ZnTe-Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} heterojunctions were prepared by vapor-transport epitaxy of ZnTe on In-doped Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} (x = 0.05, y = 0.03) single crystalline substrate in vacuum. At temperatures lower than 120 K the infrared and red electroluminescence were observed from the ZnTe-Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} diode with forward current density in the range 0.003-4.0 A/cm^{2}.
We study the anisotropic electronic transport property of ZnS-type thin-film electroluminescence displays by Monte Carlo simulation. The simulation contains an accurate and efficient description of the anisotropic band structure and various scattering mechanisms like phonon scattering and impurity scattering. The electronic transport processes in three devices with different ZnS-layer orientations are simulated. From the obtained energy population and average energy of electrons, we conclude that the 〈100〉 direction is the best for electron acceleration under high electric field. We propose that new attempts in using this direction for ZnS-layer deposition will result in an improvement of the performance of thin-film electroluminescence displays.
A method of determination of Mn concentration in ZnS:Mn based on existence of two manganese kinetic components is proposed. In the method the manganese concentration is determined by lifetime and initial intensity of electroluminescence measurements. The results of the measurements are compared with statistical distributions of single Mn^{2+} ions and Mn^{2+} -Mn^{2+} pairs in hexagonal ZnS.
The mechanism of carrier heating in ZnS-based electroluminescence devices is discussed. We show that carrier acceleration by an applied electric field is at 300 K not a loss-free (ballistic carriers) process. Even for large carrier energies (about 2.5 eV) inelastic scattering on polar optical phonons dominates over elastic scattering on acoustic phonons and ionized impurities.
We have studied the influence of ion implantation and post-implantation annealing regimes on the structural and optical properties of silicon matrix with ion-beam synthesized InAs nanocrystals. (100) Si wafers were implanted at 25 and 500°C, subsequently with high fluences of As and In ions. After implantation the samples were processed by furnace and rapid thermal annealing at 900, 950 and 1050°C. A part of the samples implanted at 25°C was additionally exposed to H_2^{+} ions (100 keV, 1.2 × 10^{16} cm^{-2} in terms of atomic hydrogen). This procedure was performed to obtain an internal getter. In order to characterize the implanted samples transmission electron microscopy and low-temperature photoluminescence techniques were employed. It was demonstrated that by introducing getter, varying the ion implantation temperature, ion fluences and post-implantation annealing duration, and temperature it is possible to form InAs nanocrystals in the range of sizes of 2-80 nm and create various concentration and distribution of different types of secondary defects. The last ones cause in turn the appearance in photoluminescence spectra dislocation-related D1, D2 and D4 lines at 0.807, 0.870 and 0.997 eV, respectively.
Electrical and luminescent properties of ZnS:Mn,Cu,Cl thin films were investigated. Combined both studies: scanning tunneling microscopy and scanning tunneling spectroscopy were made. The current and differential conductance versus applied voltage were measured for the ZnS:Mn,Cu,Cl thin films. Additionally, the spectral and kinetic properties of the electroluminescent cells based on the ZnS:Mn,Cu,Cl thin films were measured. The maximum of the electroluminescence lies at 586 nm. The electroluminescence was excited by rectangular wave voltage pulses with pulse length from 1μs to 1 ms. It was shown that time dependence of the electroluminescence is well explained assuming energy transfer between monomolecular centres.
In the present paper we report on the observation and study of intense spontaneous THz emission from modulation-doped AlGaN/GaN heterostructure under conditions of heating of two-dimensional electron gas in lateral electric field. The experimental results are compared with the model of blackbody-like thermal emission of hot 2D electrons. Complementary transport measurements and theoretical simulation were carried out to determine the dependence of effective electron temperature on electric field. The role of non-equilibrium optical phonon accumulation is discussed.
We report on polarization spectra of spontaneous terahertz electroluminescence from uniaxially deformed Ge(Ga). At compressive pressure of about 3±0.3 kbar in the [111] direction, near the impurity breakdown threshold, the linear polarization degree attains ≈80-90% for the main lines of the terahertz emission.
We have studied a series of polar InGaN/GaN light emitting diodes, consisting of either a blue (440-450 nm) quantum well, or combination of blue and violet (410 nm) quantum wells (with indium content 18% and 10%, respectively). The blue quantum well was always placed close to p-type region of the particular LED. We found that the electroluminescence induced by low current is characterized by light emission from the blue quantum well only. In comparison, optical excitation of our LEDs leads to light emission with energies characteristic either for blue and/or violet quantum wells. The corresponding microphotoluminescence spectra evolve depending on external polarization and variable light intensity of excitation supplied by He-Cd laser. Interplay between built-in electric field and externally applied polarization/screening decides about the band structure profiles and thus radiative recombination mechanisms.
The use of silicon based light emitting diodes may completely solve the problem of low compatibility of optoelectronics elements and silicon chip. At present time the most suitable kinds of Si-LEDs are monocrystal and porous silicon avalanche LEDs. They have advantages such as long operation lifetime (>10000 hours), continuous spectrum, which allows to filter RGB colors, operation voltages (<12 V), extremely sharp voltage-current characteristic, nanosecond response time, and high high operation current densities (up to 8000 A/cm^2 in pulse mode). Rather low energy efficiency (<1%) is not so significant for near to eyes (NTE) microdisplays. These advantages open a way to design a high performance and cost effective passive addressed microdisplays.
We recall the geometry of porous silicon and the order of magnitude of some characteristic parameters. We give a brief review of optical experiments and their different interpretations. We focus on quantitative interpretations and show that an essential concept is confinement in a quantum wire or box. In particular, the exchange energy of electron-hole pairs correlated by Coulomb interaction inside a quantum box explains results obtained between 4 I{ and room temperature. Nevertheless, the large shift of the main luminescence line for similar porous silicon but different electrolytes cannot be explained by quantum confinement alone and has to be accounted for by the difference between the dielectric constants inside and outside the porous silicon. A brief account of electroluminescence experiments is also given.
The spectra of spontaneous terahertz (THz) electroluminescence at the breakdown of shallow Ga acceptor in Ge were observed for the first time and investigated. We found and characterized the emission lines corresponding to the hole transitions between the excited states and the ground state of the impurity center as well as the transitions of the hot holes from the valence band to the impurity and within the valence band. A high quantum yield of the radiative transitions will become an important factor in designing electrically pumped THz emitters for the≈2 THz spectral range.
The light emitting devices based on the p-Zn_{1-x}Mn_{x}Te bicrystals have been fabricated. The Zn_{1-x}Mn_{x}Te devices produce red and green emission originating from the internal d-shell transitions in the Mn^{2+} ions and the donor-acceptor pairs recombination, respectively. A critical behavior of the magnetic field dependence of the green emission intensity and a positive magnetoresistance near the Curie-Weiss temperature in the Zn_{1-x}Mn_{x}Te devices was observed.
Photoluminescence and electroluminescence spectra of the absorber layer in ZnO/CdS/Cu(In,Ga)Se_2 solar cells were measured. Their dependence on temperature, excitation intensity and applied voltage were studied. Electroluminescence measurements were used to investigate light- and bias-induced metastabilities in the absorber of the cells. We showed that metastable changes of defect distributions, which produce an effect on the electrical characteristics of ZnO/CdS/Cu(In,Ga)Se_2 material, affect also the luminescence yield. The dependence of the intensity and shape of the electroluminescence spectra on the state of the sample is observed. These results fit well into the theoretical calculations of Lany and Zunger model showing that divacancy complex (V_{Se}-V_{Cu}) is responsible for metastable changes observed in ZnO/CdS/Cu(In,Ga)Se_2-based solar cells. We conclude that during light soaking or/and forward bias the probability of nonradiative recombination is decreased.
This paper reviews the experimental and theoretical results obtained during work on the modern semiconductor devices employing one-dimensional photonic structures. After short review of the physical features of structures consisting of 1D stack of the alternating high and low index layers, particular attention will be given to unique features of the devices employing microcavities: resonant cavity LEDs, resonant-cavity enhanced photo-detectors, vertical cavity surface emitting lasers, and also vertical external cavity surface emitting lasers. At the end the semiconductor saturable absorber mirrors are discussed.
The lifetime and stability of AlGaN/GaN heterostructure field effect transistors at high power levels can be enhanced by introducing field plates to reduce electric field peaks in the gate-drain region. Simulations of the electric field distribution along the channel using the 2D ATLAS software from Silvaco indicate that above a characteristic drain source voltage three spatially separated electric field peaks appear, one located at the drain-side edge of the gate foot, one at the end of the drain-sided gate field plate, and one at the end of the source shield field plate. The close correlation between lateral electric field and the electroluminescence due to hot electron related intra-band transitions can be very helpful when optimizing the electric field distribution in high power devices. Electroluminescence microscopy images of devices with gate and source shield field plate reveal the peaks located at the locations of enhanced electric field. By studying the voltage dependence of the electroluminescence peaks the influence of the field plates on the electric field distribution in source drain direction can be visualized.
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