Indium Vacancies Research Articles

Towards experimental identification of vacancy complexes in InN

AbstractIn this contribution we present ab initio calculations of positron states and annihilation at vacancies and vacancy complexes in InN. Momentum distributions of annihilating electron–positron pairs in indium (VIn) and nitrogen vacancies (VN) as well as mixed vacancy clusters are calculated. Based on the modelled data the possibility of their experimental detection and distinction using positron annihilation spectroscopy is discussed. No localization of the positron density is found for isolated VN and VN clusters of up to 4VN. On the other hand, VIn and mixed vacancy clusters act as efficient positron traps in InN. While the calculated momentum distributions for the divacancy and VIn are quite close, mixed vacancy clusters which contain one VIn and two or more VN show well distinct spectra, that could be distinguished in suitable positron annihilation experiments.

Vacancy defects in indium oxide: An ab-initio study

First-principles density functional theory is employed to study the electrical behavior of oxygen and indium vacancies in indium oxide (In 2O 3). The oxygen vacancy is found to be a double donor. The indium vacancy is a triple acceptor, which >can be a compensation center in n-type In 2O 3, leading to n-type carrier reduction. However, its high formation energy under p-type conditions makes it unlikely to be a source of p-type carriers by itself.

Comparison of Jump Frequencies of <sup>111</sup>In/Cd Tracer Atoms in Sn<sub>3</sub>R and In<sub>3</sub>R Phases Having the L1<sub>2</sub> Structure (R = Rare-Earth)

Measurements were made of jump frequencies of 111In/Cd tracer atoms on the Sn-sublattice in rare-earth tri-stannides having the L12 crystal structure via perturbed angular correlation spectroscopy (PAC). Phases studied were Sn3R (R= La, Ce, Pr, Nd, Sm and Gd). Earlier measurements on isostructural rare-earth tri-indides showed that the dominant diffusion mechanism changed along that series [4]. The dominant mechanism was determined by comparing jump frequencies measured at opposing phase boundary compositions (that is, more In-rich and more In-poor). Jump frequencies were observed to be greater at the In-rich boundary composition in light lanthanide indides and greater at the In-poor boundary composition in heavy-lanthanide indides. These observations were attributed to predominance of diffusion via rare-earth vacancies in the former case and indium vacancies in the latter. Contrary to results for the indides, jump frequencies found in the present work are greater for the Sn-poor boundary compositions of the stannides, signaling that diffusive jumps are controlled by Sn-vacancies. Possible origins of these differences in diffusion mechanisms are discussed.

Influence of Rapid Thermal Annealing on Raman Scattering of InN Epilayers

We studied the Raman scattering of the InN epilayers with rapid thermal annealing (RTA). The longitudianl optical (LO) phonon in Raman spectrum shifts toward lower frequency and increases asymmetric broadening as the RTA temperature is increased. We suggest that the formation of indium-related defects, such as metallic indium clusters or indium vacancies, are responsible for the change in the asymmetric ratio in the LO mode. The E2 (high) mode in the Raman spectrum does not exhibit significant change after RTA since the indium atom does not involve the E2 (high) mode.

The study of surface photoconductive response in indium sulfide crystals

The β-phase indium sulfide is a solar-energy absorption material with superior photoelectric conversion function applied in the near infrared to ultraviolet region due to a lot of vacant sites and surface states naturally existing in the crystals. In this study, the surface oxidation states of β-In2S3 single crystal have been characterized using surface photoconductive response (SPR) measurements in the temperature range between 30 and 300 K. In comparison with the traditional photoconductivity (PC) measurements, the SPR measurement characterizes a sample with an electric field perpendicular to the as-grown surface of β-In2S3, and this operation is similar to the general electric-field operation worked in a thin-film solar cell. There are a lot of defect, band-to-band, and surface-state transitions that can be detected in the temperature-dependent SPR spectra of 30–300 K. The defect transitions below band gap may come from the transitions of indium vacancies → sulfur vacancies in β-In2S3. The surface-state transitions are caused by higher-energy state transitions formed by β-In2S3−3xO3x. The intensities of some specific surface-state transitions are significantly enhanced in the SPR experiments as compared with those in the traditional PC measurements. The near-band-edge transitions below and above band gap of β-In2S3 are identified, and their temperature dependences of energy shift are analysed and discussed.

Vacancy–indium clusters in implanted germanium

Secondary ion mass spectroscopy measurements of heavily indium doped germanium samples revealed that a significant proportion of the indium dose is immobile. Using electronic structure calculations we address the possibility of indium clustering with point defects by predicting the stability of indium–vacancy clusters, In n V m . We find that the formation of large clusters is energetically favorable, which can explain the immobility of the indium ions.

Photocatalytic performance of tetragonal and cubic β-In2S3 for the water splitting under visible light irradiation

Tetragonal (T-In2S3) and cubic (C-In2S3) β-In2S3 were synthesized by hydrothermal method. The obtained products were characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) technologies. Their photocatalytic activity for hydrogen evolution from water under visible light irradiation (λ>400nm) was evaluated. It was revealed that the photocatalytic activity of β-In2S3 was strongly affected by the arrangement characteristic of the indium vacancies. The vacancy ordered T-In2S3 showed no activity for hydrogen production, while the vacancy disordered C-In2S3 exhibited stable activity. For C-In2S3 sample, further studies indicated that the photoactivity strongly depended on the nature and the amount of noble metal cocatalyst. The optimum loading value of Pt cocatalyst was found to be 2wt.%. With this loading amount as a reference value, the hydrogen production rate of noble-metal-loaded C-In2S3 decreased in the order Pd>Pt>Ru>Au/C-In2S3.

Vacancies and interstitials in indium nitride: Vacancy clustering and molecular bondlike formation from first principles

We investigate the structural and electronic properties and formation energies of vacancy, interstitial, and antisite defects, as well as complex formation, in wurtzite InN using first-principles calculations. The N interstitial, which forms a split-interstitial configuration with a ${\text{N}}_{2}$-like bonding, has the lowest formation energy under N-rich conditions in $p$-type material, where it is a triple donor. We find that indium vacancies have a tendency to form ``clusters,'' which results in local nitrogen-rich regions and the formation of ${\text{N}}_{x}$-molecular-like bonds. These complexes are amphoteric, have a relatively high formation energy, and are formed more readily under N-rich conditions. The nitrogen vacancy is a low energy defect under more In-rich conditions, and in $p$-type material it acts as a single and triple donor. In the neutral and negative charge states, we find nitrogen vacancies also prefer to be situated close to one another and to cluster, giving rise to local In-rich regions with electron localization at these metalliclike bonding configurations. The indium antisite in the $4+$ charge state is the lowest-energy defect under In-rich conditions in $p$-type material and thus also acts as a donor. Our findings shed light on, and help explain, recent and sometimes conflicting, experimental observations.

Native defects and their effects on properties of sputtered InN films

The concept of defect chemistry is applied to investigate the native defects in the InN films prepared by radio frequency magnetron sputtering. Growth temperature and pressure ranged from 150 to 300 °C and from 0.005 to 0.07 torr, respectively, for the purpose of changing the defects and the related properties. InN is expected to form Frenkel defects, indium vacancies, and interstitials. Other major defects for the nitrogen-rich InN films include nitrogen-on-indium antisites and nitrogen interstitials at higher nitrogen pressure, as supported by the results of x-ray photoelectron spectroscopy. Structure, composition, and electrical properties coincide with defect types and density.

Elucidation of the Excited-State Dynamics in CuInS2 Thin Films

Transient absorption (TA) and photoluminescence spectroscopy have been performed on spray-deposited CuInS2 thin films. Sulfur and indium vacancies introduce electronic states in the bandgap located at 1.5 and 0.15 eV above the valence band, respectively. Deep donor and deep acceptor doublet states at 1.1 and 0.2 eV are assigned to copper/indium antisite defects. The excited-state dynamics, which are derived from TA experiments, show electronic coupling between indium antisite defects and indium vacancies. The Shockley, Read, and Hall recombination model has been modified to account for this coupling and to simulate the TA results. Furthermore, the lifetime of the 1.1 eV state is found to be 20−50 μs, which is related to the low photovoltage of CuInS2 based solar cells.

Electronic and elastic properties of non-oxide anti-perovskites from first principles: SuperconductingCdCNi3in comparison with magneticInCNi3

Full-potential linearized augmented plane-wave method with the generalized gradient approximation for the exchange-correlation potential has been applied for the comparative study of structural, elastic, and electronic properties of the synthesized non-oxide anti-perovskites: superconducting $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ and magnetic $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$. The optimized lattice parameters, independent elastic constants (${C}_{11}$, ${C}_{12}$, and ${C}_{44}$), bulk modules $B$, compressibility $\ensuremath{\beta}$, shear modules $G$, and tetragonal shear modules ${G}^{\ensuremath{'}}$ are evaluated. The numerical estimates of the elastic parameters of the polycrystalline $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$ and $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ ceramics are performed. The band structures, total and site-projected $l$-decomposed densities of states, the shapes of the Fermi surfaces, the Sommerfeld coefficients, and the molar Pauli paramagnetic susceptibility for these anti-perovskites are obtained and analyzed in comparison with the available theoretical and experimental data. From our calculations, the stoichiometric $\mathrm{Cd}\mathrm{C}{\mathrm{Ni}}_{3}$ and $\mathrm{In}\mathrm{C}{\mathrm{N}}_{3}$ are very much alike in both structural and elastic properties but differ in electronic properties. For $\mathrm{In}\mathrm{C}{\mathrm{Ni}}_{3}$, the defect-induced magnetism associated with the indium vacancies or Ni atoms substituting for In was found.

Introduction of defects during the dry etching of InP photonic structures: a cathodo-luminescence study

Introduction of point defects during the dry etching process of InP-based photonic structures has been investigated using the spectroscopic cathodo-luminescence (CL) technique. The measurements were performed on cleaved cross-sections from standard passive waveguides with rectangular shape, different widths, etched in bulk InP using either reactive ion etching (RIE) with CH4/H2 as the etching gases, or high density—inductively coupled plasma (ICP) etching with SiCl4. Etched depths up to 4 μm were reached. In the case of the ICP process, a defect-related band appears in the CL spectra, which is tentatively attributed to some kind of complex defect involving indium vacancies, because of its energy measured at low temperature. This band does not appear for the RIE process. In addition, local stress also occurs in the etched ridges (identified from the spectral shift of the band to band transitions), which seems to arise from the occurrence of the defects. The features on the spectroscopic CL images (both in terms of the defect band and the changes in intensity related to non-radiative recombination centers) are discussed based on the nature of the hard mask material used for the etching process and the local temperature reached during processing, especially with the high density ICP process.

Investigation of vacancy defect in InP crystal by positron lifetime measurement

Positron lifetime measurements have been carried out on liquid-encapsulated Czochralski-grown undoped InP samples sliced from the middle part of ingots over the temperature range 10–300 K. And at 70 K, the spectra have been measured in darkness, under illumination of infrared LED, and with illumination off is one sample. The measurements at low temperature reveal different concentration of hydrogen indium vacancy complex V InH 4 in these samples. A relatively higher concentration of V InH 4 in samples grown from P-rich undoped InP melts can be shown. The increase of resistivity of these samples can be speculated when temperature is low enough.

The nature of nitrogen related point defects in common forms of InN

The role of point defects related to the presence of excess nitrogen is elucidated for InN thin films grown by different techniques. Elastic recoil detection analysis has shown the presence of excess nitrogen in state-of-the-art InN films. Using x-ray photoelectron spectroscopy and x-ray diffraction it is shown that two distinct forms of point defects can be distinguished; one of these appears to be an interstitial form of nitrogen, common in some forms of polycrystalline InN. The other is associated with a combined biaxial and hydrostatic strain observed for molecular beam epitaxy (MBE) and chemical vapor deposition (CVD) grown films, and may be a mixture of the nitrogen-on-metal antisite defect and lower densities of indium vacancies and interstitial nitrogen. The high density of defects present in all the InN samples examined suggests that stoichiometry related point defects dominate the electrical and optical properties of the material. The difference in the type of point defect observed for polycrystalline (rf sputtered) and epitaxial (MBE and CVD) InN supports existing evidence that the Moss-Burstein effect is not an adequate description of the apparent band-gap difference between InN samples grown by different techniques.

Investigation of Vacancy Defect in InP Crystal by Positron Lifetime

Positron lifetime measurements were carried out on liquid-encapsulated Czochralski-grown undoped InP samples sliced from middle of ingots over the temperature range of 10 ∼ 300 K. At 70 K, the spectra were measured in darkness, under illumination of infrared LED, and while illumination off respectively on one of samples. The measurements at low temperature revealed different concentration of hydrogen indium vacancy complex V In H 4 in these samples. A relatively higher concentration of V InH 4 existing in that grown from P-rich undoped InP melts could be shown. The increase of resistivity of these samples could be speculated when temperature was low enough.

Photoluminescence studies of chalcopyrite and orthorhombic AgInS 2 thin films deposited by spray pyrolysis technique

Chalcopyrite (ch) and orthorhombic (o) AgInS 2 thin films were prepared by spray pyrolysis using a ratio of [Ag] / [In] = 1.5 and 0.83 respectively. AgInS 2 polycrystalline material was annealing in a sulphur atmosphere at 400 °C for 2 h. The estimated optical gap energies were 1.87 and 2.01 eV for ch–AgInS 2 and 1.98 eV for o–AgInS 2. All the deposited films exhibited n-type conductivity. Photoluminescence (PL) studies reveal in both phases several PL bands. In ch–AgInS 2 the PL bands were observed to be centered at 1.45, 1.7 and 1.88 eV at 10 K and an excitation intensity of 10 W cm − 2 . The 1.45 eV emission is related with indium vacancies whereas the other emissions (1.70 and 1.88 eV) are related with a donor–acceptor pair recombination and free to bound transition respectively. A new PL band was observed in the annealed sample, this band was centered at 2.02 eV at 10 K and it is related to the transition between a closed level to the conduction band and the splitting valence band (0.15 eV). PL bands in o–AgInS 2 samples were observed at 1.45 and 1.524 eV at 10 K and are related with a free to bound transition. Finally o–AgInS 2 shows two emission bands located at 1.45 and 1.59 eV, the o–AgInS 2 annealed sample in a sulphur atmosphere showed a new PL band located at 2.01 eV at 10 K, this band is related with an energy transition between a level near the conduction band to the splitting valence band (0.063 eV).

Controlled growth of novel doorframe-like ITO nanostructures and their photoluminescence properties

This paper describes a thermal evaporation method that generated large-scale novel doorframe-like ITO nanostructures by regularly switching flow rate of the carried gas. Their morphology and microstructures were determined by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy and photoluminescence spectroscopy. The as-synthesized doorframe-like nanostructures are single crystal with diameters ranging from hundreds of nm to about 1 μm. The growth direction of the doorframe-like nanostructures are < 100> and < 011> and the growth process follows a self-catalytic vapor–liquid–solid mechanism. The PL spectrum of the doorframe-like nanostructures shows two emission bands around 418 and 505 nm, which is probably resulted from oxygen vacancies, oxygen–indium vacancy pairs and impurity level, respectively.

Generation and suppression of deep level defects in InP

Deep level defects in as-grown and annealed n-type and semi-insulating InP have been studied. After annealing in phosphorus ambient, a large quantity of deep level defects were generated in both n-type and semi-insulating InP materials. In contrast, few deep level defects exist in InP after annealing in iron phosphide ambient. The generation of deep level defects has direct relation with in-diffusion of iron and phosphorus in the annealing process. The in-diffused phosphorus and iron atoms occupy indium sites in the lattice, resulting in the formation of P anti-site defects and iron deep acceptors, respectively. The results indicate that iron atoms fully occupy indium sites and suppress the formation of indium vacancy and P anti-site, etc., whereas indium vacancies and P anti-site defects are formed after annealing in phosphorus ambient. The nature of the deep level defects in InP has been studied based on the results.

Influence of V/III molar ratio on the formation of In vacancies in InN grown by metal-organic vapor-phase epitaxy

We have applied a slow positron beam to study InN samples grown by metal-organic vapor-phase epitaxy with different V/III molar ratios (3300–24 000) and at different growth temperatures (550–625°C). Indium vacancies were identified in samples grown at V/III ratios below 4000. Their concentration is in the 1017cm−3 range. No strong dependence of vacancy concentration on the molar ratio was observed. At low V/III ratios, however, In droplets and vacancy clusters are formed near the substrate interface. The elevated growth temperature enhances the In vacancy formation, possibly due to limited sticking of In on the growth surface close to the decomposition temperature.

Phosphorus–hydrogen complexes in LEC‐grown InP

AbstractIn LEC‐grown InP, about 30 sharp vibrational absorption lines are measured in the frequency region 2200 to 2350 cm–1. All these lines are due to phosphorus‐hydrogen stretching modes. Experiments on InP containing both hydrogen and deuterium finally proved that the line at 2202.4 cm–1 is due to a single hydrogen atom bonded to P in an indium vacancy (VIn) and that the line at 2315.6 cm–1 is due to the complex of four P–H bonds in an VIn. In InP:H:D, this VInH4 complex gives rise to six vibrational lines in the region of P–H modes and six lines in the region of P–D modes because of the five different types of VInHnDm complexes. The measured frequencies of these 12 lines are in excellent agreement with those obtained from ab initio calculations reported in the literature. Additional P–H complexes are discussed. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)