Al rich AlN/AlGaN Quantum Wells
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0955-I02-04
Al rich AlN/AlGaN Quantum Wells Talal Mohammad Al tahtamouni, Neeraj Nepal, Jingyu Lin, and Hongxing Jiang Physics Department, Kansas State University, 116 CW Hall, Manhattan, KS, 66506
ABSTRACT Two sets of AlN/AlxGa1-xN quantum wells (QW) have been grown by metalorganic chemical vapor deposition (MOCVD). The first set consists of five samples of AlN/AlxGa1-xN QWs with (x ~ 0.65) with well width, Lw, varying from 1 to 3 nm. The second set consists of four samples of AlN/AlxGa1-xN with (Lw = 1.5 nm) with Al composition, x, varying from 0.70 to 0.85. Low temperature photoluminescence (PL) spectroscopy has been employed to study the Lw dependence of the PL spectral peak position, emission efficiency, and line width. Our results have shown that these AlN/AlGaN QW structures exhibit polarization fields of ~ 4 MV/cm. Due to effects of quantum confinement and polarization fields, AlN/AlGaN QWs with Lw between 2 and 2.5 nm exhibit the highest quantum efficiency. The dependence of the emission linewidth on Lw yielded a linear relationship. The implications of our results on deep ultraviolet (UV) optoelectronic device applications are also discussed. INTRODUCTION UV emitters and detectors operating in the 200 – 340 nm wavelength range are important devices for many applications, including water purification, bio-chemical agent detection, medical research/health care, and high-density data storage [1]. Al-rich AlGaN alloys have the capability of emitting at short wavelengths down to 210 nm, which makes them very useful for these applications. As demonstrated by light emitting diodes (LEDs), laser diodes (LDs), and electronic devices, many III-nitride based devices must take advantages of quantum well (QW) structures in order to achieve optimal device performance. To realize deep UV emission (λ < 280 nm) Al-rich AlGaN based QWs are required. Recently, several groups have been studying Alrich AlGaN-based emitters to obtain UV emission of wavelength below 300 nm [2-8]. However, the quantum efficiency (QE) of these deep UV emitters is presently still very low. Systematic studies of Al-rich AlxGa1-xN alloys and AlN/AlxGa1-xN QWs are needed in order to probe the underlying mechanisms and necessary layer structural designs for providing improved QE. EXPERIMENT In this study, two sets of AlN/AlxGa1-xN QWs have been grown by MOCVD, one set is AlN/Al0.65Ga0.35N QWs with well width (Lw) varying from 1 to 3 nm and fixed x (0.65) and a fixed barrier width of 10 nm. The other set is AlN/AlxGa1-xN QWs with x varying from (0.700.85) with fixed Lw (1.5 nm) and a fixed barrier width (10 nm). Low temperature (10 K) deep UV PL emission spectroscopy has been employed to probe the Lw dependence of the optical properties. Our results revealed that the highest QE could be obtained in QWs with Lw between 2
and 2.5 nm. The estimated value of the polarization fields (piezoelectric and spontaneous fields) induced in the well regions was found to be around 4 MV/cm, which agrees well with the calculations. A linear relationship between the
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