Metal Organic Vapor Phase Epitaxy of GaAsN/GaAs Quantum Wells Using Tertiarybutylhydrazine
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T. Schmidtling*, M. Klein, U.W. Pohl, and W. Richter Technische Universität Berlin, Institut für Festkörperphysik, Sekr. PN 6-1, Hardenbergstr. 36, D - 10623 Berlin, Germany ABSTRACT GaAsN epilayers and quantum wells with a good structural quality and surface morphology were grown by low pressure metal organic vapor phase epitaxy using tertiarybutylhydrazine as a novel nitrogen source. The dependence of nitrogen incorporation on growth temperature was studied for epitaxy with arsine and tertiarybutylarsine precursors. A nitrogen content of 6.7 % was achieved using tertiarybutylhydrazine and tertiarybutylarsine at a low growth temperature of 530 °C. The observed room temperature luminescence shows an increasing redshift with increasing nitrogen contents of the wells. INTRODUCTION Devices for optical fibre communication require emission wavelengths between 1.3 and 1.55 µm. Bandgap tuning of GaAs based devices to reach this range can be achieved by alloying GaAs with nitrogen due to the large bandgap bowing of GaAsN [1]. A nitrogen content up to 4% leading to a near band edge PL at 1.25 µm was recently achieved in Metal Organic Vapor Phase Epitaxy (MOVPE) using dimethylhydrazine (DMHy, Me2NNH2) as nitrogen source [2,3]. To further lower the bandgap, the nitrogen content in the layers has to be increased. Due to a large miscibility gap [4], growth at low temperatures is required to attain a sufficient degree of nitrogen incorporation. We used tertiarybutylhydrazine (TBHy, tBu(H)NNH2) as a novel nitrogen precursor for low pressure MOVPE of GaAsN. Due to a comparably weak tertiarybutyl-nitrogen bond strength, TBHy has a distinctly lower total decomposition temperature (around 350°C) compared to DMHy [5]. TBHy thus appears suitable to achieve a high nitrogen content in the layers. Furthermore, a decreased carbon incorporation was reported for GaN epilayers grown using TBHy [6].
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Corresponding author: phone: +49/30/31424820, fax: +49/30/31421769, email: [email protected].
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EXPERIMENTAL PROCEDURE Epitaxy was performed on GaAs(001) substrates at temperatures between 530 and 570 °C using TMGa, TBAs or AsH3, and TBHy under hydrogen carrier gas. V/III ratios were adjusted to 15 and 200 for TBAs and AsH3, respectively, using a constant TMGa flow of 20 µmol/min. The partial pressure ratio of the group V flows of the nitrogen and arsenic sources xv=PTBuHy/( PTBuHy+ PAs) was varied in the range 0.55 to 0.87. As a first step, we grew thick, relaxed layers with about 0.5 µm thickness to study the surface morphology. Based on these studies, we fabricated 20 nm thick GaAsN wells which were cladded by GaAs. Rocking curves were recorded using Cu Kα radiation in a high resolution double crystal diffractometer equipped with a double reflection Si(220) monochromator in (++-) arrangement. Thick layers were additionally characterised by Bragg Θ-2Θ scans using a single crystal diffractometer. Photoluminescence was excited using the 514 nm line of an argon laser, dispersed by a 50 cm monochromator with ~3.3 nm/mm linear d
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