Region Of Light-emitting Diodes Research Articles

Research on Degradation of GaN-Based Blue LED Caused by γ Radiation under Low Bias

GaN multiquantum-well blue light-emitting diodes (LEDs) were radiated with 60Co γ-rays for accumulated doses up to 2.5 Mrad (SiO2). The radiation-induced current and 1/f noise degradations were studied when the devices operate at the low bias voltage. The current increased by 2.31 times, and the 1/f noise increased by 275.69 times after a dose of 2.5 Mrad (SiO2). Based on Hurkx’s trap-assisted tunneling model, the degradation of current was explained. γ radiation created defects in the space-charge region of LEDs. These defects as generation-recombination centers lead to the increase in the current. In addition, based on the quantum l/f noise theory, the degradation of 1/f noise might be also attributed to these defects, which caused an increase in the Hooge constant and a decrease in the carrier lifetimes. The current and 1/f noise degradations can be attributed to the same physical origin. Compared to the current, the 1/f noise parameter is more sensitive, so it may be used to evaluate the radiation resistance capability of GaN blue LEDs.

Low-frequency generation-recombination noise behaviors of blue/violet-light-emitting diode

During the past two decades, GaN-based light-emitting diode has been used as a high-quality light-source. Low-frequency noise as a diagnostic tool for quality control and reliability estimation has been widely accepted and used for semiconductor devices. Understanding the origin of efficiency-droop effect is key to developing the ultimate solid-state light source. Various mechanisms that may cause this effect have been suggested, including carriers’ escape, loses due to dislocations, and the Auger effect. In this study, we investigate the low-frequency noise behaviors of GaN-based blue light-emitting diode with InGaN/GaN multiple quantum wells. The measured currents range from 0.1 mA to 180 mA. According to the characteristics of power spectral density of current noise and the generation-combination mechanism between electrons and holes in the active region of light-emitting diode (LED), we adopt the well-known model of low-frequency noise to fit the relationship between power spectral density of current and frequency, and find that there exists a transition between generation-combination and 1/<i>f</i> noise when the light-emitting diode begins to work. In other words, it can be derived that the low-frequency noise behaviors are dominated by generation-combination noise when the currents are between 0.1 mA and 27 mA; with the current gradually increasing, the origin source of low-frequency noise in blue/violet-light LED will transit to the 1/<i>f</i> noise. Through the analysis of the transport and recombination mechanism of the carriers, and combination with the model of low-frequency noise, we analyze the corner frequency of the generation-recombination noise. The results of this paper provide an effective tool and method to study the conversion of light-emitting diodes.

The effect of the transformation of point defects under Joule heating on efficiency of LEDs with InGaN/GaN quantum wells

It is shown that a short-time Joule heating of the active region of light-emitting diodes with InGaN/GaN quantum wells up to 125°C at a current density of 150 A/cm2 stimulates changes in the energy spectrum of defect states in the energy gap of GaN and leads to an increase in the quantum efficiency.

Localized states in the active region of blue LEDs related to a system of extended defects

Blue light-emitting diodes (LEDs) based on InGaN/GaN quantum wells (QWs) with different characters of the system of extended defects (SEDs) threading through the active region have been studied using the current-voltage (I–U), capacitance-voltage (C–V), and deep-level transient spectroscopy (DLTS) measurements in the dark and under illumination with white light in a temperature range from 100 to 450 K. The DLTS curves exhibit broad E1 and E2 peaks with amplitudes dependent on the illumination. This behavior can be explained assuming the presence of localized states related to SEDs in the active region of the LED. The LEDs with more developed SEDs are characterized by a greater concentration of donor-type traps, which leads to an increase in the density of free charge carriers in QWs, which screen the electron-hole interaction. This circumstance can be among the factors responsible for a severalfold decrease in the quantum efficiency of such LEDs.

Light-emitting diodes based on Ga1−x InxAsySb1−y solid solutions grown from lead-containing melts

Light-emitting diodes (LEDs) with the maximum emission at λ=2.3 and 2.44 μm are obtained and characterized. The active region of LEDs is based on Ga1−xInxAsySb1−y solid solutions (x=0.21 and 0.25, respectively) grown by liquid phase epitaxy from lead-containing melts. The room-temperature external quantum yield of the 2.3 and 2.44 μm LEDs is 1.6 and 0.11%, respectively.

MBE of InGaN/GaN heterostructures using ammonia as a source of nitrogen

InGaN/GaN heterostructures have been grown by molecular beam epitaxy (MBE) using ammonia as a source of nitrogen. The influence of the growth temperature and rate on the incorporation of indium into the epitaxial layers and the position of the corresponding photoluminescence peak has been studied. Based on these data, optimum growth conditions have been selected for the ammonia MBE of InGaN layers in the active region of light-emitting diodes operating in the blue/violet spectral range.

Electroluminescence in vertically aligned quantum dot multilayer light-emitting diodes fabricating by growth-induced islanding

A molecular beam epitaxy (MBE) growth-induced islanding process has been used to form self-organized multiple quantum dot layers, in which quantum dots from different layers are vertically aligned in columns and are electronically coupled. These structures are used as the active region in light-emitting diodes operating at room temperature. Light-emitting diodes are investigated using quantum dot columns containing single, 5 and 10 InAs quantum dots. These diodes emit light over a broad band with typical spectral linewidths of 120 nm, peaked between 1000 and 1100 nm. In addition to the quantum dot spectral feature, a spectral feature from a thin quantum well region, integral to the quantum dot formation process, is seen in the single quantum dot diode, but is eliminated in diodes with active regions containing columns of multiple quantum dots.