Influence of barrier growth schemes on the structural properties and thresholds of InGaN quantum well laser diodes V. Hoffmann a,n , A. Mogilatenko a , C. Netzel a , U. Zeimer a , S. Einfeldt a , M. Weyers a , M. Kneissl a,b a Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, Berlin, Germany b Institut für Festkörperphysik, Technische Universität Berlin, Berlin, Germany article info Article history: Received 18 October 2013 Received in revised form 20 December 2013 Accepted 26 December 2013 Communicated by: A. Bhattacharya Available online 3 January 2014 Keywords: A1. Interfaces A2. Metalorganic chemical vapor deposition A3. Quantum wells B1. Nitrides B2. Semiconducting indium compounds B3. Laser diodes abstract The influence of the (In)GaN quantum barrier growth temperature on the structural properties of the active region of blue–violet laser diodes has been investigated. Therefore, multiple quantum well structures were prepared by metal-organic vapor phase epitaxy, with (In)GaN barriers grown either at the same temperature as the InGaN quantum wells, or at a 60 K higher growth temperature. A 60 K higher growth temperature results in smoother quantum barrier layers with fewer defects on a microscopic scale, as revealed by scanning electron microscopy and cathodoluminescence studies. On the other hand samples with a 0 K offset showed a higher strain in the quantum wells determined by X-ray diffraction and a narrower photoluminescence emission spectra. Secondly, laser heterostructures with InGaN barriers were prepared for optical pumping using different growth schemes. The laser structure with the active region deposited with a 0 K offset exhibits significantly lower optical threshold power densities of around 200 kW/cm² compared to 700 kW/cm² for the 60 K offset sample. Also, transmission electron microscopy revealed quantum wells with improved lateral uniformity in the samples grown without temperature offset. Based on these results, a current-injection broad area laser diode with an active region growth scheme without temperature offset was prepared on (0001) GaN substrate. The diode emits around 420 nm with a threshold current density of around 1.6 kA/cm². & 2014 Elsevier B.V. All rights reserved. 1. Introduction InGaN multiple quantum well (MQW) structures are used as active regions in optoelectronic devices emitting in the UV, blue, green and even yellow wavelength range [1,2]. Since the perfor- mance of these devices strongly depends on the crystal perfection of the active region [3], the growth of InGaN with high structural perfection has been the topic of numerous publications (see [4] and references cited therein). Our earlier studies [5] were focused on the influence of the growth conditions on both the alloy homogeneity of the InGaN QW layers [6–8] and the device performance. This paper focuses on the influence of the growth temperature and the composition of the (In)GaN quantum barriers on the crystal perfection of the InGaN MQW active region and the corresponding laser device performance. Several groups reported on active regions with reduced surface roughness, a smaller density of v-shaped pits [9,10] and increased photoluminescence (PL) efficiency [11,12] by using a so called two temperature (2T) growth scheme. In this case, the barrier growth temperature is increased with respect to that of the QWs in order to get closer to optimum GaN deposition conditions. Moreover, the use of InGaN barriers with a relatively small indium mole fraction instead of GaN barriers was reported to reduce the number of non-radiative recombination centers [13,14], improve the carrier injection [15] and reduce electron leakage current in LEDs [15,16]. In this work, the consequences of the 2T growth scheme are investigated using samples of both GaN and InGaN barriers. First, a set of MQW samples with GaN quantum barriers (set A) is prepared in order to investigate the influence of the barrier growth tempera- ture on the crystal perfection of the barrier layers. Here, GaN was chosen as the barrier material since the structural properties of the InGaN MQWs can be easily revealed by high resolution X-ray diffraction (HR-XRD). Secondly, it is investigated whether the 2T growth scheme can be used to improve the performance of laser diodes with InGaN quantum barriers. Therefore, a set of laser heterostructures for optical pumping (set B), grown with and without a 2T growth scheme, were prepared and analyzed. Here, InGaN with a small In mole fraction was chosen as barrier material since it is known to be superior to GaN in terms of laser performance. Due to the layout of the active region, the structural properties of the MQWs can only be analyzed by transmission electron microscopy (TEM). Additionally, using the results of set Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jcrysgro.2013.12.046 n Corresponding author. E-mail address: veit.hoffmann@fbh-berlin.de (V. Hoffmann). Journal of Crystal Growth 391 (2014) 46–51