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Keywords:

  • semipolar AlGaN;
  • MOCVD;
  • photoluminescence;
  • AlGaN MQWs;
  • TEM

Abstract

The growth of semipolar AlN and AlGaN epilayers on m-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD) has been investigated for the first time. The implementation of pulsed MOCVD technique for the deposition of the AlN buffer, and the insertion of a strain relieving AlN/AlGaN short-period superlattice structure proved instrumental in the growth of a thick, crack-free, and single domain n-Al0.56Ga0.44N (equation image) films, which also exhibit a good crystal quality. To assess the suitability of this AlGaN/AlN/m-sapphire template for practical use in deep-ultraviolet light emitters, both polar (0001) and semipolar (equation image) AlGaN multiple quantum wells (MQWs) were grown side-by-side. The room temperature photoluminescence (PL) spectra of the semipolar MQW structure peaked at 305 nm, which was approximately 10 nm longer than the PL peak originating from the reference polar MQWs. Besides, the semipolar MQWs showed a fairly excitation-independent emission wavelength, which suggests the absence of any polarization-induced electric fields. The intensity of the luminescence from the c-oriented MQWs was, however, stronger than that of its semipolar counterpart. The result indicates that further reduction of the extended defects density in (equation image) AlGaN is critical to significantly improving the optical properties of the overlying quantum heterostructures, and potentially achieving efficient optoelectronic devices.