CORRELATION OF COMPENSATION IN Si-DOPED GaAs BETWEEN ELECTRICAL AND OPTICAL METHODS Mantu Kumar Hudait a,b and S.B. Krupanidhi a , * a Materials Research Centre, Indian Institute of Science, Bangalore-560 012, India b Central Research Laboratory, Bharat Electronics, Bangalore-560 013, India (Received 9 June 1998; accepted 3 August 1998 by H. Akai) The compensation in Si-doped GaAs by metal organic vapor phase epitaxy was studied as a function of electron concentration and growth temperature by means of photoluminescence and Hall effect measurements. The PL spectra show peaks due to Si donor–Si acceptors (Si Ga –Si As ) and Si-related complex-defects transitions, which may be attributed to Si donor coupled to a group III elemental vacancy (Si Ga –V Ga ) complexes. We showed the importance of each of these defects pair to the optical properties, as it is strongly dependent on the growth parameters. The defects pair are responsible for autocompensation and confirmed by electrical measure- ments.  1998 Elsevier Science Ltd. All rights reserved Keywords: A. semiconductors, B. photoluminescence, C. optical properties. 1. INTRODUCTION It is now well established that the Si-doped GaAs epitaxial layers are routinely employed at moderate to heavy doping levels in many devices of interest. For example, in p þ – n GaAs solar cells they form the base and buffer layers of n þ -GaAs of 1  10 18 cm ¹3 can be used to provide back-surface reflection of minority- carriers and an increase in the photovoltaic conversion efficiency. In high performance submicrometer GaAs- MESFETs, highly doped (1  10 18 cm ¹3 ) channel layers have been employed [1]. Being a group IV element, it exhibits self-compensation to a much smaller extent. It is well accepted that at low Si concentrations, the Si atoms enter into the lattice mainly as a simple substitutional impurity at the group III element sites (Ga), acting as a donor (Si Ga ) and at the As sites, acting as an acceptor (Si As ) [2–5]. The latter becoming increasingly important as the Si concentration increases, causing a saturation of the free electron concentration. Heavily doped films present a strong compensation of the free electron concentration. This compensation has been attributed in GaAs mainly to a complex defect formed by a donor atom coupled to a group III element vacancy (Si Ga –V Ga ), the so-called self-activating center [6]. This complex defect give rise to a broad photoluminescence line centered about 1.2 eV for GaAs [7] and 1.35 eV for Al 0.3 Ga 0.7 As [6] samples. Another deep photo- luminescence feature about 1.05–1.28 eV has been attributed to a Si Ga –Si As pair defect [8, 9] and responsible for the compensation. Maguire et al. [10] investigated Si doped GaAs by using local vibration modes (LVM), Hall effect and secondary ion mass spectroscopy (SIMS) and concluded that the [Si–X] was tentatively attributed to the well-known self-activated center (Si Ga –V Ga ). The LVM results do not necessarily exhaust the possibilities of forms of Si incorporation. Souza and Rao [8] mentioned that in GaAs, the Si incorporation is extremely complex and highly dependent on growth conditions. Photoluminescence and electrical experimental studies, such as Hall effect measurements were used to under- stand the dopant behavior at high doping concentrations and growth temperatures. In this communication, we show some evidence of the presence of Si Ga –Si As pair defects by studying Si doped GaAs grown under different silane (SiH 4 ) partial pressures and different growth temperatures. These Si Ga –Si As defect pairs are responsible for reducing free-carrier concentration of higher Si doping levels due to compensation effects. 457 Pergamon Solid State Communications, Vol. 108, No. 7, pp. 457–461, 1998  1998 Elsevier Science Ltd. All rights reserved 0038–1098/98 $ - see front matter PII: S0038–1098(98)00386-X * Corresponding author. E-mail: sbk@mrc.iisc.ernet.in