Конструкции блокирующих слоев для подавления паразитной рекомбинации в мощных диодных лазерах с GaAs волноводом

Using numerical simulation, a search is carried out for designs of asymmetric barrier layers (ABLs) for a laser diode having GaAs waveguide and emitting at the wavelength λ = 980 nm. A pair of ABLs, adjoining the active region on both sides, blocks undesired charge carrier flows and suppresses parasitic spontaneous recombination in the waveguide layers. Optimal designs of ABLs based on AlGaAsSb and GaInP for blocking electrons and holes, respectively, are proposed that make it possible to reduce the parasitic recombination current down to less than 1% of the initial value. To suppress electron transport, an alternative structure based on three identical AlInAs barriers is also proposed. The GaAsP spacers separating these barriers from each other have different thicknesses. Due to this, its own set of quasi-bound (resonant) states is formed in each spacer that is different from the neighbor spacer set of states. As a result of this, the resonant tunneling channels are blocked: the parasitic electron flow is reduced by several tens of times in comparison with the case of spacers of equal thickness.

23% power conversion efficiency light-emitting diodes using monolayer quantum dots

Ever since the first proposal of using colloidal quantum dots (QDs) as the active emitting layer of light-emitting diode (LED), a monolayer of QD is considered as a better option than the multilayer ones. Owing to the slow charge transport rate among different QD layers, quantum dot light-emitting diodes (QLEDs) adopting multilayer QDs need to be driven at higher than the bandgap bias voltage to achieve practically useful brightness, resulting in increased power consumptions and heat generations, and reduced device lifetimes. Unfortunately, QLEDs using monolayer QDs always suffer from unwanted recombination in hole transport layers (HTLs) and low external quantum efficiencies (EQEs) as a result of electron overflow from QDs into HTLs. Herein, we tackle this dilemma by packing QDs with large size into monolayers, which enables us to mitigate the unwanted electron overflow and retain high EQE. More importantly, it further allows us to boost the irradiative recombination current at bandgap voltage. By virtue of simultaneously obtained high EQE and irradiative recombination rate, we can achieve brightness of 1,100 cd m-2 and 3,000 cd m-2 at 100% and 105% bandgap voltages with record high power conversion efficiencies (PCEs) of 23% and 22%, respectively. Since heat generation has been depressed and devices can be operated at reduced bias voltage, they show unprecedented T95 operation lifetimes (the time for the luminance to decrease to 95% of the initial value) of more than 4,000 h with an initial brightness of 3,000 cd m-2, and equivalent T95 lifetimes of more than 20,000 h at 1,000 cd m-2.

A review of high ideality factor in gallium nitride-based light-emitting diode

Theory concerning the high ideality factor of gallium nitride (GaN) based light- emitting diode (LED) has been reviewed. The presence of a high ideality factor indicates a large forward voltage that results in efficiency reduction. The paper suggests that tunneling is the main reason defining the exponential behaviour of current-voltage measurements, which leads to a high ideality factor. However, there is also a paper that suggests that the design of current geometry in the LED chip defines the value of ideality factor. An effective current spreading geometry in the LED chip will minimize the ideality factor and make it fall between the ideal range of 1 to 2. Besides, how the ideality factor is calculated will also play a major role in defining its value. By calculating the ideality factor based solely on the radiative recombination current formula, the value of ideality factor can result in an ideal ideality factor of 1.08.

The Study of Deep Level Traps and Their Influence on Current Characteristics of InP/InGaAs Heterostructures

The damage mechanism of proton irradiation in InP/InGaAs heterostructures was studied. The deep level traps were investigated in detail by deep level transient spectroscopy (DLTS), capacitance–voltage (C–V) measurements and SRIM (the stopping and range of ions in matter, Monte Carlo code) simulation for non-irradiated and 3 MeV proton-irradiated samples at a fluence of 5 × 1012 p/cm2. Compared with non-irradiated samples, a new electron trap at EC-0.37 eV was measured by DLTS in post-irradiated samples and was found to be closer to the center of the forbidden band. The trap concentration in bulk, the interface trap charge density and the electron capture cross-section were 4 × 1015 cm−3, 1.8 × 1012 cm−2, and 9.61 × 10−15 cm2, respectively. The deep level trap, acting as a recombination center, resulted in a large recombination current at a lower forward bias and made the forward current increase in InP/InGaAs heterostructures for post-irradiated samples. When the deep level trap parameters were added into the technology computer-aided design (TCAD) simulation tool, the simulation results matched the current–voltage measurements data well, which verifies the validity of the damage mechanism of proton irradiation.