Growth and characterization of semipolar InGaN/GaN multiple quantum wells and light-emitting diodes on % MathType!MTEF!2
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Growth and characterization of semipolar InGaN/GaN multiple quantum wells and lightemitting diodes on ( 10 1 1 ) GaN templates Arpan Chakraborty, T. Onuma1, T. J. Baker, S. Keller, S. F. Chichibu1, S. P. DenBaars, S. Nakamura, J. S. Speck, and U. K. Mishra Electrical and Computer Engineering and Materials Departments, University of California, Santa Barbara, California 93106, USA. 1 Institute of Applied Physics and Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan NICP/ERATO, Japan Science and Technology Agency. ABSTRACT InGaN/GaN MQW samples were grown by metal organic chemical vapor deposition (MOCVD) on ( 1011 ) oriented GaN templates. Effects of growth temperature and reactor pressure on the photoluminescence (PL) properties were investigated. The emission intensity improved significantly when the QWs were grown at 100 Torr, compared to higher pressure growths. The effect of well-width on the luminescence properties was investigated and an optimum well width of 40 Å was determined. Excitation dependent PL measurements revealed no shift in the PL emission wavelength suggesting the absence of electric field in the quantum wells. Furthermore, LEDs fabricated on ( 1011 ) GaN templates, emitting at 439 nm, showed no shift in the EL emission wavelength with the increase in drive current, reconfirming the absence of polarization. INTRODUCTION Conventional Group-III-nitrides-based light-emitting diodes (LEDs) and laser diodes [1-2], grown along the polar c-direction, are characterized by the presence of polarization discontinuities at the heterointerfaces of the quantum wells (QWs) [3]. These gives rise to electric fields and cause band bending, which results in the quantum confined stark effect in the QWs. The consequences of this effect are decreased recombination efficiency, red-shifted emission, and blue shifting of the emission with increasing drive current [4-5]. An alternative means of reducing and possibly eliminating the polarization effects is to grow the devices on semipolar planes. Semipolar planes extend diagonally across the hexagonal unit cell and form an angle with the c-plane other than 90˚ and the polarization vector is tilted with respect to the growth direction. This result in reduced polarization effects compared to c-plane GaN. Also, for specific strain states on specific semipolar planes, there will be zero net polarization in the growth direction [6]. Therefore, optoelectronic devices grown and fabricated along semipolar direction promise to be an effective means of improving their performance over conventional devices. Recently, growth of semipolar GaN on various substrates has been demonstrated [7-9]. Growth of semipolar GaN on spinel [8] and sapphire [9] substrate was found to be stable under a wide range of growth conditions. Visible LEDs with InGaN/GaN multiple-quantum wells (MQWs) have also been demonstrated along semipolar orientations [7-10]. In this letter, we have investigated the photoluminescence (PL) characteristics o
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