Arsenic Incorporation Behavior in Nitrogen-rich GaNAs Alloys Synthesized by Metalorganic Chemical Vapor Deposition (MOCV
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Arsenic Incorporation Behavior in Nitrogen-rich GaNAs Alloys Synthesized by Metalorganic Chemical Vapor Deposition (MOCVD) M. Gherasimova, R. G. Wheeler, L. J. Guido1, K. L. Chang2, K. C. Hsieh2 Department of Electrical Engineering, Yale University, P.O. Box 208284, New Haven, CT 06520 1 Department of Materials Science and Engineering, Virginia Tech, 213 Holden Hall, Blacksburg, VA 24061 2 Department of Electrical and Computer Engineering, University of Illinois, 1406 West Green St., Urbana, IL 61801 ABSTRACT Homogeneous GaNAs alloy films containing 3 to 4 percent of arsenic anion fraction were synthesized by metalorganic chemical vapor deposition (MOCVD). Postgrowth annealing resulted in the formation of GaAs precipitates of several nanometers in size embedded in the nitrogen-rich GaN(As) matrix, while as-grown ternary films exhibited no evidence of phase segregation. Band gap reduction due to alloying was observed by the optical transmission measurements, leading to an estimate for the bowing parameter of 25 eV in the films with the arsenic content of 3.5 %. INTRODUCTION Investigation of GaNAs and related nitride alloys with mixing on the anion sublattice presents interest due to their anticipated electronic properties. In particular, GaNAs is expected to exhibit direct band gap over the entire composition range, combined with the unusually large bowing parameter [1-4]. As a result, a wide range of potential optoelectronic device applications can benefit from deep band offsets within the (Al,Ga,In)(As,N) materials system. From the practical point of view, the synthesis of nitride-arsenide alloys presents considerable difficulty due to the limited miscibility of their binary constituents [3,5]. Arsenic-rich GaNAs alloys containing a small fraction of nitrogen in the GaAs matrix were studied more extensively than their nitrogen-rich counterparts [6]. On the nitrogen-rich side, isoelectronic doping of GaN with arsenic was investigated by several groups [7-12]. Higher levels of arsenic (up to 1 % of arsenic anion fraction) were also obtained by molecular beam epitaxy [13,14]. In the present study we report on the synthesis of GaNAs alloys on GaN templates by metalorganic chemical vapor deposition (MOCVD), and the investigation of their structural and optical properties. EXPERIMENTAL DETAILS All samples were grown by MOCVD in a horizontal flow reactor at a pressure of 100 Torr, using palladium-purified hydrogen at a flow rate of 8000 standard cubic centimeters per minute (sccm) as a carrier gas. Ammonia, arsine and trimethylgallium (TMG) were used as precursors for nitrogen, arsenic and gallium, respectively. Growth temperature of 700 °C was controlled by the radio-frequency (RF) field applied to the
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SiC-coated graphite susceptor. Ammonia and TMG flows were held constant at 4000 sccm and 50 µmol/min, respectively, while the arsine flow was varied between 4 and 400 sccm. Ternary films were deposited on 1.2 µm thick GaN templates grown in situ at 1030 °C immediately prior to GaNAs deposition. Arseni
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