Equivalent-Circuit Analysis for the Electroluminescence-Efficiency Problem of InGaN/GaN Light-Emitting Diodes (original) (raw)
Related papers
2014
Electroluminescence (EL) characterization of InGaN/GaN light-emitting diodes (LEDs), coupled with numerical device models of different sophistication, is routinely adopted not only to establish correlations between device efficiency and structural features, but also to make inferences about the loss mechanisms responsible for LED efficiency droop at high driving currents. The limits of this investigative approach are discussed here in a case study based on a comprehensive set of currentand temperature-dependent EL data from blue LEDs with low and high densities of threading dislocations (TDs). First, the effects limiting the applicability of simpler (closed-form and/or one-dimensional) classes of models are addressed, like lateral current crowding, vertical carrier distribution nonuniformity, and interband transition broadening. Then, the major sources of uncertainty affecting state-ofthe-art numerical device simulation are reviewed and discussed, including (i) the approximations in the transport description through the multi-quantum-well active region, (ii) the alternative valence band parametrizations proposed to calculate the spontaneous emission rate, (iii) the difficulties in defining the Auger coefficients due to inadequacies in the microscopic quantum well description and the possible presence of extra, non-Auger high-current-density recombination mechanisms and/or Auger-induced leakage. In the case of the present LED structures, the application of three-dimensional numerical-simulation-based analysis to the EL data leads to an explanation of efficiency droop in terms of TD-related and Auger-like nonradiative losses, with a C coefficient in the 10 −30 cm 6 /s range at room temperature, close to the larger theoretical calculations reported so far. However, a study of the combined effects of structural and model uncertainties suggests that the C values thus determined could be overestimated by about an order of magnitude. This preliminary attempt at uncertainty quantification confirms, beyond the present case, the need for an improved description of carrier transport and microscopic radiative and nonradiative recombination mechanisms in device-level LED
Semiconductors, 2011
A comprehensive study of blue light emitting diodes based on quantum well InGaN/GaN struc tures with external quantum efficiencies η of up to 40% has been carried out. It is shown that, in the general case, the manner in which the efficiency depends on the current density j is determined by the competition of contributions to the radiative recombination of localized and delocalized carriers. The contribution of the latter grows with worsening structural organization of the nanomaterial, increasing temperature and drive current, and decreasing width of the depleted layer in the active region (under zero bias). The steepest effi ciency droop relative to the maximum value (by up to a factor of 2 at j ≈ 50 A cm-2) is observed in the case of heavy doping of the n + region (to 10 19 cm-3) and upon appearance of compensated layers in the active or p + region. At j > 50 A cm-2 , the contribution of delocalized carriers is predominant and the current dependences of efficiency are of uniform type, approximated with η(j) ∝ j-b , where 0.2 < b < 0.3.
Temperature-dependent light-emitting characteristics of InGaN/GaN diodes
Microelectronics Reliability, 2009
Temperature-dependent light-emitting and current-voltage characteristics of multiple-quantum well (MQW) InGaN/GaN blue LEDs were measured for temperature ranging from 100 to 500 K. The measurement results revealed two kinds of defects that have pronounced impact on the electroluminescent (EL) intensity and device reliability of the LEDs. At low-temperature (<150 K), in addition to the carrier freezing effect, shallow defects such as nitrogen vacancies or oxygen in nitrogen sites can trap the injected carriers and reduces the EL intensity. At high temperature (>300 K), deep traps due to the structure dislocations at the interfaces significantly reduce the efficiency for radiative recombination though they can enhance both forward and reverse currents significantly. In addition, the significant enhancement of trap-assisted tunneling current causes a large heat dissipation and results in a large redshift of the emission peak at high temperature.
Two channels of non-radiative recombination in InGaN/GaN LEDs
Physica B: Condensed Matter, 2009
The results of low-frequency noise study in blue InGaN/GaN light emitting diodes (LEDs) allow to suppose that there are two non-radiative recombination channels in InGaN/GaN LEDs: one of them is related to the extended defect system piercing the LED active region and other is related with the presence of point defects. The generation of new defects under current density more than 10 A/cm 2 was found. This process is reversible up to operation current density of about 200 A/cm 2 .
The Electrical Characteristics Model of GaN/InGaN/GaN Heterostructure in InGaN-based LED
2012
The calculation model of tunneling current through GaN/InGaN/GaN heterostructure in InGaN-based LED using the transfer matrix method employed to verify the result of calculation of tunneling current implemented analytically. The analytical method applied through solving theoretically the Schrödinger equation, whereas, the transfer matrix method divided the solution area into a less size of N segment compared to the observed potential width size, where the potential energy of each segment was assumed constant. Verification employed to the thickness of depletion region and bias voltage variations. The obtained result has shown that the analytical result of calculation simmilar with the calculation result using transfer matrix method. The calculation model was then extended to calculate the tunneling current for different temperature.
Impact of ballistic electron transport on efficiency of InGaN based LEDs
2011
Heterojunction light-emitting diodes (LEDs) based on the InGaN/GaN system have improved considerably but still suffer from efficiency degradation at high injection levels which unless overcome would aggravate LED lighting. Although Auger recombination has been proposed as the genesis of the efficiency degradation, it appears that the premise of electron overflow and non-uniform distribution of carriers in the active region being the immediate impediment is gaining popularity. The lack of temperature sensitivity and sizeable impact of the barrier height provided by an electron blocking layer and the electron cooling layer prior to electron injection into the active region suggest that the new concept of hot electrons and ballistic/quasi-ballistic transport be invoked to account for the electron overflow. The electron overflow siphons off the electrons before they can participate in the recombination process. If the electrons are made to remain in the active region e.g. by cooling them prior to injection and/or blocking the overflow by an electron blocking layer, they would have to either recombine, radiatively or nonradiatively (e.g. Shockley-Read-Hall and Auger), or accumulate in the active region. The essence of the proposed overflow model is in good agreement with the experimental electroluminescence data obtained for m-plane and c-plane LEDs with/without electron blocking layers and with/without staircase electron injectors.
Efficiency and efficiency retention in InGaN LEDs has recently received considerable attention. In this realm, we investigated internal quantum efficiency (IQE) and relative external quantum efficiency (EQE) of c-plane InGaN LEDs designed for emission at $420 nm from the active region which contains multiple quantum wells (MQWs) of different barrier height (either In 0.01 Ga 0.99 N or In 0.06 Ga 0.94 N barriers) and thickness (3 and 12 nm) as well as a 9-nm double heterostructure (DH). Pulsed electroluminescence (EL) and laser excitation powerdependent measurements indicated that both the relative EQE and the IQE were enhanced due to the incorporated two-layer InGaN stair-case electron injector (SEI) with indium mole fraction steps of 4 and 8% as compared to the conventional AlGaN electron blocking layer (EBL). Furthermore, the lowered In 0.06 Ga 0.94 N interwell barriers (LB) instead of the traditional In 0.01 Ga 0.99 N barriers improved the EQE and the IQE of MQW LEDs. Specifically, the MQW LEDs with the 6period 2-nm In 0.2 Ga 0.8 N quantum well and 3-nm In 0.06 Ga 0.94 N barrier structure showed 6% higher IQE at an injected carrier density of 6 Â 10 18 cm À3 and 35% higher EQE as compared to that of the same structure with a higher In 0.01 Ga 0.99 N barrier. The DH LEDs showed 30% higher EQEs compared to MQW LEDs, albeit at a relatively higher injection current density of 150 A/cm 2 . The relatively low EQE in the DH LEDs at low injection levels is attributed to spatial separation of electrons and holes due to confinement in the interfacial triangular well and thus the associated decrease in radiative efficiency and possible increase in nonradiative recombination due to degradation of material quality with increasing InGaN layer thickness.
Effect of p-GaN Layer and High-k Material in InGaN/GaN LED for Optical Performance Enhancement
Research Square (Research Square), 2023
The p-GaN layer adjacent to the quantum well is proposed for InGaN/GaN Light Emitting Diode (LED), it enhances the output optical power and internal quantum e ciency. The physical simulator Technology Computer-Aided Design (TCAD) is used to analyze the performance of the proposed LED. In the simulation, physics-based models are used to obtain optical properties such as luminous power and recombination rate. The suggested InGaN/GaN LED outperformed conventional LEDs in terms of internal quantum e ciency and luminous power. At the injection current of 700 mA, the output luminous power and internal quantum e ciency in the proposed LED are improved by 24% and 18%, respectively. Furthermore, the suggested InGaN/GaN LED has a smaller Auger recombination than conventional LEDs. Thus, the proposed p-GaN layer technique in GaN LED is a promising one for future solid-state lighting applications due to its high internal quantum e ciency of 90% at 100 mA injection current.
IEEE Photonics Technology Letters, 2000
Temperature dependence of electroluminescence (EL) efficiency in blue InGaN-GaN multiple-quantum-well (MQW) light-emitting diodes (LEDs) with different well widths is systematically investigated. The EL efficiency at 300 K shows a maximum at the input current of 4, 10, and 60 mA for the LEDs with 1.5-, 2.0-, and 2.5-nm QWs, respectively. Nevertheless, the droop behavior at 80 K is mainly dominated by the low hole mobility and near independence on the QW thickness. According to the simulation results, it is found that the distinct efficiency droop behavior for the LEDs with different well widths at high and low temperature is strongly dependent on the effects of electron overflow and nonuniform hole distribution within the MQW region.