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InGaN light-emitting diodes: Efficiency-limiting processes at high injection
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Image of FIG. 1.
FIG. 1.

(Color online) Reported Auger recombination coefficient vs bandgap for various semiconductors including conventional III-Vs and InGaN (deduced from LEDs and lasers, the latter being more reliable). The dashed lines show the “corridor” for the Auger coefficients in all the known semiconductors except for III-nitrides (after Ref. ).

Image of FIG. 2.
FIG. 2.

(Color online) Calculated IQE as function of injection current densityfor blue LEDs with 3-nm wide active region using  = 5 × 10 and  = 2 × 10 cm/s (Auger coefficient reported in Ref. ) and  = 1 × 10 s (curve 1) and 5 × 10 s (curve 2). IQE values calculated with  = 1 × 10 s,  = 5 × 10, and  = 2 × 10 cm/s (curve 3) and 5 × 10 cm/s (curve 4) are compared with the measured relative EQEs for blue LEDs with 3 nm (curve 5) and 6 nm (curve 6) wide active regions. The inset shows the calculated IQE in semilogarithmic scale.

Image of FIG. 3.
FIG. 3.

(Color online) Schematic of electron overflow caused by ballistic and quasiballistic electron transport across the InGaN active region. Upon injection into InGaN the electrons gain kinetic energy Δ . These hot electrons will either traverse the active region ballistically and quasiballistically, avoiding recombination inside InGaN, and contribute the electron overflow current, or be captured inside the active region and cooled through multiple interactions predominantly with LO-phonons. Dashed lines represent EBL and additional band bending caused by the polarization field.

Image of FIG. 4.
FIG. 4.

(Color online) Schematic depiction of the conduction band structure and the enhancement of electron thermalization in the presence of a 2-layer SEI. Recombination in the SEI layers and outside the active region is neglected.

Image of FIG. 5.
FIG. 5.

(Color online) (a) Schematic of the quad (4×) 3 nm LED structures investigated. (b) Electron overflow percentile in (b) single-DH LEDs and (c) multi-DH LEDs with different SEI thicknesses as a function of injected current density.

Image of FIG. 6.
FIG. 6.

(a) Cross-sectional STEM image of the hex (6×) 3 nm DH structure. Neither extended defects nor indium clusters are seen within the viewing field. (b) An enlarged image of the active region (courtesy of A. Yankovich, and Dr. A. Kvit and Dr. P. Voyles).

Image of FIG. 7.
FIG. 7.

(Color online) (a) Measured dependence of EL on current density for single and quad (4×) 3 nm DH LEDs with different SEI thickness: (a) integrated intensity (b) relative external quantum efficiency.

Image of FIG. 8.
FIG. 8.

(Color online) Relative EL efficiency vs pulsed injection current density (0.1% duty cycle and 1 kHz frequency) for 9 nm DH LED and MQW LED structures with six 2 nm InGaN QWs separated by 12 nm barriers of different height. All the structures have 4 + 4 nm InGaN and InGaN SEI layers.

Image of FIG. 9.
FIG. 9.

(Color online) Energy band edge profiles (solid lines) and carrier distribution functions (dots) simulated for (a) 3 nm DH and (b) 9 nm DH LEDs with 4 + 4 nm SEIs at different injection current densities. The arrows indicate the directions of changes with increasing injection. Peak emission energy shift as a function of injection current density from (c) EL measurements (d) Silvaco simulations for DH LED structures with various active regions.

Image of FIG. 10.
FIG. 10.

(Color online) coefficients of (a) single-DH and (b) multi-DH LEDs calculated using squared overlap integrals of electron and hole wavefunctions (proportional to radiative recombination rate) within the active region as a function of current density obtained from Silcaco ATLAS simulations.

Image of FIG. 11.
FIG. 11.

(Color online) (a) Integrated PL intensities of single- and multi-DH LED structures as a function of excitation power density measured at 15 K. (b) IQEs of the LEDs as function of excitation power density calculated as a ratio of room-temperature to 15-K PL intensity.

Image of FIG. 12.
FIG. 12.

(Color online) Relative external quantum efficiencies of (a) single-DH and (b) multi-DH LEDs as a function of pulsed injection current density (0.1% duty cycle and 1 kHz frequency).


Generic image for table

Calculated electron overflow percentiles for a one-intermediate layer SEI with varying SEI step height, Δ , and SEI thickness under flat band conditions ( = 0) for an LED with a 6 nm-thick InGaN active region. The values in parentheses are for  = 0.1 V.

Generic image for table

LED structures based on single- and multi-DH active regions included in the study of the effect of active-region design on EQE.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: InGaN light-emitting diodes: Efficiency-limiting processes at high injection