Light-output enhancement of InGaN light emitting diodes regrown on nanoporous distributed Bragg reflector substrates

Abstract

Utilising our novel wafer-scale electrochemical porosification approach which proceeds through the top surface by means of nanoscale vertical etching pathways, we have prepared full 2-inch wafers containing alternating solid GaN and nanoporous GaN (NP-GaN) layers that form distributed Bragg reflectors (DBRs), and have regrown InGaN-based light emitting diode (LED) heterostructures on these wafers. The NP-GaN DBR wafer is epi-ready and exhibits a peak reflectance of 95% at 420 nm prior to growth of the LED heterostructure. We observe a 1.8x enhancement in peak intensity of LED electroluminescence from processed devices, and delayed onset of efficiency droop with increased injection current.

Porous nitride semiconductors reviewed

“…Reduced strain fields have also been indicated as the cause of a blue-shift in the band-edge luminescence peak for GaN layers grown on porous GaN [34]. In our own work we have regrown LEDs on porous DBR templates and although there was significant enhancement from other effects, we did not find evidence of strain relaxation from XRD, or blueshift in the luminescence due to reduced QCSE [10]. This suggests that porosity must be on the template surface in order to provide strain relief for the regrown layer.…”

“…This eliminates the risk of unintended pores being formed in the higher layer, meaning the regrown layers can be highly doped. This method has been demonstrated to improve LED performance for both single porous layers on silicon substrates [67], as well as porous DBRs produced using vertical etch pathways on sapphire [10]. The pore morphology can be altered during regrowth, depending on the growth temperature used.…”

“…These materials have allowed the blossoming of efficient LED lighting [1] and are transforming high power transistors [2]. Porous nitride semiconductors represent a new development that broadens the potential applications for the nitrides to include sensors [3,4], catalysis [5,6], and hybrid materials [7], as well as providing routes to improve the efficiency of more conventional nitride devices [8][9][10], improve material quality [11,12] and to create novel structures, such as membranes [13,14]. Etching nitride semiconductors via traditional wet-etching methods is notoriously difficult due to their chemical stability [15], meaning that techniques for creating new nano-and micro-structures are fairly limited.…”

Preferential sublimation along threading dislocations in InGaN/GaN single quantum well for improved photoluminescence

“…Distributed Bragg reflectors composed of a stack of alternating regular GaN and nanoporous GaN demonstrated a high reflectivity and the possibility to be lattice matched on GaN. 7,8,9,10 Such distributed Bragg reflectors can be used as highly reflective bottom mirrors in different devices including resonant cavity light emitting diodes, 11,12 as well as optically pumped, 13 and electrically injected vertical cavity surface emitting laser. 14,15 Last, incorporating porous GaN layers on top of a patterned sapphire substrate can also enhance the light extraction efficiency of blue InGaN/GaN light emitting diodes thanks to the modification of the refractive index of the porous GaN.…”

Multi-colour GaN-based LEDs with trench structure

“…T he optical and electrical characteristics of GaN-based LEDs have been continuously improved through various researches. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] Also, based on these improvements, GaN-based (LEDs) are widely used in the fields of lighting and displays, replacing conventional fluorescent lamp. 15,16) Currently, these commercial LED products use a method of converting blue light from multi-quantum well (MQW) of GaN-based LEDs into yellow by using a phosphor to realize white light.…”