Atmospheric-pressure metalorganic vapour phase epitaxy optimization of GaAsBi alloy I. Moussa ⁎ , H. Fitouri, A. Rebey, B. El Jani Unité de Recherche sur l'Hétero-Epitaxie et Applications, Faculté des Sciences de Monastir, Boulevard de l'environnement 5019, Monastir, Tunisia Received 2 June 2007; received in revised form 22 February 2008; accepted 4 April 2008 Available online 16 April 2008 Abstract Metalorganic vapour phase epitaxial growth of GaAsBi alloy has been carried out at atmospheric pressure in horizontal geometry reactor. In order to achieve the growth of this alloy, we have investigated the growth conditions which allow epitaxial layers of a good crystalline quality with a maximum bismuth concentration. Growth parameters such as growth temperature, trimethylbismuth (TMBi) flow and V/III ratio were checked on a wide range. Growth temperature was varied between 365 and 450 °C, TMBi flow was checked in the range below 2 μmol/min and V/III ratio was varied between 6 and 20. According to our experimental results based on in-situ reflectivity measurements, scanning electron microscopy observations and high resolution X-ray diffraction analysis, it was found that the maximum Bi concentration reached in GaAs 1 - x Bi x layers was 3.7%. This maximum, relative to atmospheric-pressure metalorganic vapour phase epitaxy technique, was found under a growth temperature of 420 °C, a TMBi flow of 0.2 μmol/min and a V/III ratio of 9.5. © 2008 Elsevier B.V. All rights reserved. PACS: 82.60.Cx; 81.15.Gh; 73.61.Ey Keywords: Atmospheric pressure metal-organic chemical vapor deposition; GaAsBi; Reflectivity; Scanning electorn microscopy; X-ray diffraction 1. Introduction III–V–Bi semiconductor alloys have been proposed as ma- terials with temperature insensitive band gaps, which can be used in laser diodes whose wavelength stays nearly constant against temperature variations [1]. In fact this property can be obtained by combining materials with negative and positive gap-coefficients. Since conventional semiconductors have ne- gative gap-coefficients, semimetallic compounds were found to be key elements in obtaining temperature insensitive band gap materials [2]. For these reasons GaAsBi alloy is expected to have a very small temperature dependence of the band gap energy as it consists of semiconductor and semimetal compo- nents. This alloy was grown by molecular beam epitaxy (MBE) [3] and low-pressure metalorganic vapour phase epitaxy (LP- MOVPE) [4–6]. Very narrow growth conditions were reported by Oe [6] who has found that LP-MOVPE of GaAsBi epilayers can be grown at a growth temperature of 365 °C. Various V/III ratios were used; mirror like surface was obtained when V/III ratio is decreased to 11 with 0.19 Bi/Ga. By using MBE tech- nique, and after extensive experimentation with growth condi- tions, Tixier et al. [7] achieved incorporation of Bi into GaAs up to 3.1% (measured by Rutherford Backscattering) using low growth temperature (380 °C), and very low group V/III ratios. These conditions are considered far from ideal for the growth of most GaAs related alloys. Due to its large size, bismuth segregates on the surface and does not incorporate easily in the GaAs matrix. However, the exceptional features of Bi containing alloys are their large miscibility gaps and their very small equilibrium solid solubilities. For InAsBi, it was found that the solubility of InBi into InAs is less than 0.025% [8]. GaAsBi is expected to have a comparable behaviour, but this can not be confirmed since GaBi is a virtual compound (never been synthesized). High super saturation growth technique, like low temperature Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 8372 – 8376 ⁎ Corresponding author. E-mail address: imed.moussa@fsm.rnu.tn (I. Moussa). www.elsevier.com/locate/tsf 0040-6090/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.04.062