MOCVD growth of semipolar Al_xGa_1−xN on m‐plane sapphire for applications in deep‐ultraviolet light emitters

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 ($11{\bar {2}}2$) 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 ($11{\bar {2}}2$) 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 ($11{\bar {2}}2$) AlGaN is critical to significantly improving the optical properties of the overlying quantum heterostructures, and potentially achieving efficient optoelectronic devices.

High quality semipolar (11¯02) AlGaN/AlN quantum wells with remarkably enhanced optical transition probabilities

“…Although some groups have reported non-c-plane AlN or AlGaN epitaxial films or QWs, the surface flatness and the interface abruptness are insufficient to achieve high-efficiency emissions. [9][10][11][12][13][14] There are two reasons why high-quality semipolar or nonpolar films and QWs have yet to be fabricated. One is that these structures are heteroepitaxially grown on foreign substrates such as r-or m-plane sapphire and semipolar ZnO substrate.…”

“…One is that these structures are heteroepitaxially grown on foreign substrates such as r-or m-plane sapphire and semipolar ZnO substrate. [9][10][11][12][13] The other is that the optimal growth conditions differ between c-plane and non-c-plane growth due to dangling bonds, surface structure, etc. Considering the difficulties observed for homoepitaxy on m-plane AlN substrates, 14 the latter reason seems crucial.…”

Semi/non-polar nitride quantum wells for high-efficient light emitters

“…In addition, recently, semi/nonpolar AlGaN for ultraviolet emitters attain increasing interests. [9][10][11][12] In this paper, we describe the progress in understanding of the optical properties of these QWs.…”

HVPE growth of AlXGa1-XN templates for UV-LED applications

“…There are many processes to prepare the Al x Ga 1-x N compounds including metal-organic chemical deposition (MOCVD), [5][6][7][8][9][10][11][12][13] pulsed laser deposition (PLD), 14 molecular beam epitaxy (MBE), [15][16][17] and halide vapor phase epitaxy (HVPE). [18][19][20][21][22][23] Among these processes, MOCVD has been regarded as a chief apparatus for the commercial fabrication of LEDs.…”