Well width study of InGaN multiple quantum wells for blue–green emitter V. Hoffmann a, , C. Netzel a , U. Zeimer a , A. Knauer a , S. Einfeldt a , F. Bertram c , J. Christen c , M. Weyers a , G. Tr¨ ankle a , M. Kneissl a,b a Ferdinand-Braun-Institut f ¨ ur H¨ ochstfrequenztechnik, Gustav-Kirchhoff-Straße 4, 12489 Berlin, Germany b Institut f ¨ ur Festk ¨ orperphysik, Technische Universit ¨ at Berlin,Hardenbergstraße 36, 10623 Berlin, Germany c Institut f ¨ ur Experimentalphysik, Otto-von-Guericke-Universit ¨ at Magdeburg, 39106 Magdeburg, Germany a r t i c l e i n f o Article history: Received 4 December 2009 Received in revised form 25 August 2010 Accepted 7 September 2010 Communicated by R. Bhat Available online 21 September 2010 Keywords: A1. Segregation A1. High resolution X-ray diffraction A3. Low press A3. Metal organic vapor phase epitaxy B1. Nitrides B2.Semiconducting indium compounds a b s t r a c t InGaN/GaN multiple quantum well structures emitting in the blue/green wavelength region were grown by metal organic vapor phase epitaxy. By reducing the quantum well growth time the influence of the quantum well thicknesses between 3.8 and 1.1 nm on the indium incorporation and the distribution of indium in the quantum wells in growth direction were investigated. X-ray diffraction measurements show thatthe average indium mole fraction in the quantum wells decreases with reducing quantum well width due to a delay in the indium incorporation at the barrier/well interface. Quantitative analysis reveals a segregation length of about 2 nm as a measure of the graded region in growth direction. Cathodoluminescence imaging reveals that the spatial variation of the wavelength is reduced with decreasing quantum well thickness down to 1.7 nm. Reducing the width of the quantum well further results in an increase of the spatial wavelength variation. & 2010 Elsevier B.V. All rights reserved. 1. Introduction GaN based laser diodes (LD) emitting in the violet–blue wavelength region have first been demonstrated by Nakamura and colleagues [1] more than a decade ago. Presently, LDs emitting in the blue–green wavelength region [2,3] attract attention for application as light source for full-color displays and laser projectors [4]. The emission at such wavelengths requires high In mole fractions in the indium gallium nitride (InGaN) quantum wells (QW)s resulting in strong piezoelectric fields due to the high strain and the piezoelectric properties of the (Al,In, Ga)N material [5].At low excitation conditions the piezoelectric fields separate the electrons and holes in the QW and thus considerably reduce the oscillator strength [6]. Further- more, the emission is shifted towards longer wavelengths [7,6] as consequence of the quantum confined Stark effect (QCSE) [8]. For devices operating at high excitation the material gain is believed to decrease due to the degradation of the crystal quality in the active layer with increasing amount of In in the QWs [3]. Because both the wave function overlap as well as the QW material quality can be affected by the QW width (d QW ) this parameter has a great impact on the device performance. The influence of d QW on the wave function overlap and its impact on the opticalproperties such as radiative recombination [9,10],internal quantum effi- ciency [11,12] and threshold current density [13] has been extensively investigated. In this paper we concentrate on the influence of d QW on the structural properties of the active region such as the indium incorporation in the QW and the distribution of indium in growth direction and their impact on the light emission.Therefore,samples with different d QW are produced by metal organic vapor phase epitaxy (MOVPE) and investigated by X-ray reflectivity (XRR), high resolution X-ray diffraction (HRXRD), photoluminescence(PL) and cathodoluminescence (CL) spectroscopy. 2. Experimental All heterostructures were grown on 1:5 m m thick non-inten- tionally doped gallium nitride (GaN:nid) on (0 0 0 1)sapphire templates.The epitaxial growth was conducted in an AIX2400HT MOVPE system using trimethylgallium (TMGa) and ammonia (NH 3 ) as precursors and hydrogen as carrier gas for the growth of the GaN:nid buffer layer. Two sets of InGaN/GaN MQW structures with varying quantum barrier growth time (set (A)) and varying QW growth time (set (B)) were deposited on the GaN:nid templates in order to determine the structural properties of the QWs by HRXRD and XRR. A third set of MQW structures denoted as set (C) with varying QW thickness was produced using the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2010.09.013 Corresponding author. E-mail address: veit.hoffmann@fbh-berlin.de (V. Hoffmann). Journal of Crystal Growth 312 (2010) 3428–3433