Radiative Lifetime of Excitons in GalnN/GaN Quantum Wells
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Internet Journal o f
Nitride S emiconductor Research
Volume 1, Article 37
Radiative Lifetime of Excitons in GaInN/GaN Quantum Wells Jin Seo Im, Volker Härle, Ferdinand Scholz, Andreas Hangleiter 4. Physikalisches Institut, Universität Stuttgart This article was received on June 2, 1996 and accepted on November 20, 1996.
Abstract We have studied GaInN/GaN quantum well structures grown by LP-MOVPE by picosecond time-resolved photoluminescence spectroscopy. For the quantum wells we find rather long PL decay times of up to 600 ps at low temperature. At temperatures higher than about 100 K, the decay time decreases rapidly, reaching about 75 ps at room temperature. From measurements of the integrated PL intensity, we conclude that this decrease of the decay time is due to nonradiative recombination processes. By combining our data for the lifetime and the intensity, we derive the radiative lifetime, which is constant at low temperature and increases at elevated temperatures. We explain this behavior on the basis of the interface roughness at low temperature and thermal dissociation of excitons at higher temperatures.
1. Introduction The radiative lifetime of excess charge carriers is a fundamental property of semiconductor structures, which has important implications for device operation. Quantum wells from the group-III nitrides are particularly interesting for their potentially very large free exciton binding energy, making excitons stable up to rather high temperatures. Even for bulk GaN, the radiative lifetime of excess carriers is dominated by free excitons up to room temperature [1]. Due to the localization of carriers in the quantum wells, the exciton Bohr radius is expected to shrink and the radiative lifetime to reduce. For other III-V semiconductor quantum wells, the radiative decay of carriers has been studied in some detail. Feldmann et al. [2] have shown that, above some critical temperature, the radiative exciton lifetime in GaAs/AlGaAs quantum wells increases linearly with temperature. Michler et al. [3] have demonstrated the influence of exciton dissociation on the radiative decay time in GaInAs/InP quantum wells. We have studied the radiative lifetime in GaInN/GaN single quantum wells using picosecond time resolved photoluminescence spectroscopy.
2. Experimental 2.1. Samples Our samples were grown on 0001 oriented sapphire substrates using low pressure metal-organic vapor phase epitaxy (LP-MOVPE) and employing an AlN buffer layer. The growth temperature for GaN was about 1000oC, whereas GaInN was grown at about 800oC. Thick GaN samples exhibited X-ray diffraction linewidths of 50- 80 arcsecs and photoluminescence linewidths of around 2-4 meV. The net donor concentration of nominally undoped GaN was less than 1 x 1017cm3. For the quantum wells, we used a 500nm GaN buffer and a 200nm GaN cap layer. The thickness of the GaInN quantum wells was varied between 0.6nm and 20nm.
2.2. Measurement setup The carrier dynamics were investigated using a picosecond time-resolved photoluminescence setup, where t
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