Burstein-Moss Shift Research Articles

Influence of strain on the band gap energy of wurtzite InN

AbstractDegenerate wurtzite InN films with electron concentrations in the range of 1018 cm–3 were studied by using spectroscopic ellipsometry (SE) in two spectral ranges. The analysis of the frequencies of the coupled phonon‐plasmon modes in the mid‐infrared region allows the determination of the plasma frequency and thus of the carrier density in the bulk of the samples. SE from the near‐infrared to the visible range provides the dielectric function (DF) around the absorption edge. The electron concentration as an important input parameter enables accurate determination of Burstein–Moss shift and band‐gap renormalization for the analysis of the imaginary part of the DF. Taking into account the in‐plane strain of the films, which is caused by lattice mismatch between InN and buffer/substrate, we obtain a zero‐density strain‐free band gap of 0.675 eV at room temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterizations of gallium-doped ZnO films on glass substrate prepared by atmospheric pressure metal-organic chemical vapor deposition

Ga-doped zinc oxide (ZnO:Ga) films were grown on glass substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) using diethylzinc and water as reactant gases and triethyl gallium (TEG) as an n-type dopant gas. The structural, electrical and optical properties of ZnO:Ga films obtained at various flow rates of TEG ranging from 1.5 to 10 sccm were investigated. X-ray diffraction patterns and scanning electron microscopy images indicated that Ga-doping plays an important role in forming microstructures in ZnO films. A smooth surface with a predominant orientation of (101) was obtained for the ZnO:Ga film grown at a flow rate of TEG = 7.5 sccm. Moreover, a lowest resistivity of 3.6 × 10 − 4 Ω cm and a highest mobility of 30.4 cm 2 V − 1 s − 1 were presented by the same sample, as evaluated by Hall measurement. Otherwise, as the flow rate of TEG was increased, the average transmittance of ZnO:Ga films increased from 75% to more than 85% in the wavelength range of 400–800 nm, simultaneously with a blue-shift in the absorption edge. The results obtained suggest that low-resistivity and high-transparency ZnO films can be obtained by AP-MOCVD using Ga-doping sufficiently to make the films grow degenerate and effect the Burstein–Moss shift to raise the band-gap energy from 3.26 to 3.71 eV.

Characterization of Transparent Conducting Al:ZnO Thin Films Deposited by Chemical Spray Pyrolysis

Nanocrystalline undoped and Al doped ZnO thin films were synthesized by the chemical spray pyrolysis of Zinc acetate and Aluminium chloride solution. The optoelectronic properties of undoped and Al:ZnO films were investigated. The XRD patterns of films were preferably oriented along c-axis [0 0 2] plane with the hexagonal wurtzite structure. The Al-doping caused no additional X-ray diffraction peaks when compared with XRD of undoped film, indicating Al2O3 content was below the detection limit. The crystallite size of undoped and Al doped film was 48 nm and 51nm respectively, as measured from X-ray diffractogram. The films are of high optical transmittance (≥ 90%). The resistivity of the film was found to decrease because of Al doping. The dark resistivity measurement for Al:ZnO film was of the order of 10-3 Ω-1cm-1. The band gap energy of the film was found to vary from 3.25 to 3.32eV indicating the Moss Burstein shift. Al:ZnO films can be used as transparent conducting oxide layers for photovoltaic applications.

N-type doping of InGaN by high energy particle irradiation

This article reviews our extensive studies of the effects of native defects introduced by high energy particles on the electrical and optical properties of InGaN alloys. We show that the electronic properties of irradiated InGaN can be well described by the amphoteric defect model. Because of the extremely low position of the conduction band edge of InN the formation energy of native donor defects is very low in In-rich InGaN alloys. High energy particle irradiation of InN and In-rich InGaN, will therefore produce donor defects and result in more n-type materials. As the irradiation dose increases, the electron concentration increases until the Fermi energy EF approaches the Fermi stabilization energy EFS. At this point both donor and acceptor-type defects are formed at similar rates, and compensate each other, leading to stabilization of EF and a saturation of the electron concentration. Hence a large increase and then saturation in the Burstein–Moss shift of the optical absorption edge is also observed. Furthermore we also found that mobilities in the irradiated films can be well described by scattering from triply charged defects, providing strong evidence that native defects in InN are triple donors. The excellent agreement between the experimental results and predictions based on the ADM suggests that particle irradiation can be an effective and simple method to control the doping (electron concentration) in In-rich Inx Ga1–x N via native point defects. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The Al-doping contents dependence of the crystal growth and energy band structure in Al:ZnO thin films

We report the Al-doping contents dependence of crystal growth and energy band structure in Al:ZnO thin films on the quartz substrates by the sol–gel method. As the Al contents increase, the Al-doping in the lattice reveals a maximum while the dopant is 2 mol%. It is inferred that the doping deterioration attributes to the decrease of grain size, which might be induced by the pinning effect of amorphous Al 2O 3 on ZnO grains boundary. The blueshifts of optical bandgap imply the quantum size effect of crystallites and the Burstein–Moss shifts in photoluminescence spectra indicate the heavy doping level for all samples.

Electrical and optical properties of InN with periodic metallic in insertions

We report on a growth by molecular beam epitaxy of InN:In semiconductor/metal composite structures containing periodically inserted arrays of In clusters formed by intentional deposition of In metal films in a thickness range of 2–48 monolayers. It was found that indium insertions do not change markedly carrier mobility in the composites, that remains in the 1300–1600 cm2/(V s) range, while carrier concentration increases with rising In amount. Spectra of thermally detected optical absorption do not exhibit a noticeable Burstein-Moss shift of a principal absorption edge with increasing the carrier concentration, but rather complicated modification of their shapes.

What is what in the nanoworld: a handbook on nanoscience and nanotechnology

Preface to the Second Edition. Preface to the First Edition. Source of Information. A. From Abbe's principle to Axbel' - Kaner cyclotron resonance. B. Grom B92 protocol to Burstein-Moss Shift. C. From cage compound to cyclotron resonance. D. From D'Alembert equation to Dzyaloshinskii-Moriya interaction. E. From (e,2e) reaction to Eyring equation. F. From Fabry-Perot resonator to FWHM (full width at half maximum). G. From gain-guided lasers to gyromagnetic frequency. H. From habit plane to hyperelastic scattering. I. From ideality factor to isotropy (of matter). J. From Jahn - Teller effect to Joule's law of electric heating. K. From Kane Model to Kuhn-Thomas-Reiche sum rule. L. From lab-on-a-chip to Lyman series. M. From Mach-Zender interferometer to Murrell-Mottram potential. N. From NAA (neutron activation analysis) to Nyquist-Shannon sampling theorem. O. From octet rule to oxide. P. From PALM (photoactivable localization microscopy) to pyrrole. Q. From Q-control to qubit. R. From Rabi flopping to Rydberg gas. S. From Saha equation to synergetics. T. From Talbot's law to type II superconductors. U. From ultraviolet photoelectron spectroscopy (UPS) to Urbach rule. V. From vacancy to von Neumann machine. W. From Waidner-Burgess standard to Wyckoff notation. X. From XMCD (X-ray magnetic circular dichroism) to XRD (X-ray diffraction). Y. From Yasukawa potential to Yukawa potential. Z. From Zeeman effect to Zundel ion. A list and a presentation of Scientific Journals which contain the stem Nano in their title. Abbreviations for the scientific journals which appear as sources in the text. Appendix - main properties of intrinsic (or lightly doped). Semiconductors.

Annealing studies on InN thin films grown by modified activated reactive evaporation

We describe the effect of annealing in air and in vacuum on structural, electrical and optical properties of indium nitride (InN) thin films. The films were grown by modified activated reactive evaporation. Films annealed in air were transformed to In 2O 3 at 450 °C whereas films annealed in vacuum started decomposing at 500 °C. The c-lattice constant was found decreasing for increasing annealing temperature due to reduction of excess nitrogen in the films. The major changes in structural, electrical and optical properties appear around 400 °C. Both air and vacuum-annealed films show a reduction in the carrier concentration with annealing, explaining the observed reduction in bandgap (Moss-Burstein shift) for vacuum-annealed films. For air-annealed films, the bandgap increases when annealed, which may be due to oxynitride formation overcoming the effect of reduced carrier concentration. A decrease in the photoluminescence intensity was observed at 400 °C for air-annealed and 500 °C for vacuum-annealed films which can be attributed, respectively, to the presence of indium oxide and indium in the films. Optimal annealing temperature was observed between 400 and 450 °C in vacuum.

Band gap bowing parameter of In1−xAlxN

We report a band gap bowing parameter for In1−xAlxN of 4.7 eV from a study of high quality and homogenous samples with x=0.017–0.60. Optical absorption data were modeled to extract the band gaps in order to consider the complications of the band structure of In-rich InAlN, including the Burstein–Moss shift, nonparabolic conduction band, and broadening of the absorption edge. The alloy compositions were accurately determined using Rutherford backscattering spectrometry and the sample quality was evaluated using x-ray diffraction and channeling-RBS.

STUDY ON THE STRUCTURE AND OPTICAL PROPERTIES OF Zn1-xCrxO FILMS BY RF MAGNETRON SPUTTERING TECHNIQUE

Zn 1-x Cr x O (x = 0, 0.03, 0.09) films were prepared by the radio frequency (RF) magnetron sputtering technique on Si (111) and quartz glass substrates. The effects of Cr -doping on the structural and optical properties of ZnO films have been discussed. The structural properties were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) while optical properties using UV-Visible spectrophotometer (UV-VIS). XRD measurement revealed that the films were single phase and wurtzite structure with c-axis orientation. With the increase of Cr concentration, the intensity of the (002) peak and the grain size of the Zn 1-x Cr x O (x = 0, 0.03, 0.09) films decreased, and the Full Width at Half Maximum (FWHM) of (002) peak, the crystal lattice parameter c of Zn 1-x Cr x O (x = 0, 0.03, 0.09) films and the width of optical band gap increased, respectively. In the transmittance spectra of the Zn 1-x Cr x O (x = 0, 0.03, 0.09) films, the movement of the absorption edge of the ultraviolet region is the Burstein–Moss shift with the increase of Cr concentration.

Structure, conductivity, and transparency of Ga-doped ZnO thin films arising from thickness contributions

Ga-doped ZnO (GZO) films were deposited on amorphous glass substrates at room temperature by radio frequency magnetron sputtering. It is revealed that the influence of deposition parameters, such as target-substrate distance and deposition time, on the structure and properties of the films arises primarily from the variations in film thickness. For the GZO films with smaller thicknesses (≤385 nm), crystallinity is greatly improved with an increase in thickness, which leads to an increase in Hall mobility and a decrease in electrical resistivity. The carrier concentration is, however, found to exhibit only a slight change with the thickness variations. The relationship of electrical property and microstructure suggests that the resistivity of the films arises mainly from ionic impurity scattering rather than from grain boundary scattering. All the films exhibit a transmittance of over 90% in the visible wavelength range. The band gap of the GZO films is widened with increasing film thickness. In combination with the result that the carrier concentration exhibited a slight dependence on thicknesses, the broadening of the band gap with thicknesses is attributed more to the improved crystallinity than to the Moss–Burstein shift.

First-principles LDA+U studies of the In-doped ZnO transparent conductive oxide

Electronic energy band structure of In-doped ZnO transparent conducting oxide was investigated by density functional calculations using local density approximation+Hubbard U (LDA+U) scheme. By systematically calculating the formation energies and transition energy levels of In atom and In-related complex in ZnO, it has been shown that the substitutional In atom has a low formation energy and introduces a shallow donor level, which is 38 meV below the conduction-band minimum. Substitutional In atoms contribute significantly delocalized s orbitals in the conduction band states, which are expected to increase the mobility of the material. In p-type ZnO, interstitial In atom acts as a donor and has a low formation energy, making it a compensating center in the case of acceptor doping. Under O-rich growth conditions, however, interstitial In is energetically unfavorable. The modulated band structure of ZnO after In doping shows a total energy band gap widening effect due to a pronounced Burstein–Moss shift and a relatively small exchange-correlation-induced band gap narrowing.

Structural, optical and magnetic properties of (ZnO) 1− x(MnO 2) x thin films deposited at room temperature

The structural, magnetic and optical properties of (ZnO) 1− x (MnO 2) x (with x = 0.03 and 0.05) thin films deposited by pulsed laser deposition (PLD) were studied. The pellets used as target, sintered at different temperatures ranging from 500 °C to 900 °C, were prepared by conventional solid state method using ZnO and MnO 2 powders. The observation of non-monotonic shift in peak position of most preferred (1 0 1) ZnO diffraction plane in XRD spectra of pellets confirmed the substitution of Mn ions in ZnO lattice of the sintered targets. The as-deposited thin film samples are found to be polycrystalline with the preferred orientation mostly along (1 1 0) diffraction plane. The UV–vis spectroscopy of the thin films revealed that the energy band gap exhibit blue shift with increasing Mn content which could be attributed to Burstein–Moss shift caused by Mn doping of the ZnO. The deposited thin films exhibit room temperature ferromagnetism having effective magnetic moment per Mn atom in the range of 0.9–1.4 μ B for both compositions.

The effect of rf power on the growth of InN films by modified activated reactive evaporation

We report the effect of rf power on the structural, optical and electrical properties of InN films grown by modified activated reactive evaporation. In this technique, the substrates were kept on the cathode instead of ground electrode. The films grown at higher rf power shows preferential c-axis orientations for both silicon and glass substrates. The films prepared at 100 W show best structural, electrical and optical properties. The c-axis lattice constant was found to decrease with increase in rf power which can be attributed to reduction in excess nitrogen in the films. The band gap decreases with increase in rf power due to Moss–Burstein shift. The decrease in carrier concentration and optical band gap with increase in rf power can also be related to excess nitrogen in the film. The Raman spectra shows a red shift in the A 1(LO) and E 2 (high) mode from the reported value. The possible origin of the present large band gap is due to Moss–Burstein shift. The new film growth method opens opportunities for integrating novel substrate materials with group III nitride technologies.

Properties of Zinc Oxide Films Cosputtered with Aluminum at Room Temperature

The electrical, structural, and optical properties of ZnO films cosputtered with Al at room temperature using a radio frequency magnetron cosputtering system were systematically investigated. The increase in carrier concentration was initially drastic with increasing cosputtered Al content and gradually alleviative for the cosputtered films behaving as an n-type degenerated semiconductor. The Hall mobility of these degenerated samples was deeply affected by both the crystal grain size and the degree of the growth orientation, becoming a dominant factor for obtaining the film with the lowest resistivity. The shifts of the ZnO(002) diffraction peak of these cosputtered films were affected by the Al3+ substitute for the lattice Zn2+ sites as well as the excess Al content existing in the interstitials. In terms of the associated optical properties, all these cosputtered films exhibited excellent transmittance around visible wavelengths. In the ultraviolet wavelengths, an apparent blue-shift at the absorption edge due to the increase in carrier concentration correlated to the Burstein–Moss shift was also observed from these degenerated cosputtered Al–ZnO films. The depth distribution of the Al impurities was more uniform than a conventional sputtered Al-doped ZnO film at a similar Al doping level. The carrier concentration and Hall mobility of the cosputtered Al–ZnO film were found to be apparently increased due to the more effective activation of the Al–O chemical bonds and less metallic Al and Zn atoms existed in the interstitials analyzed from X-ray photoelectron spectroscopy (XPS) investigations.

The effect of annealing processes on electronic properties of sol-gel derived Al-doped ZnO films

Al-doped ZnO films with high transmittance and low resistivity were prepared by sol-gel method with a three-step annealing. By investigating the relative effect of the Al∕Zn ratio to the annealing on electrical and optical properties, the origin of electrical conduction is verified as the combining effect of the high temperature annealing which enhances crystal quality that provides higher mobility of electrons and the reduction annealing which releases the localized electrons caused by oxygen absorption. Varying the Al∕Zn ratio causes a small Burstein–Moss shift and a slight change in carrier concentration. In contrast, the annealing procedure produces significant changes in the carrier concentration and mobility.

Dielectric function of cubic InN from the mid-infrared to the visible spectral range

The complex dielectric function for cubic InN is determined by spectroscopic ellipsometry from the mid-infrared into the visible spectral region. Films were grown by molecular beam epitaxy on c-GaN/3C-SiC pseudo-substrates. The high electron densities above 1019 cm−3 cause pronounced Burstein–Moss shifts at the gap. Taking into account the non-parabolicity and the filling of the conduction band, data analysis yields renormalized band edges between 0.43 and 0.455 eV. Including carrier-induced band-gap renormalization, we estimate a zero-density band gap of ∼0.595 eV for c-InN which is about 85 meV lower than for hexagonal InN. Values for the electron effective mass, the static and high-frequency dielectric constant are reported.

Electrical Characteristics of n-ZnO/p-Si Heterojunction Diodes Grown by Pulsed Laser Deposition at Different Oxygen Pressures

Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at different pressures. These heterojunctions were found to be rectifying with a maximum forward-to-reverse current ratio of about 1,000 in the applied voltage range of −5 V to +5 V. The turn-on voltage of the heterojunctions was found to depend on the ambient oxygen pressure during the growth of the ZnO film. The current density–voltage characteristics and the variation of the series resistance of the n-ZnO/p-Si heterojunctions were found to be in line with the Anderson model and Burstein-Moss (BM) shift.

Effect of Al concentration in grain and grain boundary region of Al-doped ZnO films: a dielectric approach

Aluminium-doped zinc oxide (ZnO : Al) films have been deposited by RF magnetron sputtering on Pyrex glass substrates. The structural, electrical and optical properties of films as a function of Al concentration have been studied. Al-doped films exhibit high optical transparency and a reduction of resistivity with increasing Al concentration. The minimum resistivity value is found to be ρ = 2.2 × 10−3 Ω cm as compared with ∼104 Ω cm, for undoped ZnO. The optical band gap is observed to follow a Burstein–Moss shift with the increase in the concentration of Al doping and shows the maximum band gap of 3.53 eV. Relative variation of the grain and grain boundary scattering with doping concentration has been investigated with impedance spectroscopy.

Impacts of dislocation bending and impurity incorporation on the local cathodoluminescence spectra of GaN grown by ammonothermal method

Spatially resolved cathodoluminescence (CL) spectra of GaN films grown on freestanding GaN seeds via fluid transport by the ammonothermal method were correlated with the microstructure and growth polarity. The spectral line shape of local CL was nearly position independent for a 4-μm-thick N-polar film exhibiting featureless morphology. The spectra exclusively exhibited a broad near-band-edge (NBE) free carrier recombination emission with Burstein-Moss shift. Conversely, CL spectra at 100K of a 5-μm-thick Ga-polar film having (101¯1) and (101¯2) facets with ridges originating from central pits exhibited a NBE peak at 3.444eV and emission bands at 3.27, 2.92, and 2.22eV, all of which showed rich intensity contrasts in the CL mapping images. The NBE peak intensity was remarkably enhanced at crests of the ridges, where the density of threading dislocations (TDs) having edge components was greatly reduced by the dislocation bending. The results encourage one to grow low TD density GaN wafers by slicing thick crystals grown by the ammonothermal method.