Structural and optical characterization of (11‐22) semipolar GaN on m ‐plane sapphire without low temperature buffer layer

Abstract

We reported the high quality semipolar (11‐22) GaN grown on m‐sapphire by using the novel two‐step growth method without low temperature GaN or AlN buffer layer. It is found that macroscopic surface morphology of semipolar GaN epilayer was very smooth, while microscopic surface structure was arrowhead‐like surface structure toward the direction of [1‐21‐1]. Anisotropic crystal properties of semipolar GaN/m‐sapphire were also observed by two incident directions of X‐ray beam. Therefore, we suggested that the anisotropic crystal properties and arrow‐head like surface structure would be caused by heteroepitaxial crystallograhpic difference between semipolar GaN and m‐sapphire. Additionally, photoluminescence (PL) measurements showed the strong bandedge emission of n‐type semipolar GaN without yellow luminescence (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Study of green light-emitting diodes grown on semipolar (11–22) GaN/m-sapphire with different crystal qualities

“…1(a) and (b) showed SEM images of semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)) GaN on m-sapphire grown by N 2 /H 2 2-step (sample A) and N 2 -free only H 2 1-step (sample B) growth, respectively. The surface structures of both samples had arrowhead-like structures which may be caused by the incorporation probability and the diffusion length of surface adatoms toward anisotropic crystallographic directions such as [11-2-3] and due to the crystallographic difference between m-plane sapphire and semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN [14]. However, we could obtain smoother surface morphology of sample B than sample A by eliminating the N 2 -GaN layer as shown in Fig.…”

“…And, silane (SiH 4 ) and biscyclopentadienylmagnesium (Cp 2 Mg) were used for n-, and p-type doping process, respectively. By introducing the novel growth method without low temperature GaN buffer layer [14], we prepared two semipolar GaN/m-sapphire templates with different crystal qualities. Prior to the growth, the sapphire substrate was thermally annealed at 1080 o C in H 2 and NH 3 atmosphere to remove surface contamination and to perform nitridation process.…”

“…Semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN templates were grown on m-plane sapphire substrates in a 3 Â 2 00 in Thomasswan Close Coupledshowerhead metalorganic chemical vapor deposition (MOCVD) system. Trimethylgallium (TMGa), trimethylindium (TMIn) and ammonia (NH 3 ) were used as gallium, indium and nitrogen sources, respectively.…”

“…These anisotropic crystallographic properties could affect the incorporation of In and the formation of asymmetric V-shape defects during the growth of semipolar InGaN QWs. Therefore, in order to achieve high performance semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) GaN-based LEDs, it is important to enhance the crystal quality of semipolar GaN templates, because crystal defects could significantly deteriorate the optical performance. In this study, we investigated the interfacial and optical qualities of LEDs with green InGaN/GaN QWs grown on semipolar (11-22) GaN templates with different crystal qualities.…”

“…So far, lots of research groups have studied to achieve high performance nonpolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), (1-100) and semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), (10-1-3) GaN-based LEDs, which could reduce polarization-induced electrostatic fields [5][6][7][8]. Additionally, the advantage of the semipolar over nonpolar GaN epilayer is the higher In incorporation rate of semipolar (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) plane, which give the possibility of enhanced-radiative efficiency in a green gap region [9].…”