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Title: Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation

Abstract

The microstructure of In{sub x}Al{sub 1-x}N/GaN heterostructures (where x{approx}0.13-0.19), grown by molecular beam epitaxy, was investigated by transmission electron microscopy. Observations in the cross-section and plan-view geometries show evidence for lateral phase separation originating at the GaN surface that results in a vertical honeycomblike structure within the InAlN layers. The lateral dimensions of the honeycomb cells are {approx}5-10 nm. The vertical walls are In rich with a width of {approx}1-2 nm and align roughly perpendicular to <1120> and <1100> directions. The phase separation is attributed to random compositional fluctuations during the early stages of growth, possibly associated with misfit-strain relaxation.

Authors:
; ; ; ;  [1];  [2]
  1. Center for Solid State Science, Arizona State University, Tempe, Arizona 85287 and Department of Physics and Astronomy, Arizona State University, Tempe, Arizona 85287 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20971844
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 8; Other Information: DOI: 10.1063/1.2696206; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM COMPOUNDS; CROSS SECTIONS; CRYSTAL GROWTH; GALLIUM NITRIDES; HETEROJUNCTIONS; HONEYCOMB STRUCTURES; INDIUM NITRIDES; LAYERS; MICROSTRUCTURE; MOLECULAR BEAM EPITAXY; RANDOMNESS; SEMICONDUCTOR MATERIALS; STRESS RELAXATION; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Zhou Lin, Smith, David J., McCartney, Martha R., Katzer, D. S., Storm, D. F., and U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375. Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation. United States: N. p., 2007. Web. doi:10.1063/1.2696206.
Zhou Lin, Smith, David J., McCartney, Martha R., Katzer, D. S., Storm, D. F., & U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375. Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation. United States. doi:10.1063/1.2696206.
Zhou Lin, Smith, David J., McCartney, Martha R., Katzer, D. S., Storm, D. F., and U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375. Mon . "Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation". United States. doi:10.1063/1.2696206.
@article{osti_20971844,
title = {Observation of vertical honeycomb structure in InAlN/GaN heterostructures due to lateral phase separation},
author = {Zhou Lin and Smith, David J. and McCartney, Martha R. and Katzer, D. S. and Storm, D. F. and U.S. Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC 20375},
abstractNote = {The microstructure of In{sub x}Al{sub 1-x}N/GaN heterostructures (where x{approx}0.13-0.19), grown by molecular beam epitaxy, was investigated by transmission electron microscopy. Observations in the cross-section and plan-view geometries show evidence for lateral phase separation originating at the GaN surface that results in a vertical honeycomblike structure within the InAlN layers. The lateral dimensions of the honeycomb cells are {approx}5-10 nm. The vertical walls are In rich with a width of {approx}1-2 nm and align roughly perpendicular to <1120> and <1100> directions. The phase separation is attributed to random compositional fluctuations during the early stages of growth, possibly associated with misfit-strain relaxation.},
doi = {10.1063/1.2696206},
journal = {Applied Physics Letters},
number = 8,
volume = 90,
place = {United States},
year = {Mon Feb 19 00:00:00 EST 2007},
month = {Mon Feb 19 00:00:00 EST 2007}
}
  • The valence band offsets, {Delta}E{sub V}, of In{sub 0.17}Al{sub 0.83}N/GaN, In{sub 0.25}Al{sub 0.75}N/GaN, and In{sub 0.30}Al{sub 0.70}N/GaN heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy (XPS). The dependence of the energy position and the full width at half maximum of the Al 2p spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The {Delta}E{sub V} values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous resultsmore » due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated {Delta}E{sub V} values were 0.2{+-}0.2 eV for In{sub 0.17}Al{sub 0.83}N/GaN, 0.1{+-}0.2 eV for In{sub 0.25}Al{sub 0.75}N/GaN, and 0.0{+-}0.2 eV for In{sub 0.30}Al{sub 0.70}N/GaN. Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in {Delta}E{sub V} was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.« less
  • We present a methodology and the corresponding experimental results to identify the exact location of the traps that induce hot electron trapping in AlGaN/GaN heterostructures grown on Si substrates. The methodology is based on a combination of lateral and vertical electrical stress measurements employing three ohmic terminals on the test sample structure with different GaN buffer designs. By monitoring the evolution of the lateral current during lateral as well as vertical stress application, we investigate the trapping/detrapping behaviors of the hot electrons and identify that the traps correlated with current degradation are in fact located in the GaN buffer layers.more » The trap activation energies (0.38–0.39 eV and 0.57–0.59 eV) extracted from either lateral or vertical stress measurements are in good agreement with each other, also confirming the identification. By further comparing the trapping behaviors in two samples with different growth conditions of an unintentionally doped GaN layer, we conclude that the traps are most likely in the unintentionally doped GaN layer but of different origins. It is suggested that the 0.38–0.39 eV trap is related to residual carbon incorporation while the 0.57–0.59 eV trap is correlated with native defects or complexes.« less
  • The influence of alloy clustering on fluctuations in the ground state energy of the two-dimensional electron gas (2DEG) in AlGaN/GaN and InAlN/GaN heterostructures is studied. We show that because of these fluctuations, alloy clustering degrades the mobility even when the 2DEG wavefunction does not penetrate the alloy barrier unlike alloy disorder scattering. A comparison between the results obtained for AlGaN/GaN and InAlN/GaN heterostructures shows that alloy clustering limits the 2DEG mobility to a greater degree in InAlN/GaN heterostructures. Our study also reveals that the inclusion of an AlN interlayer increases the limiting mobility from alloy clustering. Moreover, Atom probe tomographymore » is used to demonstrate the random nature of the fluctuations in the alloy composition.« less
  • This paper reports on the electrical characterization of Ni/Au Schottky diodes fabricated on InAlN high-electron-mobility transistor (HEMT) structures grown on low dislocation density free-standing GaN substrates. InAlN HEMT structures were grown on sapphire and GaN substrates by metal-organic vapor phase epitaxy, and the effects of threading dislocation density on the leakage characteristics of Ni/Au Schottky diodes were investigated. Threading dislocation densities were determined to be 1.8 × 10{sup 4 }cm{sup −2} and 1.2 × 10{sup 9 }cm{sup −2} by the cathodoluminescence measurement for the HEMT structures grown on GaN and sapphire substrates, respectively. Leakage characteristics of Ni/Au Schottky diodes were compared between the two samples, andmore » a reduction of the leakage current of about three to four orders of magnitude was observed in the forward bias region. For the high reverse bias region, however, no significant improvement was confirmed. We believe that the leakage current in the low bias region is governed by a dislocation-related Frenkel–Poole emission, and the leakage current in the high reverse bias region originates from field emission due to the large internal electric field in the InAlN barrier layer. Our results demonstrated that the reduction of dislocation density is effective in reducing leakage current in the low bias region. At the same time, it was also revealed that another approach will be needed, for instance, band modulation by impurity doping and insertion of insulating layers beneath the gate electrodes for a substantial reduction of the gate leakage current.« less