Electron Spectroscopies of InN grown by HPCVD Department of Physics and Astronomy Georgia State University Atlanta, Georgia Rudra P. Bhatta Solid State Physics (Physics ) 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 pressure 15 bar Gas flow velocity 41 cm /s Ammonia:TMI ratio 240 Substrate HPCVD 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) Indium Metal Nitrogen Si 0.54 N 0.46 Hand book of Auger Electron Spectroscopy, 2 nd Edition, L.E.Davis et al., Physical Electronics Division, 1978

AES Lineshapes for InN and In

Peak fitting of InN Auger Spectra

Assumed linear background Integrated area under peaks carbon: 220 – 285 eV nitrogen: 358 – 392 eV indium: 392 – 418 eV oxygen: 500 – 522 eV O/In calibrated from native oxide of metallic indium (In 2 O 3 ) N/In calibrated from highest nitrogen content InN (assumed 1:1)

Atomic Fraction vs. Sample Treatment Argon Sputtered Region

Atomic Fraction vs. Sample Treatment Atomic Hydrogen Cleaning (AHC) 1000 L H 2 over 1800 K Tungsten filament with sample at 350 K L H 2 over 1800 K Tungsten filament with sample at 600 K. 1 L= 1x10 -6 torr s McConville and coworkers, Univ. of Warwick Piper et al., JVST A 23, 617 (2005).

Atomic Fraction vs. Position After Atomic Hydrogen Cleaning Flow Direction

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 60 o from normal e -  E < 500 meV (4000 cm -1 ) specular collection InN HREELS Surface Vibrational Spectroscopy High Resolution Electron Energy Loss Spectroscopy

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. Growth Direction N In 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, NH 2, or OH vibrational modes are observed.  InN surface is N-terminated and N-polar, i.e.

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.