Improvements of Structural and Optical Properties of GaN/Al 0.10 Ga 0.9 N Multi-Quantum Wells by Isoelectronic In-doping
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Improvements of Structural and Optical Properties of GaN/Al0.10Ga0.9N Multi-Quantum Wells by Isoelectronic In-doping Lianshan Wang, Soo Jin Chua and Wenhong Sun Opto-electronic System Cluster, Institute of Materials Research & Engineering, 3 Research Link, 117602 Singapore ABSRATCT The effects of isoelectronic In-doping were studied on the structural and optical properties of 3-periods and 10-periods of GaN/Al0.10Ga0.90N multi quantum wells (MQWs). The GaN/Al0.10Ga0.90N MQWs were grown on u-GaN/sapphire via metalorganic chemical deposition (MOCVD) at 1050 oC in H2 carrier gas. X-ray diffraction (XRD), and micro-Photoluminescence (PL) measurements revealed that In-doping into well layers improves the crystalline and optical properties of MQWs relative to those samples without In-doping. With increasing Trimethylindium (TMIn) flow rates from 4.2 µmol/min to 42.6 µmol/min, PL peaks from well layers obviously redshifted, due to the improvement of the strain along the interfaces between MQWS, irrespective of 3-periods or 10 periods MQWs. The improvement of the crystal quality was also confirmed by XRD. INTRODUCTION Highly significant progress in optoelectronic developments of widegap semiconductors has recently been made, especially in the areas of group III nitride-based laser diodes (LD) and lightemitting diodes (LEDs) [1]. This is because the quality of these materials, in terms of carrier mobility, dislocation density, and deep levels, has been improved remarkably. However, it is still difficult to obtain the high-quality epitaxial films using a two-step growth technique. The threading dislocation density is of 108-1010 cm-2 in the films. Very recently, a reduction in the density of TDs has been achieved by the epitaxial lateral overgrowth (ELO) or the lowtemperature-interlayer technique [2, 3]. Another approach has recently been attempted by the isoelectronic In-doping and it has been found that the photoluminescence (PL) intensity of GaN films at room temperature was greatly enhanced, which was more than 30 times stronger in PL magnitude than that of non-doped samples [4]. Several groups have reported positive effects of Indium on the improvements of optical properties of GaN films grown by metalorganic chemical vapor deposition (MOCVD) [5] and molecular beam epitaxy (MBE) [6, 7]. GaN/AlGaN multiply quantum well structures Much research has been carried out on the influence of well widths and piezoelectric field of due to the mismatch-induced strain on the optical properties of GaN/AlGaN multiquantum wells [8-10]. However, there are few reports on the Indium incorporation into well layers in GaN/AlGaN multiquantum well structures. The present paper will investigate the influence of Indium doping on the optical and structural properties of GaN/AlGaN multi quantum wells (MQWs). EXPERIMENTAL The samples in the present study were grown using low-pressure MOCVD. Trimethylgallium (TMGa), trimethylaluminium (TMAl) and ammonia (NH3) were employed for Ga, Al, and N I6.6.1
sources, respectively. The trimethylindium (TMIn)
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