Eur. Phys. J. B 50, 403–410 (2006) DOI: 10.1140/epjb/e2006-00154-5 T HE EUROPEAN P HYSICAL JOURNAL B Longitudinal-optical phonon hole-plasmon coupled modes in heavily doped p-type GaSb:Zn epitaxial films Z.G. Hu 1, a , M.B.M. Rinzan 1 , A.G.U. Perera 1, b , Y. Paltiel 2 , A. Raizman 2 , A. Sher 2 , and M. Zhu 3, c 1 Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA 2 Electro-Optics Division, Soreq Nuclear Research Center (NRC), Yavne 81800, Israel 3 Department of Physics, Shanghai Jiao Tong University, 1954 Hua Shan Road, Shanghai 200030, P.R. China Received 25 August 2005 / Received in final form 10 January 2006 Published online 5 May 2006 – c  EDP Sciences, Societ`a Italiana di Fisica, Springer-Verlag 2006 Abstract. Reflectance measurements from p-type GaSb:Zn epitaxial films with different hole concentra- tions (10 17 –10 18 cm -3 ) have been investigated over the frequency region of 100–1000 cm -1 . A minimum broadening feature corresponding to the hole plasmon was observed in the reflectance spectra. The exper- imental infrared spectra were well fitted using a Lorentz-Drude dispersion model. The real part ε1 of the dielectric function decreases with increasing hole concentration. However, the imaginary part ε2 increases with hole concentration in the far-infrared region. This indicates that the acoustic- and optic-phonons mainly participate in the free carrier absorption processes. The hole mobility obtained from Hall-effect measurements is slightly larger than that derived from optical measurements and the average ratio of mobilities is estimated to be 1.33. Owing to overdamping effects, the upper branch of longitudinal-optical phonon plasmon (LPP) coupled modes was observed. The upper LPP + frequency increases with hole con- centration and it shows a transition from phonon-like to plasmon-like behavior. A theoretical analysis with solutions in the complex frequency plane describes these experimental results. PACS. 78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) – 78.30.Fs III-V and II-VI semiconductors – 81.70.Fy Nondestructive testing: optical methods 1 Introduction Among III–V group semiconductors, gallium antimonide (GaSb) is particularly interesting for optoelectronics de- vice applications [1]. The far-infrared (FIR) optical prop- erties and/or lattice vibrations of GaSb bulk material have been investigated for several decades [2–4]. Recent progress in film growth techniques, such as metalorganic vapor-phase epitaxy (MOVPE) and molecular beam epi- taxy (MBE), makes it possible to study the optical prop- erties of GaSb epitaxial films. In order to achieve a high p-type doping, zinc (Zn) is commonly used, in which case the electrical properties have been studied before [5]. How- ever, valuable information for infrared optoelectronic ap- plication of p-type GaSb:Zn epilayers are scarce. These a Present address: Institute of Physical Chemistry, Univer- sity of Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany e-mail: Zhigao.Hu@urz.uni-heidelberg.de b e-mail: uperera@gsu.edu c Also at Department of Educational Information and Tech- nology, School of Educational Science, East China Normal University, North Zhongshan Road 3663, Shanghai, 200062, P.R. China. properties are significant for the design and development of p-type GaSb-based infrared detectors, which may have better properties than the already successful GaAs-based FIR detectors [6]. One of the main parameters needed for optoelectronic device design is the interaction of free carriers with pho- tons in the low frequency region [7,8]. For FIR or ter- ahertz (THz) detector design, the detailed and accurate knowledge of the dielectric function is necessary to evalu- ate the total optical absorption of the detectors. In order to improve the performance of Al x Ga 1-x As/GaAs THz detectors, a detailed study of the dielectric functions for p-type Al x Ga 1-x As films was done [9], and followed by the design and realization of high performance detectors [10]. The dielectric function of the GaSb material related to the high-energy critical point transitions has been studied by Adachi [11]. Paskov reported the dielectric function of GaSb with different carrier concentrations [12]. However, these studies were limited to regions near and beyond the optical band-gap energy (about 0.7 eV). Few reports were made on the infrared dielectric functions of Al x Ga 1-x Sb and GaSb [13,14]. Nevertheless, very few results were pre- sented on the low frequency dielectric functions of p-type GaSb:Zn epilayers.