Abstract
In this work, the influences of thermal annealing and chemical passivation on the optical and electrical properties of ultraviolet light-emitting-diode (UV-LED) were investigated. The electroluminescence (EL) intensities of the LEDs under KOH treatment and thermal annealing increased by 48% and 81%, respectively compared to as-fabricated LED under current level of 10 mA. Cathodoluminescence (CL) mapping of UV-LEDs confirmed no variation of the density of the non-radiative recombination centers after surface treatments, and no obvious change in surface morphology was identified due to lacking of energy for surface atom migration. However, Raman spectroscopy indicates a relaxation of compressive strains inside the thin film after both thermal and chemical treatments, and conductive atomic force microscopy (c-AFM) also illustrated reduced leakage current after KOH passivation, which are responsible for the improved luminescence properties of UV-LEDs.
Highlights
III-nitride wide bandgap semiconductors have attracted great interests among researchers due to their wide applications in light emitting diode (LED), laser diode (LD), and electronic electronics [1]–[3]
Raman spectroscopy indicates a relaxation of compressive strains inside the thin film after both thermal and chemical treatments, and conductive atomic force microscopy (c-AFM) illustrated reduced leakage current after KOH passivation, which are responsible for the improved luminescence properties of ultraviolet light-emitting-diode (UV-LED)
Little work has been done in investigating the influence of thermal or chemical treatments on the performances of LEDs, especially ultraviolet (UV) LEDs, which are critically important [16], [17]. This is because, firstly, dislocations and point defects are strongly correlated with internal quantum efficiency (IQE) of UV-LEDs as reported by Ban et al [18], and must be reduced to a maximum extent; Secondly, surface defects and traps could lead to fermi level pinning and introduce barrier height between metal and GaN contact layer [19], [20]
Summary
III-nitride wide bandgap semiconductors have attracted great interests among researchers due to their wide applications in light emitting diode (LED), laser diode (LD), and electronic electronics [1]–[3]. Little work has been done in investigating the influence of thermal or chemical treatments on the performances of LEDs, especially ultraviolet (UV) LEDs, which are critically important [16], [17] This is because, firstly, dislocations and point defects are strongly correlated with internal quantum efficiency (IQE) of UV-LEDs as reported by Ban et al [18], and must be reduced to a maximum extent; Secondly, surface defects and traps could lead to fermi level pinning and introduce barrier height between metal and GaN contact layer [19], [20]. Nanostructure-based LEDs suffer from large density of states at the free sidewalls and huge on-state resistance due to difficulties in current injection This greatly holds back the development of high-efficiency UV-LEDs. as the emission wavelength of UVLED becomes shorter, external quantum efficiency (EQE) is severely degraded due to worse crystalline quality and less efficient carrier injection. Enhanced electroluminescence intensity was observed, which can be clearly demonstrated by a combination effect of strain relaxation and surface passivation
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