Localized exciton dynamics in strained cubic In0.1Ga0.9N/GaN multiple quantum wells

Abstract

Radiative and nonradiative recombination dynamics in strained cubic (c-) In0.1Ga0.9N/c-GaN multiple quantum wells were studied using temperature-dependent time-resolved photoluminescence (TRPL) spectroscopy. In contrast to hexagonal InGaN quantum wells, low-excitation photoluminescence peak energy increased moderately with decreasing well thickness L and the PL lifetime did not strongly depend on L. The results clearly indicated that the piezoelectric field was not acting on the transition process. The TRPL signal was well fitted as a stretched exponential decay from 10 to 300 K, showing that the spontaneous emission is due to the radiative recombination of excitons localized in disordered quantum nanostructures such as In clusters. The localized states were considered to have two-dimensional density of states at 300 K (quantum disk size), since the radiative lifetime increased with increasing temperature above 150 K.

Time dependent and temperature dependent properties of the forward voltage characteristic of InGaN high power LEDs

“…Due to temperature dependent electron phonon interactions (generally leading to a decreasing band-gap energy with increasing temperature and thus to an increasing center wavelength λ Center ) and temperature dependent non-radiative losses, the emitted optical power decreases with temperature. Besides Shockley-Read-Hall (SRH) recombination, 15 also other mechanisms should be considered, such as temperature-assisted electron leakage 16 with possible trap-and field-assisted effects, 17 as well as exciton delocalization 18 that is mainly observed at low temperatures. The electrical input power decreases with increasing temperature, because of the negative temperature coefficient of the LED's forward voltage at constant forward current.…”

Reduction of Current Crowding in InGaN-based Blue Light-Emitting Diodes by Modifying Metal Contact Geometry

“…The InGaN-based blue LEDs show the significant reduction of internal quantum efficiency called 'efficiency droop' when the current level increases. Over the past years, there have been many researches to analyze and improve the efficiency droop of the LEDs [1][2][3][4][5][6][7][8]. It is known that current crowding is one of the major obstacles to solving the droop problem and increasing internal quantum efficiency [9,10].…”

Luminescence of Localised Excitons in InGaN/GaN Multiple Quantum Wells

“…The QW band redshifts with time ( [4]. The enhanced segregation of the In-rich regions leads to formation of deeper localised states that cause long-lived radiative emission of the InGaN/GaN diode structures [3,4,9]. Spatial fluctuations of In concentration can suppress internal field effects on luminescence properties [8].…”

“…Picosecond time-resolved luminescence spectra consist of the same two bands that decay nonexponentially on picosecond to nanosecond time scale. The QW band redshifts with time ( [4]. The enhanced segregation of the In-rich regions leads to formation of deeper localised states that cause long-lived radiative emission of the InGaN/GaN diode structures [3,4,9].…”

“…Although optical properties of InGaN/GaN quantum well structures are being widely investigated, the emission mechanisms in this system are still not completely understood [1][2][3][4][5][6][7]. Localised excitons is the most probable mechanism responsible for emission from InGaN/GaN MQWs, however the emission efficiency is highly sensitive to impurity and interface states, inhomogeneities and compositional separation of the InGaN alloy as well as to built-in electric field [3][4][5][6][7].Here we report on a study of InGaN/GaN MQW structures with various well thickness, d, by temperature-dependent, excitation power-dependent and time-resolved photoluminescence techniques. The samples were grown on sapphire substrates by metalorganic chemical vapour deposition.…”