Strong below-band gap absorption of N-rich side GaNSb by metal-organic chemical vapor deposition
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Metalorganic chemical vapor deposition was used to grow N-rich side GaNSb alloys under different growth conditions, and, for the first time, a considerable amount of Sb was incorporated into the GaNSb. The amount of Sb increased as the growth temperature decreased, but the maximal Sb content seemed to be limited by the solid solubility of Sb in GaN. Absorption spectroscopy of the GaNSb revealed a strong absorption band below the band gap of GaN. The below-band gap absorption extended to 0.8 eV, which makes GaNSb a promising material to serve as an infrared absorption layer on GaN. I. INTRODUCTION
Gallium nitride and its ternary alloys have been widely investigated for use in short-wavelength optical devices and high-power electronic devices. For light emission ranging from blue to green or even longer wavelengths, the usual choice is InGaN-based quantum wells (QWs). However, the range of band gap energies obtainable with InGaN is quite limited. The large strain and the strong piezoelectric field degrade the optical properties of an InGaN QW, especially one with a high In content. There are also various difficulties in growing InGaN because of the large difference in the lattice constants and in the optimum growth temperatures of GaN and InGaN. For those reasons, researchers have studied different material systems, such as GaNAs and GaNP, to obtain better band gap controllability, smaller strains, and lower piezoelectric fields. For GaNAs, the large difference in lattice constants of GaN and GaAs results in a nonlinear dependence of the band gap on As composition, with a larger bowing parameter, which helps to achieve a significant band gap change with less As and a smaller strain in the QW. However, it also appears that a large miscibility gap exists between GaN and GaAs.1–5 The presence of such a large miscibility gap would be a major obstacle for the successful growth of these ternary alloys. GaNP shows a similar behavior.6–8 To overcome the limitations of currently available material systems, it is necessary to work on a new alloy system, one that is expected to exhibit a large band gap bowing and a longer emission wavelength with a smaller strain. GaNSb is a ternary alloy of GaN and GaSb, which have a huge lattice mismatch of 35%. Because of this misa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0435 J. Mater. Res., Vol. 24, No. 12, Dec 2009
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match, several interesting behaviors, such as compositiondependent band gap bowing9 and band anticrossing,10 have been reported for Sb-rich side GaNSb. However, there are only a limited number of articles about the growth of N-rich side GaNSb. Zhang et al.11 reported that they added triethylantimony during the growth of GaN over 1000 C, but only a negligible amount of Sb was incorporated in the GaN epilayer even at high [TMSb]/[TMGa] ratios. The low incorporation rate was attributed to the low solid solubility of Sb in GaN. A small amount of Sb, acting as a surfac
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