Near band-edge optical properties of cubic GaN with and without carbon doping J.R.L. Fernandez a, * , F. Cerdeira a , E.A. Meneses a , J.A.N.T. Soares b , O.C. Noriega b , J.R. Leite b , D.J. As c , U. Ko ¨hler c , D.G.P. Salazar c , D. Schikora c , K. Lischka c a Instituto de Fı ´sica “Gleb Wataghin”, Universidade Estadual de Campinas, Caixa Postal 6165, Campinas, SP 13.083-970, Brazil b Instituto de Fı ´sica, Universidade de Sa ˜o Paulo, Caixa Postal 66318, Sa ˜o Paulo, SP, Brazil c Universita ¨t Paderborn, FB-6 Physik, D-33095 Paderborn, Germany Abstract We report the results of studying the optical properties of cubic GaN thin films with photoluminescence and photoluminescence excitation spectroscopies. The films are deposited by plasma-assisted molecular beam epitaxy on GaAs (001) substrates, with and without intentional doping with carbon atoms (p-type doping). The evolution of the optical spectra of the C-doped samples is consistent with a picture in which carbon enters into N-vacancies at low concentrations, producing a marked improvement in the crystalline properties of the material. At higher concentrations it begins to form complexes, possibly due to interstitial occupation. The temperature dependence on the absorption edge of the doped material is also measured and is analyzed with standard theoretical models. q 2004 Elsevier Ltd. All rights reserved. Keywords: Carbon doping; Photoluminescence; Photoluminescence excitation 1. Introduction The fabrication of the first c-InGaN/GaN double- heterostructure LED grown by MOCVD has been recently reported [1]. Contrary to their hexagonal counterparts, the cubic structures can be grown free from modulation due to spontaneous polarization and strain-induced piezoelectric fields. Thus, the spatial separation of the carriers wave function, induced by the quantum-confined Stark effect in the hexagonal phase, is avoided in the cubic phase. For this reason the cubic polytype nitride-based quantum wells are expected to have increased optical recombination efficiency. Hence, the growth and characterization of high-quality c-GaN epitaxial layers are essential first step on the road to high-performance devices fabricated with this material. In addition, for the fabrication of devices with this material, it is essential to be able to introduce p- and n-type doping in a controlled manner. This involves introducing dopant impurities, which produce shallow acceptor or donor levels. Understanding how these impurities enter into the GaN lattice is of fundamental importance for achieving useful doping. In the present work, we report the results of a study of the optical properties of cubic GaN thin films, deposited by plasma-assisted molecular beam epitaxy on GaAs (001) substrates, with and without intentional doping with carbon atoms (p-type doping). We used photoluminescence (PL) and photoluminescence exci- tation spectroscopy (PLE) to study the spectral region near the fundamental absorption edge of these samples. We observe a clear step-like absorption edge, resulting from the merging of the free exciton with the continuum. Quantitative values for the absorption edge energy and lifetime broadening are obtained. The temperature dependence on the absorption edge of the doped material is also measured and is analyzed with standard theoretical models. The evolution of the optical spectra of C-doped samples as the concentration of the dopant increases is consistent with a picture in which carbon enters into N-vacancies at low concentrations, producing a marked improvement in the crystalline properties of the material. At higher concentrations, it begins to form complexes, possibly due to interstitial occupation. 0026-2692/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/S0026-2692(03)00226-X Microelectronics Journal 35 (2004) 73–77 www.elsevier.com/locate/mejo * Corresponding author.