Band Gap Of InN Research Articles

AlInN/AlN HEMT’in Detaylı Optik Özellikleri

In this study, the optical properties of AlInN/AlN high electron mobility transistor (HEMT) structure, grown on c-oriented sapphire with Metal-Organic Chemical Vapor Deposition (MOCVD) technique, being investigated. Optical characterization is made Kubelka- Munk method. Transmittance, absorbance, and reflectance are investigated in detail. Also, the Kubelka-Munk theory is employed to determine the forbidden energy band gap of InN by using special functions. The energy band gap obtained by this method was compared.

Observation and mitigation of RF-plasma-induced damage to III-nitrides grown by molecular beam epitaxy

In this work, radio-frequency (RF) plasma-induced damage to III-nitride surfaces and bulk defects is observed and mitigated. It is shown that for InN films, the surface is more sensitive to plasma-induced damage than GaN films, as observed via atomic force microscopy and reflection high energy electron diffraction. In order to isolate any possible plasma-induced damage, a growth window for InN is established, and temperature ranges are determined for other damaging effects which include roughening due to low adatom mobility, InN decomposition, and indium desorption. In situ plasma monitoring and optimization are accomplished with a combination of optical emission spectroscopy as well as a remote Langmuir probe. It is shown that by increasing the plasma nitrogen flow, the positive ion content increases; however, the ion acceleration potential reduces. Additionally, a reduced RF plasma power results in a reduction of atomic nitrogen species. These plasma species and energetic variations result in variations in the bulk unintentional background electron concentrations observed by room temperature Hall effect measurements of ∼1 μm thick InN films. By increasing the nitrogen flow from 2.5 to 7.5 sccm for a constant RF power of 350 W, the background electron concentration decreases by 74% from 1.36 × 1019 cm−3 to 3.54 × 1018 cm−3, while maintaining a smooth surface morphology. Additionally, photoluminescence spectra indicate optical emission energies shift from ∼0.81 to 0.71 eV (closer to the fundamental bandgap of InN) by limiting the damaging plasma species. Finally, conditions are presented to further minimize plasma-induced damage in III-nitride devices.

Bandgap and Electronic Structure Determination of Oxygen-Containing Ammonothermal InN: Experiment and Theory

The electronic structure and band gap of InN synthesized by the ammonothermal method are studied by synchrotron-based soft X-ray absorption spectroscopy (XAS), emission spectroscopy (XES), X-ray ex...

Photoluminescence of (ZnO)<sub>0.82</sub>(InN)<sub>0.18</sub> Films: Incident Light Angle Dependence

We have fabricated a new semiconducting material, (ZnO)x(InN)1-x (called ZION hereafter), which is a pseudo-binary alloy of wurtzite ZnO (band gap: 3.4 eV) and wurtzite InN (band gap: 0.7 eV). We have succeeded in fabricating epitaxial (ZnO)0.82(InN)0.18 films on ZnO templates by RF magnetron sputtering. XRD measurements show that the full width at half maximum of the rocking curves from (101) plane and (002) plane are significantly small of 0.11 ̊ and 0.16 ̊, respectively, indicating good in-plane and out-of-plane crystal alignment. High crystal quality of the films was also proved by deducing the defect density from XRD analysis showing that the edge type dislocation density is low of 8.2×108 cm-2. Furthermore, we observed room temperature photoluminescence from ZION films as a parameter of incident angle of He-Cd laser light. The results indicate that an emission peak of 2.79 eV is originated from ZION.

The role of Cr on the electronic and optical properties of InCrN: A first principles study

In this work, structural, electronic and optical properties of InCrN are investigated by First Principles Calculations within the Density Functional Theory (DFT). The role of Cr concentration, intrinsic defects and their effects on the magnetic moment, optical behavior and electronic density of states are reported. We have employed the generalized gradient approximation (GGA) functional in the form of Perdew-Burke-Ernzherof (PBE) for the exchange–correlation energy, followed by the use of hybrid functional HSE06 to determine the optical properties. Due to the strong N-Cr interaction, the presence of Cr induces significant changes on the InCrN structure, electronic and optical properties. Interestingly, a shift in InN band gap is observed with variation of Cr concentration, leading to a half-metallic-like character. Additionally, the Cr gives rise to differences in the spin states of N atoms, affecting the overall InCrN magnetic moment.

Network of vertically c-oriented prismatic InN nanowalls grown on c-GaN/sapphire template by chemical vapor deposition technique

Networks of vertically c-oriented prism shaped InN nanowalls, are grown on c-GaN/sapphire templates using a CVD technique, where pure indium and ammonia are used as metal and nitrogen precursors. A systematic study of the growth, structural and electronic properties of these samples shows a preferential growth of the islands along [112¯0] and [0 0 0 1] directions leading to the formation of such a network structure, where the vertically [0 0 0 1] oriented tapered walls are laterally align along one of the three [112¯0] directions. Inclined facets of these walls are identified as semipolar (112¯2)-planes of wurtzite InN. Onset of absorption for these samples is observed to be higher than the band gap of InN suggesting a high background carrier concentration in this material. Study of the valence band edge through XPS indicates the formation of positive depletion regions below the surface of the side facets [(112¯2)-planes] of the walls. This is in contrast with the observation for c-plane InN epilayers, where electron accumulation is often reported below the top surface.

Probing InGaN immiscibility at AlGaN/InGaN heterointerface on silicon (111) through two-step capacitance-voltage and conductance-voltage profiles

Immiscibility of InGaN hinders epitaxial growth of high-quality AlGaN/InGaN heterojunction, which could have superior performances than AlGaN/GaN in view of high-speed devices. AlGaN/InGaN/GaN double heterostructures have been grown on silicon (111) substrate using plasma assisted molecular beam epitaxy. All growth conditions for each sample have been kept identical except the InGaN channel thickness. Alloy inhomogeneity has been found to occur in the InGaN channel by high resolution (HR) X-ray diffractometer (XRD) and cross-sectional HR- transmission electron microscopy (TEM). This non-uniformity of alloy causes reduced indium incorporation with a decrease of channel thickness along with a thin InN binary alloy. Capacitance-voltage (C-V) profile has revealed non-uniformity of alloy and spatial position of InN in the channel due to variation of band-offset and carrier confinement. Unconventional two-step profile has been obtained for the heterostructure. Higher capacitance at near zero bias corroborates the formation of InN at AlGaN/InGaN due to larger band offset. Conductance-voltage (G-V) profiles further validate mapping of InGaN phase separation in terms of carrier trapping. Lower effect of trapping has been identified due to low bandgap InN formation at the interface. Effect of epilayer relaxation on the phase separation has also been discussed in terms of threading dislocation and V-defects.

Tuning the effective band gap and finding the optimal growth condition of InN thin films on GaN/sapphire substrates by plasma assisted molecular beam epitaxy technique

InN thin films are grown on GaN/sapphire substrates with varying the nitrogen plasma power in plasma assisted molecular beam epitaxy (PA-MBE) system. In order to evaluate the effect of nitrogen plasma power on the different properties of the InN films, several characterization viz. x-ray diffraction, atomic force microscopy, photoluminescence measurement, infra-red spectroscopy and Hall measurement were performed. Two interesting phenomena observed from the measurements are described in this paper. Firstly, it is found from both the photoluminescence and infrared spectroscopy that only by varying the nitrogen plasma power (thus the III/V ratio), one can fine tune the optical absorption edge, i.e., the effective band gap of InN from ∼0.72 eV to ∼ 0.77 eV. Secondly, it is inferred that the film grown with stoichiometric condition (III/V ∼ 1) exhibits the best structural and electrical properties.

Optical properties of InN studied by spectroscopic ellipsometry**Project supported by the State Key Development Program for Basic Research of China (No. 2012CB619301), the National High Technology Research and Development Program of China (No. 2014AA032608), the National Natural Science Foundation of China (Nos. 11204254, 11404271), and the Fundamental Research Funds for the Central Universities (Nos. 2012121014, 20720150027).

With recently developed InN epitaxy via a controlling In bilayer, spectroscopic ellipsometry (SE) measurements had been carried out on the grown InN and the measured ellipsometric spectra were fitted with the Delta Psi2 software by using a suitable model and the dispersion rule. The thickness was measured by a scanning electron microscope (SEM). Insight into the film quality of InN and the lattice constant were gained by X-ray diffraction (XRD). By fitting the SE, the thickness of the InN film is consistent with that obtained by SEM cross-sectional thickness measurement. The optical bandgap of InN was put forward to be 1.05 eV, which conforms to the experimental results measured by the absorption spectrum and cathodoluminescence (CL). The refractive index and the extinction coefficient of interest were represented for InN, which is useful to design optoelectronic devices.

Surface origin and control of resonance Raman scattering and surface band gap in indium nitride

Resonance Raman scattering measurements were performed on indium nitride thin films under conditions where the surface electron concentration was controlled by an electrolyte gate. As the surface condition is tuned from electron depletion to accumulation, the spectral feature at the expected position of the (E1, A1) longitudinal optical (LO) near 590 cm−1 shifts to lower frequency. The shift is reversibly controlled with the applied gate potential, which clearly demonstrates the surface origin of this feature. The result is interpreted within the framework of a Martin double resonance, where the surface functions as a planar defect, allowing the scattering of long wavevector phonons. The allowed wavevector range, and hence the frequency, is modulated by the electron accumulation due to band gap narrowing. A surface band gap reduction of over 500 meV is estimated for the conditions of maximum electron accumulation. Under conditions of electron depletion, the full InN bandgap (Eg = 0.65 eV) is expected at the surface. The drastic change in the surface band gap is expected to influence the transport properties of devices which utilize the surface electron accumulation layer.

Effect of strain relaxation and the Burstein–Moss energy shift on the optical properties of InN films grown in the self-seeded catalytic process

For the first time, high optical quality InN films were grown on sapphire substrate using atmospheric chemical vapour deposition technique in the temperature range of 560-650 oC. Self-catalytic approach was adopted to overcome the nucleation barrier for depositing InN films. In this process, seeding of the nucleation sites and subsequent growth was performed in the presence of reactive NH3. We investigated the simultaneous effect of strain and Burstein-Moss (BM) energy shift on optical properties of InN films using Raman and photoluminescence spectroscopy. Existence of compressive strain in all films is revealed by Raman spectroscopic analysis and is found to relax with increasing growth temperature. The asymmetric broadening of the A1(LO) phonon mode is observed with the onset of plasmon-phonon interaction for films grown at 620 oC. Large blue shift of the band gap of InN (1.2 eV) is observed as a collective result of compressive strain in films as well as BM shift. Carrier density is calculated using the BM shift in the photoluminescence spectra. Finally, blue shift in band edge emission is observed further because of the presence of compressive strain in the films along with the BM effect.

More accurate predictions of band gap tuned by pressure in InN using HSE06 and GW approximations

Band structures of wurtzite InN under pressure are systematically investigated at various levels of theory. The main findings are summarized as follows: (I) The wurtzite phase remains mechanically and dynamically stable for a broad range of pressure. (II) As pressure increases, the band gap remains direct and increases nonlinearly. The G0W0+HSE06 approximation predicts the most accurate band gap for InN, which is larger than the HSE06 data and slightly smaller than the scGW0 data. The G0W0(HSE06) pressure coefficient dEg/dP and ground-state band gap is 3.10meV/kbar and 0.694eV, respectively, in excellent agreement with the experimental 3.0±0.1meV/kbar and 0.70eV (Li et al., 2003).

Bandgap energy bowing parameter of strained and relaxed InGaN layers

This paper focuses on the determination of the bandgap energy bowing parameter of strained and relaxed InxGa1−xN layers. Samples are grown by metal organic vapor phase epitaxy on GaN template substrate for indium compositions in the range of 0<x<0.25. The bangap emission energy is characterized by cathodoluminescence and the indium composition as well as the strain state are deduced from high resolution X-ray diffraction measurements. The experimental variation of the bangap emission energy with indium content can be described by the standard quadratic equation, fitted using a relative least square method and qualified with a chi square test. Our approach leads to values of the bandgap energy bowing parameter equal to 2.87±0.20eV and 1.32±0.28eV for relaxed and strained layers (determined for the first time since the revision of the InN bandgap energy in 2002), respectively. The corresponding modified Vegard’s laws describe accurately the indium content dependence of the bandgap emission energy in InGaN alloy and for the whole range of indium content. Finally, as an example of application, 3D mapping of indium content in a thick InGaN layer is deduced from bandgap energy measurements using cathodoluminescence and a corresponding hyperspectral map.

Improved theoretical model of InN optical properties

AbstractThe optical properties of InN are investigated theoretically by employing the projector augmented wave (PAW) method within Green's function and the screened Coulomb interaction approximation (GWo). The calculated results are compared to previously reported calculations which use local density approximation combined with the scissors‐operator approximation. The results of the present calculation are compared with reported values of the InN bandgap and with low temperature near infrared luminescence measurements of InN films deposited by a modified Ion Beam Assisted Deposition technique. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structural and electronic properties of elastically strained InN/GaN quantum well multilayer heterostructures

AbstractAn important step towards optimization of InN/GaN based devices is identification of the structural characteristics of the corresponding interfaces since the favourable bonding configurations determine materials polarity and consequently the direction of spontaneous polarization. We have addressed this issue through calculations on InN/GaN interfaces comprising misfit dislocations (Kioseoglou et al., J. Mater. Sci. 43, 3982 (2008) [5]). In our present study, additional calculations are performed on subcritical thickness InN/GaN QWs, which exhibit lower dislocation densities as well as reduced InN decomposition and are currently implemented in the fabrication of near‐UV light emitting diodes. Ab initio calculations are performed under modified pseudopotentials, accurately reproducing the InN and GaN band gap values, on supercells comprising multilayers of one monolayer (ML) thick InN elastically strained in 5 nm thick GaN barriers having a wurtzite or zinc blende stacking at the interface. The former is found to be energetically favorable. Subsequent calculations on supercells comprising 1 ML thick InN in 8 and 11 nm thick GaN barriers as well as 3 ML InN in 11 nm thick GaN, depict a variation in III‐N bond lengths. This variation becomes more significant as the barrier thickness decreases or the QW thickness increases. Hence the strain and consequently piezoelectric polarization are modified. Our results scrutinize recent experimental observations and could prove beneficial for tailoring the optoelectronic properties of InN/GaN QWs. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Growth of wurtzite InN on bulk In2O3(111) wafers

A single phase InN epitaxial film is grown on a bulk In2O3(111) wafer by plasma-assisted molecular beam epitaxy. The InN/In2O3 orientation relationship is found to be (0001) ‖ (111) and [11¯00] ‖ [112¯]. High quality of the layer is confirmed by the small widths of the x-ray rocking curves, the sharp interfaces revealed by transmission electron microscopy, the narrow spectral width of the Raman E2h vibrational mode, and the position of the photoluminescence band close to the fundamental band gap of InN.

Effect of interfacial lattice mismatch on bulk carrier concentration and band gap of InN

The issue of ambiguous values of the band gap (0.6 to 2 eV) of InN thin film in literature has been addressed by a careful experiment. We have grown wurtzite InN films by PA-MBE simultaneously on differently modified c-plane sapphire substrates and characterized by complementary structural and chemical probes. Our studies discount Mie resonances caused by metallic In segregation at grain boundaries as the reason for low band gap values (≈ 0.6 eV) and also the formation of Indium oxides and oxynitrides as the cause for high band gap value (≈ 2.0 eV). It is observed that polycrystallinity arising from azimuthal miss-orientation of c-oriented wurtzite InN crystals increases the carrier concentration and the band gap values. We have reviewed the band gap, carrier concentration, and effective mass of InN in literature and our own measurements, which show that the Moss-Burstein relation with a non-parabolic conduction band accounts for the observed variation of band gap with carrier concentration.

High-pressure optical absorption in InN: Electron density dependence in the wurtzite phase and reevaluation of the indirect band gap of rocksalt InN

We report on high-pressure optical absorption measurements on InN epilayers with a range of free-electron concentrations ($5\ifmmode\times\else\texttimes\fi{}{10}^{17}$--$1.6\ifmmode\times\else\texttimes\fi{}{10}^{19}$ cm${}^{\ensuremath{-}3}$) to investigate the effect of free carriers on the pressure coefficient of the optical band gap of wurtzite InN. With increasing carrier concentration, we observe a decrease of the absolute value of the optical band gap pressure coefficient of wurtzite InN. An analysis of our data based on the k\ifmmode\cdot\else\textperiodcentered\fi{}p model allows us to obtain a pressure coefficient of 32 meV/GPa for the fundamental band gap of intrinsic wurtzite InN. Optical absorption measurements on a 5.7-\ensuremath{\mu}m-thick InN epilayer at pressures above the wurtzite-to-rocksalt transition have allowed us to obtain an accurate determination of the indirect band gap energy of rocksalt InN as a function of pressure. Around the phase transition (\ensuremath{\sim}15 GPa), a band gap value of 0.7 eV and a pressure coefficient of \ensuremath{\sim}23 meV/GPa are obtained.

InGaN Solar Cells: Present State of the Art and Important Challenges

Solar cells are a promising renewable and carbon-free electric energy resource to address the fossil-fuel shortage and global warming. Energy conversion efficiencies over 40% have been recently achieved using conventional III–V semiconductor compounds as photovoltaic materials. The revision of InN bandgap to a much narrower value has extended the fundamental bandgap of the group III-nitride alloy system over a wider spectral region (from 0.64 eV for InN to 3.4 eV for GaN or 6.2 eV for AlN), raising the possibility of a variety of new applications. The tunable bandgap, predicted high radiation resistance, and strong absorption coefficient of the In $_x$ Ga $_{ 1-x}$ N material system are promising for high-efficiency photovoltaic systems. During the past few years, the interest in In $_x$ Ga $_{ 1-x}$ N solar cells has been remarkable. The development of high-performance solar cells using In $_x$ Ga $_{1-x}$ N materials is one of the most important goals when compared with the existing solar cells using Si and other III–V materials. Significant efforts and progress have been made toward this goal, while great opportunities and grand challenges coexist. In this paper, we present a review on the present state of the art of In $_x$ Ga $_{1-x}$ N-based solar cells. The most important challenges toward the high-efficiency In $_x$ Ga $_{ 1-x}$ N-based solar cells are discussed in the context of the recent results.

Investigation of indium nitride for micro-nanotechnology

We present a study of non–intentionally doped InN epilayers directly grown on sapphire substrate by metal organic chemical vapour deposition (MOCVD) technique. Structural and optical characterisations of this sample have been conducted by SEM, temperature–dependent photoluminescence and time resolved pump–probe techniques. Triangular–shaped structures of InN are observed to grow above hexagonal–shaped columnar structures as seen from the SEM image. Photoluminescence spectra reveal a peak energy of 0.75 eV, supporting the existence of the narrow bandgap of InN. So far, various papers in the literature quote the carrier lifetime in InN epilayers grown on sapphire substrate in the presence of a buffer layer such as GaN. Herein, we report carrier lifetime measurements conducted on InN epilayer deposited directly on sapphire substrate, in the absence of GaN as a buffer layer.