PIERS ONLINE, VOL. 4, NO. 2, 2008 286 Miniband Structure Formation of p-type Delta-doped Superlattices in GaAs I. Rodriguez-Vargas, A. del Rio de Santiago, J. Madrigal-Melchor, and S. J. Vlaev Unidad Acad´ emica de F´ ısica, Universidad Aut´onoma de Zacatecas Calzada Solidaridad Esquina con Paseo la Bufa S/N, Zacatecas 98060, ZAC., M´ exico Abstract— We present the electronic structure of finite p-type delta-doped superlattices in GaAs. We use the first neighbors sp 3 s * tight-binding approximation including spin for the miniband structure analysis. The calculation is based on analytical expression for the Hartree potential of the inhomogeneous part, previously obtained within the Thomas-Fermi (TF) ap- proximation. This potential is considered as an external potential in the computations, so, it is added to the diagonal terms of the tight-binding Hamiltonian. We give a detail description of the delta-doped superlattices, this is, we study the miniband formation as a function of the impurity density (n 2D ) and the superlattice period (d), obtaining the regions of superlattice, multiple well and isolate well behavior. We also compare our results with the theoretical and experimental data available, obtaining a reasonable agreement. 1. INTRODUCTION The delta-doped semiconductor superlattices are important structures for the optoelectronic devices due to their particular properties — high carrier density and miniband formation — that can be exploited in devices based on parallel or vertical transport [1]. Besides, these structures are ideal systems to test the resolution of image techniques [2], to study self-compensation [3] and intermixing effects [4], as well as to analyse the disorder effects [5]. In particular, p-type delta-doped superlattices have been studied both experimentally and theo- retically by several authors [6–14]. Carbon delta-doped superlattices in GaAs have been successfully grown by chemical beam epitaxy with Carbon tetrabromide (CBr 4 ) as doping source [6, 7]. The Carbon shows a great electrical activation (3.5 × 10 13 cm -2 ) and very narrow doping profiles (5 ˚ A) mainly due to its high solubility and low diffusivity. Spatially indirect transitions have been reported for the first time in Zn delta-doped GaAs layers by optical spectroscopy [8]. It is ob- served that the transitions depend strongly on the temperature and excitation density. In GaN and AlGaN epilayers an enhancement of the p-type lateral and vertical conductivities is observed [9]. A good material quality is achieved by employing Mg delta-doping [9]. The systems of [8, 9] are not properly superlattices, however they are very promising systems for lateral and vertical transport devices due to the absence of extra barriers as in the case of heterostructures. There are some theoretical reports in p-type superlattices in GaAs and Si [10–14]. The methodology relies on the k · p multiband effective mass equation from four, six and eight bands. Detail information about the potential profile, hole subband levels, Fermi level position and luminescence signatures for overall system parameters is given. However, it is important to mention that particularly in GaAs there are not reports dealing with a detail analysis of the miniband-formation evolution [10–12]. So, the aim of the present work is to fill this gap and to show that the tight-binding methodology together to the Thomas-Fermi approximation are an alternative methodology to study inhomogeneous semi- conductors systems. In the present paper we analyse the miniband structure formation of p-type delta-doped GaAs superlattices within the nearest neighbors sp 3 s * tight-binding model including spin. The confin- ing potential induced by the ionized impurities and the electronic charge is obtained analytically through the Thomas-Fermi approximation. This potential is considered as an external perturbation in the tight-binding methodology and it is added to the diagonal terms of the tight-binding Hamil- tonian. A detail information of the miniband structure formation as a function of the impurity density, the interwell distance and the number of periods is given, as well as, a comparison with the available theoretical and experimental data is discussed.