(/* Single phase InxGa1−xN 0.25 ≤ x ≤ 0.63 alloys synthesized by metal organic chemical vapor depositionPantha, B.N. et al., 2008. Single phase InxGa1−xN 0.25 ≤ x ≤ 0.63 alloys synthesized by metal organic chemical vapor deposition. Applie)
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'''Abstract:''' Author(s) present the results of single phase InxGa1−xN alloys for the In composition ranging from 25% to 63% synthesized by metal organic chemical vapor deposition. Single peak of x-ray diffraction θ-2θ scans of the (002) plane in InGaN alloys confirms that there is no phase separation. It was found both electron mobility and concentration increase with an increase of In content. Atomic force microscopy measurements revealed that the grown films have a surface roughness that varies between 1.5 and 4.0 nm and are free from In droplets. The results suggest that it is possible to synthesize single phase InGaN alloys inside the theoretically predicted miscibility gap.
'''Abstract:''' Author(s) present the results of single phase InxGa1−xN alloys for the In composition ranging from 25% to 63% synthesized by metal organic chemical vapor deposition. Single peak of x-ray diffraction θ-2θ scans of the (002) plane in InGaN alloys confirms that there is no phase separation. It was found both electron mobility and concentration increase with an increase of In content. Atomic force microscopy measurements revealed that the grown films have a surface roughness that varies between 1.5 and 4.0 nm and are free from In droplets. The results suggest that it is possible to synthesize single phase InGaN alloys inside the theoretically predicted miscibility gap.
====[http://apl.aip.org/resource/1/applab/v75/i18/p2776_s1 Determination of the critical layer thickness in the InGaN/GaN heterostructures<ref name="Parker, C.A">Parker, C.A. et al., 1999. Determination of the critical layer thickness in the InGaN/GaN heterostructures. Applied Physics Letters, 75, p.2776</ref>]====
'''Abstract:''' Author(s) present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, Author(s) identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements.


== References ==
== References ==

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This is in a series of literature reviews on InGaN solar cells, which supported the comprehensive review by D.V.P. McLaughlin & J.M. Pearce, "Progress in Indium Gallium Nitride Materials for Solar Photovoltaic Energy Conversion"Metallurgical and Materials Transactions A 44(4) pp. 1947-1954 (2013). open access
Others: InGaN solar cells| InGaN PV| InGaN materials| InGan LEDs| Nanocolumns and nanowires| Optical modeling of thin film microstructure| Misc.

This page describes selected literature available on InGaN Material Characterization.

Effects of Substrate Temperature on Indium Gallium Nitride Nanocolumn Crystal Growth[1]

Abstract: Indium gallium nitride films with nanocolumnar microstructure were deposited with varying indium content and substrate temperatures using plasma-enhanced evaporation on amorphous SiO2 substrates. Field emission scanning electron microscopy and X-ray diffraction results are presented, showing that more crystalline nanocolumnar microstructures can be engineered at lower indium compositions. Nanocolumn diameter and packing factor (void fraction) was found to be highly dependent on substrate temperature, with thinner and more closely packed nanocolumns observed at lower substrate temperatures.

Optical characterization of InxGa1-xN alloys[2]

Abstract: InGaN layers were grown by molecular beam epitaxy (MBE) either directly on (0 0 0 1) sapphire substrates or on GaN-template layers deposited by metal-organic vapor-phase epitaxy (MOVPE). Author(s) combined spectroscopic ellipsometry (SE), Raman spectroscopy (RS), photoluminescence (PL) and atomic force microscopy (AFM) measurements to investigate optical properties, microstructure, vibrational and mechanical properties of the InGaN/GaN/sapphire layers.

The analysis of SE data was done using a parametric dielectric function model, established by in situ and ex situ measurements. A dielectric function database, optical band gap, the microstructure and the alloy composition of the layers were derived. The variation of the InGaN band gap with the In content (x) in the 0 < x ≤ 0.14 range was found to follow the linear law Eg = 3.44–4.5x.

The purity and the stability of the GaN and InGaN crystalline phase were investigated by RS.

Optical band gap in Ga1-xInxN (0<x<0.2) on GaN by photoreflection spectroscopy[3]

Abstract: The optical band gap in 40 nm Ga1−xInxN/GaN single heterostructures is investigated in the composition range 0<x<0.2 by photoreflection spectroscopy (PR) at room temperature and compared with photoluminescence (PL) data. Clear PR oscillations at the GaInN band gap are observed as originating in the large piezoelectric field. Effective band gap bowing parameters b are derived for pseudomorphically stressed GaInN on GaN: b = 2.6 eV (PR) and b = 3.2 eV (PL in localized states). Using experimental deformation potentials of GaN, b = 3.8 eV is extrapolated for the optical band gap in relaxed GaInN material. Previously reported smaller values are discussed.

Small band gap bowing in In1-xGaxN alloys[4]

Abstract: High-quality wurtzite-structured In-rich In1−xGaxN films (0 < x < 0.5) have been grown on sapphire substrates by molecular beam epitaxy. Their optical properties were characterized by optical absorption and photoluminescence spectroscopy. The investigation reveals that the narrow fundamental band gap for InN is near 0.8 eV and that the band gap increases with increasing Ga content. Combined with previously reported results on the Ga-rich side, the band gap versus composition plot for In1−xGaxN alloys is well fit with a bowing parameter of ~1.4 eV. The direct band gap of the In1−xGaxN system covers a very broad spectral region ranging from near-infrared to near-ultraviolet.

Spectroscopic ellipsometry characterization of (InGa)N on GaN[5]

Abstract: Pseudodielectric function spectra of hexagonal (InGa)N epitaxial layers on GaN were obtained by spectroscopic ellipsometry and compared with photoreflection spectra. Composition and thickness of the InxGa1−xN layers grown by metalorganic chemical vapor deposition, were varied between 0.04 < x < 0.10 and 15–60 nm, respectively. The pseudodielectric function exhibits a clear maximum at the fundamental gap energy of the (InGa)N, which allows a determination of the In content via the composition dependence of that gap energy. The pseudodielectric function spectrum of a complete GaN/(InGa)N/(AlGa)N/GaN light-emitting diode structure shows maxima arising from fundamental gap interband transitions of all constituent layers including the (InGa)N active region.

Structural and optical properties of an InxGa1-xN/GaN nanostructure[6]

Abstract: The structural and optical properties of an InxGa1−xN/GaN multi-quantum well (MQW) were investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE) and photoluminescence (PL). The MQW structure was grown on c-plane (0 0 0 1)-faced sapphire substrates in a low pressure metalorganic chemical vapor deposition (MOCVD) reactor. The room temperature photoluminescence spectrum exhibited a blue emission at 2.84 eV and a much weaker and broader yellow emission band with a maximum at about 2.30 eV. In addition, the optical gaps and the In concentration of the structure were estimated by direct interpretation of the pseudo-dielectric function spectrum. It was found that the crystal quality of the InGaN epilayer is strongly related with the Si doped GaN layer grown at a high temperature of 1090 °C. The experimental results show that the growth MQW on the high-temperature (HT) GaN buffer layer on the GaN nucleation layer (NL) can be designated as a method that provides a high performance InGaN blue light-emitting diode (LED) structure.

Photoluminescence measurements on cubic InGaN layers deposited on a SiC substrate[7]

Abstract: In this work Author(s) report optical experiments on pseudomorphic cubic InxGa1−xN epilayers grown on cubic GaN/3C-SiC templates. We make a detailed study of photoluminescence (PL) and photoluminescence excitation spectroscopy on these samples, with spectra taken at various temperatures (between 2 K and 300 K) and using variable wavelength sources to excite the PL spectra. The combined use of these techniques suggests the existence of indium-rich clusters, constituting a negligibly small fraction of the volume of the total layer. Our results reinforce the notion that the large Stokes-like shift (a difference of approximately 300 meV between emission and absorption) observed in these samples is due to the fact that light absorption occurs in the bulk alloy of average composition while recombination occurs within the indium-rich clusters.

Dielectric function and Van Hove singularities for In-rich InxGa1-xN alloys: Comparison of N- and metal-face materials[8]

Abstract: Spectroscopic ellipsometry is applied in order to determine the complex dielectric function (DF) for In-rich InxGa1−xN alloys with N-face polarity from near-infrared into the vacuum ultraviolet spectral region. The results are compared to corresponding data for metal-face films. The optical properties of both types of hexagonal films agree in the essential features which emphasizes that the extracted DFs do not depend on the polarity but represent therefore bulk characteristics. Besides the band gap, five critical points of the band structure are clearly resolved within the composition range of 1>x>0.67. Their transition energies are determined by a fit of the third derivative of the DF. With increasing Ga content, all transitions undergo a continuous shift to higher energies characterized by small bowing parameters. Model calculations of the imaginary part of the DF close to the band gap that take the influence of band filling and conduction-band nonparabolicity into account are presented. A comparison to the experimental data yields the position of the Fermi energy. With the calculated values for the carrier-induced band-gap renormalization and the Burstein-Moss shift, the zero-density values for the fundamental band gaps are obtained. Their dependence on the alloy composition is described by a bowing parameter of b=1.72 eV.

Indium incorporation into InGaN and InAlN layers grown by metalorganic vapor phase epitaxy[9]

Abstract: Experimental data on indium incorporation in InGaN and InAlN layers grown by metalorganic chemical vapor epitaxy (MOVPE) on bulk GaN substrates are presented and discussed. For the step-flow growth mode, realized for InGaN layers grown at relatively high temperatures (around 800 °C), incorporation of indium increases with growth rate, and similarly, with a decrease in GaN substrate misorientation. Both dependences are explained by a higher velocity of flowing steps incorporating the indium atoms. For InAlN layers, three-dimensional nucleation takes place, and thus no significant changes of indium incorporation versus either growth rate or GaN substrate misorientation were observed.

Band gaps and lattice parameters of 0.9 µm thick InxGa1-xN films for 0<x<0.140[10]

Abstract: The c0 lattice parameter, band gap, and photoluminescence spectra of n-type 0.9 μm thick InxGa1−xN films with x=0, 0.045, 0.085, and 0.140 were examined. The c0 lattice parameter followed Vegard’s law using c0=0.5185 nm for GaN and c0=0.569 nm for InN. Band gap measurements by photocurrent spectroscopy fit well with data published by one other research group, with the combined set being described by the equation Eg=3.41−7.31x+14.99x2 for 0⩽x⩽0.15. Photoluminescence measurements with a pulsed nitrogen laser showed a peak well below the measured band gap, as well as significant luminescence above the measured band gap. The above-gap luminescence appears to be due to band filling by the high intensity laser pulses.

Determination of the critical layer thickness in the InGaN/GaN heterostructures[11]

Abstract: Author(s) present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, Author(s) identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements.

The critical thickness of InGaN on (0 0 0 1)GaN[12]

Abstract: The critical thickness for the relaxation of InGaN layers grown on (0 0 0 1) GaN on sapphire for an indium content between 10% and 20% has been determined experimentally. The layers were grown by metal-organic vapour phase epitaxy (MOVPE). The indium content was varied by changing growth temperature between 700 and 750 °C. In-situ ellipsometry could identify a growth mode transition during layer growth, from relatively smooth InGaN layer to a rougher layer with higher indium content. X-ray diffraction found a completely strained layer with lower indium content and a completely relaxed layer with higher indium content. These findings were consistent with absorption and photoluminescence measurements.

Strain relaxation and quantum confinement in InGaN/GaN nanoposts[13]

Abstract: Nanoposts of 10–40 nm top diameter on an InGaN/GaN quantum well structure were fabricated using electron-beam lithography and inductively coupled plasma reactive ion etching. Significant blue shifts up to 130 meV in the photoluminescence (PL) spectrum were observed. The blue-shift range increases with decreasing post diameter. For nanoposts with significant strain relaxation, the PL spectral peak position becomes less sensitive to carrier screening. On the basis of the temperature-dependent PL and time-resolved PL measurements and a numerical calculation of the effect of quantum confinement, Author(s) conclude that the optical behaviours of the nanoposts are mainly controlled by the combined effect of 3D quantum confinement and strain relaxation.


Schottky behavior at InN–GaN interface[14]

Abstract: In this work, GaN Schottky diodes were fabricated by depositing InN on GaN surfaces. The junction between these two materials exhibits strong rectifying behavior. The barrier heights were determined to be 1.25 eV, 1.06 eV, and 1.41 eV by current-voltage, current-voltage-temperature, and capacitance-voltage methods, respectively. These values exceed those of any other metal/GaN Schottky barriers. Therefore, the conduction-band offset between InN and GaN should not be smaller than the barrier heights obtained here.

Efficient rainbow color luminescence from InxGa1−xN single quantum wells fabricated on {11math2} microfacets[15]

Abstract: Rainbow color luminescence from InxGa1−xN single quantum wells (SQWs) is achieved and almost covers the entire visible range when the layers are fabricated on {11math2} facets with a few micron-width using a regrowth technique on striped GaN templates. These facets are tilted 56° with respect to the (0001) facets and border the (0001) and {11math0} facets. The emission wavelength on the {11math2} facets is redshifted from the {11math0} side to (0001) side due to the variations of the In composition, which leads to the color contrast with the rainbow geometry. The temperature dependence of the photoluminescence intensity shows that the internal quantum efficiency at room temperature is 33% due to the very small internal electric fields and a small threading dislocation density compared to that in conventional (0001) InxGa1−xN SQWs. Since the emission efficiency does not show a noticeable emission wavelength dependence, this type of structure has potential as light-emitting devices with multiwavelengths that perform numerous color controllability such as pastel and white colors.

Single phase InxGa1−xN 0.25 ≤ x ≤ 0.63 alloys synthesized by metal organic chemical vapor deposition[16]

Abstract: Author(s) present the results of single phase InxGa1−xN alloys for the In composition ranging from 25% to 63% synthesized by metal organic chemical vapor deposition. Single peak of x-ray diffraction θ-2θ scans of the (002) plane in InGaN alloys confirms that there is no phase separation. It was found both electron mobility and concentration increase with an increase of In content. Atomic force microscopy measurements revealed that the grown films have a surface roughness that varies between 1.5 and 4.0 nm and are free from In droplets. The results suggest that it is possible to synthesize single phase InGaN alloys inside the theoretically predicted miscibility gap.

References

  1. ↑ Keating, S. et al., 2010. Effects of Substrate Temperature on Indium Gallium Nitride Nanocolumn Crystal Growth. Crystal Growth & Design, 11(2), pp.565-568
  2. ↑ Gartner, M. et al., 2006. Optical characterization of InxGa1-xN alloys. Applied Surface Science, 253(1), pp.254-257
  3. ↑ Wetzel, C. et al., 1998. Optical band gap in Ga[sub 1-x]In[sub x]N?(0<x<0.2) on GaN by photoreflection spectroscopy. Applied Physics Letters, 73, p.1994
  4. ↑ Wu, J. et al., 2002. Small band gap bowing in In[sub 1-x]Ga[sub x]N alloys. Applied Physics Letters, 80, p.4741
  5. ↑ Wagner, J. et al., 1998. Spectroscopic ellipsometry characterization of (InGa)N on GaN. Applied Physics Letters, 73, p.1715
  6. ↑ Korçak, S. et al., 2007. Structural and optical properties of an InxGa1-xN/GaN nanostructure. Surface Science, 601(18), pp.3892-3897
  7. ↑ Pacheco-Salazar, D.G. et al., 2006. Photoluminescence measurements on cubic InGaN layers deposited on a SiC substrate. Semiconductor Science and Technology, 21, pp.846-851
  8. ↑ Schley, P. et al., 2007. Dielectric function and Van Hove singularities for In-rich In_{x}Ga_{1-x}N alloys: Comparison of N- and metal-face materials. Physical Review B, 75(20), p.205204
  9. ↑ Leszczynski, M. et al., 2011. Indium incorporation into InGaN and InAlN layers grown by metalorganic vapor phase epitaxy. Journal of Crystal Growth, 318(1), pp.496-499
  10. ↑ Beach, J.D. et al., 2002. Band gaps and lattice parameters of 0.9 µm thick In[sub x]Ga[sub 1-x]N films for 0=x=0.140. Journal of Applied Physics, 91, p.5190
  11. ↑ Parker, C.A. et al., 1999. Determination of the critical layer thickness in the InGaN/GaN heterostructures. Applied Physics Letters, 75, p.2776
  12. ↑ Leyer, M. et al., 2008. The critical thickness of InGaN on (0 0 0 1)GaN. Journal of Crystal Growth, 310(23), pp.4913-4915
  13. ↑ Chen, H.-S. et al., 2006. Strain relaxation and quantum confinement in InGaN/GaN nanoposts. Nanotechnology, 17(5), pp.1454-1458
  14. ↑ Chen, N.C. et al., 2005. Schottky behavior at InN–GaN interface. Applied Physics Letters, 87(21), p.212111
  15. ↑ Nishizuka, K. et al., 2005. Efficient rainbow color luminescence from InxGa1−xN single quantum wells fabricated on {112} microfacets. Applied Physics Letters, 87(23), p.231901
  16. ↑ Pantha, B.N. et al., 2008. Single phase InxGa1−xN 0.25 ≤ x ≤ 0.63 alloys synthesized by metal organic chemical vapor deposition. Applied Physics Letters, 93(18), p.182107
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