Study of Be d-doped GaAs/AlAs multiple quantum wells by the surface photovoltage spectroscopy B. C ˇ echavicˇius a, * , J. Kavaliauskas a , G. Krivaite˙ a , V. Karpus a , D. Seliuta a , G. Valusˇis a , M.P. Halsall b , M.J. Steer c , P. Harrison d a Semiconductor Physics Institute, A. Gosˇtauto St. 11, LT-01108 Vilnius, Lithuania b Department of Electronics and Electrical Engineering, University of Manchester, P.O. Box 88, Manchester M60 1QD, UK c Department of Electronic and Electrical Engineering, University of Sheffield, Mappin St., Sheffield S1 3JD, UK d Institute of Microwaves and Photonics, School of Electronic and Electrical Engineering, University of Leeds, Leeds LS2 9JT, UK Available online 18 January 2006 Abstract We report a surface photovoltage and differential surface photovoltage (DSPV) study of Be d-doped GaAs/AlAs multiple quantum wells (QWs) with widths ranging from 3 to 20 nm and sheet doping densities from 2  10 10 to 2.5  10 12 cm 2 per well aiming to characterize their electronic properties and structural quality. From a line shape analysis of room temperature DSPV spectra the interband excitonic transition energies and broadening parameters for a large number of QW-related subbands have been established. A study of well-width and quantum number dependencies of the excitonic linewidths allowed us to evaluate the various broadening contributions to the spectral line shapes in QWs of different design. It was found that an average half monolayer well-width fluctuations are the dominant broadening mechanism of the excitonic line for QWs thinner than 10 nm. In QWs thicker than 10 nm, the spectral line broadening originates mainly from thermal broadening as well as Stark broadening due to random electric fields of ionized impurities and exciton scattering by free holes. # 2005 Elsevier B.V. All rights reserved. PACS: 78.67.De; 73.21.Fg Keywords: Photovoltage spectroscopy; Modulation spectroscopy; Quantum wells 1. Introduction The increasing demand for terahertz (THz) electronics has stimulated considerable impetus to study semiconductor nanostructures as possible active components of compact THz devices. A particular concern are the intersublevel transitions of shallowimpuritiesplacedinaQW,asachangeofitswidthallows one to tune their energy levels across the terahertz range in a controllable way. In this respect, the Be d-doped GaAs/AlAs multiple QW (MQW) system is of special interest as it gives the maximum possible tuning range for the dipole-allowed 1s–2p transitionoftheBeacceptorinaGaAshost [1,2].Therefore,such structures seem to be very attractive for fabrication of THz detectors and emitters [3]. For the technological development of such devices, knowledge about the physical properties and the structural material quality – the presence of internal electric fields, interface roughness, defect density, etc. – of d-doped GaAs/AlAs structures is particularly important. A great deal of useful information concerning the optical and electronic properties as well as structural inhomogeneities of low- dimensional semiconductor structures can be obtained by non-destructivesurface photovoltage (SPV) [4] and differential SPV (DSPV) [5] spectroscopies. They offer the possibility of carrying out investigations of quantum structures with high spectral sensitivity conveniently at room temperature. In this article, we report a room temperature SPV and DSPV study of optical interband transitions in Be d-doped GaAs/AlAs MQW structures. Analyzing the lineshape of the DSPV spectra allowed us to extract information on the excitonic parameters for a large number of QW subbands. Special attention was paid to examination of exciton line broadening, which is directly related to the structural quality of MQW systems. www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 5437–5440 * Corresponding author. Tel.: +370 5 261 94 75; fax: +370 5 262 71 23. E-mail address: bronius@pfi.lt (B. C ˇ echavicˇius). 0169-4332/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2005.12.028