Study of High Nitrogen Compositions GaNAs and GalnNAs Material Quality by X-ray Diffraction and Photoluminescence
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Study of High Nitrogen Compositions GaNAs and GaInNAs Material Quality by X-ray Diffraction and Photoluminescence T. K. Ng1, S. F. Yoon1, S. Z. Wang1, W. K. Loke1, and W. J. Fan1 1 School of Electrical and Electronic Engineering (Block S1) Nanyang Technological University, Nanyang Avenue, Singapore 639798. Email address: [email protected] ABSTRACT GaNAs and GaInNAs growths are subjects of considerable interest due to its technological importance in long wavelength lasers emitting within the optical-fiber communication wavelength window (1.31 – 1.55 µm). We study GaNAs and GaInNAs materials growth on (100) semiinsulating GaAs substrate with high nitrogen compositions (>2%) using a solid source molecular beam epitaxy (SSMBE) system in conjunction with a RF plasma source. GaNAs layer with high nitrogen compositions of 4.85% and 6% with good XRD peak intensities were successfully grown. GaInNAs quantum wells (QWs) were then grown with reference to the nitrogen compositions measured in the GaNAs materials to obtain nitrogen compositions > 2%. The photoluminescence (PL) peak positions of the GaInNAs QWs blueshifted after annealing at 840oC and 10min. It was found that the blueshift of PL peaks are highly dependent on nitrogen compositions. INTRODUCTION Small bandgap nitride compound semiconductors, such as GaNAs and GaInNAs, are currently important materials for optoelectronic devices such as lasers operating at 1.3 and 1.55 µm [1], and their demand is driven by high-speed data link and optical networks. However, it is known that asgrown GaNAs and GaInNAs materials are relatively defective, an effect caused by the large difference in atomic sizes of Ga, In and As atoms compared to N atom [2, 3], and bombardment of energetic nitrogen ions during growth [4]. Post-growth thermal treatment is therefore required to anneal the defects and hence obtain better photoluminescence (PL) properties [4-11], which are essential for laser applications. Although there are reports on post-growth annealing of GaInNAs grown using metal-organic chemical vapour deposition (MOCVD) [12-14] and chemical beam epitaxy (CBE) [15-17], few reports exist on high temperature (> 800oC) treatment of this material grown by radio-frequency (RF) nitrogen plasma source in conjunction with solid source molecular beam epitaxy (SSMBE). In this paper, fundamental studies of nitrogen incorporation in GaAs bulk material are first reported. High nitrogen compositions of >2% was successfully grown with good structural quality. This is followed by the investigation of the PL properties of GaInNAs QWs after a 10min high temperature (840oC) post-growth thermal annealing cycle. The mechanism that influences the large PL wavelength shift after high temperature annealing was found to be highly dependent on nitrogen composition. The study stresses the importance of increasing indium composition, instead of nitrogen composition in designing and producing GaInNAs QW lasers. EXPERIMENTAL PROCEDURES The sample structure for GaNAs consists of a bulk (100nm or 300nm) GaNA
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