Application of reactor neutrons to the investigation of the radiation resistance of semiconductor materials of Group III–V and sensors

The investigation of the radiation resistance of Group III–V semiconductor materials is an important and urgent problem. Magnetic sensors based on radiation resistant semiconductor materials are widely used in magnetomeasuring systems of thermonuclear industrial and experimental reactors. The basic approaches to the study of semiconductor materials under conditions of neutron irradiation and the results of some experiments on testing indium-containing semiconductor materials InSb, InAs, and their alloys InAs _x Sb_{1 ? x} are presented. The presented experience of the development of equipment for on-line testing of materials and magnetic diagnostic sensors under radiation conditions can be used for testing a wide range of materials under conditions close to those of the ITER and other thermonuclear reactors.     

Surface energy and crystal structure of nanowhiskers of III–V semiconductor compounds

A theoretical model has been proposed for calculating the surface energy of nanowhiskers in the nearest neighbor approximation. The surface energy has been calculated for different faces of III–V semiconductor crystals with cubic and hexagonal structures. The effect of the formation of the hexagonal wurtzite phase in nanowhiskers of III–V semiconductor compounds has been considered using the obtained data. Estimates for the critical radius of the phase transition in III–V semiconductor nanowhiskers are presented.     

Theory of band gap bowing of disordered substitutional II–VI and III–V semiconductor alloys

For a wide class of technologically relevant compound III?CV and II?CVI semiconductor materials AC and BC mixed crystals (alloys) of the type A _x B_1?x C can be realized. As the electronic properties like the bulk band gap vary continuously with x, any band gap in between that of the pure AC and BC systems can be obtained by choosing the appropriate concentration x, granted that the respective ratio is miscible and thermodynamically stable. In most cases the band gap does not vary linearly with x, but a pronounced bowing behavior as a function of the concentration is observed. In this paper we show that the electronic properties of such A _x B_1?x C semiconductors and, in particular, the band gap bowing can well be described and understood starting from empirical tight-binding models for the pure AC and BC systems. The electronic properties of the A _x B_1?x C system can be described by choosing the tight-binding parameters of the AC or BC system with probabilities x and 1 ? x, respectively. We demonstrate this by exact diagonalization of finite but large supercells and by means of calculations within the established coherent potential approximation (CPA) We apply this treatment to the II?CVI system Cd _x Zn_1?x Se, to the III?CV system In _x Ga_1?x As and to the III-nitride system Ga _x Al_1?x N.     

Solution epitaxy of gallium-doped ZnO on p-GaN for heterojunction light-emitting diodes

We report white light emission from a Ga-doped ZnO/p-GaN heterojunction light-emitting diode which was fabricated by growing gallium-doped ZnO film on the p-GaN in water at 90°C. As determined from Ga-doped ZnO films grown on (111) oriented MgAl₂O₄ spinel single crystal substrates, thermal treatment at 600°C in nitrogen ambient leads to a carrier concentration of 3.1×10²⁰ cm⁻³ (and carrier mobility of 28 cm²/Vs) which is two orders of magnitude higher than that of the undoped films. Electroluminescence emissions at wavelengths of 393 nm (3.155 eV) and 529.5 nm (2.4 eV) were observed under forward bias in the heterojunction diode and white light could be visibly observed. The high concentration of electrons supplied from the Ga-doped ZnO films helped to enhance the carrier recombination and increase the light-emitting efficiency of the heterojunction diode.     

Hydrogen interaction with GaN metal–insulator–semiconductor diodes

Interaction mechanism of hydrogen with GaN metal–insulator–semiconductor (MIS) diodes is investigated, focusing on the metal/semiconductor interfaces. For MIS Pt-GaN diodes with a SiO₂ dielectric, the current–voltage (I–V) characteristics reveal that hydrogen changes the conduction mechanisms from Fowler–Nordheim tunneling to Poole–Frenkel emission. In sharp contrast, Pt-Si_xN_y-GaN diodes exhibit Poole–Frenkel emission in nitrogen and do not show any change in the conduction mechanism upon exposure to hydrogen. The capacitance–voltage (C–V) study suggests that the work function change of the Schottky metal is not responsible mechanism for the hydrogen sensitivity.     

A wire-form emitter metal–insulator–semiconductor tunnel junction

Physical effects arising due to change of configuration of a MIS system from planar to cylindrical, are theoretically analyzed. Attention is paid to the voltage partitioning and all the components of tunneling current. A simple simulation model is developed enabling prediction of the band diagram details and calculation of the currents. The trends expected with decreasing system radius are elucidated. Cylindrical geometry can be faced with when quantum wire is used as an electron emitter. Similar form may also be roughly attributed to an edge region of conventional MIS capacitors.     

Electric field control of spin splitting in III–V semiconductor quantum dots without magnetic field

We provide an alternative means of electric field control for spin manipulation in the absence of magnetic fields by transporting quantum dots adiabatically in the plane of two-dimensional electron gas. We show that the spin splitting energy of moving quantum dots is possible due to the presence of quasi-Hamiltonian that might be implemented to make the next generation spintronic devices of post CMOS technology. Such spin splitting energy is highly dependent on the material properties of semiconductor. It turns out that this energy is in the range of meV and can be further enhanced with increasing pulse frequency. In particular, we show that quantum oscillations in phonon mediated spin-flip behaviors can be observed. We also confirm that no oscillations in spin-flip behaviors can be observed for the pure Rashba or pure Dresselhaus cases.     

Fabrication of cosputtered Zn–In–Sn–O films and their applications to organic light-emitting diodes

Zn–In–Sn–O (ZITO) films have been grown by rf magnetron cosputtering system from ceramic oxide targets of ZnO and ITO onto glass substrate. X-ray diffraction analysis shows that the microstructure is amorphous below the substrate temperature of 250 ^°C. The films exhibit sheet resistance as low as 16.7 Ω/□ and optical transparency comparable to grater than that of Sn-doped indium oxide (ITO) films. The work function ranged 5.05–5.19 eV, which is a higher work function compared to ITO (4.7 eV). The fabricated ZITO films are used in fabrication of organic light-emitting diodes (OLEDs). The ZITO anode with the zinc content of 12.5 at.% [Zn/(Zn+In+Sn)] fabricated at 250 ^°C-based OLED shows lower turn-on voltage and higher current density compared to that of ITO-based control device.     

Metal–organic–vapor phase epitaxy of InGaN quantum dots and their applications in light-emitting diodes

In GaN quantum dot is a promising optoelectronic material,which combines the advantages of low-dimensional and wide-gap semiconductors.The growth of In GaN quantum dots is still not mature,especially the growth by metal–organic–vapor phase epitaxy(MOVPE),which is challenge due to the lack of 、itin-situ monitoring tool.In this paper,we reviewed the development of In GaN quantum dot growth by MOVPE,including our work on growth of near-UV,green,and red In GaN quantum dots.In addition,we also introduced the applications of In GaN quantum dots on visible light emitting diodes.     

Analysis of interface states and series resistance for Al/PVA:n-CdS nanocomposite metal–semiconductor and metal–insulator–semiconductor diode structures

This paper presents the fabrication and characterization of Al/PVA:n-CdS (MS) and Al/Al₂O₃/PVA:n-CdS (MIS) diode. The effects of interfacial insulator layer, interface states (N _ss ) and series resistance (R _s ) on the electrical characteristics of Al/PVA:n-CdS structures have been investigated using forward and reverse bias I–V, C–V, and G/w–V characteristics at room temperature. Al/PVA:n-CdS diode is fabricated with and without insulator Al₂O₃ layer to explain the effect of insulator layer on main electrical parameters. The values of the ideality factor (n), series resistance (R _s ) and barrier height (? _b ) are calculated from ln(I) vs. V plots, by the Cheung and Norde methods. The energy density distribution profile of the interface states is obtained from the forward bias I–V data by taking into account the bias dependence ideality factor (n(V)) and effective barrier height (? _e ) for MS and MIS diode. The N _ss values increase from mid-gap energy of CdS to the bottom of the conductance band edge for both MS and MIS diode.     

I–V characteristics of vanadium-flavonoid complexes based Schottky diodes

In this study, we have investigated the current–voltage characteristics of the Schottky diodes of two vanadium complexes, VO₂(3-fl) (1) (3-fl=3-hydroxyflavone) and VO(acac)₂ (2), (acac=acetylacetonate), and their composites with TiO₂. Thin films of vanadium complexes and their composites were deposited by the centrifugation method. Current–voltage characteristics of the samples were processed by the modified Shockley equation, Cheung functions and space-charge limited currents (SCLC) approaches. Different junction parameters, such as series resistances, reverse saturation currents, ideality factors and barrier height of the samples, were determined.     

Investigations on mesa width design for 4H–SiC trench super junction Schottky diodes

Mesa width(WM) is a key design parameter for SiC super junction(SJ) Schottky diodes(SBD) fabricated by the trench-etching-and-sidewall-implant method. This paper carries out a comprehensive investigation on how the mesa width design determines the device electrical performances and how it affects the degree of performance degradation induced by process variations. It is found that structures designed with narrower mesa widths can tolerant substantially larger charge imbalance for a given BV target, but have poor specific on-resistances. On the contrary, structures with wider mesa widths have superior on-state performances but their breakdown voltages are more sensitive to p-type doping variation. Medium WMstructures(～ 2 μm) exhibit stronger robustness against the process variation resulting from SiC deep trench etching.Devices with 2-μm mesa width were fabricated and electrically characterized. The fabricated SiC SJ SBDs have achieved a breakdown voltage of 1350 V with a specific on-resistance as low as 0.98 m?·cm~2. The estimated specific drift onresistance by subtracting substrate resistance is well below the theoretical one-dimensional unipolar limit of SiC material.The robustness of the voltage blocking capability against trench dimension variations has also been experimentally verified for the proposed SiC SJ SBD devices.     

Theoretical models of ferromagnetic III–V semiconductors

Recent materials research has advanced the maximum ferromagnetic transition temperature in semiconductors containing magnetic elements toward room temperature. Reaching this goal would make information technology applications of these materials likely. In this article we briefly review the status of work over the past five years which has attempted to achieve a theoretical understanding of these complex magnetic systems. The basic microscopic origins of ferromagnetism in the (III,Mn)V compounds that have the highest transition temperatures appear to be well understood, and efficient computation methods have been developed which are able to model their magnetic, transport, and optical properties. However many questions remain.     

New interpretation of C–V measurements for determining the concentration profile in a semiconductor

The well-known C–V technique for determining the doping profile in a semiconductor is re-examined. Based on an analysis of the Poisson equation, a modification of the conventional procedure for evaluating the space-charge density distribution within the depletion layer of a semiconductor is presented. This procedure involves a developed integral-capacitance technique, which proves to be generally valid and gives the correct basis for determining the space-charge density near the edge of the depletion layer rather than the real doping profile. The relationship between the proposed method and the conventional differential-capacitance technique is revealed and a comparison of the effectiveness of both of them is also made. The method proves to be useful if shallow diffusion profiles within low-doped substrates are analyzed, when the conventional C–V profiling technique is not applicable. Experimental results obtained with an n⁺/n epitaxial layer are given and discussed as an illustration of the represented study. Received: 18 September 2000 / Accepted: 4 December 2000 / Published online: 3 May 2001     

A europium(III) organic ternary complex applied in fabrication of?near UV-based white light-emitting diodes

A β-diketone, 2-acetylfluorene-4,4,4-trifluorobutane-1,3-dione (HAFTFBD), and its three europium(III) complexes, Eu(AFTFBD)₃⋅2H₂O, Eu(AFTFBD)₃(TPPO)₂ and Eu(AFTFBD)₃phen, were designed and synthesized, where TPPO was triphenylphosphine oxide and phen was 1,10-phenanthroline. The complexes were characterized by IR, UV-visible, photoluminescence (PL) spectroscopy and thermogravimetric analysis (TGA). The results show that the Eu(III) complexes exhibit a high thermal stability,and wide and strong excitation bands when monitored at 613 nm. Excited by ∼395 nm near UV light, the complexes emitted strong and characteristic red light due to f–f transitions of the central Eu³⁺ ion, and no emission from the ligands was found. The photoluminescence mechanism of the europium(III) complexes was investigated and proposed as a ligand-sensitized luminescence process. Among the three europium(III) complexes, Eu(AFTFBD)₃phen exhibits the highest thermal stability and the most excellent photoluminescence properties. A bright red light-emitting diode was fabricated by coating the Eu(AFTFBD)₃phen complex onto an ∼395 nm-emitting InGaN chip, and the LED showed appropriate CIE chromaticity coordinates (x=0.66, y=0.33). A white LED with CIE chromaticity coordinates (x=0.32, y=0.32) was prepared with Eu(AFTFBD)₃phen as red phosphor, indicating that Eu(AFTFBD)₃phen can be applied as a red component for fabrication of near ultraviolet-based white light-emitting diodes.     

Luminescence of II–VI and III–V nanostructures

Photoluminescence of HgCdTe epitaxial films and nanostructures and electroluminescence of InAs(Sb,P) light-emitting diode (LED) nanoheterostructures were studied. For HgCdTe-based structures, the presence of compositional fluctuations, which localized charge carriers, was established. A model, which described the effect of the fluctuations on the rate of the radiative recombination, the shape of luminescence spectra and the position of their peaks, was shown to describe experimental photoluminescence data quite reasonably. For InAs(Sb,P) LED nanoheterostructures, at low temperatures (4.2–100 K) stimulated emission was observed. This effect disappeared with the temperature increasing due to the resonant ‘switch-on’ of the Auger process involving transition of a hole to the spin-orbit-splitted band. Influence of other Auger processes on the emissive properties of the nanoheterostructures was also observed. Prospects of employing II–VI and III–V nanostructures in light-emitting devices operating in the mid-infrared part of the spectrum are discussed.