Pivotal role of ballistic and quasi-ballistic electrons on LED efficiency

Ni, X.; Li, X.; Lee, J.; Liu, S.; Avrutin, Vitaliy; Matulionis, A.; Özgür, Ü.; Morkoç̌, H.

doi:10.1016/j.spmi.2010.05.009

Cited by 37 publications

(26 citation statements)

References 50 publications

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“…Баллистический перенос характеризуется временем релаксации носителей заряда; наиболее вероятным ме-ханизмом рассеяния энергии в GaN является взаимодей-ствие с оптическими фононами [23]. При упругом рассе-янии время релаксации, как и длина свободного пробега электронов, увеличивается при снижении температу-ры [30], что должно приводить к росту баллистической утечки.…”

Section: низкотемпературные потериunclassified

“…Кроме того, рассматривались возможные причины инверсии температурной зависимости КВ для высокой плотности тока, связанные с изменением коэффициента B при сни-жении T вследствие изменения плотности состояний в валентной зоне [20]. Также стоит отметить, что рост КВ при снижении T может наблюдаться в случае эффектов разогрева светодиода или стягивания тока [20,23], если некорректно выбраны условия измерений или конструк-ция экспериментальных образцов. Полный анализ воз-можных причин инверсии температурной зависимости КВ необходимо проводить с учетом конкретных условий эксперимента и структуры образцов.…”

Section: Introductionunclassified

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Влияние баллистической утечки на температурную зависимость квантового выхода светодиодов на основе множественных квантовых ям InGaN/GaN

Prudaev¹,

Kop’ev²,

Romanov³

et al. 2017

Физика И Техника Полупроводников

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В работе исследованы зависимости квантового выхода от температуры и уровня возбуждения для светодиодов на основе множественных квантовых ям InGaN/GaN. Эксперимент проводился для двух режимов возбуждения люминесценции. Сравнение результатов, полученных при фото- и электролюминесценции, показало, что в области высокой плотности тока наблюдаются дополнительные низкотемпературные потери (дополнительные к потерям, связанным с оже-рекомбинацией). Это обусловливает инверсию температурной зависимости квантового выхода при температурах меньше 220-300 K. В результате анализа установлено, что потери связаны с утечкой электронов из активной области светодиода. Для объяснения экспериментальных данных привлечена модель баллистической утечки. Результаты моделирования качественно согласуются с экспериментальными зависимостями квантового выхода от температуры и плотности тока. DOI: 10.21883/FTP.2017.02.44112.8251

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Section: низкотемпературные потериunclassified

Section: Introductionunclassified

Влияние баллистической утечки на температурную зависимость квантового выхода светодиодов на основе множественных квантовых ям InGaN/GaN

Prudaev¹,

Kop’ev²,

Romanov³

et al. 2017

Физика И Техника Полупроводников

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“…The dependence of efficiency on the active region design will be discussed in Section 8. For simplicity, the electrons are assumed to move in the direction normal to the hetero-interfaces only and, as discussed in Section 4.2, the total electron overflow is obtained by summing the contributions from both ballistic and quasi-ballistic electrons for a given bias voltage [73]. The injected current density vs. bias was obtained using a commercial simulator, Silvaco Atlas, with parameters appropriate for nitride materials as reported in Ref.…”

Section: Optimizing Electron Cooler For a Given Active Regionmentioning

confidence: 99%

“…The injected current density vs. bias was obtained using a commercial simulator, Silvaco Atlas, with parameters appropriate for nitride materials as reported in Ref. [73]. Figure 14b, the rate of the electron overflow reduces with increasing active region width.…”

Section: Optimizing Electron Cooler For a Given Active Regionmentioning

confidence: 99%

“…This is in agreement with the calculated electron overflow percentiles shown in Figures 14b and 14c predicting substantially higher overflow for the single 3 nm DH LED. One can then draw the conclusion that the low EQE of the single 3 nm DH structure is due to higher carrier overflow in the thinner active layer facilitating ballistic and/or quasi-ballistic electron transport across the active layer without recombination [73]. The SEI thickness should be larger for single 3 nm DH to provide hot electrons more time to sufficiently thermalize before being injected into the active region.…”

Section: Experimental Datamentioning

confidence: 99%

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Saga of efficiency degradation at high injection in InGaN light emitting diodes

Avrutin¹,

Hafiz²,

Zhang³

et al. 2014

Turk J Phys

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Abstract:What has turned into highly complex and somewhat misunderstood efficiency loss mechanisms occurring in light-emitting diodes (LEDs) based on the InN-GaN material system at high injection levels are discussed. Suggestions are made as to the dominant mechanism(s) in an open forum format as well as pointing out some of the shortcomings of the methodologies used and premises forwarded. It is unequivocally known that increased junction temperature would cause a reduction in radiative power due to mainly the reduction in radiative recombination efficiency. Another obvious mechanism is the asymmetry in doping in wide bandgap semiconductors, such as GaN, wherein the hole concentration lags well behind that of electrons in the active region. Because an electron and a hole are required for radiative recombination, the radiative efficiency cannot keep up with increasing carrier injection due to progressively lagging hole population. This results in either electron escape without radiative recombination or electron accumulation, which in turn changes the internal bias of the device, manifested as reduced internal forward bias, which reduces the rate of increase in light intensity.Some of the reports ascribe the efficiency loss at high injection levels to Auger recombination (mainly through indirect and recently reportedly direct deductions) as the main and or the only source of efficiency loss by in many cases simply relying on the temperature and injection independent (not well taken) A, B, C coefficients to fit a third order polynomial to the efficiency vs. injection current. As for the direct deduction, the spectroscopic analysis of Auger kicked hot electrons as they traverse through the Γ and L bands before being emitted into the vacuum by means of cesiated surface challenges the existing theories and some experiments regarding carrier scattering and Γ -L separation. Despite just a few reports to the contrary, the bulk of the resonant optical emission experiments do not support the Auger argument as being the main cause. In parallel, there exists a body of theoretical and experimental reports for electron overflow of ballistic/quasi-ballistic electrons traversing the active region to p-GaN, escaping recombination altogether in the active region. In fact and from the get go, the LED industry ubiquitously employed, and continues to do so, an (Al,In)GaN electron-blocking layer (EBL) to prevent electron escape for improved light output that in and of itself would more than suggest that the electron escape (overflow) does indeed occur. The only adverse effect of EBL is * Correspondence: vavrutin@vcu.edu 269 AVRUTIN et al./Turk J Phys that it impedes hole injection due to the valence band offset between the p-type (Al,In)GaN EBL and p-GaN and also generates piezoelectric (if not lattice matched) and differential spontaneous polarization induced fields that pull down the conduction band edge at the interface reducing EBL's effectiveness. To at least reduce the aforementioned aggravating factors to some extent, the ele...

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On the quantum efficiency of InGaN light emitting diodes: Effects of active layer design, electron cooler, and electron blocking layer

Zhang

Okur

et al. 2011

Physica Status Solidi (a)

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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 In0.01Ga0.99N or In0.06Ga0.94N barriers) and thickness (3 and 12 nm) as well as a 9‐nm double heterostructure (DH). Pulsed electroluminescence (EL) and laser excitation power‐dependent 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 In0.06Ga0.94N interwell barriers (LB) instead of the traditional In0.01Ga0.99N barriers improved the EQE and the IQE of MQW LEDs. Specifically, the MQW LEDs with the 6‐period 2‐nm In0.2Ga0.8N quantum well and 3‐nm In0.06Ga0.94N barrier structure showed 6% higher IQE at an injected carrier density of 6 × 1018 cm−3 and 35% higher EQE as compared to that of the same structure with a higher In0.01Ga0.99N barrier. The DH LEDs showed 30% higher EQEs compared to MQW LEDs, albeit at a relatively higher injection current density of 150 A/cm2. 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.

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Pivotal role of ballistic and quasi-ballistic electrons on LED efficiency

Cited by 37 publications

References 50 publications

Влияние баллистической утечки на температурную зависимость квантового выхода светодиодов на основе множественных квантовых ям InGaN/GaN

Влияние баллистической утечки на температурную зависимость квантового выхода светодиодов на основе множественных квантовых ям InGaN/GaN

Saga of efficiency degradation at high injection in InGaN light emitting diodes

On the quantum efficiency of InGaN light emitting diodes: Effects of active layer design, electron cooler, and electron blocking layer

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