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7 Aug 1995

Volume 67, Issue 6, pp. 733-874

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Comparison of high temperature thermal stabilities of Ru and RuO2 Schottky contacts to GaAs

Yong Tae Kim, Chang Woo Lee, and Sung Kwan Kwak

Appl. Phys. Lett. 67, 807 (1995); http://dx.doi.org/10.1063/1.115450 (3 pages) | Cited 5 times

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Thermal behaviors of ruthenium (Ru) and ruthenium dioxide (RuO2) Schottky contacts have been compared after rapid thermal annealing at 550–900 °C for 30 s without arsenic overpressure or capping layer. Rutherford backscattering measurements and x‐ray diffraction indicate that no metallurgical interactions take place between RuO2 and GaAs. I–V characteristics of RuO2 Schottky contacts reveal that barrier height increases from 0.83 to 0.85 eV even after RTA at 900 °C, in contrast with the degradation of barrier height from 0.75 to 0.59 eV for the Ru Schottky diodes. This means that RuO2 Schottky contacts have higher thermal stability than Ru contacts to GaAs. The reason is ascribed to the diffusion barrier property of RuO2 preventing the interdiffusion of Ga and As. © 1995 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Md Surface thermodynamics, surface energies
73.30.+y Surface double layers, Schottky barriers, and work functions

Fabrication of (001) InP‐based 1.55‐μm wavelength lasers on a (110) GaAs substrate by direct bonding (A prospect for free‐orientation integration)

Y. Okuno, M. Aoki, T. Tsuchiya, and K. Uomi

Appl. Phys. Lett. 67, 810 (1995); http://dx.doi.org/10.1063/1.115451 (3 pages) | Cited 10 times

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We examine the direct bonding of (001) InP and (110) GaAs and demonstrate its application to device fabrication. Cross‐sectional observation shows that these wafers can be united without generating dislocation. (001) InP‐based 1.55‐μm wavelength lasers are fabricated on (110) GaAs. The light–current characteristics of the lasers are almost identical to those of lasers fabricated on (001) GaAs, while the turn‐on voltage is higher by about 0.4 V due to the large band discontinuity. The results show that the direct bonding technique is promising for allowing new concept ‘‘free‐orientation integration.’’ © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Current transport in amorphous silicon n/p junctions and their application as ‘‘tunnel’’ junctions in tandem solar cells

Steven S. Hegedus, Frank Kampas, and Jianping Xi

Appl. Phys. Lett. 67, 813 (1995); http://dx.doi.org/10.1063/1.115452 (3 pages) | Cited 10 times

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Current transport in a‐Si based n/p (‘‘tunnel’’) junctions is investigated using current‐voltage‐ temperature and quantum efficiency measurements. Currents are nearly ohmic and temperature independent under typical solar cell operating conditions. Incorporating a thin a‐Si(B) p+ layer between the n and p layers and replacing either a‐Si layer with a microcrystalline layer improves the device by reducing the resistance and increasing the recombination. Light soaking improves the devices slightly. These results are consistent with a recently proposed recombination‐tunneling model. Incorporating improved interconnect junctions in tandem solar cell devices improved the initial and stabilized performance. © 1995 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.40.Gk Tunneling
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Picosecond laser dynamics of gain‐coupled and index‐coupled InGaAs/InGaAlAs quantum well distributed feedback lasers

J. Kovač, H. Schmidt, C. Kaden, V. Hofsäss, H. P. Gauggel, H. Schweizer, A. Hase, and H. Künzel

Appl. Phys. Lett. 67, 816 (1995); http://dx.doi.org/10.1063/1.115453 (3 pages) | Cited 1 time

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High frequency modulation of gain‐coupled (GC) and index‐coupled (IC) InGaAs/InGaAlAs distributed feedback (DFB) lasers is investigated. Laser dynamics of conventionally fabricated IC DFB lasers are compared with GC DFB lasers realized by the new technology of masked implantation enhanced intermixing. Band structure dependence of the modulation response at low temperature (T=2K) is analyzed by detuning the emission energy of the DFB lasers with respect to the gain maximum using different grating periods. Pulse widths decreasing from 53 ps down to 4.5 ps with increasing emission energy demonstrate the capability of both coupling types. The experimental results are in excellent agreement with a theory without any fit parameter based on laser rate equations. © 1995 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.-v Laser optical systems: design and operation

Improved compositional abruptness at the InGaAs on GaAs interface by presaturation with In during molecular‐beam epitaxy

R. Kaspi and K. R. Evans

Appl. Phys. Lett. 67, 819 (1995); http://dx.doi.org/10.1063/1.115454 (3 pages) | Cited 36 times

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Surface segregation of In atoms during molecular beam epitaxy of InGaAs layers greatly influences the composition profile in the vicinity of both the normal and the inverted Ga(Al)As/InGaAs interface, inherently limiting compositional abruptness. We find, for example, that the intended alloy composition in In0.22Ga0.78As is not reached until nearly 35 Å from the InGaAs on GaAs interface for growth at 500 °C. We propose and demonstrate how the compositionally graded region in InGaAs can be eliminated by preadsorbing a fixed amount of In onto the GaAs surface to match the surface segregated layer during steady state, before depositing the InGaAs layer. © 1995 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Thin films of CoAs from low‐temperature metalorganic chemical vapor deposition of a novel single‐source precursor compound

Franz‐Robert Klingan, Alexander Miehr, Roland A. Fischer, and Wolfgang A. Herrmann

Appl. Phys. Lett. 67, 822 (1995); http://dx.doi.org/10.1063/1.115455 (3 pages) | Cited 11 times

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A new structurally defined precursor compound for the low‐temperature metalorganic chemical vapor deposition (MOCVD) of CoAs thin films is reported. The easily accessible 1,3‐bis(tert‐butyl)‐2‐[tetracarbonyl‐cobalt(‐l)]‐1,3,2‐diazarsolidine was decomposed by hot‐wall low pressure CVD. Thin films of cobalt arsenide with retention of the stoichiometry of the precursor (Co:As=1/1) were formed at temperatures as low as 210 °C. Electron micrographs show uniform films, energy dispersive x‐ray spectroscopy, and Auger electron spectroscopy confirm their bulk composition, and powder diffraction patterns and conductivity measurements prove their crystallinity and electrical properties. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Preparation and characterization of Cu(In1−xGax)3Se5 thin films

Takayuki Negami, Naoki Kohara, Mikihiko Nishitani, Takahiro Wada, and Takashi Hirao

Appl. Phys. Lett. 67, 825 (1995); http://dx.doi.org/10.1063/1.115456 (3 pages) | Cited 49 times

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Polycrystalline Cu(In1−xGax)3Se5 thin films were prepared by four source evaporation with controlling and shielding of the molecular beams from elemental sources. Ga content x, can be controlled by deposition times of CuIn3Se5 and CuGa3Se5 layers, which form Cu(In1−xGax)3Se5 films through the interdiffusion. X‐ray diffraction analyses showed that the films with x≲0.5 have an ordered vacancy chalcopyrite and the films with x≳0.5 have a zinc blende structure. The optical band gap of the films linearly increased from 1.23 eV (x=0) to 1.85 eV (x=1) with increasing Ga content. The conductivity of the films was about 10−6/Ω cm and about 10−7/Ω cm under and above x=0.3, respectively. © 1995 American Institute of Physics.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors

Transport characteristics of polycrystalline‐silicon wire influenced by single‐electron charging at room temperature

Kazuo Yano, Tomoyuki Ishii, Takashi Hashimoto, Takashi Kobayashi, Fumio Murai, and Koichi Seki

Appl. Phys. Lett. 67, 828 (1995); http://dx.doi.org/10.1063/1.115457 (3 pages) | Cited 32 times

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Conductance of ultrathin polycrystalline silicon wire was measured and periodic plateaus, which provide evidence of the Coulomb staircase at room temperature, are observed. This shows that single‐electron charging effects are important to transport in a semiconductor system at room temperature. The very small (∼10‐nm diam) silicon‐grain structure is presumably playing a key role in creating the observed effects. From the temperature dependence, the electron transport is clearly dominated by the thermal emission, whose activation energy is more than 400 meV. This reveals that the treatment beyond well‐established single‐electron tunneling, including thermal‐emission transfer, is essential to understand such high‐temperature charging effects in semiconductor systems. © 1995 American Institute of Physics.
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73.40.Gk Tunneling
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Structural phase behavior in II–VI semiconductor nanoparticles

R. J. Bandaranayake, G. W. Wen, J. Y. Lin, H. X. Jiang, and C. M. Sorensen

Appl. Phys. Lett. 67, 831 (1995); http://dx.doi.org/10.1063/1.115458 (3 pages) | Cited 76 times

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Cubic structured CdS, CdSe, and CdTe, II–VI semiconductor nanoparticles have been synthesized using aqueous solution precipitation at room temperature. The ‘‘as‐prepared’’ particles have a size of about 30 Å. Thermal annealing causes (a) an increase in particle size; (b) a structural transition from the cubic to the bulk, hexagonal structure for CdS and CdSe; and (c) no structural transition for CdTe. The unexpected cubic phase for small particles of CdS and CdSe may be due to either metastability or an equilibrium surface effect. The latter would imply a strong correlation between structure and the size and surface properties, and that there is a minimum size for hexagonal phase stability. © 1995 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices
81.10.Dn Growth from solutions

Defect density measurements of low temperature grown molecular beam epitaxial GaAs by photothermal deflection spectroscopy

M. H. Chan, S. K. So, K. T. Chan, and F. G. Kellert

Appl. Phys. Lett. 67, 834 (1995); http://dx.doi.org/10.1063/1.115459 (3 pages) | Cited 6 times

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The subgap optical absorption of GaAs layers grown by low temperature molecular beam epitaxy is measured by photothermal deflection spectroscopy (PDS). The absorption increases as the growth temperature decreases at a fixed wavelength. Defect densities evaluated from the absorption spectra and the known absorption cross sections are between 1018 and 1019 cm−3. It is shown that complementary PDS phase spectra can be used to separate the absorption of the epitaxial layers from the bulk. © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

A high‐current‐gain, high‐speed P‐n‐p AlGaAs/InGaAs/GaAs collector‐up heterojunction bipolar transistor

H. C. Tseng, R. C. Hsieh, K. C. Hwang, and J. M. Ballingall

Appl. Phys. Lett. 67, 837 (1995); http://dx.doi.org/10.1063/1.115521 (3 pages) | Cited 3 times

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A P‐n‐p AlGaAs/InGaAs/GaAs collector‐up heterojunction bipolar transistor (C‐up HBT), grown by three‐stage molecular beam epitaxy, has been fabricated, and its dc and high‐frequency performances have been evaluated. The use of a graded InxGa1−xAs (x=0.0–0.09) is shown to improve the common‐emitter current gain (β) and to greatly reduce the base transit time (τb) for the P‐n‐p C‐up HBTs. A maximum current gain (β) of 150 was measured for a 16×17 μm2 device. From S‐parameter measurements, a best unity‐gain cutoff frequency fT=43 GHz at a collector current of −10 mA was achieved using a 5×10 μm2 collector area. The results show that the P‐n‐p C‐up HBTs may be useful for future planar integrated circuit applications. © 1995 American Institute of Physics.
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85.30.Pq Bipolar transistors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Exciton lifetimes in GaN and GaInN

C. I. Harris, B. Monemar, H. Amano, and I. Akasaki

Appl. Phys. Lett. 67, 840 (1995); http://dx.doi.org/10.1063/1.115522 (3 pages) | Cited 58 times

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Results from temperature dependent photoluminescence (PL) transient measurements on metalorganic vapor phase epitaxy grown epitaxial layers of GaN and GaInN are reported. In sufficiently pure GaN layers the free‐exciton PL dominates even at the lowest temperatures (2 K), and the intrinsic excitonic lifetimes can be obtained. We report a value of about 125 ps for the radiative lifetime of the free exciton in GaN at 2 K, as obtained from the PL transients of a 3 μm buried undoped GaN layer sandwiched between AlN and GaInN. The PL decay time in the ternary alloy GaInN, which is dominated by localized excitons at low temperatures, is much longer, about 500 ps. © 1995 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena

On the CdS/CuInSe2 conduction band discontinuity

Alex Niemegeers, Marc Burgelman, and Alexis De Vos

Appl. Phys. Lett. 67, 843 (1995); http://dx.doi.org/10.1063/1.115523 (3 pages) | Cited 29 times

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Recent calculations of the electron affinity difference between CdS and CuInSe2 indicate that the conduction band (CB) minimum of CuInSe2 is below the CB minimum of CdS. As a consequence, a spike occurs in the CB at the CdS/CuInSe2 interface. Such a spike is commonly considered as in conflict with good photovoltaic performance of heterojunction solar cells. It is outlined here that the simple assumption of thermionic emission across the junction can explain an unimpeded electron transport in the case of an n+p structure (n‐type window, p‐type absorber), even when a spike in the CB occurs. © 1995 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
84.60.Jt Photoelectric conversion

Breaking up of misfit dislocations in GaAs/In0.3Ga0.7As/GaAs heterostructure

J. Wu, W. Li, T. W. Fan, Z. G. Wang, and X. F. Duan

Appl. Phys. Lett. 67, 846 (1995); http://dx.doi.org/10.1063/1.115524 (2 pages) | Cited 1 time

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The effect of GaAs cap layer with different thicknesses in the GaAs/In0.3Ga0.7As/GaAs heterostructure on misfit dislocation is investigated with transmission electron microscopy, and it is found that lines of misfit dislocation break up and move out of the structure when the GaAs cap layer thickness exceeds a certain amount. The breaking up and moving out of misfit dislocations, initially confined in the (001) substrate/InGaAs epilayer interface, occur mainly along the [110] direction on the interface in the structure. © 1995 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Exploring the dissipative regime of superconductors for practical current‐lead applications

Milind N. Kunchur, D. K. Christen, C. E. Klabunde, and Kamel Salama

Appl. Phys. Lett. 67, 848 (1995); http://dx.doi.org/10.1063/1.115525 (3 pages) | Cited 6 times

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A pulsed‐current technique was used to measure the extended I–V characteristics of a wide variety of prototype high‐temperature‐superconductor (HTS) leads. It was found that the average resistivity rises with J(≳Jc) more gradually than in conventional superconductors—often remaining very small compared to silver, for values of J(≫Jc) that are high enough to be practically useful. This observation, combined with the low thermal conductivity (∼50 times smaller than Ag), should extend the utility of HTS leads to the dissipative regime where J/Jc≫1. © 1995 American Institute of Physics.
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74.25.F- Transport properties
74.25.-q Properties of superconductors
74.72.-h Cuprate superconductors

Jc enhancement of electrophoretically deposited YBa2Cu3O7−δ superconducting wire by BaF2 addition

S. Cho, Y. T. Yao, J. B. Ketterson, and K. L. Telschow

Appl. Phys. Lett. 67, 851 (1995); http://dx.doi.org/10.1063/1.115526 (3 pages) | Cited 3 times

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We have prepared YBa2Cu3O7−δ (YBCO) superconducting wires by electrophoretic deposition. Ag wire was used as a substrate. Adding a small amount of BaF2 tends to remove cracks in the YBCO layer which develop during the heating process. The suppression of cracks produced a dramatic improvement in the critical current density (Jc). At 77 K, Jc increased from 18 A/cm2 for BaF2‐free YBCO wire to 646 A/cm2 for a critical concentration of 2.7 wt% BaF2 after which it decreased monotonically with increasing BaF2 content. © 1995 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

High transport critical currents in flexible screen‐printed Ag‐(Bi,Pb)2Sr2Ca2Cu3Ox tapes

A. Oota, K. Ogawa, J. Maeda, and K. Shibata

Appl. Phys. Lett. 67, 854 (1995); http://dx.doi.org/10.1063/1.115527 (3 pages) | Cited 2 times

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We fabricated screen‐printed Ag‐(Bi,Pb)2Sr2Ca2Cu3Ox monofilament and multifilament tapes with filament number 1≤N≤5. As N increases, the critical current Ic increases monotonically until it reaches 54 A (77 K, 0 T) for N=5, while the critical current density Jc is around 1.6×104 A/cm2 (77 K, 0 T) nearly independent of N. The bend strain tolerance is found to decrease with increasing N. For monofilament tapes the strain tolerance is 2%–3% strain while for multifilament tapes it decreases to ∼1% at N=3 and ∼0.4% at N=5. © 1995 American Institute of Physics.
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84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.72.-h Cuprate superconductors

Role of magnetic anisotropy in the magnetoimpedance effect in amorphous alloys

R. L. Sommer and C. L. Chien

Appl. Phys. Lett. 67, 857 (1995); http://dx.doi.org/10.1063/1.115528 (3 pages) | Cited 62 times

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The magnetoimpedance (MI) effect of amorphous Co70.4Fe4.6Si15B10 ribbons, subjected to different annealing conditions with and without an external field, has been measured up to a frequency of 100 kHz. We show that the large MI effect is the result of transverse magnetic anisotropy, which is present in the as‐cast and the suitably field‐annealed samples. © 1995 American Institute of Physics.
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72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Kj Amorphous and quasicrystalline magnetic materials

Transport‐magnetism correlations in the ferromagnetic oxide La0.7Ca0.3MnO3

M. F. Hundley, M. Hawley, R. H. Heffner, Q. X. Jia, J. J. Neumeier, J. Tesmer, J. D. Thompson, and X. D. Wu

Appl. Phys. Lett. 67, 860 (1995); http://dx.doi.org/10.1063/1.115529 (3 pages) | Cited 203 times

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We present results of temperature and magnetic field dependent resistivity ρ(H,T) and bulk magnetization M(H,T) measurements on post‐annealed La0.7Ca0.3MnO3 thin films that were grown via pulsed‐laser deposition. Both the resistivity and the anomalously large negative magnetoresistance peak near the ferromagnetic ordering temperature (Tc=250 K), with Δρ/ρ0=−85% at 50 kOe. A clear correlation is found between ρ and M that is described by the phenomenological expression ρ(H,T)∝exp[−M(H,T)/M0]. This correlation reflects the important interplay between transport and magnetism in this system, and suggests that the transport below Tc involves polaron hopping. © 1995 American Institute of Physics.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.50.-y Studies of specific magnetic materials
75.30.-m Intrinsic properties of magnetically ordered materials

What determines the lateral bonding speed in silicon wafer bonding?

U. Gösele, S. Hopfe, S. Li, S. Mack, T. Martini, M. Reiche, E. Schmidt, H. Stenzel, and Q.‐Y. Tong

Appl. Phys. Lett. 67, 863 (1995); http://dx.doi.org/10.1063/1.115530 (3 pages) | Cited 11 times

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In silicon wafer bonding, the initial contact area spreads laterally with a typical speed on the order of 10 mm/s. We observed that this lateral bonding speed increases with decreasing ambient pressure, and is independent of the distance of the contact front to the rim of the wafers and independent of wafer thickness. From these results, we conclude that the lateral bonding speed is mainly determined by pressing the ambient gas out between the two wafers from a very localized area close to the propagating bonding front. © 1995 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics

Voltage shifts and imprint in ferroelectric capacitors

W. L. Warren, D. Dimos, G. E. Pike, B. A. Tuttle, M. V. Raymond, R. Ramesh, and J. T. Evans

Appl. Phys. Lett. 67, 866 (1995); http://dx.doi.org/10.1063/1.115531 (3 pages) | Cited 98 times

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Voltage offsets in the polarization‐voltage characteristics of Pb(Zr,Ti)O3 capacitors can be induced by either thermal or optical processes. The thermally (optically) induced voltage shift occurs by heating (illuminating) the sample under remanence or a saturating bias. Generally speaking, the thermally induced voltage shifts are greater than those obtained optically; this is attributed to the role of oxygen vacancy‐related defect dipoles throughout the film. We find that the inclusion of a dopant element that occupies a portion of the Ti(Zr) sites and has an oxidation state greater than +4 reduces the thermally induced voltage shifts observed in the capacitors. This may result because these particular dopants reduce the oxygen vacancy density and, hence, the defect‐dipole contribution to the voltage shift. © 1995 American Institute of Physics.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
61.72.J- Point defects and defect clusters
77.80.Fm Switching phenomena

A simple velocity model for low‐pressure metalorganic chemical vapor deposition

Cetin Aktik and Said Belkouch

Appl. Phys. Lett. 67, 869 (1995); http://dx.doi.org/10.1063/1.115532 (3 pages)

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A new simple transport model is used to describe the dependence of the electrical characteristics of the epitaxial layer on the growth parameters in low‐pressure metalorganic chemical vapor deposition. The important parameters of this model are the mean velocity of the gases and the [V]/[III] ratio. Undoped GaAs epitaxial layers are prepared at various operating pressures. A semi‐empirical correlation relating the reactor pressure and flow rate is established that dictates the operating conditions for a single set of film properties. This enables growth of a material with constant characteristics while pressure can be varied. © 1995 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
73.61.Ey III-V semiconductors

High aspect ratio micromachining Teflon by direct exposure to synchrotron radiation

Y. Zhang, T. Katoh, M. Washio, H. Yamada, and S. Hamada

Appl. Phys. Lett. 67, 872 (1995); http://dx.doi.org/10.1063/1.115533 (3 pages) | Cited 29 times

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Micromachining Teflon was achieved by direct exposure to synchrotron radiation and the microstructures made had the smallest surface detail down to 20 μm with structural height of more than 200 μm, that is, aspect ratio on the order of 10. The quality of micromachining Teflon by this process was found to be critically dependent on photon flux of the synchrotron radiation. Analysis of the mass distribution of gaseous species formed upon this process suggested that photochemical processes rather than pyrolytic processes may still dominate. © 1995 American Institute of Physics.  
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.65.-b Surface treatments
82.50.-m Photochemistry
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