AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique
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1068-C05-07
AlGaN/GaN multiple quantum wells grown by using atomic layer deposition technique Ming-Hua Lo, Zhen-Yu Li, Shih-Wei Chen, Jhih-Cang Hong, Ting-Chang Lu, Hao-Chung Kuo, and Shing-Chung Wang Photonics & Institute of Electro-Optical Engineering, National Chiao Tung University, No.1001, Ta Hsueh Rd., Hsinchu City 300, Taiwan, R.O.C., Hsinchu, 300, Taiwan ABSTRACT We report the successful growth of high quality ultraviolet (UV) AlGaN/GaN multiple quantum wells (MQWs) structure using atomic layer deposition (ALD) technique. The AlGaN/GaN MQW sample grown on the sapphire substrate consisted of three GaN QWs and four AlGaN barriers comprised AlN/GaN superlattices (SLs). From atomic force microscope measurement, the root-mean-square value of the surface morphology was only 0.35 nm, and no crack was found on the surface. The dislocation density was estimated to be as low as 2×108 cm2 . X-ray and transmission electron microscope data show the grown MQW has shape interface with good periodicity. The sample has a deep UV photoluminescence emission at 334 nm (3.71 eV) with a very narrow linewidth of 45 meV at 13K. The cathodoluminescence image show fairly uniform luminescence pattern at room temperature. In conclusion, the AlGaN/GaN MQW grown by ALD technique should be useful for providing high crystalline quality AlGaN/GaNbased MQW for fabrication of AlGaN/GaN-based UV light emitting devices such as light emitting diodes and lasers. INTRODUCTION The AlGaN/GaN multiple quantum wells (MQWs) have attracted much attention because of their many excellent properties, such as high conduction band offset, large LO phonon energy, ultra-fast carrier and/or intersubband relaxation [1, 2] and so on. Therefore, the AlGaN/GaN MQWs are promising candidates for realizing ultraviolet (UV) light emitting diodes (LEDs), edge emitting laser diodes (LDs) [3, 4] and vertical cavity surface emitting lasers (VCSELs) [5]. Besides, the large LO phonon energy inherited in AlGaN/GaN systems could allow roomtemperature operation of quantum cascade laser (QCL) possible [6]. Recent reports indicated that the optical and electrical properties of AlGaN/GaN MQWs were very sensitive to the threading dislocation density (TDD) in AlGaN/GaN epilayer suggesting high crystalline quality AlGaN/GaN MQWs could dramatically improve the device performance [7, 8]. So far most MQWs structures were grown on lattice-mismatched foreign substrates such as sapphire. As a result it is relatively difficult to grow device-quality AlGaN/GaN MQWs on sapphire substrate due to the lattice mismatch and the misfit in the thermal expansion coefficients between these two material systems. In addition, the growth rate of the epilayer using conventional metalorganic chemical vapor deposition (MOCVD) is relatively fast making the MQW thickness and quality control difficult. Recently the high quality AlGaN/GaN heterostructures using quasi AlGaN as barrier layers formed by AlN/GaN super-lattice was reported [9, 10], and their results mainly focused on the electrical properties of Al
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