Photoluminescence at up to 2.4 μm wavelengths from GaInAsBi/AlInAs quantum wells Renata Butkutė n , Vaidas Pačebutas, Bronislovas Čechavičius, Ramūnas Nedzinskas, Algirdas Selskis, Andrius Arlauskas, Arūnas Krotkus Center for Physical Sciences and Technology, A. Goštauto 11, Vilnius, Lithuania article info Article history: Received 23 October 2013 Received in revised form 20 December 2013 Accepted 12 January 2014 Communicated by Dr. A. Brown Available online 21 January 2014 Keywords: A1. Photoluminescence A3. Molecular beam epitaxy A3. Quantum wells B1. GaInAsBi abstract 5 nm, 10 nm and 20 nm-thick GaInAsBi quantum wells were grown on the InP:Fe(100) substrates by molecular beam epitaxy. The top and bottom barriers of quantum structures were 50 nm and 100 nm- thick lattice-matched AlInAs, respectively. Quantum wells were grown at the substrate temperature of about 240 1C. The maximum bismuth content in the wells was 5.0%. Transmission electron microscopy images revealed sharp interfaces between the wells and barrier layers as well as homogeneous Bi incorporation. Photoluminescence (PL) measurements demonstrated signals from all QW up to the room temperature. PL intensity was stronger in thinner quantum wells where relaxation and clustering effects were avoided. The longest emission wavelength registered reached 2.4 mm. & 2014 Elsevier B.V. All rights reserved. 1. Introduction III–V semiconducting alloys containing dilute amounts of bismuth have recently attracted considerable interest due to the large band gap reduction with relatively small Bi incorporation, which makes them promising materials for optoelectronic appli- cations in the near and mid-infrared (MIR) spectral range [1–3]. In GaAs 1 x Bi x with x o0.05 this reduction is as fast as  88 meV/% Bi [4]. Moreover, as Bi incorporation affects mainly the valence band of the alloy, its spin–orbit splitting Δε SO increases, and for x 40.1 it becomes larger than the energy band gapε g . This is important for suppressing Auger recombination losses and for improving performance characteristics of light emitting devices having active bismide layers. Photoluminescence at 1.5 μm wave- length from the GaAs 1 x Bi x layer containing  10% Bi and grown on the GaAs substrate was already observed in Ref. [4]. Even longer PL wavelengths can be achieved if ternary GaInAs is alloyed with dilute amounts of bismuth. It has been predicted that GaInAsBi layers lattice-matched with the InP substrate can have an energy band gap corresponding to optical transitions at wavelengths up to 6 μm [5]. Such a material will be highly requested for MIR semiconductor lasers emitting in continuous wave at room tem- perature because the fundamental absorption bands of many molecular species are located in that spectral range [6]. Ga 0.47 In 0.53 As 1x Bi x layers with up to 7% Bi have already been grown by molecular beam epitaxy (MBE) on InP substrates [7,8]. The band gap ε g of these layers was decreasing in accordance with the theoretical predictions. Photomodulated reflectance spectroscopy was employed for the investigation of the energy band structure of Ga 0.47 In 0.53 As 1x Bi x in Refs. [9] and [10], and it has been found that the spin–orbit splitting Δε SO of the valence band becomes larger than ε g for x values in the range from 0.033 to 0.043 [10]. At the liquid nitrogen temperature a photoluminescence signal with wavelength as long as 3 μm was observed from these layers [7]; however in the room temperature the photoluminescence was detected only in Ga 0.47 In 0.53 As 1x Bi x with a Bi content not exceeding 2.4% [10]. This lack of radiative transitions could be ascribed to low temperatures used for the bismide growth and a large number of structural defects serving as electron traps. However, a weak PL signal could also be caused by the insufficient photoexcited carrier confinement and the influence of surface recombination. In this work we will present the investigations of the Ga 0.47 In 0.53 As 1x Bi x single quantum wells (SQWs) with AlInAs barriers. Due to the better carrier confinement and improved material quality the room temperature photoluminescence was evidenced for a number of SQWs with thicknesses ranging from 5 nm to 20 nm; the longest emission wavelength registered was equal to 2.4 μm. 2. Sample growth and structural characterization Thin GaInAsBi layers and GaInAsBi/AlInAs quantum well structures were grown on semi-insulating (100) InP:Fe substrates by molecular beam epitaxy. The growth was performed in a SVT-A reactor equipped with metallic Al, In, Ga, and Bi sources and a two-zone valved cracker source for production of As 2 molecules. Native oxide from the InP:Fe 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.2014.01.009 n Corresponding author. Tel.: þ370 52627469; fax: þ370 52627123. E-mail address: renata@pfi.lt (R. Butkutė). Journal of Crystal Growth 391 (2014) 116–120