GaP Light-emitting Diodes Research Articles

Властивості вихідних та опромінених фосфідо-галієвих світлодіодів

Spectral features of the original and irradiated with electrons with E = 2 MeV GaP light emitting diodes (LEDs) were studied. Recombination lines of the exciton bound on the N isoelectronic center and on the pair complexes NN1 were detected. The change in the spectral composition of radiation when passing through a section of negative differential resistance is analyzed. Dose dependences of luminescence intensity were obtained for green GaP(N) and red GaP(Zn-O) LEDs. The maximum critical radiation dose was established, after which the LEDs lost their characteristic exciton emission mechanism. The results of the annealing of irradiated LEDs are given.

Control of LED Emission with Functional Dielectric Metasurfaces

AbstractThe improvement of light‐emitting diodes (LEDs) is one of the major goals of optoelectronics and photonics research. LED integration to complex photonic devices requires precise control of the wavefront of the emitted light. Metasurfaces are spatial arrangements of engineered scatters that may enable this light manipulation capability with unprecedented resolution. Most of these devices, however, are only able to function properly under irradiation of laser light with a large spatial coherence. LEDs, on the other hand, have angularly broad, Lambertian‐like emission patterns characterized by a low spatial coherence, which makes the integration of metasurface devices on LEDs challenging. A novel concept for metasurface integration on LED is proposed, using a cavity to increase the LED spatial coherence through an angular collimation. The experimental demonstration of the proposed concept is implemented on a GaP LED architecture including a hybrid metallic‐Bragg cavity. By integrating a silicon metasurface on top, two different functionalities of these compact devices are demonstrated: directional LED emission at a desired angle and LED emission of a vortex beam with an orbital angular momentum. The presented concept is general, being applicable to other incoherent light sources and enabling metasurfaces designed for plane waves to work with incoherent light emitters.

A study of deep centers in microplasma channels in GaP light-emitting diodes with green-emission spectrum

The statistical delay of microplasma breakdown in GaP light-emitting diodes with the green-emission spectrum is studied. The unusual profound effect of deep centers on the statistical delay of avalanche breakdown is observed in the temperature range of 300–380 K; this effect is caused by a variation in the charge state of these centers due to a reduction in the reverse bias applied to the p–n junction. Four deep levels are revealed and their parameters are determined.

Low doses effect in GaP light-emitting diodes

Low doses effect in GaP light-emitting diodes

EXCITON RADIATION PECULIARITIES OF RED GALLIUM-PHOSPHIDE LEDS

Electroluminescence spectra of red GaP light-emitting diodes were investigated. Besides the main emission line hν = 1.845 eV, it was detected the additional short-wave component hν = 2.206 eV the existence of which is connected with donor-acceptor transitions between Zn-Sn pairs. It was observed intensity increase of this line at low currents (I 90 mA) due to the thermal effect. The nature of the spectral lines anomalous broadening was discussed.

Degradation of electrooptical characteristics of serial GaP light-emitting diodes, caused by fast electrons

Degradation of electrooptical characteristics of serial GaP light-emitting diodes, caused by fast electrons

Optimization of dressed-photon–phonon-assisted annealing for fabricating GaP light-emitting diodes

Using the two-level two-state model, we analyzed the characteristics of enhanced electroluminescence intensity from a GaP LED fabricated by dressed-photon–phonon-assisted annealing. In this model, we utilized the fact that the adiabatic potential barrier of the electronic excited level in configuration space is lower than that of the ground level. It was confirmed by experiments that, in an actual excited level, the barrier was reduced to 0.48 eV. From this finding, it was shown that the spatial distribution of Zn atoms can be changed by means of current injection and light irradiation even at room temperature. In addition, we showed that a structure that is suitable for light emission via DPPs is formed by means of a transition between a low-barrier excited level and a high-barrier ground level, due to stimulated emission. Also, regarding the optimized conditions for maximizing the effect of DPP-assisted annealing, it was found that the optimum ratio of the number of injected electrons to the number of irradiated photons is close to 1, and this was confirmed experimentally.

Systematic Root Cause Analysis for GaP Green Light LED Degradation

High-brightness light-emitting diodes (LEDs) are now commonly employed in many applications. In order to ensure long-term applications with insignificant degradation, the root cause analysis of their degradation is important. While failure analysis of failed LEDs can usually be traced with observable defects, the defects that cause LEDs to degrade are generally less obvious. In this paper, we present a systematic method to identify the root cause of green GaP LED degradation. The various steps in the procedure from nondestructive to destructive analysis are described, and the root cause is found to be the excessive doping of zinc in the p-layer.

Thermal characterization of light‐emitting diodes in the frequency domain

AbstractWe report on a method for measurement of thermal relaxation time constants within light‐emitting diodes (LEDs) using harmonic modulation of the driving current. The method is based on the phase shift of the forward voltage waveform in respect to that of the modulated current. The phase shift is due to the sensitivity of the forward voltage to junction temperature, which responds to the modulation of the heat generation depending on the thermal relaxation rate. The frequency dependence of the phase shift was shown to exhibit characteristic dips at angular frequencies equal to inverse thermal time constants. Such an approach for thermal characterization was demonstrated for common GaP, AlGaAs, AlInGaP, and InGaN LEDs. In particular, low‐power p‐n and double‐heterostructure LEDs as well as high‐power truncated‐inverted‐pyramid and flip‐chip LEDs were investigated. The measured thermal time constants (∼ 0.1–100 ms) were tentatively assigned to heat flows within the multilayer structure of the LEDs and collated with the numerical estimates based on thermal resistance and heat capacitance of the LED components. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical properties and efficiency of GaNP light emitting diodes

Ga N P ∕ Ga P is promising for yellow-amber-red light emitting diodes (LEDs). In this study, pressure and temperature dependent electroluminescence and photocurrent measurements on bulk GaP∕GaN0.006P0.994∕GaP LED structures are presented. Below ∼110K, emission is observed from several localized nitrogen states. At room temperature, the band-edge energy increases weakly with pressure at a rate of +1.6meV∕kbar, substantially lower than the Γ band gap of GaP (+9.5meV∕kbar). Thus, despite the multiplicity of nitrogen levels, the band anticrossing model reasonably describes this system based on an average of the nitrogen states. Furthermore, carrier leakage into the X minima of GaP reduces the efficiency in GaNP-LEDs with increasing pressure.

Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells

Features of current-voltage characteristics inherent to GaP light-emitting diodes with quantum wells

An investigation on the influence of electromagnetic interference induced in conducting wire of universal LEDs

Electromagnetic Interference (EMI) has a detrimental effect upon the performance of Optical-Fiber Communication (OFC) systems. The present study considers the case where EMI is induced in a conducting wire (CW), and derives equations to establish the influence of the induced EMI on GaP and GaAsP Light-Emitting Diodes (LEDs). These equations are then verified experimentally. The results indicate that the degree of influence of the EMI upon both LED devices depends upon the interference power, the interference frequency, the induced power, the input resistance of the device, the inverse saturation current, and the ideal factor of the LED. Moreover, it is found that the induced interference current increases with an increasing interference frequency and that the EMI has a greater influence on devices with a lower input impedance. The theoretical results are found to be in good agreement with the experimental data.

Deep-level recombination spectroscopy in GaP light-emitting diodes

Deep-level parameters determined from an analysis of the differential coefficients of the forward-bias current-voltage curves are compared in the example of commercial GaP LEDs. It is shown that these parameters are suitable for deep-center diagnostics. The proposed measurements can be performed on semiconductor wafers in the industrial environment without sealing or dividing into individual crystals.

Determination of the parameters of deep levels using the differential coefficients of the current-voltage characteristics

Deep levels were determined in GaP light-emitting diodes using the differential coefficients of the current-voltage characteristics. The parameters determined by different methods showed agreement. The measurement conditions are such that the measurements can be made using wafers, which makes the proposed methods extremely promising.

Blue-Green Light-Emitting Diodes and Violet Laser Diodes

Short-wavelength-emitting devices, such as blue laser diodes (LDs) and light-emitting diodes (LEDs), are currently sought for a number of applications, including full-color electroluminescent displays, laser printers, read-write laser sources for high-density information storage on magnetic and optical media, and sources for undersea optical communications. For these purposes, II–VI materials such as ZnSe and SiC, and III–V-nitride semiconductors such as GaN have been investigated intensively for a long time. However it was impossible to obtain high-brightness (over 1 cd) blue LEDs and reliable LDs. Much progress has been achieved recently on green LEDs and LDs using II–VI-based materials. The short lifetimes prevent II–VI-based devices from commercialization at present. The short lifetime of these II-VI-based devices may be caused by the crystal defects at a density of 103/cm2 because one crystal defect would cause the propagation of other defects leading to failure of the devices. Another wide-bandgap material for blue LEDs is SiC. The brightness of SiC blue LEDs is only between 10 mcd and 20 mcd because of the indirect bandgap of this material.On green LEDs, the external quantum efficiency of conventional, green GaP LEDs is only 0.1% due to the indirect bandgap of this material. The peak wavelength is 555 nm (yellowish green). As another material for green emission devices, AlInGaP has been used. The present performance of green AlInGaP LEDs is an emission wavelength of 570 nm (yellowish green) and maximum external quantum efficiency of 1%.

InGaN Light-Emitting Diodes with Quantum-Well Structures

ABSTRACTInGaN single-quantum-well-structure (SQW) light-emitting diodes (LEDs) with an emission wavelength between violet and orange were fabricated. The maximum on-axis luminous intensity of green LEDs was 12 cd and the external quantum efficiency was as high as 6.3 % at a forward current of 20 mA, while those of blue LEDs were 2 cd and 9.1 %, respectively. The peak wavelength and the full width at half-maximum of the green LEDs were 520 nm and 30 nm, respectively, while those of blue LEDs were 450 nm and 20 nm, respectively. The color of green InGaN SQW LEDs was greener than those of conventional GaP and AlInGaP LEDs.

Electroluminescence from Er-doped GaP

The electroluminescent properties of the Er-doped GaP light-emitting diodes prepared by metalorganic vapor phase epitaxy and diffusion were investigated. Strong characteristic Er3+ intra-4f-shell emission at 0.80 eV is observed over the temperature range of 12–300 K. The electroluminescence intensity is only weakly temperature dependent, decreasing less than 40% as the temperature increases from 20 to 300 K.

Controversy regarding the 0.85-eV deep hole level in GaP

Thermal emission rate data have been obtained on a 0.85-eV deep hole level in liquid-phase-epitaxial GaP light-emitting diodes using dark capacitance transients. Published emission rate data on this level exist for vapor-phase-epitaxial GaP. Detailed comparison with available data reveals a wide spread in emission rates casting serious doubts on the hitherto presumed origin of this level.

High-speed photoconductivity of GaP light-emitting diodes at liquid-nitrogen temperature

In GaP : N (Zn,Te) light-emitting diodes, extrinsic photoconductivity was excited by modelocked TEA CO 2 laser pulses at liquid-nitrogen temperature, showing a current sensitivity of 2.10 −5 A/W and a response time of the order of 0.5 ns.

High-speed photoconductivity and infrared to visible up-conversion in GaP light-emitting diodes

In GaP:N (Zn,Te) light-emitting diodes extrinsic photoconductivity and infrared to visible up-conversion have been investigated by short laser pulses at 10-μm wavelength. A time constant of the order of 1 ns was observed indicating that free infrared excited hole to bound donor recombination yields the fast response.