Investigation of Ultrafast Carrier Dynamics in InGaN/GaN‐Based Nanostructures Using Femtosecond Pump–Probe Absorption Spectroscopy

Abstract

III-V compound semiconductors laid the foundation for optoelectronic devices and solid-state lighting with wavelengths ranging from infrared to ultraviolet regions. Infrared to green light-emitting diodes (LEDs) were invented in the early 1960s. [1][2][3] However, blue LEDs took another three decades to get established, considering the challenges in defect-free high-quality growth, [4][5][6] and controlled p-doping of wide-bandgap semiconductors. [7][8][9][10] The success of blue LEDs was accomplished by the development of gallium-nitride (GaN) alloyed with indium and aluminum in the late 1980s. [11,12] GaN and related materials have a wurtzite crystal structure and direct bandgap, making them ideal for bright LEDs and laser diodes (LDs). In order to move the emission wavelength to the visible range (2-3.4 eV), InN is alloyed with GaN. [13,14] Advancement in GaN-based LEDs revolutionized the white broadband lighting when laminated with yellow phosphorous coating. Nakamura et al. developed the first high-quality InGaN back in 1992, which paved the way for III-nitride blue and green LEDs/ LDs. [15] In 1995-1996, Nakamura made true blue LEDs possible by developing recombination regions with InGaN. [16] III-nitride devices acquire a wide area of applications due to their wavelength tunability by varying the alloy composition of In and Al in InGaN and AlGaN, respectively. [17,18] Moreover, an additional degree of freedom can be achieved using quantum-confined nanostructures. Emission wavelength and surface/interface material properties can be altered by reducing the dimensionality/size of the devices. [19][20][21] quantum well (QW; 2D), [22][23][24] vertical/lateral nanowires (1D), [25][26][27][28][29] and quantum dots (QDs; 0D) [30][31][32][33] are among the most important quantum-confined nanostructures used in the active regions of modern optoelectronic devices including LEDs, lasers, photodetectors, and solar cells. Improved internal quantum efficiency, [34][35][36] large surface-to-volume ratio, [37] low power

Reduced Auger Coefficient through Efficient Carrier Capture and Improved Radiative Efficiency from the Broadband Optical Cavity: A Mechanism for Potential Droop Mitigation in InGaN/GaN LEDs

“…BTB (b 4 ) and SRH (b 5 ) dominate at a very long time (∼ t 3 ), by which the residual carriers decay from the QW. It may be noted that these assignments of processes at various time scales t 1 , t 2 , and t 3 (obtained values of these time constants are given in Figure ) are in congruence with the quantum mechanically estimated time constants. − The time constant associated with the combined effect of the transitions (mostly) a 1 and (partly) b 1 is obtained by the single exponential fit to the initial carrier kinetics, where Δα reaches its peak negative value. The fit for the control sample near the initial kinetics at the InGaN band edge is shown in the inset of Figure a.…”

Revealing photoluminescence and nonlinear optical absorption characteristics of PbMo0.75W0.25O4 single crystal for optical limiting applications

“…Carriers from the band-edge quickly get trapped into these states within a short span of 10-100 ps. More the number of traps faster is the trapping rate [62]. Further decay of excess carriers take place through band-to-band or excitonic radiative recombination.…”

“…Further decay of excess carriers take place through band-to-band or excitonic radiative recombination. The radiative recombination lifetime of typical compound semiconductors is in the range of 0.1-100 ns [62].…”

Real-time observation of delayed excited-state dynamics in InGaN/GaN quantum-wells by femtosecond transient absorption spectroscopy

“…Unlike Gallium Arsenide (GaAs), GaN heterostructures with wurtzite crystal structures have polarisation fields, causing the spatial separation of electrons and holes, leading to the quantum-confined stark effect (QCSE) [11]. QCSE decreases the overlap of electron and hole wave functions, reducing the radiative efficiency and intensity of emission.…”

“…QCSE decreases the overlap of electron and hole wave functions, reducing the radiative efficiency and intensity of emission. However, the extent of QCSE varies with time for the switching characteristics of LEDs, LDs, and PDs (such as sources or detectors in various communication systems or reading and writing elements in data storage) [11][12][13]. This necessitates time-dependent studies like pump-probe spectroscopy to understand and control this transient QCSE.…”