The Role of AlN Interlayer in Al x Ga 1-x N/GaN Heterostructures with high x from 0.35 to 0.50 Grown on Sapphire (0001)
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The Role of AlN Interlayer in AlxGa1-xN/GaN Heterostructures with high x from 0.35 to 0.50 Grown on Sapphire (0001) In-Seok Seo, Seung-Jae Lee, Seong-Hwan Jang, Jeong-Mo Yeon, Jae-Young Leem 1, Yong-Jo Park 2, Cheul-Ro Lee School of Advanced Material Engineering, RCAMD, Engineering College, Chonbuk National University, Chonju 561-756, Chonbuk, Korea 1 Department of Optics, Engineering College, Inje University, Kimhae 621-749, KyungNam, Korea 2 Samsung Advanced Institute of Technology(SAIT), P. O. Box 111, Suwon 440-600, Korea ABSTRACT We report the role of thin AlN interlayer in the fabrication of AlxGa1-xN/GaN heterostructures with high x from 0.35 to 0.50 on sapphire (0001) by MOVPE. After growing the AlN interlayer of 20 nm thick on GaN/sapphire (0001) epitaxy, the AlxGa1-xN epitaxial layers of 1.0 um thick were grown on it with increasing the flow rate of TMA. The measured Al mole fractions of AlxGa1-xN/GaN heteroepitaxy grown using the thin AlN interlayer from each TCD rocking curve are 0.35, 0.37, 0.45 and 0.50, respectively. As incorporation rate of Al in the AlxGa1-xN increases, the crystallinity is getting well and the RMS values scanned by AFM of their surfaces become lower. And also, the optoelectronic characteristics of those heteroepitaxy evaluated by cathodeluminescence(CL) are improved with the increase of x. To the contrary these trends, it is usually known that crystallinity, surface morphology and optical property of the AlxGa1-xN/GaN heteroepitaxy grown without AlN interlayer between them become worse with the increase of x above 0.2. Meanwhile, electrical resisitivities of Al0.35Ga0.65N, Al0.37Ga0.63N, Al0.45Ga0.55N and Al0.50Ga0.50N epitaxy, which were grown with the thin AlN interlayer, measured by four point probing method are 13.5, 18.1, 31.7 and 36.2 Mohm-cm, respectively. These resisitivities increase by degrees in spite of the advance of characteristics with the raising of x. INTRODUCTION Among nitride alloys, the ternary AlxGa1-xN is an important material in nitride based optoelectronic devices such as light emitters and detectors operating in ultraviolet wavelength range[1-3]. AlxGa1-xN epitaxial layers are commonly used for carrier confinement as barrier layers in quantum well light emitting and laser diodes. And, this ternary semiconductor material is also needed for fabricating electronic devices such as AlxGa1-xN/GaN heterostructure field effect transistor(HFET), high-power electronic devices, high-speed electronic devices and them operating at high temperature and hostile environments[4-6]. But, so far, there have been relatively only a few publications on the properties of the AlxGa1-xN alloy system[7-9]. Among them, most of these papers are dedicated to the studies on the characteristics of AlxGa1-xN /GaN heterostructures having low x below 0.2. Until now, only a few researchers studied the growth characteristics of AlxGa1-xN epitaxial layers having high Al mole fraction x above 0.2[10,11]. Lee et al.[9] studied AlxGa1-xN for x between 0 and 0.7 and found that there was an abrupt
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