Semiconductor Light-emitting Diodes Research Articles

Experimental and Numerical Study of Charge-Pump Pixel Addressing for Organic Light-Emitting Diode Displays

A charge-pump (CP) pixel addressing method for an organic light-emitting diode (OLED) display panel is shown to be feasible by implementing pixel arrays of both OLEDs and semiconductor light-emitting diodes (LEDs). It is also shown that the light output from the CP-OLED can be made to last for the entire panel scanning period and that the crosstalk between pixels can be minimized by a proper choice of drive signal waveforms. A SPICE circuit model is developed, and a pn-junction model is found to be effective in the numerical simulation of CP-OLED display panels. It is also found that a high contrast ratio and a high luminance level can be achieved using the new pixel addressing method.

Improvement of GaN-based light-emitting diode by indium-tin-oxide transparent electrode and vertical electrode

A sapphire-etched vertical-electrode nitride semiconductor (SEVENS) light-emitting diode (LED) is fabricated by means of a selective chemical wet-etching technique. The SEVENS-LED formed on sapphire substrate exhibits excellent device performance compared to a conventional NiAu lateral-electrode (LE) GaN-based LED formed on the same sapphire substrate. The integral light-output power of SEVENS-LED is /spl sim/7 mW, which is 1.75 times stronger than that of the conventional NiAu LE-LED (/spl sim/4 mW). The external quantum efficiency of SEVENS-LED is estimated to be approximately 13%.

GaN-Based Light-Emitting Diode with Indium–Tin–Oxide and Vertical Electrode

A sapphire-etched vertical-electrode nitride semiconductor (SEVENS) light-emitting diode (LED) is fabricated by a selective wet-etching technique. The SEVENS-LED has an indium–tin–oxide (ITO) transparent metal electrode (TME) and a sapphire via hole. The SEVENS-LED exhibits excellent device performances compared with a lateral-electrode (LE) GaN-based LED formed on a sapphire substrate. The light-output power of the SEVENS-LED is ∼7 mW at a 20 mA junction current, which means 13% external quantum efficiency (EQE). The electrostatic discharge (ESD) test shows excellent ESD characteristics of the SEVENS-LED compared with those of the ITO LE-LED. The reverse ESD amplitude of SEVENS-LED is approximately 200 V, which is two times higher than that (∼100 V) of the ITO LE-LED. These improvements of ESD properties are attributed to the change of the lateral electrode to a vertical electrode, without requiring the transfer of the sapphire substrate to a conducting substrate.

Vertical chip of GaN‐based light‐emitting diode formed on sapphire substrate

AbstractIn order to improve GaN‐based light‐emitting diode (LED) performance, a sapphire‐etched vertical‐electrode nitride semiconductor (SEVENS) LED is fabricated by a chemical wet etching technique. The light‐output power, heat dissipation, and reverse electrostatic discharge (ESD) characteristics of SEVENS‐LED are improved compared to those of the conventional NiAu lateral‐electrode (LE) GaN‐based LED formed on the sapphire substrate. The 20 mA light‐output power and reverse ESD pulse amplitude of SEVENS‐LED are approximately 4.5 mW and 2000 V, respectively. The improved LED performance is attributed to changing a lateral electrode to a vertical electrode although the sapphire substrate is not transferred to a conducting substrate. The device fabrication method will be useful for providing us high‐brightness and high‐power GaN‐based LEDs for future solid‐state general lighting applications. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Compact semiconductor light-emitting diodes for dynamic imaging of neuronal circuitry

We describe the use of compact green light-emitting diodes (LEDs) for fluorescence optical imaging and demonstrate this for dynamic recording from cultured neurons. The efficient gallium-nitride-based LEDs have individual element sizes comparable to typical biological cells and are operated in proximity illumination mode for individual neurons. As periodic arrays, and with direct electrical control of each LED, a spatially periodic multicellular target can be induced to fluoresce in a predesigned spatiotemporal sequence, thereby providing a new approach to dynamic recording of small neural circuits.

Vertical chip of GaN-based blue light-emitting diode

We demonstrate a sapphire-etched vertical-electrode nitride semiconductor (SEVENS) light-emitting diode (LED) fabricated by a selective wet etching between sapphire substrate and GaN-based layers. The SEVENS-LED performance is enhanced compared to a conventional NiAu lateral-electrode (LE) GaN-based LED formed on the same sapphire substrate. The 20-mA light-output power and reverse electrostatic discharge (ESD) pulse amplitude of SEVENS-LED are approximately 4.5 mW and 2000 V, respectively. The variation of peak wavelength with increasing a junction current is less for the SEVENS-LED than for the LE-LED. The improved LED performance is attributed to changing a lateral electrode to a vertical electrode although the sapphire substrate is not transferred to a conducting substrate.

Vertical Electrode GaN-Based Light-Emitting Diode Fabricated by Selective Wet Etching Technique

In order to improve the device performance and productivity, a sapphire-etched vertical-electrode nitride semiconductor (SEVENS) light-emitting diode (LED) is fabricated by a selective wet-etching technique. The sapphire substrate is removed by chemical wet etching and transferred to a conducting Si substrate with a reflector metal. The SEVENS-LED exhibits excellent device performance. Integral light-output power is approximately 3.5 mW at a 20 mA junction current, which indicates a 6.6% external quantum efficiency (EQE). The light-output power was linearly increased with increasing junction current, and the peak wavelength was saturated even with a higher junction current. The enhanced performance of the SEVENS-LED is attributed to changing the lateral electrode to a vertical electrode and transferring a sapphire substrate to a Si receptor with a reflector metal. The SEVENS-LED technique is anticipated to be useful for improving the performance of GaN-based LEDs for future solid-state general illumination applications.

Semiconductor Lamp for Investigation and Control of Photophysiological Processes in Plants

A semiconductor light-emitting diode based lamp with variable spectrum for investigation and control of photophysiologicprocesses in plants under artificial-climate conditions is described. High-power emitters with the peak wavelengths of the spectral powerdistribution functions at 453 nm (the flux density from 0 to 9 μmol/m2s), 640 nm (0 to 150 μmol/m2s), 660 nm (0 to 10 μmol/m2s) and731 nm (0 to 3 μmol/m2s) were used for the spectral ranges, which are responsible for control of the photosynthetic andphotomorphogenetic processes in plants.Results on the influence of variable-spectrum illumination of vegetables (lettuce Grand Rapids, radish Saxa) are presented. Analysisof photosynthetic and photomorphogenetic processes shows that these processes can be controlled by selection of a particular spectralcomposition of the incident light and circadian regime of illumination. Ill. 11, bibl. 4 (in Lithuanian, summaries in Lithuanian, Russianand English).

High-Brightness Light Emitting Diodes Using Dislocation-Free Indium Gallium Nitride/Gallium Nitride Multiquantum-Well Nanorod Arrays

We demonstrate the realization of the high-brightness and high-efficiency light emitting diodes (LEDs) using dislocation-free indium gallium nitride (InGaN)/gallium nitride (GaN) multiquantum-well (MQW) nanorod (NR) arrays by metal organic-hydride vapor phase epitaxy (MO−HVPE). MQW NR arrays (NRAs) on sapphire substrate are buried in spin-on glass (SOG) to isolating individual NRs and to bring p-type NRs in contact with p-type electrodes. The MQW NRA LEDs have similar electrical characteristics to conventional broad area (BA) LEDs. However, due to the lack of dislocations and the large surface areas provided by the sidewalls of NRs, both internal and extraction efficiencies are significantly enhanced. At 20 mA dc current, the MQW NRA LEDs emit about 4.3 times more light than the conventional BA LEDs, even though overall active volume of the MQW NRA LEDs is much smaller than conventional LEDs. Moreover, the fabrication processes involved in producing MQW NRA LEDs are almost the same for conventional BA LEDs. It is, thus, not surprising that the total yield of these MQW NRA LEDs is essentially the same as that of conventional BA LEDs. The present method of utilizing dislocation-free MQW NRA LEDs is applicable to super-bright white LEDs as well as other semiconductor LEDs for improving total external efficiency and brightness of LEDs.

Light-Induced Absorption in Bismuth Titanium Oxide Crystals Illuminated with Narrow-Band Light

Results of investigations into the dynamics of light-induced absorption in bismuth titanium oxide crystals doped with calcium (Bi12TiO20:Ca) illuminated with quasimonochromatic light of semiconductor light-emitting diodes at two wavelengths from the set λ = 870, 660, and 525 nm are presented. Based on an analysis of the experimental data, a model of charge transfer by defect centers describing the observed phenomena is suggested.

Dynamics of the Light-Induced Absorption in a Bi 12 TiO 20 : Ca Crystal

The results of investigations into the dynamics of the light-induced absorption and of its dark relaxation in a Bi12TiO20 : Ca single crystal are presented. To illuminate the crystal and to measure the induced changes in the absorption, narrow-band radiation of an incoherent semiconductor light-emitting diode with the wavelength λ = 660 nm close to that of a helium-neon laser was used. The material parameters of the crystal are estimated based on a comparison of the experimental data with the results of calculations for a theoretical model that takes into consideration doubly ionized donor centers and shallow traps.

Enhanced coupling to vertical radiation using a two-dimensional photonic crystal in a semiconductor light-emitting diode

Enhanced coupling to vertical radiation is obtained from a light-emitting diode using a two-dimensional photonic crystal that lies entirely inside the upper cladding layer of an asymmetric quantum well structure. A sixfold enhancement in light extraction in the vertical direction is obtained without the photonic crystal penetrating the active material. The photonic crystal is also used to couple pump light at normal incidence into the structure, providing strong optical excitation.

Spontaneous emission model of lateral light extraction from heterostructure light-emitting diodes

We investigate the extraction of light from semiconductor light-emitting diodes made of dielectric multilayer stacks with quantum-well sources. The model is a combination of a rigorous vertical model of dipole emission and an in-plane ray-tracing model. The vertical model is shown to conveniently provide the relevant horizontal decay length of the various kinds of in-plane propagating modes. The proposed combination of the two models accounts for the lateral extraction as well as light recycling in the active layers.

Polycrystalline nitride semiconductor light-emitting diodes fabricated on quartz substrates

We demonstrate the feasibility of polycrystalline nitride semiconductor light-emitting diodes (LEDs). Here, polycrystalline LEDs were deposited on quartz substrates, incorporating a layer structure identical to that used for epitaxially grown LEDs. The deposition exhibits a tendency to produce c-oriented crystallites. Violet-blue (430 nm) operation of a polycrystalline LED is demonstrated, with spectral width of 38 nm, and emission efficiency approximately two orders of magnitude lower than for single-crystal LEDs. These LEDs could potentially be incorporated in large-area displays, since the deposition of polycrystalline materials avoids single-crystal substrates required for conventional nitride semiconductor light emitters.

Decoding the TV remote control

Digital infrared pulses are generated by a semiconductor light-emitting diode in the remote control devices used with consumer electronics. The pulse string is detected and analyzed using a silicon solar cell as a receiver and educational data taking and analyzing computer programs.

Growth, Spectroscopy, and Laser Application of Self-Ordered III-V Quantum Dots

The development and application of semiconductor light-emitting and laser diodes has been a huge success during the last 30 years in key areas of modern technology like communications, recording, and printing. Still there is ample room for improvement through combination of the atomlike properties for zero-dimensionally localized carriers in quantum dots (QDs) with state-of-the-art semiconductor-laser technology. Low, temperature-insensitive threshold current; high gain; and differential gain have been predicted since the early 1980s.In the past two decades, the fabrication of QDs has been attempted using colloidal techniques (see the article by Nozik and Mićić in this issue), patterning, etching, and layer fluctuations (see the article by Gammon in this issue). However a break-through occurred recently through the employment of self-ordering mechanisms during epitaxy of lattice-mismatched materials (see the next section) for the creation of high-density arrays of QDs that exhibit excellent optical properties, particularly high quantum efficiency, up to room temperature. The zero-dimensional carrier confinement and subsequent atomlike electronic properties have a drastic impact on optical properties (see the section on Spectroscopy). Also intimately connected is the applicability of QDs as a novel gain medium in state-of-the-art laser diodes with superior properties (see the section on Lasers).

Hybrid organic–inorganic semiconductor-based light-emitting diodes

We demonstrate that the ability of GaN-based light-emitting diodes to emit in the short-wavelength regime makes possible “hybrid” organic–inorganic semiconductor light-emitting diodes that consist of two parts: a GaN-based electroluminescent part and an organic thin-film-based fluorescent part that absorbs the electroluminescence and fluoresces at a longer wavelength resulting in color conversion. We also show that organic films with much improved surface smoothness may be obtained by deposition at reduced temperatures.

Theory of noise in p-n junction light emitters

The intensity noise of light generated by semiconductor lasers and light-emitting diodes is treated by semiclassical Langevin equations. An independent equation for the junction voltage dynamics is considered, and the non-Markoffian nature of the pump current is decomposed into Markoffian carrier injection and a regulation mechanism due to charging effect at the junction. The intensity noise power spectrum and squeezing bandwidth predicted by these equations agree well with recent experimental results. External current noise generated as a result of the internal noise process and subsequent relaxation process is calculated. Also, correlations between the carrier-number fluctuation and the junction-voltage fluctuation, and between the emitted photon flux fluctuation and the junction-voltage fluctuation are studied in detail.

A luminescence mapping technique for rapid evaluation of visible-light-emitting materials used in semiconductor light-emitting diodes

A technique for the rapid evaluation of the optical performance of wafers grown for fabricating visible-light-emitting diodes (LEDs) is presented. The technique is simple, non-destructive and can be used to qualify wafers prior to the relatively expensive device-processing stage. The technique resolves the problem resulting from the lack of correlation between photoluminescence measurements on as-grown materials and electroluminescence on the final structures. The lack of such correlation has been a pertinent problem for the material growth industry. The materials used for this investigation are those grown specifically for the fabrication of high-performance LEDs.

Uncooled 4.2 μm light emitting diodes based on InAs 0.91Sb 0.09/GaSb grown by LPE

The report describes the epitaxial growth and fabrication of efficient room temperature InAs 0.91Sb 0.09 semiconductor light-emitting diodes operating in the infrared wavelength region at 4.2 μm. These devices have attracted much recent interest as viable infrared light sources for use in carbon dioxide detection. A study of the LPE growth of lattice matched InAs 1− x Sb x onto GaSb substrates from Sb-solution by the supercooled growth method is described. The electrical transport properties and photoluminescence are presented. The n-i-p-InAs 0.91b 0.09/P-GaSb light emitting diodes (LEDs) are studied and the quantum efficiency is discussed.