Structural and Electronic Properties of Inn Surfaces and Interfaces

Structural and Electronic Properties of InN Surfaces and Interfaces

L. Fishwick Surface, Interface and Thin Film Group

Post-grad Seminar 12 February 2009

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 1 / 14 Introduction

Introduction The Highly Mismatched Compounds group: Techniques Academics: XPS CAICISS

Future Research

Prof. Chris McConville Dr. Tim Veal Supervisor EPSRC career acceleration fellow

PhD students:

Mr. Philip D. C. King Ms. Louise R. Bailey Mr. Liam Fishwick Mr. Wojciech Linhart rd nd st 3 year 2 year 1 year

Mismatched I also work closely with Dr. Marc Walker and Mr. Matthew Brown Highly performing ion scattering experiments. ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 2 / 14 Highly Mismatched compounds

Introduction A highly mismatched compound is compound with a distinct cation/anion Techniques size and electronegativity mismatch. The particular branch of HMC that is XPS CAICISS the focus of research in the group at warwick are SCAMS. Future Research SCAMS: Signiﬁcantly Cation-Anion Mismatched Semiconductors. The cation is much larger and less electronegative than the anion, e.g. InN, ZnO, CdO.

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 3 / 14 Importance of indium nitride

Introduction Indium nitride is a narrow band gap semiconductor with a band gap of ∼ Techniques 0.64 eV. XPS CAICISS

Future Research Exhibits an electron accumulation layer at the surface

InGaN ternary alloy is known now to have a band gap spanning from the near IR for InN to the UV for GaN.

Branch point energy is well above the conduction band minimum (∼ 1.5 eV).

Mahboob et al., Phys. Rev. Lett., 92, 036804, 2004 King et al.. Phys. Rev. B., 77, 045316, 2008

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 4 / 14 Importance of scandium nitride

Introduction Scandium nitride was initially thought to be a semi-metal, but after more Techniques careful calculation was found to be a semiconductor with a direct transition XPS CAICISS at the Γ point of ∼ 2.1 eV. Future Research Interest in use as buffer layers in III-N compounds, e.g. GaN/InN.

Demonstrates downwards band bending at the surface.

May exhibit interesting electronic properties.

Lambrecht, Phys. Rev. B, 62, 20, (2000)

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 5 / 14 Techniques

Introduction Important techniques for this project: Techniques XPS X-ray photoelectron spectroscopy CAICISS

Future Research Co-axial impact collision ion scattering spectroscopy

Low energy electron diffraction

Some complementary techniques that will also be utilised:

Scanning electron microscopy

Hall measurements

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 6 / 14 X-ray photoelectron spectroscopy

Introduction An incident x-ray photon causes the ejection of a core level electron, which Techniques is then accelerated towards an electron energy analyser. XPS X-ray Source Hemispherical Analyser CAICISS

Future Research γ e-

Sample

The binding energy of the detected electron is:

EB = Eγ − Ek − φanalyser

Each element produces a characteristic set of peaks in the spectra at specﬁc binding energies directly identifying that species (usually!)

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 7 / 14 X-ray photoelectron spectroscopy

Sample

The binding energy of the detected electron is:

EB = Eγ − Ek − φanalyser

Each element produces a characteristic set of peaks in the spectra at specﬁc binding energies directly identifying that species (usually!)

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 7 / 14 X-ray photoelectron spectroscopy

Sample

The binding energy of the detected electron is:

EB = Eγ − Ek − φanalyser

Each element produces a characteristic set of peaks in the spectra at specﬁc binding energies directly identifying that species (usually!)

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 7 / 14 XPS Data

Introduction Sample XPS spectra for a Sc2p region. Fitted for different surface Techniques preparations and take off angles. XPS

CAICISS

JH35 As l oaded 30 T OA

JH35 As l oaded 90 T OA Data Future Research Data

Sum of Peaks Sum of Peaks

Sc2p Components Sc2p Components

N1s Component N1s Component

Extra component

for shoulder

o o

JH35 2x2hr Anneal . 30 T OA Data JH35 2x2hr Anneal . 90 T OA Data

Sum of Peaks Sum of Peaks Intensity (arb. units) Sc2p Components Sc2p Components

N1s Components N1s Component

Mismatched Highly 408 406 404 402 400 398 396 394 408 406 404 402 400 398 396 394

ompounds@warwick Binding Energy (eV) C Structure and Electronic properties of InN Surfaces and Interfaces – 8 / 14 Co-axial impact collision ion scattering spectroscopy

Introduction Ion scattering can be illustrated as a simple collision between hard Techniques spheres. Incident ions scatter off atoms in the near surface region. XPS CAICISS

Future Research

CAICISS is a novel low energy ion scattering technique, where ions with ◦ incident energy of 1 – 5 keV are incident on the surface and 180 backscattering geometry is utilised for detection. Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 9 / 14 Co-axial impact collision ion scattering spectroscopy

Introduction Techniques

XPS CAICISS

Future Research

At Warwick we have the only CAICISS chamber in the country. Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 10 / 14 Co-axial impact collision ion scattering spectroscopy

Introduction The data is compared with simulations such as those created by the FAN Techniques package XPS CAICISS

Future Research

Mismatched Figure 1: FAN trajectory cones from the near surface region of Au/Cu Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 11 / 14 In-adlayers in InN

Introduction Previous CAICISS work performed by the group has led to a model for Techniques wurtzite InN to be formed with In adlayers at the surface of In terminated XPS CAICISS InN. Future Research

Figure 3: InN adlayer schematic, top view and side view shown

Figure 2: Idealised bulk terminated

Mismatched InN and In adlayer model shown Highly ompounds@warwick with experimental result below C Structure and Electronic properties of InN Surfaces and Interfaces – 12 / 14 Future Research

Introduction Techniques Further investigation into the structural and electronic properties of XPS InN and ScN. CAICISS Future Research Study other HMC’s.

Develop cleaning techniques for InN.

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 13 / 14 Cleaning InN

Introduction Some issues faced when cleaning InN are: Techniques XPS ◦ Low non-congruent temperature ∼ 450 C. CAICISS

Future Research Preferentially sputter N from surface.

Weak material so cannot withstand Ar+ ion bombardment.

Need to develop cleaning methods that maintain both the electronic and structural properties of the surface, without introducing many defects. Currently atomic hydrogen cleaning is performed, however, hydrogen acts as a donor defect altering the electronic properties.

Mismatched Highly ompounds@warwick C Structure and Electronic properties of InN Surfaces and Interfaces – 14 / 14