)

IndiumMetal

NitrogenSi0.54N0.46

Hand book of Auger Electron Spectroscopy, 2nd Edition, L.E.Davis et al., Physical Electronics Division, 1978

300 350 400 450 500Energy (eV)

N

InN

In

388

402

409

AES Lineshapes for InN and In

350 375 400 425 450 475

dN

/dE

Energy (eV)

InN as received

InN sputtered

Indiumnative oxide

MetallicIndium

N In

350 375 400 425 450 475

N(E

)

Energy (eV)

InN as received

InN sputtered

Indiumnative oxide

MetallicIndium

N In

Peak fitting of InN Auger Spectra

200 250 300 350 400 450 500 550

N(E)

Energy (eV)

indiumnitrogen

oxygen

carbon

Peak fitting of InN Auger Spectra

Assumed linear backgroundIntegrated area under peaks

carbon: 220 – 285 eVnitrogen: 358 – 392 eVindium: 392 – 418 eVoxygen: 500 – 522 eV

O/In calibrated from native oxide of metallic

indium (In2O3)

N/In calibrated from highest nitrogen content

InN (assumed 1:1)200 250 300 350 400 450 500 550

N(E)

Energy (eV)

indiumnitrogen

oxygen

carbon

Atomic Fraction vs. Sample Treatment

0

0.1

0.2

0.3

0.4

0.5

0.6

0 40 220 840

C N In O

Ato

mic

Fra

ctio

n

Argon Sputtering (A s/cm2)

ArgonSputtered

Region

Atomic Fraction vs. Sample Treatment

Atomic Hydrogen Cleaning (AHC)

1000 L H2 over 1800 K Tungsten

filament with sample at 350 K

+1000 L H2 over

1800 K Tungsten filament with

sample at 600 K.

1 L= 1x10-6 torr s

0

0.1

0.2

0.3

0.4

0.5

0.6

0 40 220 840 AHC

C N In O

Ato

mic

Fra

ctio

n

Argon Sputtering (A s/cm2) AHC

McConville and coworkers,

Univ. of WarwickPiper et al., JVST A

23, 617 (2005).

Atomic Fraction vs. Position

After Atomic Hydrogen Cleaning

Flow Direction

0

0.1

0.2

0.3

0.4

0.5

0.6

2 3 4 5 6 7 8 9 10

N In O

Ato

mic

Fra

ctio

n

Position from edge (mm)

Schematic of LEED optics operated as RFA

Sample sits at

the center of the grids. Grid 1&4 are grounded. Grids 2 &3 are at

potential slightly

less than that of

electron gun. Only elastically

scattered electrons

reach to the

fluorescent screen.

LEED: A technique used for the determination of surface structure

LEED image of InN

Spot positions yield information on the size, symmetry and rotational alignments of surface

unit cell with respect to substrate unit cell.

Distance between the spots gives information about the distances

between the atoms.

Sharpness of the

spots gives insight on how well ordered the surface atoms are arranged. E = 39.5 eV

e-

E = 12.5 eV 60o from normal

e-

E < 500 meV (4000 cm-1) specular collection

InN

HREELSSurface Vibrational Spectroscopy

High Resolution Electron Energy Loss Spectroscopy

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

No InH stretch (~1700 cm-1)

No NH2 bend (~1500 cm-1)

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

N-H bend870

N-D bend640

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

N-H bend870

N-D bend640

Fuchs-Kliewersurface phonon

550

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

N-H bend870

N-D bend640

Fuchs-Kliewersurface phonon

550

Surface-NH(ND)bounce

360 InN surface is N-terminated

HREELS of InN after AHC

0 500 1000 1500 2000 2500 3000 3500

HR

EE

LS

Nor

mal

ized

Int

ensi

ty

Energy Loss (cm-1)

x 25

60

cm-1

AtomicHydrogenCleaned

AtomicDeuterium

Cleaned

x 25

N-D stretch2410

N-H stretch3260

N-H bend870

N-D bend640

Fuchs-Kliewersurface phonon

550

Surface-NH(ND)bounce

360

* No plasmon due to electron

accumulation (~2000 cm-1)

* Small CH stretch (~2950 cm-1)

* No OH stretch (~3600 cm-1)

HREELS of InN after AHC

Surface Structure of InN after AHC

N-polar surface consists of N atoms bonded to three In atoms in the second layer and one dangling bond normal to the surface.

Atomic hydrogen saturates the dangling bonds to stabilize the surface.

Gro

wth

Dir

ecti

on

N

In

)1000InN(terminatedHydrogen

H

Summary

Indium nitride sample grown by high pressure chemical vapor deposition was investigated by AES, LEED, and HREELS.

The composition of the InN surface was determined by integrating areas under peaks in N(E) Auger Electron Spectra.

Sputtering produces nitrogen deficient surface.

Atomic hydrogen cleaning (AHC) produces a contaminant-free, well-ordered c-plane InN surface with a 1x1 LEED pattern.

HREELS of InN after atomic hydrogen (deuterium) cleaning shows

NH (ND) stretch, bend and bounce vibrational modes.

No InH, NH2, or OH vibrational modes are observed.

InN surface is N-terminated and N-polar, i.e. ).1000(InN

Future work

To study the desorption rate of hydrogen from the surface at different temperature by the process of HREELS and

temperature programmed desorption (TPD).

To study the reaction of ammonia and trimethyl indium (TMI) on the indium nitride surface in order to understand the surface reaction during the growth.

Thank you for your attention.