High-efficiency (49%) and high-power photovoltaic cells based on gallium antimonide
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ICS OF SEMICONDUCTOR DEVICES
High-Efficiency (49%) and High-Power Photovoltaic Cells Based on Gallium Antimonide V. P. Khvostikov^, M. G. Rastegaeva, O. A. Khvostikova, S. V. Sorokina, A. V. Malevskaya, M. Z. Shvarts, A. N. Andreev, D. V. Davydov, and V. M. Andreev Ioffe Physicotechnical Institute, Russian Academy of Sciences, Politekhnicheskaya ul. 26, St. Petersburg, 194021 Russia ^e-mail: [email protected] Submitted February 21, 2006; accepted for publication March 3, 2006
Abstract—High-efficiency GaSb-based photovoltaic cells designed for conversion of high-power laser radiation and infrared radiation of emitters heated by concentrated solar radiation are fabricated and studied. The maximum efficiency of conversion of the radiation with λ = 1680 nm was 49% at the photocurrent density of 50–100 A/cm2 for the fabricated photovoltaic cells. The methods for reducing the losses at ohmic contacts to p- and n-GaSb are investigated. The minimum values of the specific resistance, (1–3) × 10–6 Ω cm2, of contact to p-GaSb with the doping level of 1020 cm–3 were obtained using the Ti/Pt/Au contact system. The minimum values of the specific contact resistance were (1–3) × 10–6 Ω cm2 in the case of n-GaSb with the doping level of 2 × 1018 cm–3 if the Au(Ge)/Ni/Au and Au/Ni/Au contact systems are used. PACS numbers: 84.60.Jt, 78.55.Cr, 42.79.Fk, 73.50.Pz, 72.80.Ey DOI: 10.1134/S1063782606100216
1. INTRODUCTION Photovoltaic cells that can efficiently convert incident radiation with a power density as high as 100 W/cm2 are required for photovoltaic conversion of concentrated solar radiation and the radiation of hightemperature emitters in the case of the thermal–photovoltaic method of power conversion. In the case of thermal radiation of emitters in thermal–photovoltaic generators, it is promising to use high-current photovoltaic cells based on gallium antimonide; these cells were developed previously with the aim of increasing the efficiency of conversion of concentrated solar radiation in combination with GaAs photovoltaic cells [1, 2]. In the case of the fabrication of high-power photoconverters based on gallium antimonide, it is important to reduce the series resistance of the semiconductor structure since the losses at the internal ohmic resistance of the device increase inevitably as the density of radiation incident on the photovoltaic cell increases. The problems related to the formation of ohmic contacts to n- and p-GaSb using various technologies were considered, for example, in [3–10]. The reported values of the specific resistance of ohmic contacts Rc to p+ GaSb are in the range from 1 × 10–4–5 × 10–7 Ω cm2 [3–5]. It is worth noting that it is mentioned in some publications that such contacts to p+ GaSb can be obtained immediately after the metal deposition without an additional heat treatment [4], whereas it is stated in other publications that fairly high heat-treatment temperatures are needed for attaining small values of Rc [5, 10]. The results obtained in the case of n GaSb also
feature an appreciable spre
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